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Reactions of small molecules with rhodium porphyrin complexes Thackray, David Carden 1990

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R E A C T I O N S O F S M A L L  M O L E C U L E S  W I T H R H O D I U M P O R P H Y R I N  C O M P L E X E S  by David C. Thackray B.Sc, Concordia University, 1978 M.Sc, The University of British Columbia, 1983  A THESIS SUBMITTED IN PARTIAL FTJLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES THE DEPARTMENT OF CHEMISTRY  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA May, 1990 © David C. Thackray, 1990  In presenting  this thesis in partial fulfilment of the  requirements for an  advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference  and  study. I further agree that permission for extensive  copying of this thesis for scholarly purposes may department  or  by  his or  her  representatives.  be  It is understood  publication of this thesis for financial gain shall not be permission.  Department The University of British Columbia Vancouver, Canada  DE-6  (2/88)  granted by  the head of  my  that  or  copying  allowed without my  written  ii  Abstract The reaction of Rh(OEP)(H) (OEP - 2,3 J,8,12,13,17,18-octaemylporphyrin) with O2 in organic solvents was examined by visible, proton and phosphorus nuclear magnetic resonance spectroscopy (nmr) as a candidate system for the net insertion of O2 into the metal-hydride bond. The nmr data for a thermally unstable Rh (OEP)(OOHXH20) mtennediate were obtained at -40 °C m  in CD2C12- Addition of O2 to CH2CI2 solutions of Rh(OEP)(H) with triphenylphosphine resulted in reaction with solvent forming Rh(OEP)(Cl)(PPh3) and Rh(OEP)(CH2Cl)(PPh3) as the major species (in equimolar amounts), without concomitant formation of OPPh3. The sensitivity of the reaction of Rh(0£P)(H) with O2 to initial conditions, and the observation of products containing Rii (LI) and RI1-CH2G, suggest a radical mechanism. Initiation/tenniriation: 2Rh(OEP)(H) ^  [Rh(OEP)] + H 2  [Rh(OEP)] ^=  2  2Rh(OEP)-  2  and in the presence of PPI13 [Rh(OEP)] + PPh ^=s?-Rh(OEP)(PPh ) + Rh(OEP)2  3  3  Propagation: Rh(OEP)- + O2  Rh(OEP)(Q2)  Rh(OEP)(02) + Rh(OEP)(H)  Rh(OEP)(OOH) + Rh(OEP)-  Teimination: Rh(OEP)(OOH) + Rh(OEP)(H)  [Rh(OEP)] + H 0 +1O2 2  2  and in the presence of PPI13 •Rh(OEP)(PPh ) + CH2CI2 ^=^Rh(OEP)(a)(PPh ) + -CH2C1 3  3  Rh(OEP)- + -CH2C1 ^=^Rh(OEP)(CH Cl) 2  The reaction of Et3N with Rh(por)(a)(L) (par = OEP or 5,10,15,20teti^esitylporphyrmfTMP), L = H2O, (CH3)2CHOH, CH3CN) gave products, identified by visible (scanning and stopped-flow) and proton nmr spectroscopy to be Rh(por)(CH(Me)NEt2),  iii Et2NH as Rh(por)(Cl)(Et2NH), and Rh(por)(CH2CHO). This indicated amine C-H and C-N  cleavage and net one-electron reduction of Rh(JU) to Rh(U) species ([Rh(OEP)]2). Of other amines examined, aniline, N-methyl-diphenylarriine and N-ethyl piperidine all formed complexes of the type Rh(OEPXClXamine). Proton Sponge andtiibutylaminewith Rh(OEP)(Cl)(H20) give [Rh(OEP)]2 as a major product under anaerobic conditions. Only the mechanism of the Et3N system was examined in detail. Stopped-flow data indicated that Et3N initiallyreplacedL in the Rh (por)(Cl)(L) species m  to form a Rh (por)(Cl)(Et3N) complex. An equilibrium involvingreductionof Rh to Rh m  111  n  resulted and, in aromatic solvents under anaerobic conditions, slow reaction of Rh (por) with Et3N n  occurred to give Rh(por)(CH(Me)NEt3>. In CH2CI2,reactionof Et3N with Rh(por)(Cl)(L) was fast, giving a mixture principally of Rh(por)(CH2Cl)(amine) and the T| -ylidic enamine complex, 1  Rh(por)(Cl)(CH2CH=NEt2) with minor mounts of Rh(por)(CH(Me)NEt3). The Rh(por)(Cl)(CH2CH=NEt2) and Rh(por)(CH(Me)NEt3) species were unstable, both ultimately giving Rh (por)(Cl)(Et2NH). m  The synthesis, along with characterization by visible, proton and phosphorus nmr spectroscopy, of the previously structurally characterised, mono-phosphine complex Rh(OEP)(Cl)(PPh3) are presented. Additionally, spectroscopic evidence is presented for solution equilibria of Rh(OEP)(Cl)(PPh ) involving formation of Rh(OEP)(L)2 (L = PPh , P"Bu3) via +  3  3  thermal reactions, and Rh(OEP)(Cl)(L') (L* = CO, THF, CH3CN) via photochemical processes. Thermodynamic data (AH = -33 ± 2 kJ mol" and AS = -146 ± 8 J K^moH) have been 0  1  0  estimated for formation of the bis(uiphenylphospnine) species in CH2CI2: K  Rh(OEP)(Cl)(PPh ) + PPh ^== [Rh(OEP)(PPh ) ]+ + Cl3  3  3 2  Some complexes of Rh (OEP) containing l,4-bis(diphenylphosphino)butane (dppb), m  l,2-bis((hphenylphospliino)ethane (dppe), bis(diphenylphosphino)methane (dppm) and 1,3bis(&phenylphosphho)propane (dppp) have been characterized in situ using visible, proton and phosphorus nmr spectroscopy. The diphosphines (PP) are bound to Rh(HI) porphyrins in a monodentate dangling fashion (Rh (OEP)(Cl)(PP) and [Rh (OEP)(PP)2] ), or a bridging mode m  m  between two metal centers ([RhIH(OEP)(Cl)]-uPP-[Rhni(OEP)(Cl)]).  +  iv  Table of contents Abstract  ii  Table of Contents  iv  List of figures  vii  List of tables  xii  Abbreviations  xiv  Acknowledgements  xvii  Chapter 1. Introduction and literature review  1  1.1.  Introduction  1  1.2.  Metallation  3  1.3.  Non-Organometallic Complexes 1.3.1. Homo- and hetero-bimetallic complexes 1.3.2. Lewis-Base donor complexes 1.3.2.1. Halides/pseudo-Halides 1.3.2.2. O-and S-donors 1.3.2.3. N-and P-donors 1.3.3. Hydride complexes 1.3.4. Carbonyl complexes 1.3.5. Nitric oxide complexes 1.3.6. Isocyanide complexes 1.3.7. Dioxygen complexes  6 7 9 9 10 11 13 14 15 15 16  1.4.  Organometallic Complexes 1.4.1. o-Bonded complexes (mono-hapto) 1.4.2. Carbene complexes 1.4.3. Tt-Bonded complexes (dihapto)  17 17 21 21  1.5.  Stoichiometric Reactions 1.5.1. Ligand Substitution and Exchange 1.5.2. Oxidative-Addition and Reductive-Elimination 1.5.3. Insertion 1.5.4. Electrophilic Aromatic Metallation 1.5.5. Reactions at an axial ligand 1.5.6. Migrations between metal and porphyrin 1.5.7. Photochemistry  21 22 25 30 35 35 37 38  1.6.  Catalytic Reactions 1.6.1. Reactions of dihydrogen 1.6.2. Reactions of dioxygen 1.6.3. Dehydrogenation/Hydride transfer 1.6.4. Borane transfer reactions 1.6.5. Carbon-carbon bond formation  39 39 40 41 42 43  1.7.  Summary  44  1.8.  Goals of the present work  44  V  Chapter 2. Experimental methods  45  2.1.  General techniques used 2.1.1. Infrared spectra 2.1.2. Electronic spectra 2.1.3. NMR spectra 2.1.4. Mass spectroscopy 2.1.5. Micro-analysis 2.1.6. Chromatography 2.1.7. Hectrochemistry 2.1.8. Stopped-flow measurements  45 45 45 47 49 49 49 50 50  2.2.  Materials 2.2.1. Solvents 2.2.2. Gases 2.23. Other materials 2.2.3.1. Amines 2.2.3.2. Phosphines 2.2.4. Porphyrins 2.2.5. Rhodium porphyrin complexes 2.2.5.1. Rh(OEP)(Cl)(L) 2.2.5.1.1. L = H 0 , Rh(OEP)(Cl)(H 0)H 0 2.2.5.1.2. L = CH3CN, Rh(OEP)(Cl)(CH CN) 2.2.5.1.3. L = PPh ,Rh(OEP)(Cl)(PPh ) 2.2.5.2. Rh(OEP)(H) 2.2.5.3. Rh(TMP)(Cl)(L) 2.2.5.3.1. L = iPrOH,Rh(TMP)(Cl)(iPrOH) 2.2.5.3.2. L = CH3CN, Rh(TMP)(Cl)(CH3CN) 2.2.5.3.3. L • none, Rh(TMP)(Cl) 2.2.5.4. Rh(TMP)(H)  52 52 52 52 52 52 53 53 53 53 56 57 58 60 61 63 64 65  2  2  2  3  3  3  Chapter 3. Reactions involving Rh(OEP)(H)  67  3.1.  Introduction  67  3.2.  Results and Discussion 3.2.1. Reaction of Rh(OEP)(H) with O2 3.2.1.1. In benzene and toluene 3.2.1.2. I n C H C l 3.2.2. Reaction of Rh(OEP)(H) with O2 in presence of PPh3 3.2.2.1. Reaction of Rh(OEP)(H) with PPI13 3.2.2.1.1. In CH C1 solvent 3.2.2.1.2. In benzene and toluene 3.2.2.2. Reaction with 0 in CH C1 3.2.2.3. Reaction with O2 in benzene and toluene 3.2.3. Reaction of Rh(OEP)(H) with CO and O2/air  69 69 69 77 86 87 87 93 95 100 104  General Discussion  107  2  2  2  2  3.3.  2  2  2  Chapter 4. Thereactionof Rh (por)(Cl)(L) complexes with tertiary amines m  110  4.1.  Introduction  110  4.2.  Results and Discussion of Product Analysis 4.2.1. Aminereactionwith Rh(OEP)(Cl)(L) in benzene or toluene 4.2.2. Amine reaction with Rh(TMP)(Cl)(L) in benzene or toluene 4.2.3. Arnine reaction with Rh(OEP)(a)fJH 0) in CH C1  111 111 123 132  2  2  2  VI  4.2.4. Amine reaction with Rh(TMP)(CI)(L) in C H 2 C I 2 4.3. Results and discussion of kinetic studies 4.4. General Discussion Chapter 5. Characterisation and chemistry of Rh (pOT) phosphire complexes 5.1. Introduction 5.2. Results and Discussion 5.2.1. Reaction of Rh(OEP)(a)(PPh3)wimn»nc9hosphines 5.2.2. Solution equilibrium measurements 5.2.3. Reactions of Rh(OEP)(Cl)(PPh ) with CO 5.2.4. Reactions of Rh(OEP)(a)(H20) wim diphc)sphines ffl  3  5.3. General Discussion Chapter 6. General conclusions and suggestions for further work References  136 145 151 154 154 155 155 158 163 164 174 177 182  Appendix A. Literature data summary for rhodium porphyrin organometallies  192  Appendix B. Spectral data for Rh(TMP)(a)(phosphine) complexes  198  Appendix C. The derivation of equation 5.3  199  Appendix D. Tables of Kobs for reaction 5.1 at various ionic strengths and temperatures Appendix E. Assignment of the ligand *H nmr resonances of Rh(OEP)(CH(Me)NEt2)  200 205  vii  List o f figures Figure 1.1. Figure 1.2.  The structures of un-metallated tetraphenyl- and cctaemyl-pcnphyrins showing the numbering scheme far the pcnphine core. The structure of 5,15-Ws(2-pvridyl)ociaemylporphyrin and of its Rh(ILT) chloride dirner.  2 7  Figure 1.3.  The binding of the amino acid esters to chloro- and acerylmethyl-trans-5,15bis(2-hyciroxy-l-riaphmyl)octaethylpcq>h 12  Figure 1.4.  The isoshielding lines of the OEP porphyrin ring current of Rh^OEPXR) complexes, based on datafroma modified Johnson-Bovey equation.  Figure 1.5. Figure 1.6.  Cis- and trans-isomers of Rh (por)(CH2C(0)CH3) (por = 5,15-bis(2hydroxy-l-naphthylHxnaemylporphyrin).  18  m  23  Canonic TC- and o-complex intermediates in Aereactionof Rh^vOEPXQ) and vinylethers.  34  Figure 2.1.  Tonometer for anaerobic sample handling.  46  Figure 2.2.  Example of temperature variation of the H nmr shifts of C7D8.  48  Figure 2.3.  A small scale bulb-to-bulb distillation apparatus.  50  Figure 2.4.  The arrangement of reagentreservoirsfor handling air-sensitive solutions  l  during stopped-flow experiments using the Durrum Stopped-flow.  51  Figure 2.5.  The *H nmr spectrum of Rh(OEP)(a)(H20)H20in C D C I 3 .  55  Figure 2.6.  The IR spectrum (in Nujol) of Rh(OEP)(Cl)(H20)H20.  56  Figure 2.7.  The IR spectrum of Rh(OEP)(H).  60  Figure 2.8.  The *H nmr spectrum of Rh(TMP)(a)(iPrOH)iPrOH in C^De, at 20°C.  63  Figure 2.9. Figure 2.10. Figure 3.1.  The IR spectrum of Rh(TMP)(Cl)(CH3CN). Vacuum pyrolysis tube. The 300 MHz *H nmr spectra of (a) Rh(OEP)(H) in C6D6 and (b) 30 min  64 65  after addition of O2 at 20°C.  70  Figure 3.2.  The visible spectrum of the nmr sample illustrated in Fig. 3.1b.  72  Figure 3.3.  The visible spectrum of the products of thereactionof Rh(OEP)(H) and O2 in C6D6 30 min after addition of O2. 72 Change in apparent extinction coefficient at 542 nm during thereactionof Rh(OEP)(H) with O2 in benzene from various sources. 73  Figure 3.4. Figure 3.5.  The visible spectra of Rh(OEP)(H) in Cg>6 (in vacuo) dried only over ketyl and 30 min after addition of O2. 74  Figure 3.6.  The IR spectrum of a purple precipitate isolated from thereactionof Rh(OEP)(H) and O2 in benzene.  75  Figure 3.7. Figure 3.8. Figure 3.9.  Change in apparent extinction coefficient at 542 nm during thereactionof Rh(OEP)(H) with Q2 in toluene from various sources.  The 300 MHz H nmr spectra of (a) Rh(OEP)(H) in CD2CI2 and (b) 15 min after addition of O2 at 20°C. 78 !  The visible spectra of Rh(OEP)(H) in CD2CI2 and 30 min after addition of 79  O2.  Figure 3.10.  77  Change in apparent extinction coefficient at 542 nm during thereactionof Rh(OEP)(H) with O2 in freshly dried CD2CI2 for various [Rh] . 0  80  Figure 3.11. Changes in the 80 MHz *H nmr spectra during thereactionof Rh(OEP)(H) withO2at-40°CinCD2a281 Figure 3.12. The IR spectrum of theresiduefrom the reaction of Rh(OEP)(H) and O2 in CD2CI2.  83  Figure 3.13. Expansion of an upfieldregionof a 400 MHz *H nmr spectrum during the reaction of Rh(OEP)(H) with O2 in 05202 at -40 °C. Figure 3.14.  Changes in the methineregionof the 80 MHz *H nmr spectra during (a) cooling a solution of Rh(OEP)(H) in 03202 to -40 °C and (b) addition of O2at-40°C.  83  85  Figure 3.15. The 32.3 MHz P{ *H } nmr spectrum of Rh(OEP)(H) with excess PPI13 31  in CD202 at -60 °C.  87  The 300 MHz *H nmr spectra of Rh(OEP)(H) with PPI13 in CD2CI2 at -60 °C.  88  Figure 3.17. The 121.42 MHz 31p{lH } nmr spectra of Rh(OEP)(H) wittiPPly in C D 0 a t -60 °C.  88  Figure 3.16.  2  Figure 3.18.  2  The 300 MHz H VT nmr spectra of Rh(OEP)(H) with PPh3 in CD2CI2 over the temperature range 20 to -60 °C. l  90  Figure 3.19. The 121.42 MHz 31p{ lH } V T nmr spectra of Rh(OEP)(H) with PPh in CD2CI2 over the temperature range 20 to -60 °C.  90  Figure 3.20. The visible spectrum of the nmr sample illustrated in Fig. 3.18/19 for Rh(OEP)(H) with PPh in C L ^ a *  91  Figure 3.21. The 300 MHz H nmr spectrum of Rh(OEP)(H) with PPh3 in 0 ^ 0 2 at 20 °C.  92  Figure 3.22. The 300 MHz *H nmr spectra of Rh(OEP)(H) with PPI13 in C7D8 over the temperature range 20 to -60 °Q  94  3  3  l  Figure 3.23. The 121.42 MHz 3lp{ lH } nmr spectra of Rh(OEP)(H) with PPI13 in C7D8 over the temr^rature range 20 to -60 °C. 94 Selected regions of the 300 MHz H nmr spectra of (a) Rh(OEP)(H) with PPh3mCH2O2and(b)20mkafterad^tionofC>2at20 C.  96  Figure 3.25. The 121.42 MHz 3lp{ lH} nmr spectra of (a) Rh(OEP)(H) with PPh in CH2Q2 and (b) ~ 30 nrin after addition of 6 2 at 20°C.  96  Figure 3.24.  l  0  3  IX  Figure 3.26.  The visible spectrum of the nmr sample illustrated in Figs. 324/25, after the reaction of Rh(OEP)(H) with PPI13 and O2 in 01202. 97  Figure 3.27.  A selectedregionof the 300 MHz H nmr spectra of (a) Rh(OEP)(H) with PPh3mCT>2a2 and (b) 20 imn after ad^  Figure 3.28.  l  The 121.42 MHz 31p{ lH} nmr spectra of (a) Rh(OEP)(H) with PPh in 3  03202 and (b) ~ 30 min after addition of 62 at 20°C. Figure 3.29.  97 98  The visible spectrum of the nmr sample illustrated in Figs. 327/28 for the reaction of Rh(OEP)(H) with PPh and O2 in 03202 with the spectrum of Rh(0EP)(O)(PPh ) overlaid. 98 3  3  Figure 3.30. Figure 3.31. Figure 3.32. Figure 3.33. Figure 3.34. Figure 3.35. Figure 3.36.  The visible spectrum of the products of thereactionof Rh(OEP)(H) with PPh3and02inOi2Cl2. The 300 MHz *H nmr spectra at 19°C of (a) Rh(OEP)(H) with PPI13 in C7D8,fl>)30 min after addition of O2 at 19°C and (c) 5 days later. The 121.42 MHz 31p{ lH} nmr spectrum at 19°C of Rh(OEP)(H) with PPh3 in C7D8 5 days after addition of O2. The visible spectrum of the nmr sample illustrated in Fig. 3.30b, for the reaction of Rh(OEP)(H) with PPI13 and O2 in C7D8.  99 101 102 103  The visible spectrum of Rh(OEP)(H) with PPI13 in C6H6 and 30 min after addition of O 2 .  104  The IR spectrum of theresiduefrom thereactionof Rh(OEP)(H) and aircontaminated GO in benzene.  105  The changes in *H nmr spectra during the reaction in Q£>e of Rh(OEP)(H) with CO contaminated with O2.  106  Figure 4.1.  The *H nmr spectrum of Rh(0EP)(O)(Et2NH) in C6TJ>6 at 20 °C.  112  Figure 4.2.  The *H nmr spectrum of a CoT>6 solution of Rh(OEP)(Cl)(H20), 4 h after addition of Et3N. 112 The visible spectrum in C ^ at 25 °C of Rh(0EP)(O)(Et2NH) a few minutes after preparation in situ, and a solution of Rh(0EP)(O)(H20) ~6 h after addition of Et3N. 113  Figure 4.3.  Figure 4.4. Figure 4.5.  The *H nmr spectrum of a C&>6 solution of Rh(0EP)(O)(H20) (a) 15 min after addition of Et3N and (b) 7 days later. The visible spectrum of a solution of Rh(OEP)(0)(H20) wth Et3N, 30 min after the addition of Et N. 3  116 119  Figure 4.6.  The *H nmr spectrum of the CoT>6 solution sample illustrated in Figure 4.4, immediately after exposing to air. 120  Figure 4.7.  The visible spectrum of a CoHo solution of Rh(OEP)(0)(H20) wth Et3N 100 min after the addition of Et3N and then 90 min after addition of O2.  Figure 4.8.  The *H nmr spectrum of a Cg>e solution of Rh(TMP)(0)(iPrOH) (a) 10 min after addition of EtsN and (b) 3.5 days later.  122 124  Figure 4.9. Figure 4.10. Figure 4.11. Figure 4.12.  The *H nmr spectrum of a C7D8 solution of Rh(TMP)(a)(iPrOH) 1 day after addition of Et3N.  127  Plot of the *H nmr shifts of the ortho-methyls of the unknown complex vs. temperature.  128  The *H nmr spectrum of a C7D8 solution of Rh(TMP)(a)(iPrOH) with E13N, after addition of O2.  130  The *H nmr spectrum of a CD2CI2 solution of Rh(OEP)(a)(H20) and Et N, 2 h after addition of Et N. \  133  3  Figure 4.13.  3  The H nmr spectrum of a CD2CI2 solution of Rh(OEP)(a)(H20) and !  Et3N, 3 days after addition of Et N.  135  3  Figure 4.14.  Plot of the *H nmr shifts of selected amine  Figure 4.15.  The U nmr spectrum of a CD2CI2 solution of Rh(TMP)(a)(iPrOH) and Et3N, 10 min after thawing a liquid nitrogen frozen sample.  137  The *H nmr spectrum of a CH2CI2 solution of Rh(TMP)(a)(iPrOH) and Et3N, at varioustimesafter thawing a liquid nitrogen frozen sample.  140  The H nmr spectrum of a CD2CI2 solution of Rh(TMP)(a)(iPrOH) and Et3N, at varioustimesafter thawing a liquid nitrogen frozen sample.  142  Figure 4.16. Figure 4.17. Figure 4.18.  resonances.  136  l  l  The H nmr spectrum of a CD2CI2 solution of Rh(TMP)(a)(iPrOH) and Et N, 14 days after thawing a liquid nitrogen frozen sample, at various temperatures: J  3  Figure 4.19. Figure 4.20.  The comparison of H nmr spectra of solutions of Rh(TMP)(a)(iPrOH) with added Et3N in (a) CH2CI2 at -53 °C and (b) CD2CI2.  144  A typical stopped-flow trace of the change of absorbance at 540 nm of Rh(OEP)(a)(CH3CN) during thereactionwith Et3N in CH Cl2.  146  2  Figure 4.21.  143  !  Changes of the visible spectrum during the first 2 seconds of the reaction of Et N with Rh(OEP)(a)(CH3CN) in CH C1 . 147 3  2  2  Figure 4.22.  Changes of the visible spectrum during the first 10 seconds of the reaction of Et3N with Rh(TMP)(Cl)(CH3CN) in CH2CI2. 147  Figure 5.1.  Spectroscopictitrationof Rh(OEP)(Cl)(PPh3) with added PPI13 in CH2CI2 at25°C  159  Figure 5.2.  Plot of login Kobs vs.  Figure 5.3.  Variation of P{ H) nmr S-8free shifts for the PP ligand of 31  ji 0  5  for data in Table 5.3.  161  l  Rh(OEP)(Cl)(PP) with the chain length of the diphosphine backbone.  167  Figure 5.4.  The 31p{ lH} nmr spectrum of [Rh(OEP)(dppm)2j in CDCI3 at 20 °C.  168  Figure 5.5.  The P{ H) nmr spectrum of a C&k solution of Rh(OEP)(Cl) in the  +  31  l  presence of ~2.4 equivalents of dppm at 20 °C.  168  Figure 5.6.  The COSY spectrum of a C7D8 solution of [Rh(OEP)]2-udppm at -10 °C.  171  Figure 5.7.  Sketch of a possible conformation for dppm in [Rh(OEP)]2-Hdppm.  172  Figure 5.8.  Sr^troscopictitrationof Rh(OEP)(Cl)(H20) with added dppm in CH2CI2 at 25 °C.  Figure E.2.  Atom kbelling scheme for the -(CH(Me)NEt2) ligand of Rh(OEP)(CH(Me)NEt ). 2  Figure E.2.  The 300 MHz partially decoupled *H nmr spectra of the -(CH(Me)NEt2) ligand of Rh(OEP)(CH(Me)NEt2), prepared in situ in C7D8 solution at 20°C.  xii  List of Tables Table 1.1. Table 1.2.  Values of K i and K2 for anation reaction NastRhJDCTPPSJCH^^] with a-,Br,I-andNCS-at25°C.  22  Values of AH* and AS* for substitution of the first H2O ligand of Na3[Rhni(TPPS)(H20)2]witha%Br,I-andNCS-.  23  Table 1.3.  Binding constants of amines with Rh (por)(CH2C(0)CH3) (por = cis- and trans-5,15-rjis(2-hydroxy-l-naphthyl)oc^ in CHCI3 at 15 °C. , 23  Table 1.4.  Formation constants for binding of P P h to Rh^fjxnOCR) to form Rh (por)(R)(PPh3).  m  3  24  m  Table 1.5.  Some thermodynamic parameters for insertion into Rh-Rh and Rh-H bonds.  32  Table 2.1.  The P{ H] shifts of PPI13 relative to 85% H3PO4 in various solvents.  Table 2.2.  The H nmr data for H2TMP in various solvents at 20 °C.  Table 2.3.  The *H nmr data for Rh(OEP)(Cl)(H20)-H20 in various solvents at 20 °C.  55  Table 2.4.  The *H NMR spectral data for Rh(OEP)(Ci)(PPh3) at 20 °C.  57  Table 2.5.  Room temperature P{ U) NMR spectral data for Rh(OEP)(Cl)(PPh3) at 20 °C. The *H nmr spectral data for Rh(OEP)(H) in various solvents and temperatures.  Table 2.6. Table 2.7. Table 2.8. Table 3.1.  31  l  53  J  31  48  l  58 59  The *H NMR spectral dataforRh(TMP)(a)(iPrOH)iPrOH in various solvents.  62  The *H NMR spectral data for Rh(TMP)(Cl) in 01202 and C7D8 at various temperatures.  66  The visible spectral data for [Rh(OEP)]2 and for the product of the reaction of Rh(OEP)(H) with O2 in benzene.  73  Table 3.2.  Some IR data for M-OOH and M-OH species from the literature.  Table 3.3.  Some *H nmr chemical shifts for hydroxyl and hydroperoxo protons of MOH and M-OOH complexes from the literature. 84 Selected nmr dataforRh(0EP)(Cl)(PPh3) and [Rh(OEP)(PPh3>2] as  Table 3.4.  76  +  observed in CD2CI2 solution of Rh(OEP)(H) with PPI13 at ca. 20°C.  91  Table 4.1.  The H nmr spectral data for various Rh(OEP)(a)(amine) complexes.  115  Table 4.2.  Ligand H nmr spectral data for RhOEP(CH(Me)NEt2).  118  Table 4.3.  The *H nmr spectral data for various Rh(TMP) complexes in CoLhj or C D .  125  Ligand *H spectral nmr data for Rh(TMP)(CH(Me)NEt2).  127  l  !  7  Table 4.4  8  XUl Table 4.5.  Ligand *H nmr spectral data for Rh(OEP)(a)(CH2CH=NEt2).  133  Table 4.6.  The *H NMR spectral data for various RhfTMP) complexes in the H nmr l  spectrum illustrated in Fig. 4.15.  138  Table 4.7.  Ligand ^ nmr spectral data for Rh(TMP)(a)(CH2CH=NEt2).  139  Table 4.8.  Pseudo first-order rate constants for the disappearance of Rh(por)(Cl)(Et3N) in OfcCfc Pseudo first order rate constants for the reaction of Rh(por)(a)(CH3CN) with PPI13 and CO in CH2CI2.  Table 4.9 Table 5.1.  149 151  NMR spectral data far Rh(OEP) complexes of monodentate phosphines and other axial ligands.  156  Table 5.2.  Visible spectral data at 25 °C for Rh^OEP) complexes.  157  Table 5.3.  Variation of Kobsforreaction 5.1 in CH2CI2 at 25 °C.  162  Table 5.4.  Various H and P{ H) nmr spectral data for Rh(OEP) complexes of monodentate diphosphines. Various *H nmr spectral data for the phenyl protons of monodentate diphosphine ligands in Rh(OEP) complexes.  Table 5.5. Table 5.6.  l  31  l  166 167  Various H and P{ H} nmr spectral data for Rh(OEP) complexes l  31  l  containing bridging diphosphines.  170  Table A . l .  Rh (poT)(R) species (R = hydrocarbyl), and methods of their synthesis.  192  Table A.2.  Rh (por)(R) species containing heteroatoms, and methods of their  m  m  synthesis.  193  Table A.3.  Rh (EP)(R) species prepared from the "out-of-plane" Rh(I) complexes.  195  Table A.4. Table B.l.  Rh (TTP)(R) species electrochemically prepared from Rh (TPP). The H NMR spectral data for PJi(TMP)(Cl)(phosphine) complexes in  197  m  m  n  l  C6D .  198  6  Table D. 1.  Variation of Kob for reaction 5.1 in CH2CI2 at 10 °C.  200  Table D.2. Table D.3. Table D.4.  Variation of Kobsforreaction 5.1 in CH2CI2 at 15 °C. Variation of Kobsforreaction 5.1 in CH2CI2 at 20 °C. Variation of Kobs for reaction 5.1 in CH2CI2 at 25 °C.  201 202 203  Table D.5.  Variation of Kobsforreaction 5.1 in CH2CI2 at 30 °C.  204  Table E.l.  Ligand H nmr spectral data for Rh(OEP)(CH(Me)NEt2).  S  l  206  xiv  Abbreviations Ac  acyl group  acac  acetoacetonate  Ar  aryl group  BAP+  1 -benzyl-3-acetylpyridMum ion  BDE  bond dissociation energy  BNA+  1-tjenzylnicotinamide  CV  cyclic voltammetry  DMF  dimemylfcsTJiamide  dppb  l,4-bis(diphenylphosphino)butane  dppe  l,2-bis(diphenylphosphmo)etharie  dppm  bis(diphenylphosphmo)methane  dppp  13-bis((hphenylphosphino)propane  e  extinction coefficient (M^cm* ); dielectric constant  E1/2  half-wave potential (in cyclic voluunmetry)  EC  EC mechanism: fast (reversible) electron transfer process followed by  1  an irreversible, first-order chemical reaction Ep  peak potential (in cyclic voltammetry)  eq'n  equation  esr  electron spin resonance  <X>  quantum yield  FAB  fast atom bombardment (mass spectroscopy)  FED  flame ionization detector (GC)  fig.  figure  FTTR  Fourier transform infrared (spectroscopy)  GC  gas chromatography  H2EP  etioporphyrin(I)  H2MePDEE  mesoporphyrmCTX)-diethyl ester  H2MePDME  mesoporphyrm(LX)-dimethyl ester  H2MePME  mesoporphyrin(LX)-methyl ester  H2OEP H2por  2,3,7,8,12,13,17,18-octaemylpc^hyrin unspecified porphyrin  H2TAPP  5,10,15-trianubracenyl-20-(4-memoxyphenyl)porphyr^  H2TMP  5,10,15,20-tetramesitylporphyrin  H2T0TP  5,10,1520-tetra-o-tolylporphyrin  H TPP  5,10,15,20-tetraphenylporphyrin  H TPPS  S,10,15^0-tetra-p-sulfonatopbxnylporphyrin  H TTP  5,10,15,20-tetra-p-tolylporphyrin  H TXP  5,10,15,20-tetra-(3,5 diinethylphenyl)porphyrin  hv  light (photons)  iPr  isopropyl  IR  infrared (spectroscopy)  L, L'  ligand, usually a Lewis base  M (alone)  Molarity  M(asinMLn)  metal atom  N  Nujol™, used as a label in an IR spectrum  NAD(P)+  nimrinamidft cne.n7yme.  nmr  nuclear magnetic resonance (spectroscopy)  NOE  nuclear overhauser enhancement  Ph  phenyl group  pip  piperidine  31p{lH}  proton decoupled phosphorus 31 (nmr spectroscopy)  PP  diphosphine  py R  pyridine  RDS  rate (tetermining step  ref.  reference  SCE  standard calomel electrode  sect.  section  SET  single electron transfer  T  lifetime; chemical shift  TBAP  tetrabutlyammonium perchlorate  THF  tetrahydrofuran  TLC  thin layer chromatography  TMS  temunethylsilane  Vis  visible region (380—780 nm in electronic absorption spectroscopy)  VT  variable temperature  X  halide or pseudo-halide; inorganic anionic group  XPS  x-ray photoelectron spectroscopy  n-  ionic strength  u-L  prefix for a bridging ligand, L  2  2  2  2  alkyl group  The structure of Proton Sponge™ (used in Chapter 4):  Acknowledgements I thank Dr. Brian James for his support, guidance and encouragement Much thanks is due to my fellow graduate students for helpful discussions and support I particularly thank Dr. M. Camenzind in this regard and Dr. TJP. Wijesekera for help in obtaining the porphyrin ligands. Dr. A. Matsumoto also deserves thanks for his assistance in cyclic voltammetry experiments which, in the end, were not used in this thesis. I also thank the support staff in the department without whom little could be achieved. A teaching stipend and other financial support from the Department of Chemistry are gratefully acknowledged.  1  Chapter 1 Introduction and literature review  1.1.  Introduction There is a strong motivation to develop metal complex catalysts that will utilize molecular  oxygen under mild conditions far the selective oxidation of organic substrates (1,2), and it is very reasonable to look to analogues of components of natural systems, which normally operate under ambient conditions. In this thesis certain aspects of the chemistry of rhodium porphyrins and small molecules will be investigated. The thesis work will begin with the reaction of hydridorhodiumfJII) octaethylpoiphyrin with dioxygen, presented in Chapter 3. Chapters 4 and 5 present chemistry involving amines and phosphines. The first chapter of the thesis presents a review of the current literature of rhodium porphyrin chemistry and provides a relevant background to the research which constitutes this thesis. Of particuler relevance to the compounds discussed in the present work are section 1.2, on the metallation of porphyrins, and sections 1.3.3,1.3.7 and 1.4.1, on the hydrides, dioxygen and o-bonded organometallic complexes of rhodium porphyrins,respectively.Much of section 1.5, Stoichiometric Reactions, is critical to the mechanistic investigation. The porphyrin ligand is a planar macrocycle (Fig. 1.1) with an 18-electron TC system that displays aromaticity, and behaves as a quadridentate, soft-base ligand (3). Porphyrins are particularily characterised by intense colours, due to the extensive delocalised TC-system. In metalloporphyrins the colours are sensitive to the metal, its oxidation state and the nature of its other ligands (4). The XPS binding energies of the nitrogen Is electrons in metalloporphyrins show that the nitrogen atoms bound directly to the metal center are all equivalent sp type (5). 2  The historical motivation for the study of metalloporphyrin complexes of group 8 transition metals was an interest in the mechanisms of the photosynthetic,respiratory,enzymic and organometallic chemistry of biological systems (3). Regarding the last two areas, focus has tended to be on P-450 (Fe) (6,7) and vitamin B-12 (Co) (8) type chemistry, although B-12 chemistry is actually based on the corrin ligand and not the less flexible porphyrin (9). The light harvesting capabilities of porphyrins have of course been of continuing interest (energy storage or photosynthesis (10,a), tumor reduction via photodynamic therapy (10b)). Interest in catalytic  2 applications of biological and bicmimetic oxidations is high and provides the general motivation for the work presented in this thesis (1).  Figure 1.1.  The structures of un-metallated tetraphenyl- and octaethyl-porphyrins showing the numbering scheme for the porphine core.  In terms of Rh porphyrin (Rh(por)) species attention has focused on a relatively narrow range of artificial porphyrins, particularily D4h octaalkyl- and tetraaryl-rx)rphyrins (cf. Fig. 1.1) which have simpler spectra to interpret than the natural porphyrins of lower symmetry. "Direct" application to biological systems has been limited to reconstitution of myoglobins with Rh(IH) complexes (including Rh(Tn)-Me as an *H nmr probe (11)). At onetimeinterest focused on the use of metaUoporphyrins as non-paramagnetic shift reagents because of their strongringcurrent (sect. 1.4.1, Fig. 1.4 for visualization), the shift of the *H nmr resonances of cc<ffdinated ligands being a very useful diagnostic feature. Within the field of organometallic rwiphyrin chemistry there has been a number of recent reviews looking at the field from the point of view of electrochemistry and structural properties of metaUoporphyrins with metal-carbon and metal-metal bonds (12,13), organometallic aspects of P-450 metabolism (7), porphyrins and related macrocycles (3), and organometallic chemistry (13,14). The literature on the chemistry of Rh(por) in particular is expanding of late so that a  3  comprehensive review is lacking, although aspects have been thoroughly treated within broader reviews such as on organometallic compounds  (15),  or electrochemistry (12,13). As will be  discussed in section 1.6 there is considerable interest in catalytic application of Rh(por) species, especially by workers in Japan. Hydride transfer, superoxide generation, photochemical and Lewis acid (aldol condensation) activity are the areas so far explored. In France, C - C bond formation via cyclopropanation has been investigated. Application of steric control in Rh(por) species is a critical concern in the C-C bond forming processes. 1.2.  Metallation  The goal of almost all metallation recipes has been to obtain Rh(UI) species, which are usually air stable and easily manipulated for further derivatization at the metal center. The general route to Rh (por)(X) is based on the reaction of [Rh(CO)2Cl]2 with the appropriate free base m  porphyrin. Under mild conditions (room temperature), and in inert noncoOTdinating solvents, "out-of-plane" (16) Rh(I) dicarbonyl complexes form (for example, Scheme 1.1). These are oxidized to Rh(III) by air (17-21), by photolysis(22,23), electro-oxidation (24), or chemical procedures using acetoacetates, fluorosulphonates,  H C O 2 R , (RC(0))20,  RCHO,  RC(0)CH3,  RC(0)X, RX or X 2 (sect. 1.4.1 and 1.5.2), with concomitant shift of the Rh(IU) into the plane of the porphyrin.  -HCI benzene 2 h, R.T. -HCI (recrystallize)  ci —  Rh—  H0 2  — NN NN' CO  Scheme 1.1. Metallation of H2OEP using [Rh(CO)2Cl]2.  4 Formation of "out-of-plane" Rh(I) dicarbonyl complexes of the kind illustrated has been shown to be general for a number of symmetric and unsymmetrical tetraalkyl- and meso-tetraarylporphyrins, azaporphyrins, oxophlorins, corroles and thiaphlorins (the last two polypyrrole macrocycles give mono-Rh^CO^ adducts only) that are not sterically hindered (25-29). After oxidation (often by refluxing in air briefly) one Rh ends up in the macrocycle as 1  Rh(m).  Oxidation by addition of I2  during work-up has yielded Rh (por)(I) species (por = meso-, deutero-porphyrin (10,26-29); por m  = TPP -, ToTP ", TMP - (30)) in good yield. The more hindered porphyrins (T0TP -, TMP -) 2  2  2  2  2  required prolonged reflux in 12-dichloroethane (16-36 h). For less hindered porphyrins, forcing conditions can lead to complications. For example, after OEPH2 and Rh(CO)2Cl2 were refluxed for 7 h in CHCI3, [OEPH4][Rh(CO)2Cl2]2 has been isolated and characterized by x-ray crystallography (28,31); however, coupling photolysis with similar conditions (benzene/CCU reflux 8 h) gave moderate yields of Rh (por)(Ci) (por = OEP -, EP -) (32). In benzene the m  2  2  paramagnetic complex Rh (TPP)(Cl)(C6H5) has been obtained after prolonged reflux (33,34). rv  Combining reflux with photolysis in toluene gave benzylrhodium(III) complexes rather than Rh (por)(Cl), which was obtained under otherwise identical conditions in benzene (32). In  A series of Rh (por)(Cl) complexes, where por = octaethylporphyrin meso- substituted m  with various Lewis base functional groups (phenolic, quinolyl, methoxy, pyridyl), were prepared from [RhCl(CO)il2 in benzene or NaOAc/HOAc (35). Mixtures of atropisomers were obtained which were separable in some cases. When N-alkyl porphyrins or corroles are reacted with [Rh(CO)2Cl]2 in CHCI3, only one Rh (CO)2 unit is bound trans to the N-alkyl group(25,36). The complexes formulated as N,NI  [Rh(CO)2Cl]2[por], or [(por)(Rh(CO)2)][Rh(CO)2a2], were also found (17,36,37); gentle I  heating of these resulted in formation of alkyhhom'um(IIJ) complexes (sect 1.5.6). The rate of metal incorporation into the N-alkyl porphyrins was much faster than into the non-N-alkylated porphyrins. In summary, the low-valent routes yield "out-of-plane" Rh dicarbonyl complexes that are 1  moderately air-stable and can be isolated from the product mixtures at short reaction times. Usually longer reactiontimesand/or higher temperatures are required to increase the proportion of  5 more desirable in-plane R h complexes; however, application of long reflux periods and/or m  photolysis can also lead to unexpected results. Workup is usually by column chromatography, yields are often variable and unexpected products can result For example, reaction (1.1) is used to obtain Rh(TPP)(02) (41-44). If the carbonyl is not added slowly to the porphyrin much of the rhodium is lost as metal (41). [Rh(CX)) Cl] 2  H TPP  2  Rh (TPP)(02) (after chromatography) m  2  HOAc/NaOAc reflux, N  (1.1)  2  In spite of "fme-turiing" required to achieve reliable and good yields the preferred metallation route (relative to those to be discussed below) is via the reaction of [Rh Q(CO) ]2 with H2por to form I  2  ultimately Rh (por)(X). In addition, the "out-of-plane" Rh dicarbonyl complexes are quite m  1  sensitive to RX oxidative addition, which can be useful preparatively. The use of other Rh(I) complexes as precursors has not been explored. A mention of [Rh(cyclooctene)2Cl]2 as being useful has been made but details are not available (38). A RhfJU) precursor such as RhCl3-3H20 has been used in conjunction with CO as reductant (39,40). These reactions are believed to go via a Rl^tpor) species, which has not been isolated, and which is subsequently air oxidized to Rh (por)(Cl) (reaction (1.2)). m  CO, EtOH  porphyrin  RhCl -3H 0 3  -Rh (por)(Cl)(H 0) m  2  2  reflux  HOAc/NaOAc reflux 2 h, air  (1.2)  Addition of I2 during work-up of an H2TPP metallation yielded Rh (TPP)(T) in variable yields m  (45). Addition of H2 during work-up of an H OEP metallation gave Rh(OEP)(H) (46). 2  Variations of the general method of Adler et al. (47) for metal la ting pc*rphyrins in DMF have been used with RhCl3-3H 0. Depending on the exact recipe, and the type of px>rphyrin used, 2  one obtains Rh (por)(Cl)(NHMe2) (48,49), pUi (por)(NHMe2)2]Cl (50) (sometimes mixed with m  m  [Rh (^or)(NHMe2)2][Rh(CO)2Cl2] (51)), or mixtures of Rh°I(por)(a)(NHMe2) and m  [Rh (por)(NHMe2)2]Cl (52). m  6 For example: RhCl -3H 0 3  2  H TPP  DMF  2  reflux, 30 min  Rh (TPP)(Cl)(NH(CH3) ) DMF + reflux 24 h, air [Rh (TPP)(NH(CH ) ) ]Cl m  2  m  3 2 2  (1.3)  The amine ligand appears to be derived from decarbonylation of the solvent, N,Ndimethylacetamide, N-methylformamide and N-ethylformamide giving HNMe2, H2NMe and H2NEt ligands, respectively. However, the more sterically hindered N,N-diemylformamide gave Rh (por)(Et) (por = OEP -, TPP *). The decarbonylation is proposed to occur after metallation m  2  2  because substitution of Rh (por)(Cl) for "RhCbjx^O + H2por" in the metallation procedures m  gave identical products (53). The non-amine ligated, water soluble Na3[Rh (TPPS)(H20) ] has m  2  been prepared in a DMF/MeOH/H20 solvent mixture by a similar procedure (54,55). 1.3.  Non-Organometallic Complexes Four-coordinate ("bare") porphyrin complexes have been proposed for Rh in oxidation  states I, II and HJ. These complexes are unusually reactive and only for the more oxidatively stable Rh(LTI) state has such a complex been isolated, although it is possible to prepare such stable Rh(I) species in solution. Evidence supporting the ccordinative unsaturation includes the strong nucleophilicity of [Rh^or)]-, the radical chemistry of "Rh (por)" and the strong electrophilicity of n  [Rh (por)] as discussed in section 1.5. m  +  Air sensitive "4-coordinate" [Rl^tpor)]' has been formed in situ under inert atmospheres but not yet isolated (sect 1.3.3 re: H[Rh(TPP)]). Reduction of Rh (OEP)(Cl)-2H20 in EtOH m  with NaBH4/NaOH(aq) gives [Rh^OEP)]- (17). Alternatively Rh(por)(H) can be deprotonated to give the corresponding Rh(I) anion. Thus Rh(OEP)(H) in CQHO is deprotonated by stirring with alcoholic-hydroxide solutions (56). An elegant approach is to deprotonate Rh(por)(H) (por = TPP ", TTP ") in CoD6 with KOH solubilised by 18-crown-6-ether (57). Characterization of 2  2  [Rh(por)]- as a symmetric monomer is based on its reactivity as a nucleophile (sect. 1.3.3 and I  1.5), as well as uv-vis and *H nmr spectroscopy; however, detailed structural studies of the solution species are lacking.  7 The Rh (por) radical is proposed to exist only as an intermediate in most situations (sect n  1.5). The monomer readily dimerizes to form diamagnetic [Rh(por)]2 (see sect 1.3.1), but can reportedly be trapped in a low-temperature matrix. Based on uv-vis and esr data, irradiation of Rhin(TPP)(Cl) (at X <400 nm), or [Rh(TPP)] (at X < 310 nm) in 2-Me-THF, gives Rh (TPP) n  2  at 77 K (58). The cationic complex [Rh (OEP)]X (X = CILV, BF4-) can be isolated in ca. 50% yield ra  from the reaction of Rh (OEP)(Cl) with either AgC104 or AgBF4 in dry 01202- The anions are m  non-coordinating and the Rh(DT) cation is a powerful electrophile (sect 1.5) (21). The first reduction of [Rh (TPP)]C104, generated in situ by electro-oxidation of Rh (TPP)(C(0)CH3), is m  m  an irreversible 1-electron process at -0.67 V (vs SGE) in PhCN to form Rh(TI) (59). As for the case of [Rh^or)]-, detailed solution studies of [Rh (OEP)]X are lacking. m  1.3.1. Homo- and hetero-bimetallic complexes Dimerization of 5,15-bis(2-pyridyl)octaethylporphyrinato rhodium(III) chloride occurs in CDCI3.  The upward facing pyridyl groups on the periphery coordinate to the Rh metal center of  another molecule of the monomer (Fig. 1.2); the dimer did not form in pyridine-ds (60).  Figure 1.2.  The structure of 5,15-bis(2-pyridyl)octaemylporphyrin and of its Rh(ItI) chloride dimer (adapted from ref. 60).  The only isolated metal-metal bonded homo-bimetallic complexes of Rh(por) are formally in the +2 oxidation state and are formulated as [Rh(por)]2. The 14 d electrons of this complex are proposed to be in the configuration oh&ryhi**, yielding a diamagnetic species with a net single metal-metal bond (61). The BDE for the metal-metal bond of [Rh(OEP)]2 has been estimated,  8 from *H nmr line broaderiing data, as 16.5 kcal/mol in benzene and 17.5 kcal/mol in cyclohexane (62,63). The diamagnetic dimers are prepared from Rh(por)(H) in aromatic solvents by oxidative cleavage in air (por = OEP -) (64,65), or by thermal (64) or photolytic (43,57,61) homolytic 2  cleavage (por = OEP -, TPP -, TTP -). For example (reactions 1.4 - 1.5), in toluene the OEP 2  2  2  dimer can be prepared by either route. 2 Rh(OEP)(H) + air —[RhD(OEP)] + H 0 2  (1.4)  2  2 Rh(OEP)(H) + heat or hv —[Rhn(OEP)] + H 2  (1.5)  2  The isolated tetiwylporphyrin complexes have been characterized only by *H nmr. Photolysis of (H-TPP)[Rh (CO) ] in benzene is reported to yield [Rh (TPP)] dimer via formation of I  n  2 2  2  Rh (TPP) monomer (22). The identity was made on the basis of uv-vis data and reactivity toward n  0 but has been subsequently suggested to be Rh(TPP)(H) also on the basis of the uv-vis data 2  (52). Heating Rh(TPP)(0 ) at 150 °C in vacuo results in sublimation of a diamagnetic RhfTPP) 2  compound tentatively formulated as [Pvh (TPP)] , on the basis of reactivity and unpublished n  2  spectral data (42). The isolated R h ( I I ) dimers have not been examined electrochemically. However, electrochemical reduction of Rhni(TPP)(Cl)(NHMe ) or [RhDl(TPP)(NHMe )J Cl in PhCN, 2  2  2  THF, or py gives [Rh (TPP)] via a 1-electron EC mechanism (sect. 1.3.2.3). The dimer has not n  2  been isolated but cyclic voltarnmetry shows a reversible 2-electron reduction of the species at -1.95 V (vs. SCE) in PhCN (0.1 TBAP). Similar reductions occur in THF at -1.83 V and py at -1.90 V. The reduced species is proposed to be a radical anion on the basis of uv-vis data. The [Rh (TPP)] species is irreversibly oxidized during the anodic sweep at Ep = -0.24 V in PhCN, n  2  Ep = -0.22V in THF and Ep = -0.40V in py. No cathodic peak was coupled to the oxidation in the second cycle and the product is believed to be Rh (TPP)(solvent) . Some dissociation of the m  +  dimer to Rh (TPP) monomer is indicated and the Ep for its oxidation was ~ -1.0 V (52). The n  monomelic Rh(U) species generated in situ readily reacts with halogenated and unsaturated compounds to generate organometallic products (sect. 1.4).  9  A hetero-bimetallic Rh(l>In(in) dimer, Rh^OEPJInHKOEP), is synthesised by the reaction of Rh^OEP)-, prepared in situ by deprotonation of Rh(OEP)(H) with NaN(SiMe3)2), and In (OEP)(a) in THF. The spectral and x-ray crystallographic data are consistent with a single m  metal-metal bond. The Rh(T)^-*In(in) formulation is supported by the quantitatively +  regioselectivereactionwith Mel to form Rh(OEP)(Me) and In(OEP)(I) (66). Hetero-bimetallic complexes of the type Rh(TPP)(MLn), MLQ = Mn(CO)5, Co(CO)4, GeChj, have been isolated byreactionof the corresponding metallate anions with Rh (TPP)(Cl) in m  THF. Reaction of SnCb with Rh (TPP)(Cl) gives Rh(TPP)(SnCl3). The complexes are believed m  to be 5-ccordinate, akin to Rh (TPP)(X) on the basis of preliminary IR, uv-vis and *H nmr data, m  even though the nmr data also indicate that all the complexes are symmetrical (D41O in solution (67). 1.3.2. Lewis-Base donor complexes It is relatively easy to form Rh(por)(X)(L) species in situ from Rh(por)(X)(L') species because of lability of L' (see sect. 1.5.1). The point of view of this section leans more towards isolable complexes. Ligand exchange will be treated in section 1.5.1. 1.3.2.1.  Halides/pseudo-Halides  As noted in section 1.2 on metallation, Rh (por)(X) is the usual product of metallation. m  The chloride complex is usually obtained because RI1CI3XH2O or [RhCl(CO)2]2 is the common starting material; however, air is usefullyreplacedby I2 as oxidant in which case Rh(LU) iodide complexes form. A bromide complex, Rh^OEPJiT^fJWs), has been isolated and will be discussed in section 1.3.2.3 on N- and P-donor complexes. There are noreportsof the isolation of in-plane Rh(por) halide complexes in oxidation states other than +3, with the exception of Rh  rV( pp)(Ci)(C H ) (33,34). T  6  5  The XPS binding energies for the Rh 3d electrons in Rh (por)(Cl) (por = OEP -, TPP -) ra  2  2  are consistent with a RhfJJJ) oxidation state (68). Also consistent with the RhfJTJ) oxidation state is the hypso-type uv-vis spectra (17,69). The first oxidation of Rh (OEP)(Cl) is a reversible m  1-electron process at 0.82 V (vs. SCE, CH2CI2) and for the TPP analogue at 0.98 V, giving a porphyrin 7t-cation radical species, identified by esr and uv-vis (43). The electrochemistry of  Rh CrPP)(Cl)(L) (L = amine, phosphine) is similar and will be discussed in section 1.3.2.3. m  Thefirstoxidation is a reversible 1-electron process at the porphyrin to generate a Rh(HJ) porphyrin cation radical, and thefirstreduction is an irreversible 1-electron process at the metal giving Rh(II) with loss of the CI* ligand. Little interest has been shown in pseudo-halide complexes of Rh(por). The CI ligand of -  Rhm(MePDEE)(Cl)(H 0) has been replaced with SCN- (N-bonded), CN\ or N - (38). A 2  3  thiocyanate complex has been prepared in situ from Na3[Rh (TPPS)(H20)2] (sect 1.5.1), but the m  bonding mode is uncertain (54,55). 1.3.2.2.  O- and S-donors  Most of the complexes containing Rh-0 moieties (exclusive of O2 complexes to be discussed in sect. 1.3.6) are aquo complexes (see below). The carboxylate complex Rh (EP) (O2CCH3) has been reported but with few details (28). The ethene complexes Rh (OEP)(X)(CH =CH ) (X = CF3CO2-, CF3SO3-) have been observed by *H nmr (sect. 1.5.3 m  2  2  and 1.5.5) (70). Solvato complexes in THF are known (sect 1.3.3 and 1.5.6). Oxygen bound intermediates are proposed during the abstraction of the acetyl group from N^-dimethylacetamide (71), the dehydrogenation of secondary alcohols (sect. 1.6.3.), and the enolization of ketones (sections 1.5.5 and 1.6.5). Dicarboxylate complexes of Rh(IH) thkpWorin have been reported (28). Aquo complexes of Rh (OEP)(Cl) and RhDI(OEP)(R) (R = n-GuHp, n-GpHig) have m  been isolated (17), as well as the water soluble Na3[Rh (TPPS)(H 0) ]-22H 0. The pK i and m  2  2  2  a  pKja for the TPPS complex in H 0 (25 °C; \i= LOOM NaCIO*) are 7.01 and 9.80, respectively 2  (54,55). [RhDIcrPPS)(H 0)2] - =  [Rh"TfTPPS)(H20)(OH)]4-  3  2  [Rh"T(TPPS)(OH)]5-  (1.6)  2  The [Rh (TPPS)(H 0) ] - complex shows moderate phosphorescence (O £ IO") in m  3  2  2  2  H 0 at room temperature, as do Rh (por)(Cl)(MeOH) species (por = OEP -, TPP ", MePME ") m  2  2  2  2  11 formed in situ in MeOH. Strong phosphorescence (4> = 0.23) was observed for Rh (EP)(Cl)(2m  Me-THF) in 2-Me-THF at 77 °K (50). There are no examples of isolated complexes containing a Rh-S bond. Metastable complexes of the type [Rh (OEP)(thiolate)2] (thiolate = thioglycolate ethyl ester, thioglycolate m  +  n-octyl ester, thioglycolate octadecyl ester, methyl 3-mercaptopropionate, 2-mercapto acetanilide, thioalide, thiosalicylic acid, Me- and halo-thiophenols) can be prepared in situ by the reaction of Rh (OEP)(Cl) with the appropriate thiolate in a number of solvents, the thiolates being prepared in ni  situ using B 1 1 4 N O H . The bis-thiolato complexes have a split-Soret hyperporphyrin spectrum similar to that of P-450 and decompose with concomitant catalytic reduction of O2 to 02' (sect. 1.6.2) (72). The position of the Soret peaks (over a 20 nm range) correlate linearly with Hammett o values of thiophenol substituents indicating an inductive dependance; linear correlation with the dielectric constants of 5 alcohol solvents was also found (over ~10 nm range). 1.3.2.3.  N- and P-donors  As mentioned in section 1.2, metallation of H2por in amide solvents usually gives amine complexes of the type Rh (pOT)(Cl)(amine) or [^ (por)(amine)2]X (amine = primary or m  ra  secondary). The counter ion (X = CI) can be exchanged for PF^" by treatment with AgPFg in -  acetone (51). Irradiation of Rh (OEP)(Cl) in toluene in the presence of NHMe2 gives m  [Rh (OEP)(NHMe2)2]Cl but, if Rh (EP)(Cl) is used in 12-dichloroethane, the CI is not replaced m  m  and Rh (EP)(Cl)(NHMe ) is obtained (32). The ammonia complexes Rh (OEP)(X)(NH ) (X = m  m  2  3  Br, I") are obtained by a somewhat novel route, by reaction of Rh (OEP)(Cl)(H20) with EtMgX m  followed by workup in aqueous NH4CI (17). Reaction of [Rh(OEP)]2 with Etl, followed by recrystallization (after chromatography) from n-hexane/pyridine, gives Rh (OEP)(I)(py) (64). ra  Pyridine complexes of the type Rh (OfZP)(CH3)(amine) (amine = 4-CH3-py, py, 4-CN-py) can m  be isolated in the presence of excess pyridine, but equilibrate to a imxture of 5- and 6-coordinate species in solution (17). Chloro- and meuhyl-momum(III) complexes of trans-5,15-bis(2-hydroxy-l-naphthyl)and 5,15-bis(l-naphmyl)octaethylporphyrin form 1:1. amine adducts with L-phenylalanine methyl ester and L-leucine methyl ester, as well as with 2-phenylemylarriine and 3- or 4-armnoheptane in  12 CHCI3. The bmding of the non-ionic amino acid esters is both at Rh (by the amino group) and at  naphtholic functions on the periphery of the porphyrin (by the ester group) (Fig. 1.3) (73).  ^—' Figure 1.3.  CH,  >  —'  The binding of the amino acid esters to chloro- and acetylmethyl-trans-5,15bis(2-hydroxy-l-naphthyl)octaethylporphy  (adapted from ref. 73).  In the particular case of some [Rh (pOT)(NHMe2)2]X complexes, there is evidence of m  close association of the anion with the cationic complexes, by hydrogen bonding. For example, X-ray crystallography reveals that the CI" of [PJi (EP)(NHMe2)2]Cl-H20 is in a roughly m  tetrahedral environment, hydrogen-bonded to two N-H groups on different complexes and two water molecules, and the water molecules are not linked to any other moieties (49). The tightness of ion pairing in [Rh (por)(NHMe2) ]X (por = OEP ', TPP ") is believed to increase with X in m  2  2  2  the order [Rh(CO)2Cl2? < PF6' < CP, this being based on IR data, ligand N-H *H nmr resonance shapes and positions, and on ligand N-Me and OEP meso C-H mutual 2D NOE correlations in CDCI3 solution (51).  The electrochemistry and spectrcelectrochemistry of Rh (TPP)(Cl)(NHMe2) and in  [Rh (TPP)(NHMe2)2]Cl have been studied. Depending on the solvent used, a reversible m  1-electron oxidation of the porphyrin occurs at 1.3 - 1 V (vs. SCE) to form a Rh(IJJ) porphyrin cation radical. A 1-electron reduction occurs at an Ep of -1.28 to -1 V (vs. SCE) to give ^Rh (TPP)]2 via an EC process involving a transient Rh(LI) species (detected at -78°C by CV), n  previously mentioned in section 1.3.1 (52). Strong phosphorescence is observed for pih (EP)(NHMe2)2]Cl in 2-Me-THF at 77 K m  (Op =0.23, Tp = 0.73(2) ms) (49) and has been discussed in the context of iterative extended Htickel calculations (74).  13 As described in this Thesis (Chap. 5), addition of PPI13 to Rh^OEPXCl) in benzene gives Rh (OEP)(a)(PPh3) which is characterized spectroscopically and crystallographically. The m  octahedrally cc<jrdinated Rh atom is displaced by 0.077 A from the mean plane of the porphyrin N atoms towards the PPh3 ligand (75). The cationic complexes [Rh (por)(L)2]PF6 (por = OEP ", m  2  EP , TPP ; L = PPh2Me, P(OMe)3) can be prepared by addition of excess phosphine to 2-  2-  acetone solutions of Rh (por)(PF6), prepared in situ; alternatively, the OEP complexes can be m  prepared by photolysis of [Rh (OEP)(NHMe2)2]PF6 in the presence of the phosphine (32). A m  rjy ni( pp)(pp ) ]+ 1  T  h3  2  com  piex can also be prepared in situ from Rh(TPP)(02) through a  Rh(TPP)(02)(PPh3) intermediate (sect. 1.3.7). The rhodium phosphonate complex Rh (OEP)(P(0)(OCH3)2) is formed by the reaction m  of P(OCH3)3 with [Rh (OEP)]2. An unstable Rh(H) phosphite complex, which loses a methyl n  radical, is proposed as an intermediate (76). There are no examples of isolated low-valent Rh complexes contacting N- or P-donors. The XPS binding energies for the Rh 3d electrons in [Rh (TPP)(PPh3)2]PF6 and ra  [Rh (OEP)(PPh2Me) ]PF6 are consistent with a RhfJOT) oxidation state (68). The electrom  2  chemistry of in situ [Rh (TPP)(P)2] species (P = PPI13, PPhMe2) varies with the phosphine m  +  ligand. The PPhMe complex in CH2CI2 (0.1 M TBAP) has a reversible 1-electron oxidation at 2  E1/2 = 1.20 V (SCE) to give a Rh(ni) porphyrin cation radical, and a reversible 1-electron reduction at E1/2 = -1.14 V (SCE) to give a Rh(ni) porphyrin anion radical (77). The PPI13 complex is reduced at Ep = -0.98 V (SCE) via an 1-electron EC process that is metal-centered and is followed by loss of PPI13; electro-oxidation was not reported on (44). 1.3.3. Hydride complexes In iPrOH or DMF at 20 °C, dihydrogen reacts with Rh(TPP)(02) to give Rh(por)(H), originally formulated as H[Rh (TPP)]-2H 0 (41). Reaction of H with RhHI(OEP)(Cl) in I  2  2  methanol at room temperature precipitates Rh(OEP)(H) but in low yield (~20%) (65,78), while better yields (80%) are obtained if in situ Rh (OEP)(Cl) species is used (46). Reaction of m  Rhni(por)(D (por = TPP ", TTP ") with sodium formate in MeOH, followed by workup under H , 2  2  2  gives Rh(por)(H) in 78% yield (57). Rhodium hydride complexes can be prepared also via  protonation of Rh© species generated in situ from borohydride reduction of Rh(m) complexes. Typically RhHI(por)(X) (por = OEP -, X = CI* (65,78); por = TPP -, TTP2-, X = I" (57)) in EtOH 2  2  is reduced with NaBHU followed by protonation with AcOH. Yields of 60 - 80% of Rh(por)(H) are reported. Acidification with AcOD gives Rh(por)(D). The electronic spectrum of Rh(OEP)(H) is similar to the hyp so-type spectra of Rh (OEP)(R) complexes, and thus the oxidation state of rhodium is considered correctly assigned m  as three (65). The diamagnetic Rh(por)(H) complexes are all characterized by a solvent dependent doublet hydride *H nmr resonance upfield of TMS in the -29 to -42 ppm region, and thus in solution the species are better formulated as Rh(por)(H)(solvent). The H nmr spectrum of !  Rh(OEP)(H) in benzene is temperature dependent, probably due to exchange with small amounts of [Rh (OEP)]2 (46) (sect. 1.3.1). The porphyrin H nmr resonances of Rh(TPP)(H) and n  !  Rh(TTP)(H) in C£>e are broadened and also the hydride resonance is not seen because of the exchange with dinuclear species (equilibrium 1.7) (57). Thermodynamic data for the equilibrium: [Rh(OEP)] + H « r 2Rh(OEP)(H) 2  (1.7)  2  has been measured: AH = -13 ± 4 kJ mol" ; AS° = 3 ± 8 J K mol' . As the BDE of [Rh(OEP)] 0  1  _1  1  2  is known (sect. 1.3.1), the Rh-H bond energy of Rh(OEP)(H) has been estimated to be 259 kJ mol (46,63). Conversion of Rh(por)(H) to [Rh (por)] and H is a typical decomposition path -1  n  2  2  observed for the hydrides (sect. 1.3.1 and 1.5). Although the Rh-H bond can be considered to be largely covalent, the hydrides can be deprotonated by MOH (M = Na+ in EtOH; M = K [18-crown-6-ether] in benzene) (41,57,80), +  and this is just the reverse of the synthesis of Rh(por)(H) via protonation of Rh (por) . Solutions I  _  of Rh(TPP)(H) in DMF are conducting, and the proton is titratable (41). The Rh-H pK has not a  been reported in any solvent system, although the terraarylporphyrin complexes are considered to be more acidic than the octaalkylporphyin complexes (65). 1.3.4. Carbonyl complexes Carbonylation of Rh(TPP)(Cl) in CH C1 with 1 atm CO precipitates Rh(TPP)(Cl)(CO), 2  2  Vco = 2100 cm . The CO appears to be labile and the complex was not stable enough to -1  15 withstand chromatography (82). The coordinated CO is susceptible to nucleophilic attack at carbon (sect 1.5.3). Reactions of CO with [Rh(OEP)]2 in toluene give an equilibrium system including 3 species besides [Rh(OEP)J2: a 1:1 adduct [Rh(OEP)]2CO (vco = 2094 cm- ), a metallo-ketone 1  [Rh(OEP)]2-uCO (vco = 1733 cnr*) and a double insertion product [Rh(OEP)]-C(0)C(0)[Rh(OEP)] (sect 1.5.3).. In situ characterisation was by H and C nmr, and IR (83-85). !  1 3  Another 1,2-ethanedionyl complex, [RhCTXP)]-C(0)C(0)-I^(TXP)], has been similarly characterised (85a). The monomeric Rh (TMP) complex reacts with CO to form Rh(TMP)(CO), n  containing a bent 17-electron M-CO unit, found in equilibrium with pihCrMP)]-C(0)C(0)[Rh(TMP)] (85b). 1.3.5. Nitric oxide complexes Nitric oxide reacts with [Rh(OEP)]2, Rh(OEP)(H) and Rh(por)(Cl) (por = OEP -, 2  TPP ") in toluene solution, or the solid state, to give ultimately Rh(por)(NO). On the basis of epr 2  data Rh(por)(NO) is formulated as diamagnetic Rh (por)(NO-). The Rh(OEP)(NO) complex m  undergoes a reversible 1-electron oxidation in CH2CI2 at 0.77 V (vs. SCE) and the TPP analogue is similarly oxidized at 0.94 V, giving porphyrin n-cation radical species. The reaction of the Rh(por)(Cl) complexes with NO proceeds through a paramagnetic porphyrin 7t-cation radical mterrnediate species Rh (por )(Cl-)(NO-). In the presence of excess NO, Rh(por)(NO) m  +  reversibly adds further NO to form a paramagnetic porphyrin 7C-cation radical species Rh (por+')(NO-)2. Solutions of Rh(OEP)fNO) are air-sensitive, slowly giving Rh(por)(N02) ni  (43). 1.3.6. Isocyanide complexes The cationic complexes (T*h (porXt-BuNC)2]PF6 (por = OEP *, EP ", TPP -) can be m  2  2  2  prepared by addition of excess t-BuNC to acetone solutions of ^"^(porJJPF^ prepared in situ. Alternatively, the OEP complex can be prepared by photolysis of [Rh (OEP)(NHMe2)2]PF6 ffl  the presence of excess isocyanide (32).  m  16 1.3.7.  Dioxygen complexes It should be noted that no crystal structures, elemental analyses or isolated yields have yet  been reported for any of the dioxygen species discussed in this section. The paramagnetic dioxygen adduct Rh(TPP)(02) can be isolated from the metallation reaction of H2TPP with [Rh(CO)2Cr]2 in DMF (41,42). The complex can reportedly also be made by borohydride reduction of "any Rh (TPP)(X)" complex with subsequent addition of O2 (43). The analogous m  Rh(OEP)(02) complex is thermally unstable, but could be prepared at -80 °C by slow diffusion of dry O2 into a toluene solution of [Rh (OEP)]2. The O2 is believed to be coordinated end-on as a n  superoxide, based on esr data at -160 °C and IR data (v^ = 1075 cm ) of an impure solid isolated -1  at -20 °C; warming solutions of the superoxide species to room temperature results in formation of the |i-peroxide Rh (OEP)-C>2-Rh (OEP), as judged by its diamagnetism, disappearance of VQ^, m  m  and "unpublished H nmr data indicative of a Rh (OEP)(L) complex" (42). At low temperature, l  m  Rh(OEP)(C>2)(L) (L = py, pip, (BUCO3P) species were detected by esr (42,43). The electrochemistry of the Rh(TPP)(02) complex is similar to that of Rh (TPP)(Cl)(NHMe ) and [RhHI(TPP)(NHMe2)2]Cl. Thefirstreduction is at Ep = -1.14 V m  2  (SCE) in PhCN (1.0 M TBAP) and was a 1-electron metal centered EC process forming [Rh CrPP)]2. The dioxygen complex reacts with PPly forrriing Rh (TPP)(02)(PPh3) and then n  m  [Rh (TPP)(PPh )2] in the presence of excess PPh3 (equilibria 1.8a/b; sect. 1.5.1). ffl  +  3  Rh(TPP)(0 )(solvent) + PPh -== Rh(TPP)(02)(PPh ) + solvent 2  3  3  K  Rh(TPP)(02)(PPh ) + PPh = 3  3  (l.8a)  2  [Rh(TPP)(PPh )2] + 0 " 3  +  2  (i. ) 8b  Coordination of the 7t-acid PPI13 causes a shift of the first reduction to a lower potential at Ep = -0.88 V; however, because of the nature of the CV experiment it was unclear whether this was due to changes in kinetics, geometry or stabilization of the initial Rh(H) formed in the EC process. The equilibria are unaffected by air. Direct observation of 02' was not made; indeed the product solutions are  - silent (44). It should be noted that superoxide is known to react with CH2CI2  (86,87). No mention was made of any OPPI13 formation.  The simple substitution of the dioxygen ligand by PPI13 (Le.,reaction1.8b) in aprotic solvents is akin to the behaviour of a Bronsted base, and is consistent with the O2 ligand of Rh (TPP)(02) being superoxide (87). The origin of the claimed increased stability of the TPP m  complex versus the OEP complex is not apparent 1.4.  Organometallic Complexes  1.4.1. o-Bonded complexes (mono-hapto) A large number of Rh (por)(R) complexes have been synthesized from Rh(I), Rh(U) or m  RhfTfl) porphyrin precursors. With one exception there are no known isolated complexes with the metal in other oxidation states; a paramagnetic complex Rh (TPP)(Cl)(C H5) wasreportedin the rv  0  late 1960s (including preliminary crystal structure data), but no work on this orrelatedcomplexes has appeared since (33,34). The Rh (por)(R) complexes have a hypso-type uv-vis spectrum typical of a d system, m  6  the -R group being considered to be a purely o-bonded axial ligand (17,69). The Rh-C bond length in Rh (OEP)(CH ) is 2.031 A (88), and the BDE of Rh-C in the Rh(IJJ) complexes is m  3  estimated to be 230-251 kJ moH (see below,re:Rh-CHO) (56,62). The electrochemistry of an extensive series of Rh (por)(R) species (Table A.4 in Appendix A) has been studied. The first m  reduction (1-electron, reversible) is between -1.39 and -1.44 V (vs. SCE, (terjending on solvent) and gives a Rh(DI) porphyrin radical anion. Depending on R and thetimescaleRh-C or C-X (if R = RX) cleavage can follow the first reduction. Normally, thefirstoxidation (1 e',reversible)is between 0.85 and 1.03 V (vs. SCE) and gives a Rh(D3) radical cation, but the Rh (TPP)(C(0)CH3) complex is irreversibly oxidized at the C(0)CH3 ligand rather than at the m  porphyrin Jt-system, resulting in cleavage to form [Rh(TPP)]+ (12,13,59,89-91). A series of Rh (OEP)(R) complexes have been used to calibrate an isoshielding map of m  the variation of *H nmr chemical shifts with distance from the porphyrin (Fig. 1.4) (17). The shifts are explained mainly by the diamagnetic anisotropy of the porphyrin ring current and could be estimated using the Johnson-Bovey equation (92). However, the differences, AT, between the observed shifts and the parent hydrocarbon shifts deviate from the shift differences, 8, calculated from the Johnson-Bovey equation. There is a correlation, At = 2.34(8) / - 1.08, between the 1 2  shifts, and the map was created from the data calculated using the Johnson-Bovey equation, modified by the correlation.  12  10  s Z(A)  6  4 2  0  2  4  6  8  X(A)  Figure 1.4.  The isoshielding lines of the OEP porphyrinringcurrent of Rh (OEP)(R) complexes, based on data from a modified Johnson-Bovey equation; note that the contours are of change in shift in x and that the axes are oriented as indicated in the schematic (adapted from ref. 17). m  The chemical methods to synthesize Rh^fjxw)^) complexes will be treatedfirstand then electrochemical methods. Some additional examples are also covered in section 1.5. Tables A.l and A.2 (Appendix A) summarize the Rh (por)(R) complexes that have been synthesised and the In  primary reagents used to obtain them. Note that complexes which are ''fully" characterized, i.e. isolated with elemental analysis and spectroscopic characterization, are specially marked in the Tables. The reactions corresponding to the tabulated data are briefly discussed in the following paragraphs from the point of view of the general reactivity of the Rh(por) precursor in the context  of Rh-C bond formation. The Rh^XporXR) complexes are generally 5-cc<Hxlinate in the solid state but for a few cases H 2 O occupies the sixth site (17). Generally alkylation, or arylation, of Rh (por)(X) is achieved with RLi but not RMgBr m  or RMgl, because reaction with the Grignard reagent results in halide exchange instead of Rh-C formation (17). With certain RLi reagents in excess (R = p-MeOC^Hj, o-McC^U, C6H5, or n-Bu), migration of a second mcorning R from Rh to the meso position of OEP to form Rh (OEP-R)(R) has been reported (sect 1.5.6) (93). Terminal alkynes react with Rh (por)(Cl) m  m  to give either net addition of Rh-Cl across the triple bond or Rh-C(0)R derivatives if H2O is present A unique alkene reaction has been reported, vinyl ether in EtOH reacting with Rh^tporXCl) in the presence of tertiary amine as co-reagent to give a pVacetal (94). Diazomethane, diazoacetate and diazopropionates react with R h ^ ^ r ) ® to give a variety of products (45,95). The a-metallation of methyl ketones to give Rh-CH2C(0)R is possible with Rh (por)(Cl) (por = cis- and trans-5,15-bis(2-hydroxy-l-naphthyl)-octaethylporphyrm m  tetrakis(2-hydroxy-phenyl)porphyrin, trans-5,15-di(8-qumolyl)octaethylporphyrin). The presence of phenolic hydroxyl or quinolyl nitrogen in correct orientation and proximity to the site of coordination is essential (35). The very electrophilic [Rh (OEP)]X (X = CIO4-, BF4-) complexes m  react regioselectively with activated and unactivated arenes to give Rh-arenes (21) and with methyl ketones to give Rh-CH2C(0)R (96). The reactions utilizing [Rh (por)] or Rh(por)(H) will be treated together because their n  2  chemistry is related (sect. 1.5.2 and 1.5.3). Both complexes are sources of the radical species Rh (por) which is believed to be the active Rh reagent in these reactions. Benzylic halogen (65) or n  hydrogen (56) can be abstracted and the resulting radical trapped to give R I 1 - C H R C 6 H 5 species. The monomeric Rh (TMP) species reacts with CH4 giving Rh(TMP)(CH3) and Rh(TMP)(H) n  (95a). The Rh(H) dimers add across terminal alkynes to form ^-alkene complexes (65) and across the vinyl group in styrene to form a n-alkane derivative (83). Alkenes with a terminal propylene group give rearranged products still containing a double bond ( R h - C H 2 C H = C H R ) (65). The hydride complex adds across alkenes to give the corresponding Rh-alkyl (56,83), and across the CO of aldehydes to give a-hydroxy complexes (57). Addition to CO or CNR occurs only at the  terminal C giving Rh-CHO or Rh-CH=NR complexes. Interestingly, the dimer [Rh (por)]2 in the n  presence of H2 (or CO/H2O or CO/KOH) can be used in place of Rh(por)(H) for the reaction with CO and CNR (57,81,97,98). The formyl group of Rh (OEP)(CHO) is considered to be like an m  organic aldehyde with little u-backbonding to Rh (OEP) on the basis of its short C-O distance m  (1.175 A) and high Vco of 1700 cnr . The BDE of the Rh-C bond has been estimated to be 1  -243 kJ mol-1 (46,63,97). The [Rh(por)]- complex is generated in situ (sect, 1.3), and as a nucleophile will displace I  halide from RX (17,56). Cyclopropylringswith extra strain, electron-withdrawing substituents, or containing hetero-atoms (oxiranes and azirines), are opened by [Rh(por)]% while C3H6 and I  C3H5C6H5 do not react; a proton from the reaction medium is incorporated stereospecifically trans  in the product (99). Medium involvment occurs also for the reaction with terminal alkynes and alkenes, where a net trans addition of [Rh*(por)]- and a proton occurs across the multiple bond (17). The "out-of-plane" Rh(I) dicarbonyl complexes of aetioporphyrin (section 1.2) react with acetoacetates, fluorosulphonates, HCO2R, RC(0)X, (RC(0))20, RCHO, RC(0)CH3 or RX to form Rh(IH)-R or Rh(in)-C(0)R complexes (Table A.3 for summary). Initially the substrate oxidatively adds to the Rh(I) center via C-X or C-H bond cleavage, followed by collapse of the Rh(UI) center produced into the porphyrin cavity (sect. 1.5.2). Yields are variable and concomittant carbonylation or decarbonylation can occur, frequently producing mixtures. Induction periods of several hours are noted for the reactions with anhydrides. It is interesting to note that cyclopropyl methyl ketone can be metallated withoutring-opening,unlike its reaction with [RhI(por)]-. Electrochemically generated Rh (TPP) (prepared in situ from the 1-electron reduction of n  [Rh (TPP)(NHMe2)2]Cl in THF, 0.2 M TBAP) reacts with alkyl (but not aryl) halides or m  dihalides (89,90,100), and with H C=CHR and HOCR (91) to give Rhffl(TPP)(R). The 2  reactions with alkenes or alkynes go with loss of the unsaturated C2 moiety. Table A.4 summarizes the complexes produced.  21 1.4.2. Carbene complexes Heterocarbene complexes have been proposed as intermediates in rhodium porphyrin chemistry (30,45,94,95,101,102) but only one type has been isolated and characterized. The cationic maminocarbene complexes [Rh (^r)(:C(NHR)2)(L)]PF6 (por = TPP -, R = CH2Pn, m  2  L = vacant, CNCH2Pn, P(OMe) , PPh ; por = OEP ", R = CH Ph, L = vacant, P(OMe) 2  3  3  2  3;  por = TPP , OEP ", R = p-ClPh, L = vacant) were synthesised by prolonged refluxing of 2-  2  l^rcijxH-XCNR^PFe in MeOH to form the parent [Rh (por)(:C(NHR)2)]PF6 complex in 50% ffl  yield; addition of L to chloroform solutions of [Rh (por)(:C(NHR)2)]PF6 followed by m  chromatography gave [jRh (por)(:C(NHR)2)(L)]PF6. The structure, determined by x-ray ra  diffraction, of [Rh (TPP)(:C(NHCH Ph)2)(CNCH2Ph)]PF6 showed the expected planar m  2  arrangement of the Rh-C(N)2 metallocarbene unit (103). 1.4.3. rc-Bonded complexes (dihapto) There are no examples of isolated dihapto complexes; however, 7t-bonded vinyl alcohol (70), vinyl ether (94), alkene or alkyne (17,78,94) species of Rh(I), Rh(H), and Rh(Tfl), have been proposed as intermediates. A few examples have been detected spectroscopically. Electrochemically generated transient, radicalrc-complexesRh (TPP) (H C=CHC4H9) and 2  Rh(TPP)(HO=CHC3H7) have been postulated on the basis of spectiwlectrochemical and esr data (sect. 1.5.2) (91). The ethene complexes Rh(OEP)(X)(CH =CH ) (X = CF C0 -, CF S0 ") 2  2  3  2  3  3  have been detected by VT *H nmr (sect. 1.5.3) (70). 1.5.  Stoichiometric Reactions There are a number of mechanistic studies involving Rh(por) species. The emphasis in  this area has been on metal-centered processes, although the availability of a wide range of organometallic derivatives (sect 1.4) suggests that organometallic ligand reactivity should be of increasing interest Thermal reactions are discussed in the first sub-sections with photochemistry gathered into one sub-section (sect 1.5.7).  22 1.5.1. Ligand Substitution and Exchange Reactions covered in this section do not involve a change in metal oxidation state. At present only processes at Rh(Ln) centers have been studied in any detail. The equilibrium constants for the reaction of Na3[Rh (TPPS)(H20)2] with Cl\ Br, Im  and NCS have been studied in aqueous solution (equihbrium 1.9, Table 1.1). -  Table 1.1. Values of Ki and K for anation reaction of Na3[Rh (TPPS)(H20)2] with CI", Br, IandNCS-at25 °C. m  2  a  X  Ki (M-l)  K (M-l)  NCS-  1.22 ± 0.04 x 104  3.68 ± 0.42  I-  Br  4.12 ± 0.18 x 10 1.8210.10  <0.03 <0.03  ci-  0.74 ±0.11  <0.03  2  1  a. [H+] =0.10M,n = 1.00M(NaClO ). 4  K  Ki  [Rhni(TPPS)(H 0) ] - — 3  2  2  ~x  [RhHI(TPPS)(H20)(X)] 4  2  +X -X  = [Rh (TPPS)(X) ]5m  2  (1.9)  The rates of substitution by the first anion are considered to be 102-10 greater than for 6  comparable non-porphyrin systems. Associative activation is proposed, based on the activation parameters (Table 1.2) and that addition of the first anion was first order in [anion] up to 0.90 M. The cause of the labilization is uncertain although it may in part be due to mixing of the d orbitals of the metal and 7t-ligand orbitals resulting in loss of formal d character of the Rh(m) (55). 6  Binding constants of L-leucine methyl ester and 4-aminoheptane to form adducts with Rh (por)(CH C(0)CH3) (por = cis- and trans-5,15-bis(2-hydroxy-l-naphthyl)m  2  octaemylporphyrin) (Fig. 1.5) in C H C I 3 have been determined (Table 1.3). Hydrogen bonding bythe ester group of the amino acid ester to naphtholic functions on the periphery of the transisomer of the porphyrin was estimated to contribute 8.8 kJ mol' to the stabilization energy (73), 1  and this represents a trans/cis selectivity of 42 towards the amino acid ester.  Table 1.2. Values of AH* and AS* for substitution of thefirstH2O ligand of Na [Rhni(TPPS)(H20)2] with CA; Br, I- and NCS" * 3  X  AH* (kJ moH)  AS* (J mol- K-*)  NCS-  69.0 ± 0 . 8  -43.1 ± 2 . 5  I-  53.6 ± 3.3  -97.9 ± 10.5  Br  57.7 ± 1.3  -94.6 ± 4.6  Q-  56.1 ± 2 . 5  -106 ± 8  1  a. [H+]= 0.10 M,u.= 1.00 M(NaC10 ). 4  Figure 1.5.  Cis- and trans-isomers of Rh (por)(CH2C(0)CH3) (por = 5,15-bis(2-hydroxy-1 m  naphmyl)-octaemylrx)rphyrin).  Table 1.3. Binding constants of amines with Rh (por)(CH2C(0)CH3) (por = cis- and trans5,15-bis(2-hyd^xy-l-naphmyl)-c<:taethylporphyrin) in CHCI3 at 15 °C. m  amine  K (M' ) 1  trans L-leucine methyl ester 4-aminoheptane  cis  5 x 10 2.9 x 10  1.6 x 10 3.9 x 10  6  5  5  5  The same amines form 1:1 adducts with Rh (por)(a) irreversibly, unlike the reaction with ra  Rh (por)(CH C(0)CH3), but consistent with the greater trans effect of the -CH2C(0)CH ligand m  2  (73).  3  The formation constants for the bmding of PPh3 to Rh (por)(R) (por = OEP ", R = m  2  CH3; por = TPP -, R = CH3, C2H5, C4H9) to give Rh (por)(R)(PPh3) have been measured 2  ffl  electrochemically in CH2CI2 and PhCN (Table 1.4). The binding constants were an order of magnitude lower in PhCN, indicative of coordination of PhCN to Rh (por)(R). Interestingly, the m  formation constant for Rh(por)(02)(PPh3) in CH2CI2 is two orders of magnitude greater than for Rh (por)(R)(PPh3), suggesting that a o-bonded alkyl is a better electron donor than O2". When in  the concentration of RhMfTPP)^) is less than 2 x IO" M in CH2CI2. only [Rh (por)(PPh3)2] is 5  m  +  observed, but neither the liberated R group nor Rh(por) intermediates could be detected (97). Table 1.4. Formation constants for binding of PPh3 to Rh (por)(R) to form Rhni(por)(R)(PPh3). ID  por  K(M-1) solvent  R CH2CI2  ref PhCN  CH3  1.8 x 103  2.4 x 10  1  CH  3  1.0 x 10  1  C2H5  3.9 x 10 1.2 x 10  3  4.2 x 10  C4H9  1.0 x 10  4.3 x 10  02  3.3 x 10  1 1 2  OEP TPP  3  2  2  2  3  2  5  —  1. K.M. Kadish, C. Araullo and C. Yao. OrganometaUics, 7,1583 (1988). 2. J.E. Anderson, C. Yao and K.M. Kadish. Inorg. Chem. 25, 3224 (1986).  Formation of [RhHI(TPP)(PPh3)2] from Rh(por)(02) or Rh (OEP)(Cl)(PPh3) has been ra  +  studied (equilibria l.lOa/b). Rh(TPP)(02)(solvent) + PPh  Rh(TPP)(02)(PPh3) + solvent  3  K  Rh(TPP)(02)(PPh ) + PPh — 3  3  (1.10a)  2  [RhfTPP)(PPh ) ] + 0{ +  3 2  . )  (1 10b  The equilibrium constants, Ki = 3.3 x 10 and K2 = 1.1 x 10 , were determined in CH2CI2 5  2  (0.1 M TBAP) at 25 °C (44). The corresponding K2 value for the reaction of PPh3 with  25 Rh (0EP)(Cl)(PPh3) at the highest ionic strength studied (ca. 0.02 M TBAP) has been estimated m  in the present thesis work (sect 5.2.2.) to be  =1.9 x 10 at 25 °C. The AH was estimated as 2  0  -33 ± 2 kJ mol" and AS was -146 ± 8 J moH K" at \i = 0.0 M; the overall exothermicity is 1  0  1  thought to result primarily from contributions of the solvation enthalpies of the product ions (75). 1.5.2. Oxidative-Addition and Reductive-Elimination The porphyrin ligand of the in-plane mono-nuclear Rh(por) species effectively restricts oxidative-addition and reductive-addition to single site processes such as nucleophilic substitution and to chain, or non-chain, single electron transfer (SET). This is in contrast to the usual sense (104) of simultaneous addition of two 1-electron ligands A and B by oxidative addition of a molecule of A-B to the metal center, the reverse process being reductive elirnination. In the case of the out-of-plane Rh(I) complexes oxidative-addition in the usual sense can occur but not reductiveelimination because the product of the oxidative-addition is an in-plane species. There have been no reports of in-plane Rh(I) corning out of the plane of the porphyrin to form an out-of-plane species. Net oxidative addition reactions to [Rf^tpor)]- with RX to form Rh (por)(R) have been m  previously mentioned (sect. 1.4.1); however, there have not been any explicit mechanistic studies. On the basis of the products obtained and the oxidation state changes, the reaction is believed to involve nucleophilic substitution by [Rh^Por)]- (17,44). In the case of the ring opening of cyclopropanes inversion of configuration at the reaction site occurred for nortricyclanone consistent with SN2 type reactivity (reaction 1.11) (99).  —Rh—  + OH" (l.H)  Reaction of [Rh^OEP)]* with olefins containing electron-withdrawing groups (CH2=CHX; X = CN, CO2CH3) or with phenylacetylene is proposed to go via initial formation of  a 7t-complex (Scheme 1.2).  — R h —  +  XCH=CH  2  XCH^ +H+  Scheme 1.2. Reaction of [Rh^OEP)]- with olefins containing electron-withdrawing groups.  Subsequent to the nucleophilic attack by Rh(T), a proton adds trans to Rh as evidenced by formation exclusively of cis-styryl complex from the reaction with phenylacetylene (17). For "out of plane" Rh^COh complexes, the substrate C-X or C-H (Table A.4) bonds are proposed to oxidatively add to the Rh(T) center in the normal sense. Observation of concomitant carbonylation or decarbonylation indicates migratory insertion and deinsertion can compete with the subsequent collapse of the Rh(ILT) center into the porphyrin cavity. It is noteworthy that cyclopropyl methyl ketone can be oc-metallated withoutring-opening,unlike its reaction with [Rh^or)]' but consistent with the different modes of reaction (27,29). Oxidative addition to [Rh (por)]2 occurs via chain and non-chain SET yielding Rh(TU) n  products (e.g., Tables in Appendix A) with the overall stoichiometry: M -M n  n  M -A + M -B  + A-B  ra  m  (1.12)  The mono-nuclear radical species Rh (por) is believed to be a key active Rh reagent in these n  reactions, the driving force generally being Rh-C formation. Addition of donors has been suggested to promote the cleavage of the [Rh (par)]2 species (76). n  The reaction of CoHsO^Br with [Rh(OEP)]2 (65,78) in toluene has been investigated and can be described as a free-radical chain mechanism.  27  imtiaJiorvterrnination: [Rh(OEP)]2 ^==* 2 Rh (OEP)  (1.13)  n  propagation:  RhH(OEP) + CoHsO^Br  RhHI(OEP)(Br) + CgisCn? fast  (1.14)  m  C6H CH - + [Rh(OEP)] — - Rh (OEP)(CH C6H5) + m  5  2  2  2  Rh (OEP) (1.15) n  The rate law was -d[[Rh(OEP)] ]/dt = kob [[Rh(OEP)]2]^[C^HsCH^r], where kobs = 2  s  (ki3/k.i3)l/2k = 8.5 x 1(H M-V2 - l at 26 °C (83). 14  s  In contrast, the reaction of I-C3H7X (X = C1, Br, I) with mono-nuclear Rh (TPP) n  generated electrochemicaUy from Rh (TPP)(L) + in PhCN gave Rh (TPP)(R) and X* with no m  m  2  evidence of Rh (TPP)(X). Coulometry and CV data indicate initial formation of Rh (TPP)(R) m  m  and X- when X was Br or I, but only Rh (TPP)(R) was detected with X = CI. A Scheme m  involving an electron source (S) other than the electrode was formulated to explain this. [Rh (TPP)(L) ]+ + e- —~- Rh (TPP) + 2L  (1.16)  Rh (TPP) + RX — - Rh (TPP)(R) + X-  (1.17a)  Rh (TPP) + RX —»• [Rh (TPP)(R)] + X'  (1.17b)  X- + S — X - + S+  (1.18a)  [Rh (TPP)(R)]+ + S — - Rh (TPP)(R) + S+  (1.18b)  m  n  2  n  m  n  m  m  +  m  A key relationship is between the Rh (TPP)(R)/[Rh (TPP)(R)] and X7X- couples. The m  m  +  Rh (TPP)(R)/[Rh (TPP)(R)]+ couple is near +1.0 V while the C17C1* couple is greater than m  m  +1.0 V; thus reactions 1.17b/l.18b occur rather than 1.17a/1.18a. For X = Br and I, reaction 1.17a occurs since the X7X- couple is less than +1.0 V. It was suggested that the occurrence of a radical chain process in the reaction of C6H5CH Br with [Rh (OEP)] discussed above, but not n  2  2  for n-C3H X with Rh (TPP), is due to the greater stability of the CottsCHj radical (89). n  7  Chemical reaction of [Rh(OEP)]2 with CH2CI2 in benzonitrile or THF likewise gave only Rh(TPP)(CH2Cl) without formation of Rh(TPP)(Cl) and thereactionwas proposed to be between Rh (TPP) and CH2CI2 rather than "direct reaction" between [Rh(OEP)]2 and CH2CI2 (105). n  A mechanism initiated by dissociation of [Rh(OEP)]2, but without formation of organic free radicals, has been proposed for the reaction with alkylaromatics. The rate of reaction with deutereotoluene was first order in [Rh(OEP)]2 at ca. 100 °C. Based on the product distributions and labelling studies, initial reaction apparently occurs at the benzylic carbon, which bears the weakest C-H bond, with subsequent rearrangements when necessary to less sterically constrained p-sites (56). [Rh(OEP)]  2 RhH(OEP)  2  Rh (OEP) + RH n  [Rh(OEP),-HR]  (fast)  (1.19)  (fast)  (1.20)  [Rh(OEP),-HR] + RhH(OEP) ^== Rh(OEP)(R) + Rh(OEP)(H)  (RDS) (1.21)  Rh(OEP)(H)  (slow) (1.22)  1/2 [Rh(OEP)] + 1/2 H 2  2  mterestingly, monomelic Rh (TMP) reacts reversibly with methane in benzene n  (equilibrium 1.22a). Kinetic studies reveal a large deuterium isotope effect of 8.6 ± 1.5 at 296 K; AH ~ -50 kJ mol" and AS —63 J K' mol" (95a). 0  1  0  1  1  CH4 + Rh (TMP) = = Rh(TMP)(CH ) + Rh(TMP)(H)  (1.22a)  u  3  A four-centered linear transition state is proposed:  R h - - C---H - - Rh H  Alkenes with a terminal propylene group react with [Rh(OEP)]2 to give rearranged products still containing a double bond, e.g. Rh (OEP)(CH2CH=CHR) (R = C6H5, CN, m  n-C3H7). A non-chain "SH2'" mechanism is proposed (65).  [Rh(OEP)]  2  2 Rh (OEP)  (1.23)  n  Rh (OEP) + CH2=CHCH R  Rh (OEP)(CH2CHCH2R)  n  ra  2  Rh (OEP)(CH2CHCH2R) —Rh (OEP)(CH2CH=CHR) + "H-" ra  m  (1.24) (1.25)  The reaction of terminal alkenes, H C=CHR, and alkynes, HO=CR, with electrochemically 2  generated Rh (TPP) gives Rh (OEP)(R) (for examples see sect 1.4.1), with loss of the n  m  unsaturated C unit Intermediate Rh(U)rc-alkeneand 7t-alkyne complexes have been observed, 2  but the mechanism of the C loss is unknown (91). In contrast, the reaction of styrenes or alkynes 2  with [Rh(OEP)] gives bridged Rh(UJ) products, and is discussed in section 1.5.3 on insertion. 2  The oxidative addition of H to [Rh (por)] forming Rh(por)(H) and the reverse n  2  2  reductive elimination are key reactions in the chemistry of these two Rh complexes (see especially sect 1.5.3). As previously mentioned (eq'n 1.7, page 14), a measurable equilibrium (equilibrium 1.26) is established for the OEP complexes with K = 116 ± 8 at 294 K; AH = -13 ± 4 kJ mol' ; 0  1  A S = 3 ± 8 J K-l mol" (63). 0  1  [Rh(OEP)] + H 2  2 Rh(OEP)(H)  2  (1.26)  The mechanism of the H activation is not known, but it has been noted that light (sect. 1.3.1 and 2  1.6.3) and trace amounts of rhodium metal remaining from the [Rh(OEP)] synthesis catalyse the 2  reverse reaction (56). Reductive eliinination occurs during anaerobic thermolysis of Rh(OEP)(R). When R is or - C H C H C H ( C 6 H 5 ) , the dimer, [Rh(OEP)] , and equal amounts of  -CH(C6H5)CH CH3  2  2  CH3CH=CHC6H5  and  2  2  2  CH3CH2CH2C6H5  form without formation of coupled products. A  mechanism involving formation of a geminate radical pair [Rh (OEP)/R], followed by n  subsequent reactions with a Rh (OEP)(H) intermediate was proposed (reactions 1.27-1.29). m  RhHI(OEP)(CH(C6H5)CH CH3) — - [Rhn(OEP),-CH(C6H )CH2CH ] 2  5  (1.27)  3  Abstraction of H \ accompanied by rearrangements depending on R, followed by the reaction of the intermediate Rh (OEP)(H) with the initial complex gives the Rh(H) dimer. m  [Rhn(OEP),-CH(C6H )CH CH ] —RhHI(OEP)(H) + CH CH=CHC6H5 5  2  3  (1.28)  3  RhHI(OEP)(H) + Rhni(OEP)(CH(C6H5)CH CH3) 2  [Rh(OEP)] + 2  CH CH CH C6H 3  2  2  5  (1.29)  Further evidence for a radical pair formation comes from the aerobic thermolysis of RhHI(OEP)(CH2C6H5) and Rhro(OEP)(CH(<^H)CH3) which quantitatively gives C6H C(0)H 5  5  and CoHsCXO)CH3 respectively. Dioxygen is presumed to intercept the radical pair to form a peroxy mtermediate that decomposes to a carbonyl and possibly a Rh(in) hydroxide (56). Another example of a Rhhl(OEP)(H) induced reductive ebrnination is the formation of methanol and [Rh(OEP)]2 from the reaction of RhHI(OEP)(H) and Rh (OEP)(CH20H) in toluene (106). m  1.5.3.  Insertion  A number of unsaturated molecules insert into Rh-Rh and Rh-H bonds (e.g., sect. 1.4.1). The reaction of CO with Rh (OEP)(H) (46,57,63,78,81,97), and of styrene with ffl  [Rh(OEP)] or Rh^OEPXH) (83), has been shown to go via a radical chain mechanism with the 2  mtermediacy of mono-nuclear Rh (OEP). The Rh^OEP) acts as chain carrier and the product n  formation depends on oxidative-addition to the Rh(LD center. The unusually strong Rh-C bonds are felt to contribute to the driving force. The reaction of [Rh(OEP)]2 with styrene in C£>e gives a RhfJH) u.-alkane product. An equilibrium (reactions 1.30-1.33) is attained at 25 °C with K30 = 8.5 x 10 M* (see Table 1.5 for 4  1  thermodynamic values). K30  [Rh(OEP)] + CH =CHPh = 2  Rhm(OEP)-CH CH(Ph)-Rh (OEP)  (1.30)  m  2  2  *3i  imtiation/termination: [Rh(OEP)]2 =  2 Rh^OEP)  (1.31)  k-31  propagation:  Rh (OEP) + CH =CHPh i== Rh (OEP)(CH CHPh) n  (1.32)  m  2  2  k.32  Rhni(OEP)(CH2CHPh) + [Rh(OEP)] ^ Rh (OEP)-CH CH(Ph)-Rh (OEP) + Rh (OEP) (1.33) 2  m  m  n  2  The rate law is -d[[Rh(OEP)]2]/dt = k b [[Rh(OEP)] ] / [CH2=CHPh], where kobs = 3 2  0  S  2  (k3i/k.3i) / (k3 /k.32)k33, when reactions 1.31 and 1.32 are at equilibrium and reaction 1.33 is 1 2  2  rate-lirmting. The mtermediate Rh (OEP)(CH2CHPh) radical could be efficiently trapped by m  Rh (OEP)(H). In fact, [Rh(OEP)}2 catalyses thereactionof styrene with Rh!n(OEP)(H). In the m  31 absence of added Rh(U) dimer, the reaction of CH2=CHPh with the hydride is slow because only small amounts of [Rh(OEP)]2 are formed in situ from decomposition of Rh (OEP)(H). A m  mechanism similar to the previous one can be written. RhHI(OEP)(H) + CH =CHPh = = RhDI(OEP)-CH CH2Ph 2  k  (1.34)  2  35  imriation/termination: [Rh(OEP)] = s 2 Rh^OEP)  (1.35)  2  k-35  propagation:  Rh (OEP) + CH =CHPh ====* Rh (OEP)(CH CHPh) n  (1.36)  m  2  2  k-36  RhDI(OEP)(CH2CHPh) + Rh (OEP)(H) Rh (OEP)(CH2CH2Ph) + Rh (OEP) m  m  (1.37)  n  and-dlRh^OEPJCHJJ/dt = (k35/k-35) ^(k36/^36)k37(K30)- ^[[Rh(OEP)] ]total ^[CH =CH^ 1  1  1  2  2  when equilibria  (1.30) and (1.35) are established, equilibrium (1.30) lying to theright,and reaction (1.37) is ratelimiting. At 42 °C, (k35/k.35) / (k36/k.36)k37(K3o)- ^ is 9.8 x IO" s". The corresponding 1 2  1  2  2  1  reaction of cis-stibene was accompanied by cis-trans isomerization of the unreacted stilbene, presumably via equilibrium (1.36). The reaction of CO with Rh (OEP)(H) can be described by a similar mechanism m  involving Rh (OEP) catalysis (reactions 1.38-41). A measurable equilibrium is found n  (equilibrium 1.38, Table 1.5 for thermodynamic values). At 36 °C the equilibrium constant (K38) is 5.5 x 10 M' , and the rate law is -d[Rh (OEP)(H)]/dt = 2  1  m  kobs[[Rh(OEP)]2] ^[Rh (OEP)(H)][CO], where ko = (k 9^39) ^(k4ryUo)k i (83). 1  m  1  bs  3  RhHI(OEP)(H) + CO £ L Rh (OEP)(CHO) m  4  (1.38)  k39  initiation/terrrination: [Rh(OEP)]2  2 Rh (OEP) n  (1.39)  k.39  propagation:  Rh (OEP) + CO  k40  n  Rh (OEP)(CO) m  k-40  (1.40)  32 Table 1.5. Some thermodynamic parameters for insertion into Rh-Rh and Rh-H bonds. reagent  substrate  solvent  AH° (kJmol- )  AS° (Jmol^K- )  ref  -94 ± 1 1 -54 ± 4 -42 ± 4  -63 ± 3 3 -123 ± 1 5 -91 ± 15  1 2 3  1  [Rh(OEP)] Rh(OEP)(H) Rh(TPP)(H) 2  PhCH=CH CD CO  2  C6D " "  6  1  1.  R.S. Paonessa, N . C . Thomas and J . Halpem. J . A m . Chem. Soc. 107,4333 (1985).  2.  M D . Farnos, B A . Woods and B . B . Wayland. J . A m . Chem. Soc. 108,3659 (1986).  3.  B . B . Wayland, SL. Van Voorhees and C . Wilker. Inorg. Chem. 25,4039 (1986).  Rh (OEP)(CO) + Rh (OEP)(H) - ^ i Rh (OEP)(CHO) + Rh (OEP) m  m  m  n  (1.41)  It is possible that the chain radical mechanism just described is extensible to other insertion reactions, such as Rh(LT) dimer addition across terminal alkynes to form u.-alkene complexes (65) and hydride complex addition across the CO of aldehydes to give a-hydroxy complexes (57). The utility of further studies in this area can be supported by noting that a cycle can be written, utilising stoichiometric reactions, for the conversion of H and CO to methanol 2  (Scheme 1.3).  Scheme 1.3. Possible cycle for the reduction of CO by H to C H 3 O H from combining known elementary steps; refs: insertion of CO (46,57,63,81,97,98); aluniinium hydride reduction (106); reductive elimination of MeOH (106). 2  In addition, thereremainsa lack of depth in the mechanistic studies, given the variety of proposals that all involve a Rh(H) radical species. In particular, an explanation is needed for the C—C bond cleavage proposed during the loss of the C2 unit of terrninal alkenes and alkynes (previous section) when reacted with electrochemically generated Rh(U). Terrninal acetylenes react with Rh (OEP)(Q) in benzene to give inserted products and m  oxygen-containing products in the presence of H2O (Scheme 1.4). Di-substituted acetylenes did notreact,presumably due to steric hindrance. The formation of oxygen-containing products is proposed to occur via hydration of carbenoid mtermediates. Evidence for the path via Rh (OEP)(C==CR) comes from the isolation of such complexes from thereactionin the presence m  of Et3N. Treatment of Rh (OEP)(OCC6H ) with aqueous HCI gives m  5  Rhni(OEP)(C(0)CH C6H5) (94). 2  A cationic Rh(JJJ) intermediate is also proposed in thereactionof Rh (OEP)(a) in EtOH in  with CH =CHOC2H to give Rh (OEP)(CH2CH(OC2H )2). Cationic o- andrc-complexesare m  2  5  5  considered to be in equilibrium at an intermediate stage (Fig. 1.6). Attack of the solvent on the o-complex presumably generates the acetal product (94). The acetal can be degraded via an acid promoted process to the (5-aldehyde on silica gel. These Rh(IH) reactions are probably related to the direct metallation of arenes by [Rh (OEP)]X (sect 1.5.4), where X is at best only weakly coordinating compared to the Cr m  ligand of Rh (OEP)(Cl). The initial step is likely to be coordination of an unsaturated substrate to m  the Rh(ILT) center via a dissociative or associative mechanism, which could be difficult to distinguish when X is weakly coordinating. A possible prototype for the substrate binding may be found in thereversibleinsertion of ethene into the Rh-0 bond of Rh (OEP)(CT3CC^)(CH2=CH2) m  (equilibrium 1.42), which has a AH° of -5.9 ± 0.5 kcal over a temperature range of 243 K to 315 K. Replacement of CF C02" by CF S0 - prevents the forward reaction under the same conditions 3  3  3  (70). However, no such complexes have beenreportedforreactionsinvolving acetylenes. Rh (0EP)(CF CO2)(CH2=CH ) m  3  2  Rhni(0EP)(CH CH20C(0)CF3) 2  (1.42)  Scheme 1.4.  The reaction of terminal acetylenes with Rh (OEP)(Cl) in benzene (adapted from m  ref. 94).  +  HjQn^.CH—OR  CH *  -CH—OR  2  •RhTt  Figure 1.6.  Cationic n- and o-complex intermediates in the reaction of Rh (OEP)(Cl) and m  vinylethers (adapted from ref. 94).  35 1.5.4. Electrophilic Aromatic Metallation Direct metallation of arenes by [Rh (OEP)]X (X = BF4-, QCv) occurs under mild m  conditions via ionic electrophilic substitution (10721). Yields vary from 28 to 70% depending upon the counter ion and substituent on the arene. The reactivities of substituted arenes (CgHsX; X • P-OCH3, P-CH3, H, CI, m-CX>2CH3, p-C02CH ) follow the Hammett o equation giving a p 3  value of -5.43. Substitution was exclusively para, except for the reaction of methyl benzoate, where a 92:8 ratio of meta:para was found for the benzoate product The metallation was totally inhibited by potentially donor solvents such as methanol, tetrahydrofuran and pyridine, but not by oxygen. There was no deuterium isotope effect using C5D6 instead of G5H6: the rate deterrnining step is coordination of the arene to form a cationic Rh(IU)-arene complex, followed by the rapid loss of a proton to yield the product. The deprotonation is proposed to involve the conversion of an ri -arene to o-aryl species (21). 2  [Rhni(OEP)]+ + CsH6 —— [[Rh (OEP)(C6H6)] ] — - Rh (OEP)(C6H ) + H (1.43) m  +  m  +  5  Electrochemical generation of [Rh (TPP)]C104 in PhCN by electro-oxidation of m  Rh (TPP)(C(0)CH3) is possible. The only'chemical reaction examined was the instantaneous m  reaction with CI" to form Rh™(TPP)(Cl) (59). 1.5.5. Reactions at an axial ligand  Reduction of Rh (OEP)(CHO) with HAl(iBu)2 followed by aqueous workup is reported m  to give the a-hydroxy complex Rh (OEP)(CH20H) in 30% yield (106). Proton nmr evidence m  indicates that a-hydroxy complexes of the type Rh"T(por)(CH(R)OH) (por = OEP ", R = H, Me; 2  por = TPP *, R = H) undergo slow self condensation in benzene to form bridged ether complexes, 2  which subsequendy undergo hydride-transfer disproportionation to form metallo acyl and alkyl species (57,106,108). 2 Rh(OEP)(CH(Me)OH) *-=-= Rh(OEP)-CH(Me)OCH(Me)Rh(OEP)  (1.43)  Rh(OEP)-CH(Me)OCH(Me)Rh(OEP) —*- Rh(OEP)(Et) + Rh(OEP)(C(0)Me)  (1.44)  The p-hydroxyethyl complex Rh(OEP)(CH2CH20H) can be dehydroxylated by CF3CO2H or CF3SO3H in toluene, creating an ethene complex. In the case of CF3CO2H, the VT  *H nmr data showed an equilibrium existed between Rh (OEP)(CF CO2)(CH =CH ) and m  3  2  2  RhDI(OFJP)(ai CH20C(0)CF3) (equilibrium 1.42). Addition of hydroxide reformed the 2  (J-hydroxyethyl complex (70). Nucleophilic addition of NaOC^s to Rh (TPP)(a)(C6) in ethanol gives the m  ethoxycarbonyl complex Rh(TPP)(C(0)OEt), while reaction of Rh CrPP)(Cl)(CO) with LiNEt2 m  in NHMe2 gives the analogous carbamoyl species Rh (TPP)(C(0)NEt2). In each case the metal ni  carbonyl could be reformed by reaction with dry HQ. No reaction was observed between mrrpp)(Cl)(CX)) and NaSEt (82).  Rh  Attack of OH" on Rh(por)(Cl)(CO) (por = OEP ", TPP *) in benzene is proposed to occur 2  2  during the formation of Rh(por)(H)fromRh(por)(Cl)(CXD) in the presence of CO and solid KOH, an intermediate carboxylate complex decomposing to yield the hydride and CO2. Alkyl isocyanides undergo an analogous reaction to give Rh(por)(H) and BuNCO (81,98). Rh(por)(Cl)(CO) + OH- —*~ [Rh(por)(002H)] + CI-  (1.45)  [Rh(por)(C02H)] —*- Rh(por)(H) + CO2  (1.46)  Electrophilic attack of Q2 on coordinated NO in Rh(OEP)(NO) gives a nitrite complex as judged by appearance of bands at 1222 and 1325 cm in the IR. No further details were given (43). -1  An a-metallation product is formed by enolization of coordinated acetone via bifunctional activation with Rh (por)(Cl) (por = 5,15-bis(8-quinolyl)-, 5,15-bis(2-pyridyl)octaethylporphyrin) m  (for example, Scheme 1.5). The presence of the phenolic hydroxyl or quinolyl nitrogen (acting as Br0nsted bases) was essential as is steric restraint to prevent simple combination of the basic and  Lewis acid metal centers (e.g. Fig. 1.2). The proposed mechanism involves binding the enolate, which is formed with assistancefromthe peripheral base followed by an mtramolecular rearrangement and loss of H to give the a-metallated product (35). +  37  Scheme 1.5. The enolization of acetone via bifunctional activation with Rh (por)(Cl) (por = 5,15-bis(2-pyridyl)octaemylpcq)hyrin) (adapted from ref. 35). m  Ketone a-metallation could be achieved also in the absence of peripheral base using the more electrophilic [Rh (OEP)]X (X = BF4-, QCV) complex (see also sect 1.6.5 for a related ra  catalytic system) (96). 1.5.6. Migrations between metal and porphyrin A considerable interest exists in the tide migrations, using non-Rh (i.e. Fe, Co) porphyrins, mainly in relation to suicide inhibition of P-450 enzyme systems (109). As mentioned in sect 1.2, a number of N-alkylated "out-of-plane" Rh^CO^ complexes are known and these undergo a facile irreversible oxidative addition of N-C (of the N-alkyl group) to Rh(l) to form the corresponding in-plane Rh^^po^fR) complex. Only one in-plane N-alkylated Rh(por) complex is known, but it is not believed to be formed via alkyl migration from metal to pyrrolic N. In the presence of AcOH, Rh (OEP)(Me) reacts with ethyldiazoacetate in CH2CI2 to give the stable III  N-alkylated complex [Rh (0EP-N-CH2CO2Et)(Me)]a04. Unstable, impure, salt-like, green m  products, which are also believed to be N-alkylated species, were obtained using Rh^OEP)^) and Rh (TPP)(I). A preliminary step to the N-alkylation of the iodide complexes is suggested to m  be alkylation of Rh via formation of a Rh carbene mtermediate. A molecule of protonated diazoester is believed to react directly with a pyrrolic nitrogen made more nucleophilic after the Rh  alkylation. The strength of the Rh-N bond is thought to make a bridged intermediate less favourable than for the Co analogues where carbene insertion into a Co-N bond is found (45). The possibility of interconversion of the Rh(UJ) N-alkylated complex to Rh(R) has yet to be explored. Migration of R (R = p-MeOCgrU, o-MeCgH*, C6H5, or n-Bu; R * o-MeOCotti, or Me) from Rh to the meso position of OEP to form Rh (OEP-R)(R) has been reported (93). Addition m  of excess RLi to a dry THF solution of Rh (OEP)(Me) forms the anionic brown dialkyl complex ni  (p-type hyperporphyrin) which slowly converts to the green pbJarin. The mono-meso-substituted Rh (OEP-R)(R) complexes were isolated after addition of saturated aqueous NH4CI m  (Scheme 1.6). In the case of R = o-MeOC^Hj, or Me, only the brown solution was formed, and addition of NH4CI to this solution gave only starting material. A similar transfer of H- is discussed in sect. 1.6.3. -  R  R  I  RLi  •Rh—  —  THF  1 R1  Rh—  R —Rh—<  R  green  brown  H 0, 2  NH4CI  R  I —Rh-  Scheme 1.6. Thereactionof Rh (OEP)(R) with excess RLI m  1.5.7. Photochemistry Irradiation of Rh (TPP)(Cl) (at X <400 nm) or [Rh(TPP)]2 (at \ <310 nm) in m  2-Me-THF at 77 K gives Rh (TPP), as judged by uv-vis and esr data; no photochemical reaction n  was observed when the Q bands (P and a) were irradiated (58). Photo-assistedreplacementof the amine ligand of [Rh (OEP)(NHMe2)2]X (X = CI", m  PF6) with tBu-NC, PPh2Me or P(OMe)3 in 1,2-dichloroethane has beenreported,and addition of -  NHMe2 to Rh (OEP)(Cl) in toluene to give [Rh (OEP)(NHMe2)2]Cl is also promoted by ffl  m  photolysis, but with Rh (EP)(Cl) in 1,2-dicMoroethane the chloride is not replaced and m  Rh (EP)(Cl)(NHMe2) is obtained (sect 1.3.2.3) (32). As described in this thesis (sect 52.3), m  exposure to laboratory light or sunlight of Rh (OEP)(a)(PPh3) in benzene, THF, or MeCN, in m  the presence of 1 atm CO, yields Rh (OEP)(Cl)(CO), while cessation of irradiation results in m  reformation of the PPI13 complex. If CO is absent, then the Rh (OEP)(Cl)(sorvent) species ra  forms in THF or MeCN solutions under similar conditions. In the dark, PPh3 ligand replacement with CO, THF, or MeCN is not observed (75). The hydroxymethyl complex RhIH(OEP)(CH20H) and Rhni(por)(CH ) (por = OEP ", 2  3  TPP ) photolytically (hv > 445 nm) incorporate CO to form corresponding acyl complexes. 2-  Rhm(OEP)(CH OH) + CO 2  Rhni(por)(CH ) + CO 3  RhJH(OEP)(C(0)CH20H)  (1.47)  RhHI(por)(C(0)CH3)  (1.48)  The formation of the hydroxyacyl complex is complicated by photoinduced transformation back to Rh(OEP)(H) and H2CO. Reaction between geminate radical pairs within the benzene solvent cage is suggested as the likely mechanism (57). Irradiation of the arene complexes Rh (OEP)(aryl) (aryl = -C6H5, P-OCH3-C6H4, m  P-CH3-C6H4) in degassed benzene homolytically cleaves the Rh-C bond. The photolysis yielded 4-substituted biphenyls with no evidence of 4,4'-substituted biphenyls that might be expected from coupling of the ligand radicals (21). 1.6.  Catalytic Reactions  1.6.1. Reactions of dihydrogen A paramagnetic complex, subsequently identified as Rh(TPP)(02) (42), catalyses the hydrogenation of acetylene in DMF as well as the conversion of H2/O2 rriixtures to H2O (41). Details of the catalysis, such as the turnover rates, were not reported in the communication.  1.6.2. Reactions of dioxygen Catalysis of autooxidation of cyclohexene by Rh (TPP)(Cl)(CO) and Rh (TPP)(Cl) is m  m  said to produce large amounts of, or cyclohexene hydroperoxide as sole product, although no details are available (110). Superoxide anion, detected by esr, has been generated in benzene from air using a bis(thiolato)-Rh (OEP) complex, characterized by a "split Soret band", hyperporphyrin spectrum. in  The mechanism proposed (Scheme 1.7) involves reduction of Rh by a thiolato ligand, generated 111  in situ from various thioglycolate esters (thioglycolate ethyl ester, n-octyl ester, octadecyl ester, (hWothreitol) using B114NOH. The generation of superoxide continues until the available thiolato ligand is oxidized to the disulfide form (72). • "m  C1  m  -Rh-  Scheme 1.7. Catalytic cycle for the reduction of dioxygen to superoxide using an in situ Rh (OEP)/thiolate catalyst complex (adapted from ref. 72). m  It is interesting to compare this system with the reaction of Rh(TPP)(02) and excess PPh3, which also displaces the O2 moiety as 02" (sect. 1.3.7), but where the phosphine is not capable of reducing Rh(IU) under the conditions used. It should be noted that [Rh (TPP)(PPh3)2] does not have a "split Soret band" (77), P-450 hyperporphyrin type ffl  +  spectrum (6), which is a characteristic feature of Rh^OEP)/thiolate species (72). However,  Rh(TPP)(02) could be reformed using an external reductant, for example, via the borohydride reduction of Rh followed by addition of O2 (sect 1.3.7). In Scheme 1.6, the thiolato ligand 111  plays the dual role of ejecting O2'. as well as acting as reductant 1.6.3. Dehydrogenation/Hydride transfer Secondary alcohols (2-propanol or cyclohexanol) can be photocatalytically dehydrogenated to the ketone and H2, using Rh (TPP)(Cl) (Scheme 1.8), via excitation of either m  B or Q bands. A bimolecular process between Rh(TPP)(H) complexes in the photoexcited (rc-rc*) and ground states is involved in H production within the catalytic cycle (111-114). 2  H*  ^JLl .Rh(porXa)  HCl^  Rh(por)(OCH(CH3)2) [Rh(por)]/  J  \  Y p^^CCHshCHOH rRh'(por)] [Rh(por)] /  (CHshCO  H \ Rh(porXH)  +  \  hv,  ^  /  [Rh(por)(H)]' + Rh(por)(H) |  Rh(por)(H)  »• H  2  [Rh(por)r  jl+  : photo-excited  Scheme 1.8. Photocatalytic dehydrogenation of 2-propanol using Rh (TPP)(Cl) (adapted from m  refs. 111-114). Catalytic hydride transfer to NAD(P) models has been reported (115). The +  Rh (OEP)(C(0)CH3) complex catalyses the photoreduction of 1-benzylnicotinamide (BNA ) and m  +  l-benzyl-3-acetylpyridinium ion (BAP+) to the ccrasponding 1,4-dihydro derivatives with B(CoH5)4' as reductant and alcohol as proton source; reduction of BAP+ in the presence of CH3OD results in deuteration of the 4-position of B APR Hydride donors such as NaBH4,  alkoxides and BNAH could be used in place of the alcohoVB(C6H5)4" system. In the absence of any hydride acceptor, Rh (OEP)(C(0)CH3) bleaches when irradiated, a hydride migration from m  Rh to the meso carbon of the OEP ligand followed by protonation initiating the bleaching process (also sect 1.5.6). The stoichiometric reduction of Rh (OEP)(Cl) in ROH using NaBR*. alkoxide m  (RO-; R = CH3, CH3CH2, (CH3)2CH), or BNAH to form Rh^OEP)- occurs under photochemical conditions or in the dark, and, in an inert solvent, Rh(OEP)(H) is formed from the reaction with BNAH; these stoichiometric reactions are believed to be hydride transfers. The Rh (OEP)(C(0)CH3) complex is stable to the same reagents in the dark. m  1.6.4. Borane transfer reactions  The aerobic reduction of ketones (acetophenone, cyclohexanone, methylcyclohexanones, cyclopentanone, 3-heptanone, and norcamphor) with NaBfL; in THF to the corresponding alcohol is catalysed by Rh(por)(Cl) (por = OEP " or TPP "). A key step is the transfer of borane from a 2  2  proposed intermediate Rh (por)(BH4) complex to the ketone to form a dialkoxyborane; oxidative m  "hydrolysis" of the B-0 bonds with O2 (or an O2/N2 nuxture or air) coupled to oxidation of Rh(por)(H) yields the alcohols (for example Scheme 1.9). The product distributions obtained  Scheme 1.9.  The aerobic reduction of ketone with NaBH4 in THF to the corresponding alcohol catalysed by Rh(OEP)(Cl) (adapted from ref. 116).  from the reaction were compared with the reductions by LiAlH4, NaBH4, diborane and disiamylborane ((3-methyl-2-butyl)-borane). The alcohol product stereoisomer distributions were comparable, the more stable trans isomers being favoured when less hindered ketones were used.  43 Reduction of 2-methylcyclohexanone gives the less mennedynamicalry favoured cis isomer for both the Rh (por)-catalysed and the bulky disiamylborane systems. Catalytic transfer of borane to ni  Et3N was also reported (116). Olefins have also been catalytically converted to the ccrosponding alcohols, the "hydration" being anti-Markovnikov (117). A one-pot conversion of 1-methylcyclohexene to (E)-2-methylcyclohexanol with 100% regioselectivity and up to 97% stereoselectivity was performed. Acetylenes could also be converted to alcohols. 1.6.5. Carbon-carbon bond formation  The aldol condensation of cyclohexanone is catalyzed by [Rh (OEP)]C104 under mild m  conditions. Other ketones such as acetone and methyl ethyl ketone simply undergo metallation at the methyl groups, the resulting complexes being easily cleaved by H or Br2- The key +  mechanistic step is believed to be enolization of the ketones promoted by activation with [(Rh (OEP)] acting as a Lewis acid (Scheme 1.10). A chiral modification is being pursued m  +  (96,118). o  +  o  Scheme 1.10. Catalytic C-C bond formation via enolization of ketone (adapted from ref. 118).  Cyclopropanation of ds-olefins (1-hexene, cyclohexene, 1,4-cyclohexadiene, norbornene, 2-methyl-cis-3-pentene, benzene, styrene, phenanthrene, and the pyrroles of Zn(TPP)) by ethyldiazoacetate is catalysed by Rh (por)(I) (por = (CN)OEP -, TPP ", TTP ", TMP ') using m  2  2  2  2  excess olefin at 60°C. A large cis-product selectivity relative to that obtained using more classical CuCl and Rh (pivalate) systems as catalysts, was observed, and the results were interpreted in n  terms of steric hindrance between the olefin substituents and the porphyrin ligand of the proposed Rh-carbene intermediate (30,45,102). Insertion of "CHOOOEt", from ethyldiazoacetate, into the C-H bonds of long chain alkanes (Cs-Cis), chloroalkanes (C5-C10), and aromatics (toluene, p-xylene, mesitylene) is also catalyzed by Rh (por)(I) (por = TPP ", TMP -, TDCPP ") at ~65°C. The yields are erratic, but m  2  2  2  selectivity for the terminal methyl group increases with the steric crowding of the Rh center within a carbene intermediate. Direct insertion of the carbene fragment into a C-H bond was proposed rather than H atom abstraction followed by recombination, because an isotope effect of only 2-3 was found for deuterated n-decane as the substrate (101). 1.7.  Summary Much of the chemistry of Rh(por) necessarily involves "single-site" and one-electron  chemistry from the point of view of the metal-centerd chemistry. Products of what would otherwise be migratory insertion chemistry are still accessible via one-electron radical processes (chain and cage) in spite of the formal lack of cis-coordination sites. Lewis acid/base, two-electron chemistry is also possible both at Rh(I) and Rh(LH) centers and with appropriately functionalised porphyrins. The importance of the relatively high strength of the Rh-C bond is apparent from the array of organometallic products observed and the variety of routes to those compounds. In addition, the porphyrin macrocycle enhances the labUity of the d Rh(IU) complexes relative to 6  "comparable non-porphinitic systems". 1.8  Goals of the present work The aim of this thesis is to examine the possibility of forrning Rh(por)(OOH) or  Rh(por)(OOH)(L) (L = phosphine or amine) species by reaction between O2 and a rhodium hydride, as is discussed in Chapter 3 of this thesis. As the formation of the RhfJET) hydride species often involves a lower oxidation state of Rh, the collateral discovery of the reduction of Rh(por)(Cl) by tertiary amines was also investigated. This lead to identification of some novel amine and CH2CI2 derived organometallic complexes  of Rh(por) and a partial mechanistic description of the  reaction with Et N and CH2C12- The work is presented in Chapter 4 and, in the end, provided a 3  morefruitfulline of investigation than the original one. Of importance to both the O2 and amine reactions is the common involvement of Rh(U) monomelic and dimeric species.  Chapter 2 Experimental methods  2.1.  General Techniques Used  2.1.1. Infrared spectra  Spectra over the range (3800 - 200) cm" were obtained using Nujol mulls and KBr 1  disks on a Nicolet 5DX FTIR spectrometer. 2.1.2. Electronic spectra Spectra over the range (800 - 200) nm were obtained on a Perkin Elmer 552A UV/VIS spectrophotometer, fitted with a Perkin-Elmer Model C550-0555 Thermoelectric single cell holder and a Model C570-0701 Digital Controller, or on a Hewlett-Packard 8452A diode array spectrophotometer. Conventional cells were used under aerobic conditions while air-sensitive samples were handled in a tonometer such as illustrated in Figure 2.1. Unless otherwise noted, all the visible spectra in this thesis were obtained using a 0.1 cm path cell. Typically the solid sample to be dissolved was placed in the quartz cell on the left as drawn and the solvent, and added liquid reagents as required, transferred into the volume on therightfor degassing by repetitive freezepump-thaw cycles. The solvent and solid sample were mixed bytippingthe apparatus to pour the solvent onto the solids in the cell side and shaking vigorously. Mixingtimesvaried from 17 s to several minutes depending upon the rapidity of dissolution: Rh(por) species tended to dissolve slowly (3-10 min) in aromatics but rapidly (15-50 s) in CH2CI2 or CHCI3. Most of the visible spectroscopy studies in this thesis were performed in this fashion when speed of observation was not a critical parameter. Stopped-flow techniques were used when speed and consistent mixing were critical (i.e., the kinetic studies in Chapter 4). If stock solutions were used, then degassing was done in other containers and the solutions transferred into the tonometer for rriixing. The apparatus was wrapped with black plastic electricians tape if the samples were light-sensitive.  The spectra of solutions in nmr tubes were obtained, without disturbing the integrity of the sample, using the HP diode array spectrometer. A spectrum was obtained on the thin film of solution flowing down the wall of the nmr tube after gently shaking the sample. Artifacts frequently occurred and very slight motion of the tube during the scan was helpful in reducing  Tencotip  ^_  optical path 1 mm cell  >5cm  I  View from BOTTOM  Figure 2.1.  Tonometer for anaerobic sample handling. Designed tofitcompactly in the sample compartments of PE 552A, HP 8452A and Cary 17D spectrophotometers.  these, because the HP spectrometer uses multi-pulse averaging to collect data. The quality of a spectrum obtained this way was acceptable for wavelength and relative peak intensity determination of the porphyrin chromophore but not for concentration (^termination. Weak and broad bands were poorly resolved. Solid-state spectra were obtained on mulls supported onfilterpaper. A solid sample would be mulled in Nujol and then a small piece of filter paper was soaked in the mull. The paper could be "stuck" on a face of a cell, for support in the spectrometer, and run against a blank of  47 Nujol on a similar sized piece of the same type of filter paper. The quality of a spectrum obtained this way was acceptable for wavelength detemiination of the porphyrin chromophore but not for concentration determination. Weak and broad bands were again poorly resolved. 2.1.3. NMR spectra MostH, C{ *H} and P{ to} spectra were obtained on a Varian XL-300 machine. 13  l  31  Some *H and P{ H} spectra were obtained on Broker WP-80 and WH-400 machines. Proton 31  1  and carbon spectra were normally referenced to residual solvent peak positions (124) and reported in units of 8 relative to TMS generally to 0.01 ppm accuracy, although the precision of the data was below 1 Hz. Phosphorus spectra were referenced to external triphenylphosphine in the appropriate solvents and reported relative to 85% phosphoric acid (Table 2.1) generally to 0.1 ppm accuracy. The difference in shifts between the residual phenyl and methyl resonances of C7D8 was found to be slightly temperature dependent (Fig. 2.2). This was noticeable during some VT *H nmr experiments if the spectral reference and lock were on different solvent peaks. Less variation between experiments occurred if the stopcock grease peakt at about 0.28 ppm (at 20 °C) was used as the reference and assumed to have a temperature invariant shift. A stopcock grease peak at about 0.09 ppm in C D 2 C I 2 and C H 2 C I 2 was similarily used as a reference. Some difficulty arose in quantifying the concentration changes of species during reactions under an O 2 atmosphere. In particular, comparison of initial spectra obtained under inert atmophere, or in vacuo, with those after addition of O 2 required the use of internal standards which had resonance intensities that were relatively insensitive to the increase in relaxation rates caused by the paramagnetic O 2 (126). In this thesis, the practical solution was to use the nearly ubiquitous stopcock grease peaks in the 0.0 to 1.6 ppm region of *H nmr spectra, which appeared to be insensitive to the presence of O 2 . The peaks, although generally weak, provided a convenient means to approximately normalize routine spectra before and after addition of O 2 to a particular sample. The same aquisition parameters were used across any series of experiments where comparisons were desired.  Table 2.1. The P{ H} shifts of PPI13 relative to 85% H3PO4 in various solvents. 31  1  Solvent  Figure 2.2.  8ppm  C6D6  -6.05  CD2CI2  -5.64  CDCA3  -5.46  a  Example of temperature variation of the !H nmr shifts of C7D8, plotted with reference to toluene-dg 5CH3 = 2.09 ppm. x = m.m'-H resonances of diamagnetic Rh(TMP)(Cl).  Sealed tube samples were prepared on a vacuum line. Solid samples were placed in an nmr tube with an attached B14 socket joint This tube was attached to a vacuum line and evacuated, and a pre-measured volume of nmr solvent was vacuum transferred onto the sample, under static vacuum. After the solvent transfer, and with the sample still frozen by liquid nitrogen, dynamic vacuum was re-established and the tube sealed off with a torch. 2.1.4. Mass spectroscopy Analyses of samples using FAB desorption were performed in this department's Mass Spectroscopy facility supervised by Dr. Eigendorf. 2.1.5. Micro-analysis Micro-analyses for carbon, hydrogen, nitrogen, oxygen and chlorine were performed by Mr. P. Borda of this department Samples containing TMP required addition of V2O5 as a combustion aid to prevent a low analysis for nitrogen. 2.1.6. Chromatography For column separations neutral, Brockman Activity I Alumina (80-200) mesh from Fisher Scientific was used fresh from the bottle. Activity U and DI were prepared by vigorously shaking Activity I with 2.3% and 4.5% H2O by weight, respectively. Alurninium oxide 60 F254 neutral (type E) TLC plates were used for analyses. Silica gel 60 (Merck) (70-230 mesh) was also used for column separations with silica gel 1B2-F (J.T. Baker Chemical Co.) TLC plates being used for analyses. Gas chromatography was done using an HP 5890A GC equipped with a FID and a HP 3392A digital integrator. The column was a 15 m OV 101 capillary, used with about a 100:1 split ratio at the inlet Samples of the volatile fractions to be examined were injected following vacuum distillation from metal complexes. Typically 0.8 to 1 mL bulk samples (nmr sample size scale) were prepared using the bulb-to-bulb distillation apparatus illustrated in Figure 2.3. About 1 pL was then injected for analysis.  50 Typical programmed conditions for separation of Et3N from Et2NH in toluene on the HP 5890A GC were: Detector temp: Inlet temp: Initial column temp: Initial time: Rate of temp change: Final temp: Final time:  220 °C 200 °C 70 °C 8 rnin 20°Gmin 220 °C 5 min 24 socket  Teflon tap.  Figure 2.3.  A small scale bulb-to-bulb distillation apparatus.  2.1.7. Electrochemistry Conductivity measurements were made at 25°C under anaerobic conditions using a Thomas Serfass conductivity bridge and a cell (constant: 1.0) from Yellow Springs Instrument Co. 2.1.8. Stopped-flow measurements A model 100/110 Durrum Stopped-flow apparatus was used for the measurements. The output of the single beam spectrophotometer was displayed on a Tektronix Dl 1 storage oscilloscope as voltage vs.timetraces. Polaroid photos of the display screen were taken using a Tektronix oscilloscope camera. Numerical data were obtained by measurement on the photographs and subsequendy converted to absorbance data. Temperature was controlled to ± 0.1 °C using water circulated by a high-speed pump.  51 Air-sensitive solutions were handled using the setup illustrated in Figure 2.4. Solutions prepared anasrobically were transferred under Ar into the reagent reservoirs (large Schkenk tubes) on the left using cannula, after thoroughly purging all the conecting tubes, drive syringes and stopped-flow valve block etc., with Ar. A slight pressure of Ar was used to transfer the reagent solutions through Teflon cannula into the drive syringes. As much as possible the drive syringes were kept filled and under positive pressure from the large reservoirs in order to maintain any leakage from the drive syringes outward. Due to the solution saturation with a gas (Ar, or CO, see below), bubble formation in the reaction chamber was a recurring problem. Data were accepted if the voltage vs.timeoscilloscope traces from 3 consecutive ''shots" overlapped, and the data were reasonably smooth. The precision of the absorbance data is ~± 0.015 absorbance units Oargely due to noise) and the accuracy is estimated to be ± 0.03 units based on the spectrum of a solution containing a known concentration of Rh(TMP)(Cl)(CH3CN). However some variation in the baseline voltage occurred fromtimetotimewhich introduces an offset of -0.1 absorbance unit Accordingly, the absorbance at several wavelengths was periodically rechecked during the 4-5 h required to obtain a spectrum and the order of the data collection within a wavelength range was randomized. The wavelength data are accurate to ± 1 nm, based on the same calibration solution. Teflon tubing force-fitted into Teflon-lined inlet  Drive syringes  Reagent reservoirs under slight positive pressure of Ar Figure 2.4.  The arrangement of reagent reservoirs for handling air-sensitive solutions during stopped-flow experiments using the Durrum Stopped-flow apparatus.  Reagent solutions saturated with CD at 1 atm were used for the investigation of the substitution reactions of Rh(por)(Cl)(CH3CN) (sect 4.4). The solubility of CO in CH2CI2 at 25 °C is estimated as ~7.3 x IO* M at a P c o " O- ? atm (corrected for the vapour pressure of 01202) 3  4  (127). After the reactant solutions were mixed in the reaction chamber of the stopped-flow apparatus, the [CO] was -3.65 x IO* M, 100timesgreater than the typical [Rh(por)(a)(CH3CN)] 3  of -2 x IO M used in the stopped-flow experiments. -5  2.2. Materials 2.2.1. Solvents Benzene and toluene were either spectroscopic or ACS reagent grade and were dried by distillation from benzophenone ketyl or standing over molecular sieves. Dichloromethane was reagent grade and was passed down a column of Alumina I (neutral) before drying by distillation from P2O5. N.N'-dimethylacetamide was used immediately after vacuum distillation from CaH2Deuterated solvents were obtained from MSD Isotopes. The C7D8, CoD^ CDCI3 and CD2O2  where dried over molecular sieves before use. All dry solvents were stored under Ar or vacuum in Schlenkware. Deoxygenated, dry  solvents were transferred by bulb-to-bulb vacuum transfer or cannula. If dry solvents were to be degassed after transfer to a container, then syringes or cannula were used for the transfers. 2.2.2. Gases N2 (N.F. grade), CO (CP. grade), and O2 (Ultra High Purity grade) were obtained from Linde. Ar,fromLinde, was passed through a molecular sieve and Drierite drying columnn before use. H2,fromLinde, was passed through an Engelhard Catalytic DEOXO purifier before use. 2.2.3. Other materials 2.2.3.1.  Amines  The liquid amines used were distilledfromKOH before use. Generally small amounts were prepared and usedfreshand kept in the dark as much as possible. 2.2.3.2.  Phosphines  The phosphines were reagent grade from Strem Chemicals Inc.  53 2.2.4. Porphyrins H2TPP and H2OEP were giftsfromDr. D. Dolphin. The 5,10,15,20-  tetramesitylrxjrphyrin (H2TMP) was synthesised using a literature method (119). The spectral data for the porphyrin matched the reported data. Nmr. to: (Table 2.2). Vis. ^max/  nm  inCH Cl2: 513,546,589,646. 2  Table 2.2. Thetonmr spectral data for H TMP in various solvents at 20 °C.  a  2  solvent QdV CD CDQ3 C  7  8  C  -CH=  m-H  P-CH3  0-CH3  >N-H  8.71  2.46  1.88  -1.73  8.82  7.14 d  2.42  1.89  -1.6  8.60  d  2.60  1.83  -2.53  a. All singlets, integrations matching the assignments, at 300 MHz. b. In vacuo. c. In air. d. Obscured by solvent 2.2.5. Rhodium porphyrin complexes Rhodium trichloride (RI1CI3XH2O; 42.61% Rh) was obtainedfromJohnson Matthey Chemicals Ltd. and was used without further purification. Literature methods were used to prepare [RhCl(cyclooctene)2l2 (120) and [RhCl(CO)2]2 (121). 2.2.5.1.  Rh(OEP)(Cl)(L)  Typical preparations are described below. 2.2.5.1.1.  L = H 0 , Rh(OEP)(Cl)(H 0)H 0 2  2  2  The synthesis of Rh(OEP)(Cl)(H20)-H20 was based on a Uterature method (17,18). In that method [RhCl(CO)2]2 was stirred with H OEP in C0H6 for 2 hours at room temperature, the 2  solution was.concentrated and then chromatographed on silica (100 mL dry volume of silica slurried in C^H^) with C^H^ followed by acetone/C6H6 (1:3). Solvent was removed from the  second fraction, eluted with acetone/CoHo, under reduced pressure using a rotary evaporator and the solids further dried in vacuo at room temperature. Recrystallization from EtOH, yields the purple Rh(OEP)(Cl)(H20)-H20. Reported yields were variable ranging from 21.7% (17) to 44% (18). In our hands, yields of 10% to 55% were obtained. Best yields were obtained by placing the reaction flask in a well lit place (a bubbler system exhausting to a fumehood isolated the flask) and monitoring the progress of reaction by visible spectroscopy for as long as 3 days! Workup was often complicated by formation of CO-containing organometallic porphyrins and nonporphyrin products. Subsequently an improved procedure was published (21). The same quantities of reagents were used as described above but the reactiontimeswere changed from 2 h stirring at room temperature to 6 h at room temperature then concentration to 30% volume and followed by reflux for 2 h before chromatography. Yield was 75-80% but workup was still complicated by formation of CD-containing organometallic porphyrin and non-porphyrin products. The elemental analysis and spectral data for the Rh(OEP)(Cl)(H20)-H20 obtained matched the reported data with the exception of the visible spectrum which tended to have slightly lower Xjnax values than reported (121a). For convenience this complex will be referred to as Rh(OEP)(Cl)(H20) in Chapters 3-6, unless it is necessary to emphasize the presence of the lattice H 0. 2  Anal. calc.(%) for CsgH^N^RhClO* C 61.15, H 6.84, N 7.92,0 4.52; found: C 61.14, H 7.02, N 7.61, O 4.80. Nmr. !H: (Table 2.3 and Fig. 2.5). Vis. Vax/nm (log e) in CHC1 ([Rh] = 1.52 x 1(H M, 25°C in vacuo): 400 (5.13), 517 3  (4.13), 550 (4.40). IR. (Fig. 2.6).  55 Table 2.3. The H nmr data for Rh(OEP)(a)(H20)-H20 in various solvents at 20 °C, unless otherwise noted. l  solvent  C6D  machine -CH= freq. (MHz)  6  CDCI3 CDCI3  CD2CI2  CDQ3  -CH3  other  temperature  300  10.50 s 4.07 m, 3.98 m 1.93 t  300 300 80  10.43 s 10.35 s 10.36 s  4.05 m 4.15 m 4.18 q  1.961 2.001 2.03 t 0.3 sbr  80  10.43 s 10.42 s  4.19 q  2.05 t 0.69 sbr  4.19 q  2.05 t  10.39 s  4.19 q  2.05 t -5.69 s (Rh-OH ), 1.46 s (H 0)  10.31 s  4.15 q  1.99 t  ?  C  -CH2-  b  27 °C 0°C 2  2  -40 °C  a. Solid heated at 140°C in vacuo for 2 h before dissolution. b. Two multiplets, almost resolved. c. Ref. 21. -CH,  CDCI3  -CH 2  -CH=  AN  T-  11  —r 10  Figure 2.5.  T  1  T  T 6 ppm  4, 1  2  7 3 8 5 The 300 MHz H nmr spectrum of Rh(OEP)(a)(H 0)-H20 in CDCI3, at 20 °C. !  2  ~l 0  I  i  1  3800  3200  N  I  I  —r  i  2600  N  1  I  I  1  2000 1700 1400 wavenumbers (cm )  1  1  1100  800  1  500  I  1  200  -1  Figure 2.6.  The IR spectrum (in Nujol) of Rh(OEP)(a)(H20)-H20.  2.2.5.1.2.  L = C H C N , Rh(OEP)(CI)(CH CN) 3  3  The Rh(OEP)(Cl)(H20)-H20 complex (225 mg, 0.36 mmol) was suspended in 25 mL benzene in a 50 mL Erlemeyer flask. Addition of 2 mL CH3CN resulted in a clear red-orange solution which was chromatographed on a silica gel column (ca. 100 mL dry volume of silica slurried in GSHQ). A pale yellow-brown fraction eluted with GsH6 and was discarded, following which elution with 5% CH3CN in CoHo was begun and collection of a broad orange-brown band continued until a green or bright purple band began to elute. This band was left on the column and discarded. The 5% CH3CN in Cetie fraction, after removal of solvent in vacuo, yielded 118 mg of red-brown Rh(OEP)(Cl)(CH CN) (52%). 3  Anal. calc.(%) for C3 H47N RhCl: C 64.09, H 6.65, N 9.83; found: C 64.65, H 6.83, N 9.30. 8  5  Nmr. R (300 MHz, GsD6 at 20 °C): 10.53 (s, 4H, -CH=), 4.11 (m, 8H, -CH2-), 4.00 (m, l  8H, -CH2-), 1.98 (t, 24H, -CH3), -2.96 (s, 3H, CH3CN).  57 Vis. Amax/nm (log e) in CH C1 ([Rh] = 4.82 x 10-5 M , 25°C in Ar): 400 (5.10), 518 (4.17), 2  2  550 (4.42). 2.2.5.1.3.  L = PPh , Rh(OEP)(CI)(PPh ) (122) 3  3  The Rh(OEP)(Cl)(H 0)-H 0 complex (82 mg, 0.11 mmol) and PPh (33.5 mg, 2  2  3  0.12 mmol) were placed in a small Schlenk tube under argon. The solids were dissolved in 20 mL freshly dried benzene. After ca. 15 min the solution was filtered and the filtrate volume reduced in vacuo to ~3 mL. The product was precipitated by addition of freshly dried hexanes, collected on a frit, and washed 3timeswith 2 mL portions of hexanes before drying in vacuo. Yield was 52 mg (50%) of red purple powder. The complex was found to be light-sensitive in dilute solution. Dissolution in CH3CN gave non-conducting solutions. Anal. calc.(%) for C 4H N RhClPOo.5: C 68.17, H 6.46, N 5.89; found: C 68.82, H 6.42, N 5  60  4  5.94 (contains 0.5 H 0). 2  Nmr. lH and 3lp{lH}: (Tables 2.4 and 2.5). Vis. Xmaxfnto (log e) in CgHg ([Rh] = (0.9 - 6.0) x 10-3 M, 25°C in vacuo): 351 (4.59), 422 (5.20), 533 (4.32), 564 (4.38); inNujolmull: 350,418,535,564. Table 2.4. The *H NMR spectral data for Rh(OEP)(CT)(PPh) at 20 °C. 3  solvent  machine -CH= frequency (MHz)  CD3CN  300  9.96 s  CD C1  300  9.93 s 10.06 s  2  CeD  6  2  80  -CH2-  -CH3  o-H  m-H  4.10 m, 3.97 m 4.09 m, 3.95 m  1.911 1.941  3.58 m 6.42 m 3.62 m 6.39 m  3.93 m  1.901  3.90 m  p-H  6.84 m 6.82 m  6.28 m  58 Table 2.5. Room temperature P{ H] NMR spectral data for Rh(OEP)(Cl)(PPh3) at 20 °C. 31  solvent  machine frequency (MHz) 121.421 121.421 32.21  CD3CN CD2CI2 C7H8  2.2.5.2.  l  Rh-P  ^Rh-P  9.68 d  124  9.52 d  124  9.05 d  116  Rh(OEP)(H)  Literature methods were used to prepare Rh(OEP)H (78). The hydride was prepared by protonation of [Rh(OEP)]-, itself prepared in situ in basic EtOH solution by borohydride reduction of Rh(OEP)(Cl)(H20)-H20, using HOAc. The orange Rh(OEP)(H) precipitates from the EtOH solution. An alternative "one-pot" preparation starting from [RhCl(CO)2]2 and H2OEP in glacial acetic acid was also used (46). Precipitation of Rh(OEP)(H) was induced by bubbling H2 into the solution. However, the product contained a large amount of unidentified insoluble black material characterised by IR bands at 2065 (m, sharp) and 1785 cm (vs, broad). This material could be -1  separated from the hydride by washing the mixture through celite with CH2CI2, under H2, and removal of the CH2CI2fromthe filtrate with a flow of H2. The hydride is air- and light-sensitive in solution but the solid is stable in dry air for several days. It is normally stored in the absence of light and under an Ar atmosphere. It is soluble in pyridine, THF, CHCI3, CH2Cl2» DMA or acetone, less soluble (slow dissolution) in aromatics and is poorly soluble in EtOH; alkanes or CH3CN. The elemental analysis and spectral data for the Rh(OEP)(H) obtained matched the reported data (78). Anal. calc.(%) for C3 H N Rh: C 67.91, H 7.12, N 8.8; found: C 67.23, H 7.20, N 8.62. 6  Nmr. *H: (Table 2.6).  45  4  Vw. Amax/nm (log e) in C H 2 a ([Rh] = 1.73 x 1(H M, 25 °C in vacuo): 391 (5.11), 508 2  (4.15), 542 (4.68). IR- VRhH at 2226 cm' (Fig. 2.7). 1  Table 2.6. The *H nmr data for Rh(OEP)(H) in various solvents and temperatures. solvent CoD  machine -CH= frequency (MHz)  - C H 2 - -CH3  Rh-H^jRh-H)  temperature (°Q  6  200*  10.15 sb  3.95 q  1.871  -41.28 d (44)  C6D  6  400  10.22 s  4.01 q  1.951  -41.24 d (44)  20  CD2CI2  400  9.97 s 9.73 s  4.01 q 3.89 m  1.901 1.78  -41.80 d (44) -42.03 bs  20 -40  80  9.98 s 9.98 s 9.82 s 9.54 s  -  -  n.o. -41.0 -41.3 n.o.  17 0 -40 -70  400  10.00 s  4.05 m  1.921  -39.1 d (32)  28  80  10.33 s 10.34 bs  4.05 m 3.95 bs  1.93 1 1.83 bs  -33.1 d (23) -32.8 d (23)  20 -20  THF-d pyr-d  5  8  n.o. = not observed a. Ref. 46. b. Temperature dependent: 8 H = 10.3117 - 62.61 (1/T) (ref. 46).  60  N = Nujol bands  L_J  N  N  N 3800  3200  2600  2000 3 1700 1400 wavenumbers (cm )  1100  800  500  200  -1  Figure 2.7.  The IR spectrum of Rh(OEP)(H) (in Nujol).  2.2.5.3.  Rh(TMP)(Cl)(L)  Considerable effort went into finding a metallation procedure that would yield reasonable quantities of Rh(TMP)(Cl)(L) derivatives with easily replaceable ligands. The successful methods presented below (sect. 2.1.5.3.1-2) are adaptions of the syntheses for Rh(OEP)(Cl)(H20)-H20 discussed above. A promising procedure was the reaction of RhCl3-3H20 with H2TMP in DMF which was directly adapted from the reported preparation of Rh(TPP)(Cl)(N(CH3)2H) (with [Rh(TPP)(N(CH3)2H)2]Cl as co-product) (52). Although ca. 80% of the H TMP was metallated 2  it proved impossible to purify the products which were principally: (i) Rh(TMP)(Cl)(N(CH3)2H) ( t o nmr in CDCI3: 8.63 (s, 8H, -CH=), -7.3 (m,m'-H obscured), 2.60 (s, 12H, p-CH3), 1.98  (s, 12H, 0-CH3), 1.74 (s, 12H, o'-CH ), -2.78 (d, 6H, N-CH3), -5.4 (s, IH, N-H)); (ii) 3  [Rh(TMP)(N(CH3)2H)2]Cl (ionic, very low solubility in  to  nmr in CDCI3: 8.81 (s, 8H,  -CH=), 7.30 (s, 8H, m-H), 2.63 (s, 12H, P-CH3), 1.92 (s, 24H, 0-CH3), -3.08 (d, 12H,  N-CH3), -3.89 (s, IH, N-H); mass measurement expected for C^oH66N6Rh: 973.44, found (FAB): 973); (iii) [Rh(TMP)(N(CH)2H)2][Rh(Cl)2(CX))2] (ionic, very low solubility in Co*^; 3  lH nmr in CDCI3: similar to [Rh(TMP)(N(GH )2H)2]a; IR (Nujol): VQO at 2064 and 1983 cm- , 1  3  vco reported for [Rh(OFJ>)(N(CH3)2H)2][Rh(a)2(CX))2] (51): 2064 and 1982 cnr ). 1  We recently became aware of the synthesis of Rh(TMP)(I) in 1,2-dichloroethane that utilizes I2 as oxidant (30), but have notrepeatedthis synthesis. 2.2.5.3.1.  L = iPrOH, Rh(TMP)(Cl)(iPrOH)  Most of the work in this investigation that involved RhfTMP) species used the title isopropanol complex as starting material. Unfortunately the synthesis of Rh(TMP)(a)(iPrOH) is unreliable, working only 2 times out of 5. Use of CH3CN instead of iPrOH (sect. 2.1.5.3.2.) led toreproducibleresults,although the synthesis has not been optimized. The products of the 3 "failed" experiments were not fully characterized; however, TLC data are consistent with Rh(TMP)(iPrO) as a major product (see below; comments in sect. 2.1.5.3.3. are also relevant). The [RhCl(CO)2l2 complex (108 mg, 0.38 mmol) and H2TMP (211 mg, 0.27 mmol) were placed in a 100 mL reaction flask having a Kontes Teflon valve as the only entrance. Then 28 mL dry toluene was vacuum transferred onto the solids. The flask was wrapped in foil to exclude light and the rrhxture stirred in vacuo for 18h at room temperature. The foil was removed and the temperature raised to 70°C for 2 days, after which the reaction flask was cooled to room temperature. The flask was opened to the atmosphere for about 10 min while the solution was stirred. The reaction flask was closed and the contents left to stir until the the visible spectrum of thereactionsolution had ceased changing from bands at 520 (major), 545 (weak), 590 (broad) and 640 (broad) nm to bands at 544 and 578 nm. About 30 mg of solid K2CO3 were added to neutralize the H from H2TMP, and 0.2 mL of 2-propanol was added. The mixture was stirred +  until the greentingeof the solution was gone, then about 5 mL of solvent were removed by vacuum transfer, whichresultedin disappearance of the 544 and 578 nm bands and generation of a 534 nm peak. The solution was filtered toremoveK2CO3 and fine greenish solids, before passing thereactionsolution down a silica gel column (75 -100 mL dry volume of silica slurried in CoHo), eluting with C5H6; the column was wrapped with aluminium foil to protect it from direct  light A yellow-orange band came off first then a red-orange complex group (1 broad and 2 narrow overlapped bands). The bands of this group sometimes spread out on the column during elution; adding 2-propanol to the benzene eluant (1-5%) brought the bands together and they were collected together. Theremainingmaterial at the top of the column was discarded. Prior to removal of solvent from the two fractions, 3-6 drops of 2-propanol were added to each. Solvent wasremovedunder reduced pressure using a rotary evaporator and the solids further dried in vacuo at room temperature. The first band yielded 28 mg of a purple solid (a mixture, including H2TMP and Rh(TMP)(iPrO) as judged by nmr), and the second band 145 mg of a microcrystalline lilac-purple Rh(TMP)(a)(iPrOH)-iPrOH (51%). For convenience this complex will bereferredto as Rh(TMP)(Cl)(iPrOH) in Chapters 3-6, unless necessary to emphasize the presence of the lattice iPrOH. RhCrMP)(Cl)(iPrOH)-iPrOH Anal. (V2O5 combustion additive required) calc.(%) for C62H68N4Rha02: C 71.63, H 6.59, N 5.39; found: C 70.96, H 6.40, N 5.24. Nmr. lH: (Table 2.7 and Fig. 2.8 ). Vis. Xmax/nm Gog e) in 0^6 ([Rh] = 124 x 1(H M, 25 °C in vacuo): 422 (5.33), 534 (4.39), 565 (3.41); in CH C1 ([Rh] = 5.55 x 1(H M, 25 °C in vacuo): 423 (5.46), 532 (4.40), 565 2  2  (3.40). Table 2.7. The *H NMR spectral data for Rh(TMP)(a)(iPrOH)-iPrOH in various solvents.  3  solvent  -CH= m,m'-H  P-CH3  o,o'-CH.3  8-94 7.23, 7.03  2.44  2.22, 1.71  O>30r>D  8.63  2.60  1.90  CD CjDtfA  8.83 7.24, 7.06 8.91 7.22, 6.99  2.47 2.46  2.22, 1.69 2.29, 1.68  C6D  7  6  8  7.29  coordinated iPrOH  -2.25 d (6H,-CH ), -2.67 m (IH, >CH-), -6.33 m (IH, -OH) 3  a.  A l l singlets and at 20 ° C except where noted otherwise, integrations matching assignments, at 300 M H z .  b.  A l l resonances broad.  c.  -34 ° C .  d  One non-coordinated iPrOH is also present: methyl resonance at 0.762 d, other resonances not observed.  p-Me o'Me 8=  o-Me  006  J  m-H  m'-H  r  T 5  10  Figure 2.8.  —r -5  0  8 ppm  1  10  The H nmr spectrum of PJi(TMP)(Cl)(iPrOH)-iPrOH in C^D^ at 20 °C. l  Rh(TMP)(iPrO) Nmr. lH (300 MHz, C6D6. 20 °C): 8.81 (s,8H, =CH-), 7.21 (s, 4H, m-H), 7.13 (s, 4H,  m*-H), 2.45 (s, 12H, p-CH ), 2.21 (s, 12H, 0-CH3), 1.92 (s, 12H, o'-CH3), 2.40 (m, IH, 3  0-CH<), -0.88(<L 3JHH = 6 HZ, 6H, -CH ). 3  IR. vco at 1050 cm" (within the expected region for isopropoxide ligand (123)) 1  2.2.5.3.2.  L = CH3CN,  Rh(TMP)(Cl)(CH CN) 3  The synthetic method was the same as for the synthesis of PJi(TMP)(Q)(iPrOH) except CH3CN was used in place of iPrOH. Yield of the bright orange-red Rh(TMP)(Ci)(CH3CN) was  50%. Anal. (V2O5 combustion additive required) calc.(%) for C58H N Rha: 55  7.29; found: C 72.25, H 5.76, N 7.06.  5  C 72.53, H 5.77, N  64 Nmr. lH (300 MHz, CDCI3 at 20 °C): 8.59 (s, 8H, -CH=), -7.25 (m^n'-H, obscured by  solvent), 2.60 (s, 12H, p-CH ), 1.88 (s, 12H, 0-CH3), 1.83 (s, 12H, o'-CH ), -0.179 (s, 2H, 3  3  Rh-CHjCN). ^max/ ™ 0og e) in CH C1 ([Rh] = 4.82 x 10-5 M, 25°C in Ar): 400 (5.48), 539 (4.37), 1  2  2  572 (3.59). IR. (Fig. 2.9).  1  l_  1  T  3800  3200  N  l  1  1  1  1 N  1  1  2600  Figure 2.9.  2000 1700 1400 1100 wavenumbers (cm- ) The IR spectrum (in Nujol) of Rh(TMP)(Cl)(CH CN).  2.2.5.3.3.  L = none, Rh(TMP)(Cl)  1 800  1 500  1 200  1  3  This complex could be prepared by in vacuo pyrolysis of either Rh(TMP)(Cl)(CH CN) 3  or Rh(TMP)(Cl)(iPrOH). However, if amounts of Rh(TMP)(Cl)(iPrOH) larger than 1-3 mgs were pyrolysed, a mixture of products (not characterized) was obtained. At high temperature the RhfJH) complex in the solid state is possibly reduced by its isopropanol ligand. Reduction of Rh (TPP)(Cl) by isopropanol is known in solution (sect. 1.6.3). m  65 The Rh(TMP)(a)(CH3CN) complex (30 mg, 0.03 mmol) was placed in a tube fitted with a Teflon valve and a B19 socket (Fig. 2.10). The tube was evacuated and then heated at 210 °C under dynamic vacuum (10* torr) for ~3 h to give very hygroscopic dull red-brown 5  Rh(TMP)(a). Manipulations of the complex were performed in a glovebox.  16cm  Figure 2.10.  Vacuum pyrolysis tube.  Anal. (V2O5 combustion additive required): calc.(%) for C5oH52N4RhCl: C 73.16, H 5.70, N  6.09, CI 3.86; found: C 73.46, H 5.85, N 6.06, CI 3.70. Nmr. ! H (Table 2.8). Vis. Xjnax/nm in C7H8 at 25 °C: 525 (Soret region not examined). The Rh(TMP)(a)(iPrOH) complex (3 mg, 0.003 mmol) was siinilarly heated to 220 °C under dynamic vacuum (10* torr) for 3 h to give Rh(TMP)(Cl). 5  Anal. (V2O5 combustion additive required): calc.(%) for C5oH52N4RhCl: C 73.16, H 5.70, N  6.09, CI 3.86; found: C 73.39, H 5.67, N 5.95, CI 3.66.  Table 2.8. ThetoNMR spectral data for Rh(TMP)(Cl) in CH2CI2 and C7D8 at various temperatures. 8  solvent CD 7  -CH=  8  CD2CI2  m-H m'-H  p-CH  8.78  7.28  7.02  8.79  7.27  7.00  2.47  8.79  7.26  6.99  8.80  7.23  8.81  3  0-CH3  2.48»>  o'-CH  3  temperature (°Q 20  4.46  1.51 1.50  2.47  2.45  1.50  -13  6.96  2.46  2.43  1.49  -23  7.22  6.91  2.45  2.42  1.59  -33  8.81  7.20  6.89  4.44  2.41  1.49  -43  8.70  7.31 7.30 7.31*  2.62  1.94  1.77  21  2.62  1.79  7.33  2.63 2.63  1.93 1.92  7 -18 -38  8.71 8.72  c  8.73  7.33C  1.90  1.81 1.84  8  a. All singlets; the integrations matching assignments at 300 MHz. b. P-CH3 and 0-CH3 resonances overlap. c. m-H and m'-H resonances overlap. 2.2.5.4.  Rh(TMP)(H)  This complex was never isolated pure or in large quantity. It was prepared in situ for visible spectroscopy experiments by borohydride reduction (5 mg NaBKLO of 0.8 mg [Rh(TMP)(N(CH3)2H) ]Cl in 3.2 mL EtOH containing 0.2 mL IN NaOH. The resulting air2  sensitive solution (presumed to contain [Rh(TMP)]- mtermediate: Xmax at 498 nm) was carefully acidified with AcOH, forming air-sensitive Rh(TMP)(H) in situ. A solid sample of uncertain purity was prepared for a nmr experiment by exposing 5 mg solid Rh(TMP)(Cl) toanH atmosphere for 1.5 weeks. The dull red-brown Rh(TMP)(Cl) became 2  reddish orange impure Rh(TMP)(H). Nmr. to (impure Rh(TMP)(H), 300 MHz, C D at 20 °C): 8.66 (s, 8H, -CH=), -7.15 (m,m'7  8  H, obscured by solvent), 2.47 (s, 12H, p-CH ), 2.11 (s, 12H, 0-CH3), 1.77 (s, 12H, o'-CH3), 3  -40.18 ppm (d, IH, jRh.H = 44 Hz, Rh-H) (123a). Vis. Xmax/nm in C H OH at 25 °C (in situ Rh(TMP)(H)): 415 (Soret), 528, 558(sh). 2  5  Chapter 3 Reactions involving Rh(OEP)(H)  3.1.  Introduction This chapter contains studies principally of the reactions of Rh(OEP)(H) with O2.  Reactions of some other small molecules with the hydride are included where these have some relevence. Reactions effected by homogeneous transition metal catalysts utilizing direct oxidation by molecular oxygen are not well understood relative to other areas of homogeneous transition metal catalysis (1). There is a strong motivation to develop metal complex catalysts that will utilize molecular oxygen under mild conditions for the selective oxidation of organic substrates (1,2). Much attention has focused on monoxygenase-type chemistry where two-electron oxidation of substrates (containing C-H, C=C, >N-, >S ) by O2 occurs, with one oxygen atom evolving as H 0 (e.g. P-450 cytochromes) (128): 2  P-450  RH + 0 + NADPH + H+ 2  ROH + H 0+ NADP 2  +  (3.1)  Although the natural systems are not long-lived (P-450 has a lifetime of -20 min during oxidation (129)) and so the "catalytic system" includes the support of biologicalreplication,the elementary steps involved in the enzymic process are of obvious interest. The key steps in the P-450 enzymic catalytic cycle that effect the conversion of O2 to useful transferable "O equivalents" are believed to involve a possible FeHLOOH intermediate (Scheme 3.1; the bound substrate and other components are not shown) (6,7,130). The M-OOH mtermediate has been proposed to occur in a number of transition metal non-porphyrin and porphyrin containing systems (116,131,132). Of particular interest in this laboratory were systems where M-H with O2 were involved in the oxidation of hydrocarbons and where metal hydroperoxides are likely intermediates in these 02/hydride systems. The M species  - Fe + 0  — - Fe -0-0-  n  Fe (0 ")  m  2  ffl  2  2  Fe (0 -) + FT —— Fe -0-0-H m  2  m  2  Fe -0-0-H + FT — [ F e = 0 — — F e + O] + H 0 m  v  m  2  [Fe =0] v  Scheme 3.1. Part of the catalytic cycle of cytochrome P-450.  may be recycled via M-H formation using H and the use of H2/O2 mixtures for the reductive2  activation of dioxygen has been documented (132). Scheme 3.2 is a schematic of a cycle based on an Ir, non-porphyrin, system.  Scheme 3.2. Postulated O^/hydride system (adapted from ref. 132).  The formation of MOOH via step a in Scheme 3.2 is the principle interest in the present work. The observation of MOOH formation from M-H and O2 has occurred in a few cases: [Co(H)(CN) ] " and [Rh(H)(CN) (H 0)] - (133), [Rh(NH ) (H)] (134), 3  2  5  4  2+  2  3  5  [Rh(NH3) (H 0)(H)] (135), Ir(H)(Cl) (C8Hi ) (136) and has been postulated in others (132). 2+  4  2  2  2  In addition, during the course of this study, Ir(OEP)(OOH) (137) was reported to be produced from Ir(OEP)(H) and 0 . To our knowledge, M-OOH species have yet to be crystaUographically 2  characterised. The choice of Rh(OEP)(H) as the hydride was made on the grounds of potential mechanistic simplicity, reactivity and availabihty. It is a known compound in the literature (sect. 1.3.3). The porphyrin ligand strongly restricts the formation of vacant coordination sites cis to the axial positions by virtue of its planar tetradentate nature. Rh is a second row metal and substitution  69 kineticsforRh(in) can be relatively slow. Toluene solutions of the hydride react with O2 to form [Rh(OEP)]2, at room temperature (64). In addition, a thermally unstable Rh(OEP)(02) complex is formed from the reaction of [Rh(OEP)]2 and O2 at low temperature (42). The TPP analogue, Rh(TPP)(02)» in DMF catalyses the conversion of H2/O2 mixtures to H2O (41,42). The hydride and dioxygen RhfTPP) complexes are interconvertable by alternate use of H2 and O2 (41). The Rh(OEP)(H) complex itself is formed by direct reaction of H2 with Rh(OEP)(Cl) in MeOH. 3.2.  Results and Discussion  3.2.1. Reaction of Rh(OEP)(H) with 0  2  The reaction of O2 with Rh(OEP)(H) was examined in benzene, toluene and CH2CI2. 3.2.1.1.  In benzene and toluene  When nmr samples of Rh(OEP)(H) in dry CoDg are exposed to O2 at 20 °C the solution colour quickly darkens. The *H nmr spectrum of the hydride is replaced with that of [Rh(OEP)]2 (Fig. 3.1), characterised by the relatively low shift of the porphyrin meso proton resonance due to thering-currenteffects of the cofacial porphyrins of the diamagnetic Rh(II) dimer, and by the two well-separated sets of - C H 2 - resonances of the ethyl side-chains. The multiplet - C H 2 resonahces are consistent with the presence of a diamagnetic metaUo-octaethylporohyrin complex, that is asymmetrically substituted with regard to the porphyrin plane, Le., two different axial ligands are present, in this case another metallo-porphyrin (138-141). Within such complexes the methylene protons of the ethyl side-chains become amsochronous and appear as an ABX3 multiplet (139,142). In this particular example the especially wide separation into 2 multiplets probably reflects the increasedring-currenteffects in the environment between the cofacial porphyrins (cf. Fig. 1.4). In symmetrically substituted species the - C H 2 - protons appear as a single quartet due to coupling with the adjacent - C H 3 group. Using stopcock grease as an internal "standard" (sect. 2.1.3), comparison of the *H nmr spectra from several experiments shows that [Rh(OEP)]2 has formed in up to 100% yield during the reaction (Fig. 3.1). A small amount of the dimer was present (less than 2%) before addition of O2 because of the equilibrium between Rh(OEP)(H), [Rh(OEP)]2 and H2 (reaction (1.7)). Coincident with the formation of [Rh(OEP)]2, a small peak  70  (a)  -CHa 1 = Rh(OEP)(H) 2 = [Rh(OEP)] g = grease s = solvent 2  -CH=  -CH, 1,2  10  T  9  Li 4  6  9^0  10  T 9  Figure 3.1.  I  8  T 6  T  5 (ppm)  0  The 300 MHz *H nmr spectra of (a) Rh(OEP)(H) in C ^ and (b) 30 min after addition of O2 at 20°C. [Rh] « 2 x 10" M, Ptotal = 1 atm. 3  in the 0-0.5 ppm region, due to H2O (not always observed apparendy because of exchange) increases in intensity and shifts downfield towards the position of free H2O (-0.45 ppm) indicating the formation of H2O during the reaction. The amount of [Rh(OEP)]2 remains constant when a sample is left in air for a further 2 h period. The visible spectrum of the solution in the nmr tube (Fig. 3.2) showed Soret bands at 352 and 390 nm with weak P and a bands at -520 and -550 nm similar to those reported for [Rh(OEP)J2 (64). These observations are in accordance with the reported oxidative cleavage of the Rh-H bond to form [Rh(OEP)]2 with the presumed formation of H 0 (64). 2  Sometimes precipitation occurs during the reaction. Presumably the purple precipitate is [Rh(OEP)]2 because its solid state IR shows only bands expected for the OEP ligand. The reaction could also be monitored by visible spectroscopy, which was in fact the first method used in this work to examine the reaction. The spectrum of the reaction product in these experiments has the a band at 552 nm (Fig. 3.3), which is similar, but not identical, to the spectrum obtained for the nmr sample (Fig. 3.2) and to the spectrum of [Rh(OEP)]2 (Table 3.1). Assuming, on the basis of the nmr data, that the principle product will be [Rh(OEP)]2, then the presence of an extra complex in solution is suggested by the data in Table 3.1. It turns out that the reaction of Rh(OEP)(H) with O2 is very sensitive to solvent purity. A number of experiments were pursued before the marked sensitivity was realized; the effects are briefly presented. If the change of absorbance at the a band (542 nm) of the hydride is monitored during the reaction, the absorbance vs.timecurve observed is very dependent on the benzene purity. Figure 3.4a illustrates the change in absorbance when the benzene used has been washed with cone. H2SO4 prior to drying by distillation from benzophenone ketyL A very fine suspension was found after 20 min. In benzene freshly distilled only from benzophenone ketyl there is a rapid drop in intensity at 542 nm followed by a "transition segment" and then a slower increase to ca. 65% of initial intensity (Fig. 3.4b). The spectrum of the product (solid line, Fig. 3.5) is similar (at least in peak positions) to that of the starting Rh(OEP)(H). In addition there is no precipitation and the spectrum is stable to added H2. If undistilled benzene is used, then a completely different absorbance vs.timecurve with an induction period, followed by sigmoidal decrease is seen and  72  1  <  V 300  Figure 3.2.  I  1  400  r—  500  600  Wavelength (nm)  The visible spectrum of the nmr sample illustrated in Fig. 3.1b, for the reaction of Rh(OEP)(H) and O2 in C6D - [Rh] = 2 x IO M, P 3  6  Figure 3.3.  lota  i = 1 atm.  Table 3.1. The visible spectral data for [Rh(OEP)]2 and for the product of the reaction of Rh(OEP)(H) with O2 in benzene purified by washing with cone. H2SO4 and then distilling from benzophenone ketyl. complex  AmaxQog e) Soret  [Rh(OEP)] product  2  352(4.01) 351(4.52)  388(4.09) 391(4.71)  g  a  521(3.77) 520(3.73)  550(3.76) 552(3.84)  ref. (64)* this work  a. The log e values given inref.64 for the Soretregioninref.64 are incorrectly stated judging from the spectrum shown.  60000  time (s) Figure 3.4.  Change in apparent extinction coefficient at 542 nm during thereactionof Rh(OEP)(H) with O2 in benzene from various sources: (a) washed with cone. H2SO4 then dried over ketyl, (b) only dried over ketyl, (c) ACS Spectroscopic grade and (d) is (b) stored under Ar. [Rh] » 2.6 x I O M, Ptotal = 1 atm, 25 °C. 4  U C  a  1 <  Wavelength (nm) The visible spectra of (•••) Rh(OEP)(H) in C^Hs (in vacuo) dried only over ketyl  Figure 3.5.  and (—) 30 min after addition of O2. [Rh] = 1.42 x IO" M, P ai = 1 atm, 25 °C. 4  tot  concomittant precipitation occurs (Fig. 3.4c). The soluble product shows a Soret at 392 nm and (3 and broad a bands at 524 and 546 nm. The precipitate exibits a band in the IR spectrum (Fig. 3.6) at 3605 cm which is attributable to an -OH moiety: some literature data (Table 3.2) indicate that -1  the 3605 cm band observed is probably due to the presence of Rh-OH rather than Rh-OOH -1  because all but one hydroperoxo species have VOH bands that fall below 3600 cm (132). -1  If benzene that has been purified only by distillationfromketyl is stored under Ar for more than a day or two before use, then the change of the a band is a smooth sigmoidal decrease (Fig. 3.4d) and precipitation again occurs. The precipitate does not show an IR band at 3605 cm . The soluble products have a weak a band at 544 nm, with a prominant shoulder at -1  554 nm, probably due to some [Rh(OEP)]2In toluene solution, qualitatively similar effects were observed by visible spectroscopy. Use of toluene dried with benzophenone ketyl or molecular sieves gives soluble products which have spectra similar to the product spectrum obtained from the analogous experiments in benzene. Monitoring the changes at the a band reveals differences between the ketyl- and sieves-dried  75  1  3800  j 3200  N  j 2600  N j 1 1 2000 1700 1400 wavenumbers (cm )  j 1100  1  800  1 500  j 200  -1  Figure 3.6.  The IR spectrum of a purple precipitate (in Nujol) isolated from the reaction of Rh(OEP)(H) and O2 in benzene (ACS Spectroscopic grade).  systems (Figure 3.7), the reaction in the ketyl-dried solvent showing a very fast initial reaction. If toluene is used without purification, then the reaction leads to precipitation and the soluble components have a spectrum similar to that for the comparable experiment in benzene. In summary, the reaction is very sensitive to solvent impurities and possibly trace impurities in the Rh(OEP)(H) when run at the concentrations used for visible spectroscopy (i.e., ~2 x 10" M). In C0D6. at the higher concentrations used in the nmr experiments (i.e., 4  2 x 10" M), the Rh(II) dimer forms. Otherwise, the products are uncharacterised Rh(III) 3  complexes and some [Rh(OEP)]2- One product of the impurity "driven" reactions may be Rh(OEP)(OH) judged by the observation that the IR spectra of the precipitates did show a band above 3600 cm" . 1  Table 3.2. Some IR spectral data for M-OOH and M-OH species from the literature. complex  V Q H bands (cm ) for: -1  Fe (TMP)(OH) Fe (TAPP)(OH)  OH  OQH  3650,3610 3660  m  IV  [Ru (OEP)(OH)] -p:0 [Os (OEP)(OH)] -p:0 [Os (OEP)(OH)]-nO-[Os (OEP)(OCH3)] IY  2  TV  2  IV  IV  ref 1 2  3606 3598 3602  3 3 3  [Co(en) ][Co(CN) (OOH)]-3H 0 Rh(Cl)(acac)(PPh ) (OOH) Rh(Cl)(acac)(PPh ) (OH)  3550  4 5 5  Rh(Cl)(acac)(PPh )(OH)  3502  5  3  5  3600 vs, 3440 br 3470  2  3 2  3 2  3  K [Rh(CN) (OOH)(H 0)] Ir(OEP)(OOH)  3500 vs, 3380 br 3596  4 6  "Ir -OOH" "Ir -OH" "Pt-OOH" "Pt-OH"  3495  7 7 8 8  2  4  2  m  3680, 3605  m  3585-3517 3628-3602  Ge(TPP)(OH) Sn(TPP)(OH)  2  2  1. 2. 3. 4. 5. 6. 7. 8. 9. 10.  3600 3610  9 10  J.T. Groves, R.C. Haushalter, M. Nakamura, T.E. Meno and B.J. Evans. J. Chem. Soc. 103, 2884 (1981). Y. Harel and R.H. Felton. J. Chem. Soc. Chem. Commun. 206 (1984). H. Sugimoto, T. Higashi, M. Mori, N. Nagano, Z. Yoshida and H. Ogoshi. Bull. Chem. Soc. Jpn. 55, 822 (1982). H.L. Roberts and W.R. Symes. J. Chem. Soc. (A), 1450 (1968). H. Suzuki, S. Matsuura, Y. Moro-Oka and T. Dcawa. Chem. Lett. 1011 (1982). J.P. Collman and K. Kim. J. Am. Chem. Soc. 108, 7847 (1986). M.T. Atlay, M. Preece, G. Strukul and B.R. James. Can. J. Chem. 61, 1332 (1983). G. Strukul, R. Ros and R.A. Michelin. Inorg. Chem. 21, 495 (1982); R.A. Michelin, R. Ros and G. Strukul. Inorg. Chim. Acta, 37, L491 (1979). M. Hartmann, G. Meyer and D. Wohrle. Makromol. Chem. 176, 831 (1975). L.R. Milgrom and R.N. Sheppard. J. Chem. Soc. Chem. Commun. 350 (1985).  60000  50000  a b  20000 - 50 s mixing time 10000  T  0  500  1000  time (s) Figure 3.7.  Change in apparent extinction coefficient at 542 nm during the reaction of Rh(OEP)(H) with O2 in toluene from various sources: (a) dried over ketyl, (b) dried over molecular sieves. [Rh] = 2.0 x 10" M, P al = 1 atm, 25 °C. 4  tot  3.2.1.2.  In CH C1 2  2  The reaction of Rh(OEP)(H) with O2 in dichloromethane is rapid. Some precipitation usually occurs at the concentrations used for nmr experiments and the precipitate shows IR spectral bands due only to the OEP ligand. The change in *H nmr spectrum that occurs upon reaction of Rh(OEP)(H) with O2 at room temperature is shown in Figures 3.8a and 3.8b. There is a marked reduction in the intensity of the rx>rphyrin resonances in keeping with the observation of precipitation. However, in some experiments, a similar reduction in intensity is seen when no precipitation occurs. The integration of the meso proton resonances of the porphyrin is very low compared to that of the ethyl side chains and there are several weak, broad, resonances in the 4-2 ppm region. Examination of a spectrum covering a range greater than ± 60 ppm at very good S/N revealed no other resonances beyond those already noted in Figure 3.8b. Also the [Rh(OEP)]  2  present initially does not appear to have changed in concentration during the reaction unlike the corresponding reaction in benzene.  78  (a) 1 = Rh(OEP)(H) 2 = [Pvh(OEP)]  -CH,  2  g = grease s = solvent  -CH 2  12  -CH=  11  10  Rh-H  T  ~i  r  -41  -42  -  2  ii  T 6  9  x5  UL o  (b)  2  2  11  ~T~  10  T  T  1  5  4  1  1  1  1  1  3  2  0  CD2CI2  and (b) 15 min after  5 (ppm)  9  Figure 3.8.  1  6  2  The 300 MHz H nmr spectra of (a) Rh(OEP)(H) in J  addition of O 2 at 20°C. [Rh] » 2 x 10' M, P ^ = 1 atm. 3  The reaction of Rh(OEP)(H) with  O2  in freshly dried C H 2 C I 2 can be followed by visible  spectroscopy; no precipitation occurs initially and isosbestics are not observed. The product has a Soret band at 402 and the (5 and a bands at 520 and 553 nm (Fig. 3.9) which are not those expected for [Rh(OEP)]2, being more consistent with the hypso-type spectrum of a Rh(III) species (69). The solvent could be removed and the residue redissolved in fresh solvent to give the same spectrum, thus the reaction with O 2 is irreversible. The product when redissolved in  1  -1  79  n 300  Figure 3.9.  i  i  i  400  500  600  Wavelength (nm) The visible spectra of (••••) Rh(OEP)(H) in CH2CI2 and (—) 30 min after addition of 0 . [Rh] = 1.73 x IO- M, P tai = 1 atm, 25 °C. 4  2  to  fresh solvent showed little reaction with 1 atm of H2 at room temperature, with only a small absorbance increase in the 540 nm region and decrease in the 555 nm region occurring. During the course of the O2 reaction, a sigmoidal decrease in the intensity of the Rh(OEP)(H) a band is seen (Fig.3.10). Precipitation is always observed at the end of the reaction and slowly continues over several hours. The "ti/2" of the curve progressively increases with decrease in [Rh] (traces 0  a-d) but the curves cross in several places. Using undistilled solvent gave a similar curve (trace b vs. trace e) within the experimental scatter. The course of the reaction in dichloromethane and in aromatic solvents is not similar. In particular, [Rh(OEP)]2 is not a major product in CH2CI2. There is an inconsistency between the visible spectroscopic data in dichloromethane, which suggest a Rh(UI) product, and the nmr data in dichloromethane where the resonances after addition of O2 are not consistent with a Rh(HI) porphyrin species. Possibly oxidation of the porphyrin occurs during the nmr experiments in CD2CI2 which raises the possibility of O2 activation at the metal, perhaps involving a  60000 a  b c d  e  10000  ±  0  500  1000  time (s) Figure 3.10.  Change in apparent extinction coefficient at 542 nm during the reaction of Rh(OEP)(H) with 0 in freshly dried CH2CI2 for various [Rh] : (a) 3.40 x IO" M, (b) 2.68 x IO" M, (c) 1.62 x IO' M, (d) 5.6 x 10" M and (e) 2.62 x 10" M (reagent grade solvent). Ptotal = 1 atm, 25 °C. 2  4  0  4  4  5  4  Rh(OEP)(OOH) intermediate. In fact, low temperature nmr data provide evidence for an unstable metal-hydroperoxide, and these data will be presented in the following paragraphs. A sample of Rh(OEP)(H) with CD2G2 and O2 was prepared by vacuum transferring the solvent onto the hydride and sealing the tube under ca. 0.6 atm of O2, while the sample remained frozen at liquid N2 temperature. The sample was allowed to thaw between -50°C and -40°C, and then changes followed for ca. 3 h at -40°C. It is probable that the solutions were not homogeneous at this temperature; however, sufficient material dissolved to react with the O2 diffusing into the cold solution. Resonances due to Rh(OEP)(H) decrease and the signals typical of a new diamagnetic Rh(ITI) species, "Rh(OEP)(X)'\ increase; having a meso resonance at 10.24 ppm and a single proton at -1.81 ppm (Fig. 3.11). The shifts of the meso protons of Rh(OEP)(H) and "Rh(OEP)(X)" species are not temperature-dependent over the range -50 to -20 °C. If the sample is allowed to warm above -20 °C precipitation occurs and the resonances of Rh(OEP)(H) and "Rh(OEP)(X)" decrease. The 80 MHz H nmr spectrum, taken at room temperature, of the J  81  -CH=  T  1  11  10  Figure 3.11.  Time (min)  -OOH  r  9  1  6 (ppm)  -2  —i -41  r -42  Changes in the 80 MHz *H nmr spectra during the reaction of Rh(OEP)(H) with 0 at -40 °C in C D 2 C I 2 ; x = unknown impurity.  2  remaining soluble species showed weak porphyrin resonances due an impurity, which was present in the initial material (labelled x on Fig. 3.11), and another equally weak meso resonance at 10.30 ppm. The IR spectrum of the residue (solvent removed at room temperature) showed VQ-H bands at 3603 cm-l (sharp) and 3375 cm-* (broad) (Fig. 3.12), attributed to Rh(OEP)(OH). Repeating the experiments at higher field (400 MHz) resulted in the detection of more upfield resonances (Fig. 3.13). Resonances at -1.92 and -6.15 ppm seem related to the 10.21 ppm meso signal because their relative intensities vary together consistendy for different samples. The spectrum of Rh(OEP)(H) in the absence of O2 does not show the -6.15 peak even when H2O is present, but at -40 °C Rh(OEP)(Cl)(H20) shows a resonance due to Rh-OH2 at -5.69 ppm in CD2CI2 (Table 2.2). Therefore, the "Rh(OEP)(X)" complex is believed to be  Rh(OEP)(OOH)(H20) with the resonance at -1.92 ppm tentatively assigned to be -OOH on the basis of its position and the relative intensity. The H chemical shifts of MOOH species are not well known and only one example of J  *H nmr data for a Rh-OOH species is in the literature, which is to our knowledge the only H nmr ]  data in the literature for OOH coordinated to a metal. This is a non-porphyrin complex and the shift of the hydroperoxide proton is reported in Table 3.3 along with some M(por)(OH) data for n  comparison. A rough correction to the 5 6.43 value, for the presence of the porphyrin ring current, can be made using Figure 1.4 and models of Rh (OEP) (OOH) having Rh-O-O-H dihedral angles of 0° and 180° (143), the method yielding a A8 of -4 to -8 ppm depending on conformation. On this basis, the "expected" range for the -OOH proton within Rh(OEP)(OOH) species is between 2.43 and -1.57 ppm. The observed resonance at -1.92 ppm is close to this range and, by comparison with the shift of the H2O ligand mentioned above and the -OH ligand shifts listed in Table 3.3, it seems reasonable to assign the -1.92 ppm signal to an -OOH resonance. The porphyrin resonances of the proposed Rh(OEP)(OOH)(H20) complex are broadened, but the -CH2- resonances are a broadened quartet suggesting that the axial ligands are not very different in bulk, which is also consistent with the OOH assignment. The source of the H2O is uncertain but there is sufficient H2O initially present in the CD2C12- The H2O ligand is probably exchanging at -40 °C because at the lower field the H2O resonance was to broad to observe.  83  8  i  3800  1  1  3200  2600  1  1  1  2000 1700 1400 wavenumbers (cm )  1  1  1100  800  1  500  1  200  -1  Figure 3.12. The IR spectrum of the residue (in Nujol)fromthe reaction of Rh(OEP)(H) and O 2 in  CD2CI2.  Rh-H  —r~ -42  Rh-OOH  x = impurity  8 (ppm)  -2  Figure 3.13.  Rh-OH  Expansion of an upfield region of a 400 MHz *H nmr spectrum during the reaction of Rh(OEP)(H) with O2 in CD2CI2 at -40 °C.  84  Table 3.3. Some *H nmr chemical shifts for hydroxyl and hydroperoxo protons of M-OH and M-OOH complexes from the literature. complex  solvent  5(ppm)  ref  Rh(Cl)(acac)(PPh ) (OOH)  CDCI3  6.43  1  Ge(TPP)(OH)2  CDCI3  -7.35  2  CDCI3  -7.81  CDQ3  -7.46  3  [Ru (OEP)(OH)] -uO  CDCI3  -4.20  4  [Os (OEP)(OH)] -nO  CDCI3  -3.4 br  4  CDCI3  -3.5 br  4  3 2  Ge(porphine)(OH)  2  Sn(TPP)(OH)  2  rv  2  rv  2  [Os (OEP)(OH)]-p:0-[Os (OEP)(OCH3)] rv  IV  2 s  a.  37 Hz J H -  1. 2. 3. 4.  H. Suzuki, S. Matsuura, Y. Moro-Oka and T. Dcawa. Chem. Lett. 1011 (1982). J.E. Maskasky and K.E. Kenney. J. Am. Chem. Soc. 95, 1443 (1973). L.R. Milgrom and R.N. Sheppard. J. Chem. Soc. Chem. Commun. 350 (1985). H. Sugimoto, T. Higashi, M. Mori, N. Nagano, Z. Yoshida and H. Ogoshi. Bull. Chem. Soc. Jpn. 55, 822 (1982).  1  1  9  S n coupling constant.  A problem with the described warm-up type of experiment is inconsistent thawing and mixing. However, if the Rh(OEP)(H) solution was made up at room temperature, and cooled to -40°C before diffusing O2 into the solution, then the reaction took a different course, although a homogenous solution could be achieved as was intended. During the cooling, the signal of the meso proton of Rh(OEP)(H) is revealed to be temperature-dependent (Fig. 3.14a), unlike the behaviour in the warm-up experiment The temperature dependence of the *H nmr spectrum of Rh(por)(H) has been noted previously and suggested to be due to exchange with [Rh(por)]2 (46). When O2 is injected at below -40°C and the subsequent reaction monitored at -40 °C, the meso shift moves to lower fields and quickly decreases in intensity with no appearance of any product, including the hydroperoxide (Fig. 3.14b). The amount of [Rh(OEP)]2 relative to the "impurity" remains constant throughout Precipitation probably occurs and exaorunation of the sample at end of the reaction confirmed the presence of a reddish precipitate. No sharp V O H band is seen in the IR spectrum of the residue. The effect of the method (warm-up vs. cool-down) on the outcome may reflect the establishment of the equilibrium between Rh(OEP)(H) and [Rh(OEP)]2 and its  85  -40 °C 30 °C  2  0 min  2 X  _A  o°c  Jul  L_ -40 °C 2  ~i  r 9  10  8 (ppm)  1 = Rh(OEP)(H) 2 = [Rh(OEP)] x = impurity 2  2 120 min 1  r  I  9  10  8 (ppm) (a) Figure 3.14.  (b)  Changes in the methine region of the 80 MHz *H nmr spectra during (a) cooling a solution of Rh(OEP)(H) in CD2CI2 to -40 °C and (b) addition of Q at -40 °C. 2  86  effect on the mechanism. At low temperature, the hydride/climer equilibrium is not established and littie dimer is present. In dichloromethane, the possibility exists that Rh(OEP)(CH2Cl) may form by reaction with the solvent Such a reaction will be described subsequently in this chapter and in chapter 4 of this thesis. To check this possibility, the nmr experiments were rerun using CH2CI2 as solvent instead of CD2CI2 and presaturation of the solvent resonance is applied to improve S/N. If a Rh-CH2C1 complex forms, then a proton resonance in the -2 to -3 ppm region (sect 4.2.3 and ref. 32) should be found in the fully protio system while none should be found in the deuterated system. In fact, no such signal is seen, suggesting there is no reaction with the solvent either before or after addition of O2 at thetimescales used in the reactions. The hydride is stable for months in CD2CI2 solution if kept in the dark and in the absence of O2. If a CD2Q2 solution of the hydride is exposed to fluorescent lighting then the slow formation of [Rh(OEP)]2 over several days is observed by  nmr. If left for periods of months, the amount of dimer decreases and  resonances of Rh(OEP)(Cl) appear at 10.42 ppm; even after this time some Rh(OEP)(H) i s  still  present, but there is no evidence of a Rh-CH2C1 complex. In summary, there is nmr evidence for formation of a thermally unstable Rh(OEP)(OOH)(H20) complexfromthe reaction of Rh(OEP)(H) with O2 at low temperature in CD2CI2, if the reagents are mixed at low temperature. Any other approach attempted led to  products other than the hydroperoxide complex. 3.2.2. Reaction of Rh(OEP)(H) with 0 in presence of PPh 2  3  The motivation for this study was to observe the effect of having a potentially reactive or coordinating substrate on the course of the reaction of Rh(OEP)(H) (or Rh(OEP)(H)(L)) with O2. Triphenylphosphine is useful in both contexts and a marked change in reactivityfromthe nonphosphine system is found. This is due in part to the interaction between Rh(OEP)(H) and PPh3 which is presented in the following section before describing the reactions with O2 (sect. 3.2.2.2 and 3.2.2.3) because the identities of several complexes need establishing first.  87  3.2.2.1.  Reaction of Rh(OEP)(H) with PPh  3  The experiments described in this section cover two quite separatetimeperiods of study and, to a degree, separate approaches. Early work was coincident with the finding of the proposed PJi(OEP)(OOH)(H20) complex described in sect 3.2.1.2. Nmr experiments were done on sealed tube samples containing a 2-3 fold excess of PPh over Rh(OEP)(H). The P{to)nmr 31  3  experiments were carried out on a low-field instrument (32.3 MHz) and the resonances of Rh(OEP)(H)(PPh ) (see below) were barely detectable at low temperature (Fig. 3.15), and thus 3  the identity of the species was not recognized at thattime.The work was suspended until the experiments were being written up for this chapter of the thesis, at whichtimesome of the series of nmr experiments were repeated at higherfield(300 MHz for H and 121.42 MHz for P{ H}) !  31  ]  which enabled the identification of most species which had previously been unidentified.  PPh  3  Rh(OEP)(H)(PPh ) 3  i  i  i  | 5 0  i  i  i  o(ppm)  i  |  i  i  0  Figure 3.15. The 32.3 MHz P{ to) nmr spectrum of Rh(OEP)fH) with excess PPh in 31  3  CD2CI2 at -60 °C.  3.2.2.1.1.  In CH C1 solvent 2  2  Figures 3.16 and 3.17 show the *H and P{ H} nmr data at -60 °C for a 31  !  CD2CI2  solution of Rh(OEP)(H) (~7xl0" M) containing slighdy less than an equivalent amount of PPh 3  3  88 -CH,  1  Rh(OEP)(Cl)(PPh )  2  Rh(OEP)(H)(PPh )/Rh(OEP)(H) 5  3  Rh(OEP)(CD Cl)(PPh )  4  Rh(OEP)(PPh )  3  3  2  -CH -  3  2  +  3 2  g = grease  m-H o-H  -30  ^  -3:.0  ii.a  -31.5  h  T  —r 10  T  6  8  9  Figure 3.16.  "I  T-  5  2  4  5 (ppm)  0  The 300 MHz H nmr spectra of Rh(OEP)(H) with PPh in CD C1 at -60 °C. [Rh] = 7 x IO" M, [PPh ] = 5.3 x 10" M. J  3  2  2  3  3  3  Rh(OEP)(H)(PPh ) 3  Rh(OEP)(CD Cl)(PPh ) 2  Rh(OEP)(Cl)(PPh )  Rh(OEP)(PPh )  3  +  3 2  3  1  10  Figure 3.17.  -20  -10  8 (ppm)  The 121.42 MHz 31p{ iH} nmr spectra of Rh(OEP)(H) with PPh in C D -60 °C. [Rh] = 7 x 10-3 M, [PPh ] - 5.3 x 10-3 . 3  3  M  2  C1  2  at  (~5.3xlf> M). In the 'H spectrum which is typical of those of solutions of diamagnetic 3  Rh (OEP) species, a doublet of doublets (^Rh-H » 28 Hz, Jp.n - 260 Hz) at -31.23 ppm can be m  2  matched with a corresponding multiplet at -16.66 ppm (^Rh-p -31 Hz, Jp-H ~ 260 Hz) in the 2  31  P{ *H} nmr spectrum. The largeJp-H coupling unequivocably identifies the complex as 2  Rh(OEP)(H)(PPh3). The Jp.H coupUng is observed in the P{ H} nmr data because the upfield 2  31  !  shift of the *H hydride resonance (<-30 ppm) takes it out of the range of the decoupled region used which is 7 ± 10 ppm in the *H nmr spectrum. As the sample is cooled the shifting positions of the PPh3 and principle meso resonances in the *H nmr spectra (4, Fig. 3.18) and the PPh3 resonances in the P{ H} nmr (Fig. 3.19) probably reflect the effect of temperature dependence of the 31  l  equilibria involving PPh3 magnified by the fact that Rh(OEP) species are in excess over the PPh3 and thus little free PPh3 remains at -60 °C. The temperature dependent changes are reversible. However, the *H resonances of the porphyrin are still broadened at -60 °C, even though the Jp-H 2  coupling is observed and the PP1»3 resonances appear to be in their respective slow exchange regimes. Because both Rh(OEP)(H) and Rh(OEP)(H)(PPh3) hydride resonances can be detected but only one average meso resonance for these two species (Fig. 3.18) it is assumed that the PPh3 is exchanging, but at a rate that is less than = 600 s (i.e. n-Jp.n/^Jl) (144), because Jp-H is _1  2  resolved. The meso resonance attributable to the averaging of the meso resonances of the equilibrating hydrides comprises -80% of the total porphyrin species and the visible spectrum of the nmr sample at room temperature resembles a superposition of the spectrum of Rh(OEP)(H) on a Rh(OEP)(X)(PPh ) spectrum such as Rh(OEP)(Cl)(PPh ) (Fig. 3.20; see Table 5.2 on p. 157). 3  3  Three minor species (1,2 and 3, Fig. 3.18) are also observed in the nmr spectra, comprising about 20% of the total Rh(OEP) species based on the integration of the meso H nmr !  resonances at 6.7 °C (Fig. 3.18), and these species show little evidence of chemical exchange. The same minor species, in about the same amounts relative to total porphyrin, can be observed by *H nmr in samples with a greater excess of Rh(OEP)(H) initially. Two sets of H and P{ *H} J  31  resonances (Table 3.4) in these spectra can be correlated with Rh(OEP)(Cl)(PPh3) and [Rh(OEP)(PPh3)2] , which are described in Chapter 5. The counter ion to the bis-phosphine +  cation in these in situ studies is not definite but is probably CI" (Chapter 5 and sect. 1.3.2.).  90  -CH,  -CH=  o-H 4  1 = Rh(OEP)(PPh ) * 2 = Rh(OEP)(a)(PPh ) 3 = Rh(OEP)(CD Cl)(PPh ) 4 = Rh(OEP)(H)(PPh)/Rh(OEP)(H) 3  2  3  3  2  3  P"  3  2  11\i 1 j  ill 1.  i\  Ji 2 fl 10  T  9  T  6 6 (ppm)  Figure 3.18.  4  The 300 MHz H VT nmr spectra of Rh(OEP)(H) with PPh in C D 2 C I 2 over the temperature range 20 to -60 °C. [Rh] = 7 x 10" M, [PPh3] = 5.3 x 10" M. !  3  3  1 = Rh(OEP)(PPh ) 2 = Rh(OEP)(Cl)(PPh ) 3 = Rh(OEP)(CD Cl)(PPh ) 4 = Rh(OEP)(H)(PPh )  3  +  3 2  3  2  il  3  Temp ( O 0  3  NS =4000  60  -24  NS = 2000 r  30  Figure 3.19.  20 T  10  20  ~"  1  8 (ppm)  r  T  x  -20  -10  -30  The 121.42 MHz P{ H) VT nmr spectra of Rh(OEP)(H) with PPh in C D C 1 over the temperature range 20 to -60 °C. [Rh] = 7 x 10" M, [PPh ] = 5.3 x 10' M. 31  l  3  3  2  2  3  3  91  <  I  300  Figure 3.20.  —1  r-  400  500  600  Wavelength (nm)  The visible spectrum of the nmr sample illustrated in Figs. 3.18/19 for Rh(OEP)(Ff) with PPh3 in CD2CI2.  Table 3.4. Selected nmr data for Rh(OEP)(Cl)(PPh3) and [Rh(OEP)(PPh3)2] as observed in CD2CI2 solution of Rh(OEP)(H) with PPh3 at ca. 20°C. +  Complex  *H 8  -CH=  o-H  Rh(OEP)(Cl)(PPh ) 3  9.94 s  3.62 m  6.39  6.83  [Rh(OEP)(PPh ) ]  9.72 s  3.44 br  6.39  6.83  +  3 2  m-H  a  p-H  a  3lP{lH) SX^Rh-H)  Rh(OEP)(Cl)(PPh ) 3  [Rh(OEP)(PPh ) ]  +  3 2  9.33 (124) -2.6  (88)  a. Resonances of Rh(OEP)(Cl)(PPh3) and [Rh(OEP)(PPh3) ] overlap. +  2  The remaining complex is identified as Rh(OEP)(CD2Cl)(PPh3) in CD2CI2 and Rh(OEP)(CH2Cl)(PPh3) in CH2CI2 based on the observation of a doublet at -4.44 ppm ( JRh-H = 2  2.5 Hz) in the U nmr spectra of samples in CH2CI2 (Fig. 3.21). The Rh(TPP)(CH2Cl) complex l  92 is known and has a doublet at -2.81 (2jRh-H = 2.9 Hz) ppm for the -CH2CI ligand resonance in C5D5N  (100). A similar TMP complex is reported on in chapter 4 of this thesis and has a ligand  resonance at ~2.9 ppm. The up-field shift of the ligand methylene resonances of Rh(OEP)(CH2Cl)(PPh3) is likely due to the coordination of PPh trans. Similar shifts are 3  observed when substituted pyridines coordinate to Rh(OEP)(CH3) (17) and when Rh(TMP)(CH2Cl)(NEt3) forms completely at low temperature (Fig. 4.18). 1 = Rh(OEP)(PPh ) 2 = Rh(OEP)(Cl)(PPh ) 3 = Rh(OEP)(CH Cl)(PPh ) +  3 2  -CH,  3  2  3  4 = Rh(OEP)(H)(PPh )/Rh(OEP)(H) 3  g = grease s = CH C1  -CH,  2  -CH=  2  Rh-CH C1 2  A/V  xlO  pU|lll^lljlUJ^Upill^l|IJU|IJ!Tp;  3 2 1  m-H  \  p-H  J  1 I.  T"  o-H i  T  6  r  4  10  \  g 2  T  \  /  -  0  / 1  \  1^  -4  8 (ppm) Figure 3.21. The 300 MHz *H nmr spectrum of Rh(OEP)(H) with PPh3 in CH2CI2 at 20 °C. [Rh] = 2 x 10-3 M, [PPh ] » 5.4 x 10"3 M. 3  Several points are notable about the minor species. In the absence of PPh3, Rh(OEP)(H) does not react with CH2CI2 to form Rh(OEP)(CH2Cl) (sect. 3.2.1.2), which suggests that Rh(OEP)(CH2Cl)(PPh3) arises from a PPh3-induced solvent reaction. The relative amount of the minor species does not vary with the proportion of PPh3 but is roughly in proportion to the amount of Rh(OEP)(H) initially present. This suggests that the reaction induced by the PPh3 is not stoichiometric in PPI13 but may therefore be catalytic in a Rh species.  3.2.2.1.2.  In benzene and toluene  The visible spectrum of benzene or toluene solutions containing Rh(OEP)(H) and 1.5 to 3 equivalents of PPh3 (i.e., the initial spectrum in Fig. 3.34) appears to be the superposition of principally the spectrum of Rh(OEP)(H) and a spectrum similar to that of Rh(OEP)(Cl)(PPh3) (Table 5.2, p. 157). The to nmr spectra of similarily composed samples in C6fJ>6  O R  C7D8 show  exchange broadened resonances for the porphyrin and PPh3 (Fig. 3.22) at room temperature. A weak broad hydride resonance at —34 ppm is downfield of its position in the absence of PPh  3  (8 * -42 ppm), consistent with addition of a donor ligand trans to the hydride (17). Cooling a C7D8 solution of the hydride and ~2 equivalents of PPh3 to -60 °C results in sharpening of the meso resonance at 9.95 ppm and the appearance of new resonances at 8.9 ppm and 4.45 ppm (Fig. 3.22). Below this temperature the spectrum decreases in intensity and quality. The hydride resonance moves downfield upon cooling and at -60 °C became a broad doublet with Jp-H ~ 250 2  Hz at -30.3 ppm. The spectrum in general still shows the effects of exchange; especially note the phenyl resonances of PPh3 which are largely indistinguishable. Examination of the P{ *H) 31  spectrum at -60 °C of the sample (Fig. 3.23) reveals a very broad (-1032 Hz) "resonance" at -13.3 ppm.  Superimposed on this "resonance" are the broadened resonances of Rh(OEP)(H)(PPh ), 3  doublet at -17.7 ppm f^Jp.H = 250 Hz) (see previous section) and a resonance at -8.96 ppm. In summary, there is evidence for Rh(OEP)(H)(PPh3) as a minor component in equihbrium with RhOEP(H) in the aromatic solvents, judging by the sharpening of the meso resonance at 9.95 ppm, chemical shifts consistent with Rh (OEP) species, and the behaviour of in  the hydride resonances. This is similar to the behaviour in CH2CI2 but the bulk of the PPh3 appears to be exchanging with other complexes which cannot be distinguished via the data at hand. The to nmr spectrum at the lowest temperatures shows the presence of a new resonance at 8.9 ppm which could be the averaged meso signal of a [Rh(OEP)]2PPh3 complex, akin to the known [Rh(OEP)]2CO complex (85). The resonance at -8.96 ppm in the P spectrum could then be 3 1  assigned to this complex and the 4.45 ppm resonance in the to nmr spectrum to one of the -CH 2  resonances of the [Rh(OEP)]2 moiety. Addition of donors has been suggested to promote the cleavage of [Rh(OEP)]2, to produce paramagnetic Rh(II) species (76). It could be that the PPh  3  94 -CH,-CH= Temp f°Q '[Rh(OEP)] PPh ' 2  3  -A.  11  —I  10  Figure 3.22.  7  T  4  6  6 (ppm) The 300 MHz H nmr spectra of Rh(OEP)(H) with PPh3 in C7D8 over the temperature range 20 to -60 °C. [Rh] = 3 x 10" M, [PPh3] = 6 x 10' M. J  3  3  Rh(OEP)(H)(PPh ) "[Rh(OEP)] PPh " j 1 A I Temp (°C) 3  2  3  19  30  Figure 3.23.  -r-  -1  1  10  20  5 (ppm)  -10  -30  -20  The 121.42 MHz P{ H} nmr spectra of Rh(OEP)(H) with PPh in C D over 31  l  3  7  8  the temperature range 20 to -60 °C. [Rh] = 3 x 10' M, [PPh ] « 6 x 10' M. 3  3  3  95 resonances that have not "frozen out" at low temperature are being affected by exchange amongst neutral paramagnetic Rh(JJ) species. 3.2.2.2.  Reaction with 0 i n C H C I 2  2  2  When O2 is added to dichloromethane solutions of Rh(OEP)(H) and PPI13, the colour deepens but the solutions remain homogeneous, which is unlike the behaviour in the absence of PPh3.  Figures 3.24 and 3.25 show the changes in the to and P{ to} nmr spectra of a sample 31  prepared in CH2CI2 (the full spectrum is shown in Fig. 3.21). After addition of O2 the averaged meso to nmr resonance at 9.87 ppm due to a Rh(OEP)(H)/Rh(OEP(H)(PPh3) equihbrium (sect 3.2.2.1.1) is gone, and the meso resonances of Rh(OEP)(Cl)(PPh3) at 9.94 ppm and that of Rh(OEP)(CH2Cl)(PPh3) at 9.85 ppm are increased by roughly equivalent amounts. Changes in the P{to} nmr parallel these changes, a doublet at 9.33 ppm due to Rh(OEP)(Cl)(PPh ) 31  3  becoming prominent after addition of O2, and a broad singlet lying between the positions of free PPh and of Rh(OEP)(CH Cl)(PPh ), and the doublet of [Rh(OEP)(PPh ) ] lying at -2.6 ppm. +  3  2  3  3 2  The visible spectrum (Fig. 3.26) after the reaction is similar to the spectrum of Rh(OEP)(Cl)(PPh ). 3  The appearances of the nmr spectra are different when the P P h 3 is not in excess when O2 is added to the Rh(OEP)(H)/PPh system. Figures 3.27 (to nmr) and 3.28 ( P{to}nmr) 31  3  illustrate this case. The meso proton signal for Rh(OEP(Cl)(PPh3) increases substantially from its initial intensity as does its P{ to} nmr resonance. The meso to nmr resonance for 31  Rh(OEP)(CH2Cl)(PPh3) is apparently missing after addition of O2 but a broad resonance at 9.95 ppm in the to nmr spectrum is believed to be the exchange averaged meso resonances of Rh(OEP)(CD2Cl)(PPh3) and Rh(OEP)(CD2Cl). Because of the deficiency of PPh , the 3  Rh(OEP)(CD2CI)(PPI13) complex cannot fully form and an exchange averaged meso resonance at ~9.96 ppm is more downfield towards the meso resonance of Rh(OEP)(CD Cl) at -10.15 ppm in 2  CD2CI2 (sect 4.2.3) than when the [PPh3] is higher (Fig. 3.24). The position of the singlet in the 31  P{ to) nmr at -10 ppm is more towards the position of Rh(OEP)(CD2Cl)(PPh3) (Fig. 3.28)  consistent with a Rh(OEP)(CD Cl)(PPh3)/Rh(OEP)(CD2Cl) equilibrium at low 2  \PPhi\.  The  visible spectrum of the nmr sample after addition of O2 Q?ig. 3.29) can be interpreted as the  -CH=  (a)  1 Rh(OEP)(PPh ) 2 Rh(OEP)(Cl)(PPh ) 3 Rh(OEP)(CH Cl)(PPh )/Rh(OEP)(CH Cl) 4 Rh(OEP)(H)(PPh )/Rh(OEP)(H) +  96  3 2  3  4  2  3  2  3  Rh-CH C1 2  3  1 ^  LA  (b)  3 i  10.2  1  1  10.0  9.8  1  9.6  1  1  9.4  9.2  i  -4.0  1  1  r  -4.6  -4.8  1  -4.2  -4.4  8 (ppm)  Figure 3.24.  Selected regions of the 300 MHz H nmr spectra of (a) Rh(OEP)(H) with PPh in CH Cl2 and (b) 20 min after addition of O2 at 20°C. [Rh] = 2x 10 M, [PPh ] = 5.4 x IO" M, Potal = 1 arm. 3 1 Rh(OEP)(PPh ) 2 Rh(OEP)(Cl)(PPh ) 3 Rh(OEP)(H)(PPh ) + PPh 4 Rh(OEP)(CD Cl)(PPh ) + PPh ]  3  -3  2  3  3  t  +  3 2  (a)  3  3  3  2  3  3  1  '2  (b)  4 1  20  15  Figure 3.25.  —r  -10 -15 -20 -25 0 - 5 8 (ppm) The 121.42 MHz P{ *H} nmr spectra of (a) Rh(OEP)(H) with PPh in CH C1 10  5  31  3  2  2  and (b) ~ 30 min after addition of O2 at 20°C. [Rh] = 2x 10" M, [PPh ] = 5.4 x 3  3  10" M, Ptotal = 1 atm. 3  97 ft  I.  8 8  3  30^  Figure 3.26.  4J0  500  Wavelength (nm)  600  700  The visible spectrum of the nmr sample illustrated in Figs. 3.24/25, after the reaction of Rh(OEP)(H) with PPh3 and O2 in CH2CI2.  1 = Rh(OEP)(PPh ) 2 = Rh(OEP)(Cl)(PPh ) 3 = Rh(OEP)(CD Cl)(PPh ) 4 = Rh(OEP)(H)(PPh )/Rh(OEP)(H) 5=Rh(OEP)(CD Cl) +  (a)  3 2  3  2  3  3  2  (b)  3,5 -1—  10.0  Figure 3.27.  9.8  1  9.6  8 (ppm)  1  9.4  —r~ 9.2  A selected region of the 300 MHz H nmr spectra of (a) Rh(OEP)(H) with PPI13 in l  CD2CI2 and (b) 20 min after addition of O2 at 20°C. [Rh] « 6 x 10" M, [PPh ] * 4 3  3  x 10" M, Ptotal = 1 arm. 3  98 (a)  1 Rh(OEP)(Cl)(PPh ) 2 Rh(OEP)(H)(PPh ) + PPh 3 Rh(OEP)(CD Cl)(PPh ) + PPh 3  3  2  3  3  3  NS=4000 1 (b)  1  20  ~l  10  15  i  0  T  r— -5  -10  8 (ppm)  Figure 3.28.  -  -r  ~T~ -20  -  -15  —r— -25  The 121.42 MHz 3lp{ iH} nmr spectra of (a) Rh(OEP)(H) with PPh3 in CD C1 2  2  and (b) ~ 30 min after addition of O2 at 20°C. [Rh] = 6 x 10' M, [PPh3] « 4 x 3  10-3 M, Ptotal = 1 arm.  1 o  <  T  500  Wavelength (nm) Figure 3.29.  1 600  The visible spectrum of the nmr sample illustrated in Figs. 3.27/28 for the reaction of Rh(OEP)(H) with PPI13 and Qz in CD2CI2 with the spectrum of Rh(OEP)(Cl)(PPh3) (dotted line) overlaid.  superposition of the spectra of Rh(OEP)(Cl)(PPh3) and Rh(OEP)(CD2Cl), where the -540 nm band is probably the a band of Rh(OEP)(CD2Cl) (sect. 4.4), consistent with low  [PPI13] relative  to [Rh]. A similar visible spectrum is observed for a CH2CI2 solution of Rh(OEP)(H) and 0.9 equivalents of PPh3 after exposure to O2 (solid line, Fig. 3.30a). The spectrum of a sample containing a higher [PPI13] (2.5 equivalents, dotted line, Fig. 3.30b) is much lower in intensity at -540 nm, the position of the a band of Rh(OEP)(CH2Cl), probably due to formation of Rh(OEP)(CH Cl)(PPh ). 2  3  In summary, the course of the reaction of Rh(OEP)(H) with O2 in dichloromethane is markedly affected by the addition of PPh3. In the presence of PPh3, postulated decomposition of the porphyrin is inhibited and reactivity is directed toward the solvent. Equimolar quantities of Rh(OEP)(Cl)(PPh ) and Rh(OEP)(CH Cl) (PPh ligated when the [PPh ] is sufficient) are 3  2  3  3  formed.  0-J  Figure 3.30.  1  1  500  550  r  :  600  Wavelength (nm)  The visible spectrum of the products of the reaction of Rh(OEP)QH) with PPh3 and O2 in CH2CI2: (a) (—) [Rh] = 3.40 x IO" M, [PPh ] = 3.19 x 10" M and (b) 4  4  3  (•••) [Rh] = 4.64 x IO- M, [PPh ] = 11.41 x IO" M. P tal = 1 arm, 25 °C. 4  4  3  to  100  3.2.2.3.  Reaction with O2 in benzene and toluene  Addition of O2 to Rh(OEP)(H) and PPh3 in benzene or toluene gives a homogeneous solution containing a complex mixture, as judged by the nmr spectra. Figures 3.31a and 3.31b show the to nmr spectra of a sample in C7D8, before and after reaction, respectively; the P{ H} 31  ]  nmr spectra show only noise before and after addition of O2 and are not illustrated (note that the content of Figure 3.31a has been discussed in sect. 3.2.2.1.2). The composition of the reacted sample changes withtimeand after 5 days its P{ to} nmr spectrum (Fig. 3.32) was found to 31  contain a singlet at 24.2 ppm assignable to OPPI13 and what is believed to be a doublet at 5.4 ppm (-jRh-P = 95 Hz) partially overlapped by a singlet at 5 ppm. The corresponding to nmr spectrum (Fig. 3.31c) shows O P P h 3 phenyl proton resonances at 7.67 and about 7 ppm (overlapped by solvent), while thefreePPh3 phenyl proton resonances at 7.39 and about 7 ppm (overlapped by solvent) observed in the to nmr spectrum immediately after addition of O2 (Fig. 3.31a) are now gone. Note that only a trace of the oxide is present immediately after addition of O2. Relative to the total area of the three sharp meso resonances at ca. 9.99 ppm, the set of broad resonances at 10.2, 7.62, 5.5 and 4.72 ppm have decreased as has the meso resonance at 9.97 ppm (Figs. 3.31b vs. 3.31c). Additional resonances which are similar to those of phenyl protons of  PPh3  coordinated to diamagnetic Rh (OEP) species (Table 5.1) have grown in at 6.48 and 6.23 ppm ni  overlapping the existing ones (Fig. 3.31c). Resonances at -1.28 and -1.44 ppm (Fig. 3.31b) are similar in position to those of the proposed hydroperoxide observed at low temperature in CD2CI2 (sect. 3.2.1.2). However, this hydroperoxide is unstable above -20 °C and it is hard to reconcile the presence of a similar complex at room temperature in the presence of PPh3 and H2O (146). Thus the Rh(OEP) species produced in the C>2-reaction are not known. Speculative possibilities include Rh(II) species, which would account for the broad resonances. Unfortunately there are no reports of to nmr data on paramagnetic Rh(U) porphyrin species to compare with. Metallation of a phenyl group of PPh3 is plausible, especially because attack on dichloromethane solvent has already been shown to occur (sect 3.2.2.2). Sterically reasonable structures could be para- or meta-metallated species.  101  1 Rh(OEP)(X)(PPh ) 3  8 (ppm) Figure 3.31.  The 300 MHz H nmr spectra at 19°C of (a) Rh(OEP)fH) with PPh3 in C D , (b) 30 min after addition of O 2 at 19°C and (c) 5 days later. [Rh] = 3 x 10" M, [PPh3] - 6 x IO' M, Ptotal = 1 atm. }  7  3  3  8  102  OPPh  3  i  35  1  30  1  25  1  20  1  15  1  10 8 (ppm)  1  1  5  0  1  r  -5  -10  Figure 3.32. The 121.42 MHz 31p{ to} nmr spectrum at 19°C of Rh(OEP)(H) with PPh in 3  C7D8 5 days after addition of O2. [Rh] - 3 x 10' M, [PPh3] « 6 x 10' M , Ptotai 3  3  = 1 atm.  The p-metallated phenyl complexes Rh(OEP)(C6H4-p-X) (X = CH3, OMe or CI) show o-H resonances between -0.43 and -0.49 ppm in CDCI3 (107) and the observed resonances at ca. -1.3 to -1.4 ppm are not far from this, and the remaining resonances of the metallated ligand (10.2, 7.62,5.5 and 4.72 ppm) could be affected by exchange at the dangling phosphine. The singlet at 5 ppm in the 31p{ to} nmr spectrum, and the new phenyl resonances observed in thetonmr spectrum, could be assigned to such a complex (147).  p-metallated  m-metallated  103 The visible spectrum Q7ig. 3.33) of the nmr sample immediately after addition of Q2 is similar to those obtained in CH2CI2 where PPh3 was in excess. Following the same reaction by visible spectroscopy gives a product spectrum similar to the nmr sample (Fig. 3.34). The rather broad Soret peaks of these spectra cover the 420 nm region where the Soret of a PPh3 ligated complex is expected (Table 5.2, p. 157). Clearly the effect of PPh3 on the reaction of Rh(OEP)(H) and O2 in toluene is different from the non-PPh3 system in aromatic solvents and that in dichloromethane. The nmr spectra are not obviously interpretable at this time, although the presence of Rh(II) and PPh3 metallated complexes are possibilities.  300  400  500  Wavelength (nm)  600  700  Figure 3.33. The visible spectrum of the nmr sample illustrated in Fig. 3.30b, for the reaction of Rh(OEP)fH) with PPh and O2 in C D . 3  7  8  104  Wavelength (nm) Figure 3.34. The visible spectrum of (•••) Rh(OEP)(H) with PPh in C^6 and (—) 30 min after 3  addition of 0 . [Rh] = 2.86 x IO" M,[PPh ] = 8.4 x IO" M, P al = 1 atm, 4  4  2  3  tot  25 °C.  3.2.3. Reaction of Rh(OEP)(H) with CO and 0 /air 2  The reaction of Rh(por)(H) with CO in CoHo to form Rh(por)(CHO) has been extensively reported upon in the recent literature (57,63,81,83,97,98). During the early part of the experimental work of this thesis, this reaction was examined to obtain reference data and was found to be very sensitive to air or 0 at levels commensurate with accidental contamination such 2  as incomplete purging of gas inlet lines. At thetimethe evidence was uninterpretable, and the work was not pursued further. In the last few years, high pressure nmr and C labelling studies 1 3  have been published which allow partial interpretation of the earlier observations which are presented here. A benzene solution of Rh(OEP)OH) under an atmosphere of CO in a Schlenk flask was briefly exposed to air by opening the tap on the flask to air and the solvent removed using a stream of CO. The IR spectrum of the oily residue (Fig. 3.35) has several bands in the regions where CO and carbonyl stretching bands are expected. Bands at 2089,1731(sh) and 1709 cnr can be 1  assigned to [Rh(OEP)] CO, 2  [Rh(OEP)] nCO 2  (85) and Rh(OEP)(CHO) (97), respectively. The  band at 2336 cm can be independendy shown to be CC^ in solution. Atmospheric C 0 does not -1  2  105  dissolve sufficiently in Nujol to be observed, and thus the 2336 cm band may come from the -1  decomposition of a complex during the mulling but more probably was an impurity in the CO and became trapped in the oily residue. There is no evidence of the VRh-H of Rh(OEP)(H) which would be expected at 2226 cm* . The other bands in the 2000 cm* region are unassigned and 1  1  there are probably a number of additional bands in the (1550 - 1750) cm region, besides those -1  assigned above, that are not due to porphyrin bands.  B 2089 [Rh(OEP)] CO 2  1731 [Rh(OEP)]2UCO  1709 Rh(OEP)(CHO)  2600  T  2000  1900  1800  wavenumbers (cm )  —I— 1700  —I— 1600  —I  1500  -1  Figure 3.35. The IR spectrum of the residue (in Nujol)fromthe reaction of Rh(OEP)(H) and aircontaminated CO in benzene.  The reaction of CO (0.6 atm) with Rh(OEP)(H) (~10"M) in benzene to form 3  Rh(OEP)(CHO) is complete within 20 min and the meso *H nmr resonance of the formyl complex is at 10.30 ppm (Fig. 3.36a). The progress of the reaction for similar samples in benzene under CO atmospheres contaminated by small amounts of air or O2 can be followed by H nmr. Figure l  3.36b shows the progress for the first hour and Figure 3.36c shows the spectra of a similar sample  (c)  (b)  +1 h  i  J  "^V^^V^-  +1/2 h  —  10 days  1 = Rh(OEP)(CHO) 2 = Rh(OEP)(H) 3 = [Rh(OEP)]  2  4 = [Rh(OEP)] CO  3,4,5  2  fV^inv^V  initial  1  5 = [Rh(OEP)] uCO 2  3 days  (a)  3,4,5  T-  1 2  Figure 3.36.  1 1  u . 1 0  9  5 (ppm)  -A  20 min  1 0  The changes in U nmr spectra during the reaction in C6D6 of Rh(OEP)(H) with CO contaminated with O2: (b) in thefirsthour l  (80 MHz) and (c) over 10 days (400 MHz). Spectrum (a) (80 MHz) is of Rh(OEP)(CHO) formed in situ using pure CO. [Rh]. 2 x 10 M, Pt tal = 0.6-1 atm, ambient temperature. -3  0  o  107 at -20 min, 3 days and 10 days after mixing. The meso resonances at 10.19 and 10.30 ppm are due to Rh(OEP)(H) and Rh(OEP)(CHO) (97), respectively, and resonances due to the formyl (8 = 2.85 ppm) and hydride protons (8 »-41 ppm) are found upfield. Resonances at ~9.30 ppm are probably those of [Rh(OEP)]2, [Rh(OEP)]2CO and [Rh(OEP)]2uCO; that at 9.31 ppm is the exchange average of the meso protons of [Rh(OEP)]2 and [Rh(OEP)]2CO, and the slightly downfield meso that slowly grows in over several days is that of the CO bridged species (85). There are 2 resonances of equal intensity, at 9.07 and 9.61 ppm, in this region that appear to correlate (Fig. 3.36b) with the dissappearance of the initial major meso resonance at 10.44 ppm. The 2 resonances are probably due to an unsymmetric dirhodium species (see below). Besides the meso resonance at 10.44 ppm, there is a signal at —0.5 ppm integrated at about 1 proton relative intensity, and this resonance is present only when the meso signal at 10.44 ppm is present; when the latter disappears so does the high-field peak. The ethyl side-chain resonances are complex due to the overlapping resonances of the many different OEP ligands present and the symmetry of the species is not direcdy apparent. This species is tentatively assigned as Rh (OEP) (C(O)OH) which has been reported as an intermediate observed during the reaction of Rh(OEP)(H) and CO/KOH in benzene to form the formyl complex, although supporting data were not published (98). There are unassigned bands ca. 1700 cnr in the IR 1  spectrum illustrated in Figure 3.35 that could be assigned to a carboxy species. The unsymmetric dirhodium species mentioned above is believed to be [Rh(OEP)]-0(0)0-11^(OEP)]. The meso signal at 9.07 ppm is near to those of analogous -CH2CH2- and -CH=CH- bridged dimers (57,65) and would therefore be assigned to the Rh-C containing moiety, and the remaining meso resonance at 9.61 ppm to the Rh-0 containing moiety. 3.3.  General Discussion The behaviour of the O2 reactions as followed by visible spectroscopy, the sensitivity to  initial starting conditions, and the observation of Rh(U) and Rh-Cf^Cl containing products, strongly indicate radical mechanisms. A radical chain mechanism is plausible, where the reaction of O2 with the Rh center follows a series of steps sirnilar to those for the [Rh(OEP)]2 catalysed reaction of styrene with  Rh(OEP)(H) in benzene to give a net Rh-H addition across an unsaturated bond in the substrate (83): Imtiation/termination: 2Rh(OEP)(H) ^ [Rh(OEP)] ^ 2  [Rh(OEP)] + H 2  (3.2)  2  (3.3)  2Rh(OEP)-  Propagation: Rh(OEP)- + O2  (3.4)  ^ Rh(OEP)(C>2)  Rh(OEP)(C>2) + Rh(OEP)(H)  Rh(OEP)(OOH) + Rh(OEP)-  (3.5)  The chemistry of reactions (3.2) and (3.3) is well established in the hterature (sect. 1.5.2 and 1.5.3). The chemistry of equation (3.4) has been reported to occur at low temperature in dry toluene and formation of a symmetric u.-peroxo species is postulated to occur on warming to room temperature. This could occur via equation (3.6), written by analogy to the reaction of styrene with [Rh(OEP)] in benzene, to give a bridged dirhodium species (83). 2  RhCOEPXC^) + [Rh(OEP)]  2  [Rh(OEP)] (u-0 ) + Rh(OEP)- (3.6) 2  2  However, in the present work, the nmr data appear to show [Rh(OEP)] to be stable (at 2  least for several hours) in the presence of 1 atm of 0 at room temperature, implying that at least 2  equilibrium (3.4), if correctly formulated, lies very much to the left side. When one also considers that Rh(TPP)(0 ) is an isolable stable species then one is forced to consider the contradictory 2  nature of the data on the OEP system In section 4.2.1 [Rh(OEP)] is also noted react very slowly 2  with 0 in GsD6 under an O2 atmosphere ifH2O is added but reacts instantly under dry conditions. 2  Water is also present in the solutions after the reaction of O2 with Rh(OEP)(H) and may be competing with O2 (in reaction (3.4)), or Rh(OEP)(0 ) (in reaction (3.7)) for a coordination site. 2  There are only *H nmr data at low temperature to support the existence of a thermally unstable Rh(OEP)(OOH) species (sect. 3.2.1.2) but, assuming its existence, then this hydroperoxide or a decomposition product could react further with Rh(OEP)(H) (reaction (3.7)). In essence, the reactions consume H- and release "Rh(OEP)" and H 0 in excess of the 2  propagation steps of reactions (3.4) and (3.5) in a reaction analogous to the decomposition of H2O2 to H2O and O2 and is consistent with the formation of [Rh(OEP)]2 and H2O in good yield from the reaction of Rh(OEP)(H) with O2 (sect. 3.2.1.1) (64). *-[Rh(OEP)] + H 0 +102  Rh(OEP)(OOH) + Rh(OEP)(H)  2  2  (3.7)  The reaction of Rh(OEP)(H) with Q2 in CH2Q2 did not lead to [Rh(OEP)]2 at room temperature. Instead, uncharacterisable species were observed by nmr, probably because of the reaction of radical intermediates of the reaction with CH2CI2, or reaction of O2', dissociated from Rh(OEP)(02), with CH2CI2 (86). There does not appear to be any rapid reaction between [Rh(OEP)J2 or, by implication, monomelic Rh (OEP), with the CH2G2 solvent. n  The addition of PPh to solutions of Rh(OEP)(H) promotes a rapid reaction with the 3  CH C1 solvent giving Rh(OEP)(Cl)(PPh ), Rh(OEP)(CH Cl)(PPh ) and [Rh(OEP)(PPh ) ] in +  2  2  3  2  3  3 2  -20% yield relative to the hydride species. Addition of O2 to these solutions appears to further promote the solvent reaction to the extent that the Rh(OEP)(Cl)(PPh ) and 3  Rh(OEP)(CH2Cl)(PPh ) become the major species (in equimolar amounts) in solution without the 3  apparent decomposition that occurs in the absence of PPh , and without the concomittant formation 3  of OPPh . Strong donors, such as P(OMe) , have been suggested to promote the cleavage of 3  3  [Rh(OEP)]2 and subsequent radical reactions of Rh (OEP) in C6H6 (sect. 1.5.2) (76). It seems n  reasonable to propose several equilibria, reactions (3.8-3.10), the effect of O2 addition being to increase the effective [Rh(OEP)] via reactions (3.2-3.6), so long as the reaction of PPh with the 3  dimer and the subsequent solvent reactions are much faster than the "decomposition" reactions that occur in the absence of PPh . 3  [Rh(OEP)] + PPh ^=^Rh(OEP)(PPh ) + Rh(OEP)  (3.8)  Rh(OEP)(PPh ) + CH2CI2 ^^=tth(OEP)(Cl)(PPh ) + -CI^Cl  (3.9)  Rh(OEP) + -CH C1 ^=^Rh(OEP)(CH Cl)  (3.10)  2  3  3  3  3  2  2  110  Chapter 4 The reaction of Rh (por)(CI)(L) complexes with tertiary amines in  4.1.  Introduction In this chapter the mechanisms of the reactions of some tertiary alkylamines (principally  Et3N) with Rh (por)(Cl)(L) are explored. The formation of [Rh (OEP)]2 species under mild m  n  conditions is observed with some amines and a number of novel organometallic derivatives of Et N have been found. Tertiary amine oxidative dealkylation to the dialkylarnine is observed. 3  Detailed spectroscopic examination of the reaction of Rh(por)(a)(L) with Et3N revealed a complex manifold of reactions. However, enough mechanistic information about the reaction has been extracted to provide a useful framework from which more exhaustive studies can be undertaken in the future. Comparison is made between results obtained using two porphyrins: OEP and TMP. The principle reason for the choice is steric rather than electronic, formation of [Rh (por)]2 being n  blocked in the case of TMP, because the ortho-methyl groups of the mesityl groups of TMP hinder a sufficiendy close approach (119). Although tetraaryl- and octaemyl-rxHphyrins, on coordination to metals, differ in their cis effects (69), similar chemistry at Rh occurs for both Rh(OEP) and tetraaryl RhfTPP) species (Chapter 1) and so the use of TMP to prevent dimerization is not considered to change the chemistry to any significant degree other than by steric effects. , In addition, the reactions were studied in chlorinated (01202) and non-cMorinated (benzene, toluene) solvents. As observed in Chapter 3 and elsewhere (sect 1.4.1), some Rh(lX) species react with C H 0 solvent and similar reactivity is observed in the presence of Et N. 2  2  3  The results and discussion section of the chapter is in two parts: so-called product analysis and kinetic analysis. The product analysis results cover reactiontimesgreater than 5-15 nun after mixing and were largely obtained using nmr and scanning uv-vis spectroscopy. The kinetic analysis results covertimesdown to -10 ms using stopped-flow techniques and from 15 s  to 5 min using diode array and conventional scanning uv-vis spectroscopy. This "kinetic/product" division also reflects the typical reaction sequence observed. The metaUoporohyrin reagent was consumed in an initial rapid reaction sequence (over secondtyminutes), and then the initial products underwent less rapid reactions (over minutes/hours). The emphasis was semi-quantitative because not enough products and intermediates were confidently identified for quantitative kinetic analysis. 4.2.  Results and Discussion of Product Analysis  4 . 2 . 1 . Amine reaction with Rh(OEP)(Cl)(L) in benzene or toluene  Under aerobic conditions, Rh(OEP)(Cl)(H20) in CgOo can be seen by to nmr spectroscopy to rapidly coordinate Et2NH to form only diamagnetic Rh(OEP)(Cl)(Et2NH), after addition of 1 equivalent of the neat amine (Fig. 4.1). The - C H 2 - resonances of the ethyl sidechains appear as a multiplet indicative of asymmetric substitution with regard to the porphyrin plane, i.e., two different axial ligands are present causing the - C H 2 - resonances to appear as an ABX3 multiplet (138-141). The coordination of the single Et2NH ligand is shown by the shifting  of the Et2NH resonances by the strong porphyrin ring-current from their normal positions to positions up-field of TMS. The triplet at -2.71 ppm is assigned to the Et2NH ligand methyl protons, and the two overlapped multiplets at -3.80 ppm are assigned to the diastereotopic methylene protons of the single coordinated Et2NH ligand; the NH proton is at -6.4 ppm. The complex is stable in solution for days in the absence of hght, but a black solid precipitates if a sample is left in laboratory hght. Repeating the experiment using 1 equivalent of EtsN also yields Rh(OEP)(Cl)(Et2NH) as the main product (after 4h: 60% yield estimated by to nmr) (Fig. 4.2). A small amount of intractable black precipitate is visible at this point, but was insignificant relative to the amount of dissolved material. Some Et2NH and unreacted EtjN are detected by GC in samples prepared similarly to those used in the nmr experiments but with up to a 20-fold excess of Et3N. The amount of Et2NH was always less than the initial Rh species and thus there was no evidence of any catalytic dealkylation.  112 -CH, -CH,  -CH=  P MIII IT[1111J TTTTj N11111 I Ij MII11(1M11 111)  \  /  \  -CH,  \  \  \  12  "i  10  Figure 4.1.  -CH 2  H,0 2  _>  r  8 (ppm)  N-H  0  -r -6  -r  I  -2  The 300 MHz H nmr spectrum of Rh(OEP)(Cl)(Et2NH) in CeF>6 at 20 °C. Prepared in situ, [Rh] = 3x 10-3 M, [Et2NH] = 3 x 10-3 M . l  -CH,  -CH,  -CH,  -CH -  H0  2  2  12  T  10  4  Figure 4.2.  1  2  JL.A  r  8 (ppm)  T  0  _>  -r 4  -2  N-H -6  The 300 MHz R nmr spectrum of a C6D6 solution of Rh(OEP)(Cl)(H20), 4 h l  after addition of Et3N. [Rh] » 4 x Kr M, [Et3N] - 4 x IO' M, 20 °C. 3  2  0  -8  113  The Rh(0EP)(Cl)(Et2NH) product is observable also by visible spectroscopy, using either of the two amines in excess over Rh(OEP)(Cl)(H20). Nearly identical hypso-porphyrin spectra with (3 and a bands at 522 and 552 nm respectively (Fig. 4.3) were obtained for the Rh(OEP) products consistent with formation of Rh(OEP)(Cl)(Et2NH) regardless of the amine used. The reaction with Et2NH is complete within the mixingtimeof ~3 min (sect. 2.2.2), which is consistent with the rapid formation of Rh(OEP)(Cl)(Et2NH) as expected on the basis of the nmr experiments, but for the Et3N reaction, complex changes are observed during thefirst6 h of the reaction, with little change thereafter. When the Et3N and PJi(OEP)(Cl)(H20) are mixed, the Rh(OEP)(Cl)(H20) bands at 519 and 552 nm are immediately replaced by bands at 522 and 553 nm (but probably not those of Rh(OEP)(Cl)(Et2NFf)). A subsequent slow decrease at 553 nm is accompanied by an increase at -552 and ~544 nm. The latter band is light sensitive and decreases on exposure to light, i.e., when the sample is removed from the spectrometer to check homogeneity. The intensity at 552 nm increases as that at 544 nm decreases, without further exposure to room light, until the final spectrum shown in Figure 4.3 is obtained after ~6 h.  1 500  1  520  540  1 560  1  1  580  600  Wavelength (nm) Figure 4.3. The visible spectrum in at 25 °C of (•••) Rh(OEP)(Cl)(Et2NH) a few minutes after preparation in situ, [Rh] » 3.5 x 10" M, [Et2NH] « 7 x 10" M and (—) a solution of Rh(OEP)(Cl)(H 0) ~6 h after addition of Et N ([Rh] = 3.54 x IO" M, [Et3N] = 7.19 x 10" M); the Soret at 403 nm is not illustrated. 4  3  4  2  3  3  Dealkylation of amines commonly involves initial oxidation of the amine (148). A redox process involving the metaUoporphyrin is indicated because Et3N does not spontaneously dealkylate under sirriilar conditions without Rh(OEP)(Cl)(H20). Indeed, [Rh(OEP)]2 is detected by  nmr spectroscopy as one of the mtermediates in the experiments just described, and is the  first major product observed by nmr under anaerobic conditions (see following discussion). Several other amines were "screened" for a similar reactivity by adding a few uL of the amine to C6D6 solutions of Rh(OEP)(a)(H20) ([Rh] - 5 x IO" M) under Ar and examining the H nmr 3  !  spectra of the reaction solutions, within the first hour, for the formation of [Rh(OEP)]2 or dealkylated products. Aniline, N-memyl-diphenylamine and N-ethyl piperidine all form complexes of the type Rh(OFJ)(Cl)(airhrie) (Table 4.1), although the N-ethyl piperidine complex decomposes >  within 24 h. Proton Sponge and tributylamine give [Rh(OEP)]2 as a major product and, in the latter step, the Rh(OEP)(Cl)( Bu2NH) complex is also observed (Table 4.1). Only the reaction of n  Et N 3  will be discussed further in this chapter, because its reaction appeared to be more amenable to  study, particularly by *H nmr spectroscopy. When equimolar quantities, or a small excess, of Et N relative to Rh(OEP)(Cl)(H20) are 3  reacted together in a nmr tube under dry, anaerobic conditions in G5D6, or CjD^ the concentration of [Rh(OEP)]2 grows in as the initial major product observed by *H nmr spectroscopy (Fig. 4.4a), being complete in <15 min. Typically, the yield of dimer was high. For example, the proportion of [Rh(OEP)]2 estimated from integration of the meso peaks in in the 10.6-9.0 ppm region of Figure 4.4a was 77%. Some of the resonances assignable to Rh(OEP)(Cl)(Et2NH), in ~5 % yield, are identifiable (10.37 (s, -CH=) and coordinated Et2NH at -2.68 (t, -CH ), -3.8 (m, 3  CH2-)). The remaining "Rh(OEP)" species were not identifiable although the positions of the  meso proton resonances are appropriate for Rh^OEP) species. Broad resonances at 2.40 and 0.96 ppm are attributed to ethyl groups of an uncoordinated amine but from these data it is not clear whether the resonances where those of Et N (2.39 q, 0.961) or Et2NH (2.64 q, 0.98 t). Over a 3  few days at room temperature, in the dark, the resonances of the [Rh(OEP)]2 decrease as those of Rh(OEP)(Cl)(Et2NH) and a new species Rh(OEP)(CH(Me)NEt2) (see below) increase in intensity (Fig 4.4b). The ainine resonances at 2.40 and 0.96 ppm are no longer present The composition  Table 4.1. The H nmr spectral data for various Rh(OEP)(Cl)(amine) complexes.  3  l  amine PhNH  -CH=  -CH  -CH 2  10.24 s 4.04 m, 3.91m  2  other  3  1.92 t  -4.92 s (NH ), 1.68 d (o-H), 5.49 t (m-H), 2  5.87 t (p-H) Ph2NMe  ~4m  10.12 s  b  1.95 t=  c  -3.19 s (NMe), 2.46 s (o-H), 5.64 m (m-H), 5.99 m (p-H)  EtNpip n  Bu2NH  e  10.41 s  4 03 m  1.92 t  d  10.32 s  -3.97 m  1.95 t  -6.12 s (N-H), -4.06 m/-3.60 m (N-CH -), 2  -2.46 m (-CH -), -0.87 m (-CH -), 2  2  -0.23 t (-CH ) 3  Et NHf  10.42s  Et NH8  10.27  2  4.02 m  1.92 t  -6.40 s (N-H), -3.80 m (N-CH -), -2.71 t 2  (-CH ) -6.57 s (N-H), -3.90 m (N-CH -), 3  2  -4.13 m  -1.97 t  h  h  2  -2.28 t (-CH ) 3  a. Formed in situ in C£)e at 20 °C unless otherwise noted; 300 MHz, integrations match appropriate assignments. b. In equilibrium with Rh(OEP)(Cl)(H 0). 2  c. Overlaps with ethyl resonances of Rh(OEP)(Cl)(H 0). 2  d. The EtNpip ligand resonances are labelled according to the perspective diagram ; the tentative assignments are based on integrations, selective decoupling and chemical shifts. -0.47 m  e. [Rh(OEP)] also present. 2  f.  Slighdy temperature dependent.  g. In CD C1 , Sect. 4.2.3. 2  2  h. Overlapped by ethyl side chain resonances of other species.  116  -CH, (a)  1 = [Rh(0EP)]  2  2 = Rh(OEP)(Cl)(Et NH) 2  -CH=  "T~  T  10  3 = Rh(OEP)(CH(CH )NEt )  -CH,-  6  T 4  (b)  -CH=  3  i  " T  10  -2  -4  -r -6  -CH,33  T 6  Figure 4.4.  -r  -CH,  1  T -  0  2  2  iL T"  4  ill j  T  UJL  2  r  0  8 (ppm)  3 3  3  T  "T-  T -6  -2  -r -8  The 300 MHz H nmr spectrum of a C£>6 solution of Rh(OEP)(Cl)(H20) (a) 15 min after addition of Et3N and (b) 7 days later. [Rh] « 8 x 10" M, [Et3N] » IO" M, 20 °C, in vacuo in a sealed nmr tube. !  3  of such solutions in sealed tubes remained unchanged for periods of months implying that the above mentioned free amine was Et3N. Samples with slightly more initial Et3N have proportionately more Rh(OEP)(CH(Me)NEt2) at this point  2  The new complex, Rh(OEP)(CH(Me)NEt2) is identified by selective decoupling, COSY and integration of its H nmr spectrum (Fig. 4.4b, Table 4.2, Appendix E). The ligand methyl l  resonance at -3.96 ppm (d, 3H) is close to that of the ligand methyl resonance of Rh(OEP)(CH(Me)C6H ) (-4.30 ppm) (56). A COSY experiment and selective decoupling linked 5  the doublet to a weak signal at -2.30 ppm which is assigned to the neighbouring methylene proton. The ethyl group resonances comprise two methyl resonances at —0.9 ppm (t, 3H) that are each coupled to one of two pairs of well separated (one separated by 0.27 ppm and the other by 1.69 ppm) weak resonances assigned to four non-equivalent - C H 2 - protons of the ethyl groups. The large range of - C H 2 - proton shifts suggests that steric congestion of the ethyl groups with each other, the pVmethyl, and the porphyrin plane are greater for this ligand man the steric interactions within the Et2NH ligand of Rh(OEP)(Cl)(Et2NH), but the triplet nature of the associated methyl resonances indicates that sufficient ligand motion still remains to average the coupling constants. The analogous, but more sterically restricted, TMP complex has a similar ligand spectrum and will be discussed in a later section (sect. 4.2.2). A conformation where the - C H 3 groups of the ethyl groups are roughly equidistant from the plane of the porphyrin is suggested by their nmr shifts and a labelled model is illustrated below Table 4.2. Note that within one methylene pair (Hy and H2O the protons must be at very different distances from the porphyrin plane because they differ considerably in shift; the choice of position assigned in the diagram is arbitrary but requires that one ethyl group be canted relative to the other. The Et N reaction with Rh(OEP)(Cl)(H20) was also monitored by visible spectroscopy 3  under anaerobic conditions. In the presence of Et N (1-20 equivalents), the P and a bands of 3  Rh(OEP)(Cl)0H2O) at 519 and 552 nm decrease in intensity and red-shift, becoming broader and less intense bands at 526 and 557 nm within ~30 min (e.g., Fig. 4.5). The band positions and apparent extinction coefficients of the spectrum after 30 min of reaction are approximately the same over the range of added Et N, although further small decreases in absorbance slowly occur over 3  several hours at higher [Et3N]. The P and a band positions and apparent e values of the spectrum (Fig. 4.5) are not those expected for [Rh(OEP)]2 (Table 3.1) which is the product expected on the basis of the nmr experiments nor do they correspond to Rh(OEP)(a)(Et NH) (Fig. 4.3). The 2  118  Table 4.2. Ligand H nmr spectral data for Rh(OEP)(CH(Me)NEt2). :  a  proton  6  integral  H-  -0.61 m  IH  H  -0.811  3H  -0.95 t -1.60 m  3H  -1.87 m  IH  Hr  -2.28 m  IH  H Hp  -2.30 m  IH  -3.96 d  3H  2  3  H' 3  H2(i) Hi( ) 2  a  IH  a. 300 MHz; measured in C 7 D 8 solution at ~20°G see Appendix E for details.  principle band in the Soret region is at 412 nm and this along with the 526 nm (|J) and 557 nm (a) bands are typical of the hypso type spectra of Rh species (3,69). However, the intensity of the ra  spectrum is decreased relative to mat of the starting Rh(ni) complex and bands at about 350 and 392 nm are present as expected for [Rh(OEP)]2 (inset, Fig. 4.4); therefore the spectrum is believed to be the superposition of that of the Rh(II) dimer and Rh (OEP) species. A white precipitate m  formed during the some of the experiments when 1-2 equivalents of amine were used. This was not isolated but was most likely to be amine hydrochloride (see p. 131).  1 400  0.00-j 300  —I  1  500  Figure 4.5.  1 500  600  1 1 1 1 520 540 wavelength (nm)  A  1 560  1  1— 580  The visible spectrum of a Q H s solution of Rh(OEP)(Cl)(H20) wth Et3N, 30 min after the addition of Et N. [Rh] = \Et3N] = 4.31 x 10^ M, 25 °C, in vacuo. 3  As will be discussed in section 4.3, use of Rh(OEP)(Cl)(CH3CN) instead of Rh(OEP)(Cl)QH20) or addition of excess CH3CN slowed the initial reaction with Et3N in C6H6  a s  monitored by visible spectroscopy but did not affect the "product" spectra appreciably. Clearly the nmr and visible spectroscopy experiments in the absence of air do not show Rh(OEP)(Cl)(Et2NH) as the sole or main product, so it appears that air is critical for its formation. The most likely components of air that could be important to completion of the reaction, as it was originally observed, are O2 and H2O, alone or in combination. However, addition of air after formation of [Rh(OEP)] , Rh(OEP)(Cl)(Et NH) and Rh(OEP)(CH(Me)NEt ) does not result in 2  2  2  formation of Rh(OEP)(Cl)(Et2NH) as the major product. A nmr sample which was known to have equilibrated to a mixture of [Rh(OEP)] , Rh(OEP)(Cl)(Et NH) and Rh(OEP)(CH(Me)NEt ) in 2  2  2  vacuo, whose spectrum is illustrated in Figure 4.4, was opened in air and the *H nmr spectrum rerun (Fig 4.6). The [Rh(OEP)]2 and Rh(OEP)(Cl)(Et2NH) species are still present in roughly unchanged proportions, but the Rh(OEP)(CH(Me)NEt2) meso proton resonance at 10.00 ppm is no longer evident A new meso proton resonance appears at 10.21 ppm along with a number of very small signals in the meso proton region. Resonances at the positions expected for  120  1 = [Rh(OEP)]  2  2 = Rh(OEP)(Cl)(Et NH) 2  3 = Rh(OEP)(CH CHO) 2  -CH=  4 = free amine s = C6D  6  r~  ~r~  10  6  Figure 4.6.  T 4  8 ppm  —r  r  -2  —r  -  -8  -6  The 300 MHz *H nmr spectrum of the C&>(> solution sample illustrated in Figure 4.4, immediately after exposing to air. [Rh] = 9 x 10' M, [Et3N] ~ IO' M, 20 3  2  0  °C, in air.  free amine (2.40,0.99) also appear. The spectrum remains unchanged for hours. The meso resonance at 10.21 ppm and a new doublet of doublets (~2H integration, JH-H ~ JRh-H = 4.2 Hz) at -5.22 ppm, found to be coupled to another triplet (~1H integration) at 3.35 ppm, are assigned as Rh(OEP)(CH2CHO). The fi-aldehyde complex has previously been isolated from the reaction of [RhOEP]2 with CH2=CH-OEt in CgHo (149); the ligand resonances in CDCI3 solution are reported to be 2.90 ppm (t, CHO, JH-H = 5 Hz) and -5.55 ppm (dd, RI1-CH2-, JRh-H = 4 Hz).  Note that Rh(OEP) (CH2CHO) resonances are also present in the spectrum illustrated in Figure 4.2.  Similar results are obtained using O2, in the presence of added H2O, instead of air. Adding deoxygenated water to an equilibrated sample, under Ar in a septum capped nmr tube, of similar composition to that whose spectrum is shown in Figure 4.4 results in no changes in the *H nmr spectrum except for the appearance of H2O resonances. Sweeping the Ar atmosphere out with O2 and shaking the sample result in the rapid removal of Rh(OEP)(CH(Me)NEt2) and the  appearance of Rh(0EP)(CH2CH0) while the resonances of [Rh(OEP)]2 and Rh(OEP)(Cl)(Et2NH) appear unchanged, just as observed for the samples exposed to air. New, broad resonances at -2.1 and -2.9 ppm are also observed and are attributed to free amine exchanging with amine bound to a Rh(OEP) species. The species in question is believed to be Rh(OEPXCH2CHO)(amine), because the -CHO proton resonance couplings were not resolved due to broadening and such exchange is observed for the TMP complex (see below). When the sample was checked 1 month later [Rh(OEP)] is not present but Rh(OEP)(Cl)(Et2NH) and Rh(OEP)(CH CHO) were still present in 2  2  roughly unchanged proportions. In contrast, exposure of a C^De solution containing [Rh(OEP)J2, Rh(OEP)(Cl)(Et2NH) and Rh(OEP)(CH(Me)NEt2) to dry O2 alone (i.e., with H2O only from Rh(OEP)(Cl)(H 0)H 0), 2  2  results in the immediate consumption of [RhOEPh as well as the Rh(OEP)(CH(Me)NEt ) species. 2  The only Rh(OEP) products, observed by nmr spectroscopy, are Rh(OEP)(Cl)(Et2NH) and Rh(OEP)(CH2CHO). Again some amine appeared to be exchanging with Rh(OEP)(CH CHO). 2  When the sample was checked one month later, Rh(OEP)(Cl)(Et2NH) and Rh(OEP)(CH CHO) 2  were still present in roughly unchanged proportions. Analogous visible spectroscopy experiments confirm the nmr observations in a limited way. If O2 is added to a C6H6 solution of Rh(OEP)(Cl)(H20) that has been allowed toreactwith -7 equivalents of Et3N, in vacuo, for ~100 rriin (i.e., a similar extent of reaction to that illustrated by Fig. 4.5) then a new, more complex visible spectrumresults(Fig. 4.7). The spectrum remains unchanged for hours, and is not changed when the sample is exposed to room light nor when 2 equivalents of Et3N are added. The band at 552 nm is believed to be due to Rh(OEP)(Cl)(Et2NH) (cf. Fig. 4.3) and that at 544 nm to Rh(OEP)(CH2CHO), because the complex isreportedto have an a band at 544 nm in CHCI3 (150). A possible shoulder at ~390 nm on the Soret "band" at -407 nm, illustrated in the inset of Figure 4.7, is close to the Soret of Rh(OEP)(CH CHO) 2  reported at 386 nm. The shoulder at -554 nm indicates that other species are present, perhaps Rh(OEP)(CT2CHO)(amine). So, to the extent that Rh(OEP)(Cl)(Et2NH) and Rh(OEP)(CH2CHO) appear to be present, the visible experiments are consistent with the nmr data, but only at the lower ratios of [Et3N] to [Rh]. Although a spectrum similar to the solid line in  122  500  Figure 4.7.  wavelength (nm)  600  The visible spectrum of a Cglf, solution of (••••) Rh(OEP)(Cl)(H20) wth E t 3 N , 100 min after the addition of EtsN and then (—) 90 min after addition of O2. [Rh] = 4.74 x IO" M, [Et3N] = 3.30 x 10-3 M, 25 °C. 4  0  Figure 4.7 is obtained for a sample with 20 equivalents of Et3N initially added under O2, this solution with the higher [Et3N] is light-sensitive. Exposure to room light triggered a thermal reaction that led to a spectrum identical to that of Rh(OEP)(Cl)(Et2NH) (i.e., Fig. 4.3) upon leaving the solution standing over-night in the dark. In summary, the reaction of Et3N with Rh(OEP)(Cl)QH20) gives products that indicate amine C-H and C-N cleavage (Rh(OEP)(CH(Me)NEt2), Et2NH as Rh(OEP)(Cl)(Et2NH), and Rh(OEP)(CH2CHO)) and net 1-electron reduction of Rh(DI) to Rh(H) species ([Rh(OEP)] ). The 2  high yield of [Rh(OEP)]2 using equimolar quantities of Et3N and Rh(OEP)(Cl)fJl20) under anaerobic conditions, while available Et3N reacts further to form Rh(OEP)(CH(Me)NEt2), indicates a Et N:Rh(IIJ) stoichiometry of < 1:1 for the reduction. The reduction reaction is slow in 3  the presence of a competing donor ligand (CH3CN) implying coordination of Et3N is required for reduction. In fact, subsequent coordination of Et2NH to form Rh(OEP)(Cl)(Et2NH) probably prevents dealkylation catalysis under the conditions used.  Theresultsalso show that there is arequirementfor an oxidant (i.e., air or O2) to produce at least some of the C-N cleavage products, but that oxidation after formation of Rh(OEP)(CH(Me)NEt2) does not always lead to the same products as when air is present initially during thereactionof Et3N with Rh(OEP)(Cl)(H20). The stability of Rh(OEP)(CH(Me)NEt2) in the presence of H2O implies that the O atom in the Rh (OEP) (CH CHO) species is from the added 2  0. 2  The effect of excess H2O on the fate of [Rh(OEP)]2, in the presence of O2, during the conversion of Rh(OEP)(CH(Me)NEt2) to Rh(OEP)(CH CHO), is marked but not easily 2  rationalisable. The [Rh(OEP)]2 dimer is known to be stable to O2 (cf. Chapter 3) but the TPP dimer isreportedtoreactwith dry O2 in toluene to form Rh(TPP)(02) (42,151). 4.2.2. Amine reaction with Rh(TMP)(Cl)(L) in benzene or toluene The [Rh(OEP)]2 dimer is the product of thereactionof some tertiary amines with Rh(OEP)(Cl)(H20). However, a [Rh(TMP)J2 dimer is not expected to form because the steric interactions of the ortho-methyl groups of TMP would prevent a close approach to form a Rh-Rh bond, and indeed thereactionof Et3N with Rh(TMP)(Cl)(iPrOH) intially differs from that with the OEP complex. Unlike Rh(OEP)(Cl)(H20), the TMP complexreactedvery slowly in aredoxprocess with Et3N in benzene under air, taking days rather than hours. The *H nmr spectrum of a C6D6 solution of PJi(TMP)(Cl)(iPrOH) 10 min after addition of ~2 equivalents of Et3N is shown in Figure 4.8a. A Rh(TMP)(Cl)(Et3N) complex is formed initially, but most of its H nmr l  resonances are broadened because of exchange processes, particularily the ortho-methyl proton resonances at ~2.52 and ~1.5 ppm and theresonancesup-field of TMS at about -1.6 and -2.4 ppm due to a single coordinated EtsN. The assignments (Table 4.3) in the illustration are made using VT nmr data, and are consistent with a diamagnetic complex, asymmetrically substituted with regard to the porphyrin plane. The large difference between the ortho-methylresonancesof the TMP ligand (1.05 ppm at -14 °C)reflectthe steric bulk of the Et3N ligand relative to the trans CI". Comparably large separations of 0.914,1.189 and 0.950 ppm were also observed for Rh(TMP)(Cl)(PPh ), Rh(TMP)(Cl)(P Bu3) (Table B.l) and "Rh(TMP)(Cl)(C D )" (Table 2.7). n  3  7  8  124 p-Me  (a)  1 = Rh(TMP)(Cl)(Et N) 3  f = free Et N 3  8  =  0^6  -CH= o'-Me  o-Me  Et N 3  1 1 ~T~ 4  I  6  10  p-Me (b)  T 0  T  -r  —4  -  -6  -2  l  -8  o,o'-Me 1 = Rh(TMP)(Cl)(Et NH)  1  2  2 = Rh(TMP)(CH CHO) 2  -CH=  -CHO  Rh-CH 2  2 1  4  10  Figure 4.8.  AiUu. T "  5 ppm  0  —r -2  -r  -r~  -  -6  -4  i  -8  The 300 MHz H nmr spectrum of a CoD solution of Rh(TMP)(Cl)(iPrOH) (a) 10 l  6  min after addition of Et3N and (b) 3.5 days later. [Rh] - 4 x 10" M, [Et3N] - 8 x 3  10- M,at20 C,inair. 3  o  Table 4.3. The *H NMR spectral data for various Rh(TMP) complexes in complex  -CH= m,m'-H P-CH3 o,o'-CH3  Rh(TMP)(Cl)(Et N)b 3  8.79 7.27,6.97 2.50 2.46,1.45  C6H0  or C7D8  3  other -1.691 (-CH3), -2.51 q (-CH2-)  Rh(TMP)(Cl)(Et NH)c 2  8.87 7.22,7.03 2.44 2.16,1.77  -1.991 (-CH3), -2.80 m (-CH2-), -3.12 m  (-CH -), -5.80 ppm s (NH) -4.29 dd (-CH -), 4.321 (-CHO) 2  Rh(TMP)(CH CHO)c 2  8.77  <*  2.50 2.18, 1.87 d  2  a. At 20 °C, unless otherwise noted; 300 MHz; all singlets unless noted otherwise; integrations match assignments. b. InsituinC7Dg,at-14 C. c. In situ in CfPs. 0  d.  Obscured by resonances of Rh(TMP)(Cl)(Et NH). 2  Very little change occurs in the *H nmr spectrum over the next hour but after 3.5 days the spectrum in Figure 4.8b is observed. The principle species seen is Rh(TMP)(Cl)(Et NH) with 2  some Rh(TMP)(CH CHO) as a minor product The resonances of Rh(TMP)(Cl)(Et NH) (Table 2  2  4.3) are assigned by comparison to that of the complex rapidly formed in situ by the addition of 3 equivalents of Et NH to Rh(TMP)(a)(iPrOH). The diamagnetic complex has two ortho-methyl 2  resonances at 2.16 and 1.77 ppm indicative of non-symmetric substitution with regard to the porphyrin plane. Coordination of one Et NH ligand is shown by the up-field shift of the Et NH 2  2  resonances from their normal positions due to the ring-current of TMP. The ligand assignments: -1.99 (t, 6H, -CH3), -2.80 and -3.12 (2 m, 4H, -CH -) and -5.80 ppm (s, IH, NH) are similar to 2  those of the OEP congener (sect. 4.2.1). The wider separation of the - C H ^ resonances (0.32 ppm) of the Et NH ligand of the TMP complex compared to those of the OEP complex 2  (overlapped; Fig. 4.1) reflects the greater steric hindrance caused by the ortho-methyl groups of TMP. The multiplet at -2.80 ppm has a smaller coupling constant to NH indicating that it is the resonance of the methylene proton cis to the NH proton. The methyl resonances of the displaced iPrOH are overlapped by broadened free Et3N resonances at -1.2 ppm, but the septet (5 lines  126  detected) methine proton resonance is at 3.68 ppm. The assignments, established by selective decoupling, for the fJ-aldehyde ligand of Pvh(TMP)(CH2CHO) (Table 4.3) are similar to those of the OEP congener, the difference of the ortho-methyl proton resonances of TMP is relatively small (0.31 ppm).  The aerobic Et3N reaction was also followed by uv-vis in C6H6 but very little redox change was seen in the first hour, consistent with the nmr exr^riments. The fj and a bands of Rh(TMP)(Cl)(iPrOH) at 531 and 562 nm are instandy replaced by new bands at 536 and 569 nm, and this spectrum is essentially unchanged for hours. A similar spectrum is obtained from addition of Et2NH to PJi(TMP)(Cl)(iPrOH) in C ^ . If the spectrum of Rh(TMP)(Cl)(Et3N) is similar to that of Pvh(TMP)(Cl)(Et2NH), which is likely, then the initial change is consistent with formation ofRh(TMP)(Cl)(Et N). 3  When the reaction of Rh(TMP)(Cl)(iPrOH) with 1.4 - 3.5 equivalent of Et3N under dry, anaerobic conditions in C6D6 or C7D8 is examined by H nmr a few minutes after addition of J  Et3N, the spectra show broadened resonances like the previously discussed experiment in air. When the sample is examined one day later, the Rh(TMP)(Cl)(Et3N) resonances are completely replaced by resonances of several new complexes indicated by the multiple pyrrole proton resonances at -8.6 ppm (Fig. 4.9), and the principal complex is believed to be Rh(TMP)(CH(Me)NEt2). The pattern of the ligand resonances is similar to that of Rh(OEP)(CH(Me)NEt ) but shifted down-field by 0.55 - 0.88 ppm (Table 4.4) and is readily 2  assigned by selective decoupling. The pyrrole proton is at 8.54 ppm, the para-methyl protons at ca. 2.96 ppm, and the inequivalent ortho-methyls at 2.35 and 1.64 ppm. A smaller amount of Rh(TMP)(Cl)(Et2NH) was also present in this day-old solution and a number of unidentified complexes were present in minor amounts. The identity of the other major species which has a "pyrrole" resonance at 8.53 ppm has not been solved. At longer times, less of this complex is present Pairs of ortho-methyl resonances (12 H each) can be found for Rh(TMP)(Cl)(Et2NH) and Rh(TMP)(CH(Me)NEt2) in the spectrum illustrated in Figure 4.9. A singlet at 1.99 ppm of ~ 24 H intensity (o-Me) relative to the 8 H resonance at 8.53 ppm can also be found, suggesting a symmetrical (E>4) complex; however this single resonance is a n  1 = Rh(TMP)(Cl)(Et NH)  121  p-Me  2  2 = Rh(TMP)(CH(CH )NEt ) 3  2  3 = Rh(TMP)(?) f = free amine s= C D 7  8  2 T"T  T—I—I—I—1  3  ».'•  1—I—I—|—I—1—!  t.o  a.'e  Figure 4.9.  T  i 4  -  -2  -A  -r—  -6  The 300 MHz lH nmr spectrum of a C7D8 solution of Rh(TMP)(Cl)(iPrOH) 1 day after addition of EfcN. [Rh] « 3 x 10" M, [Et3N] » 1 x IO" M, at 18 °C, sealed in vacuo. 3  Table 4.4  -r  I  8 ppm 0  -i—I—i—i—i—r-  I.'S  f  2,1^^1  10  If  2  Ligand H nmr spectral data for Rh(TMP)(CH(Me)NEt2). l  a  proton  5(ppm)  integral  H' H HH (i) Hi( ) H Hr Hp  -0.06 m -0.44 t -0.51 t -1.08 m -1.17 m -1.40 m -1.66 m -3.12 d  IH 3H 3H IH IH IH IH 3H  2  3  3  2  2  a  a. 300 MHz; measured in C7D8 solution at ca. 20°C; the labels are the same as in Table 4.2.  128 consequence of two coincident temperature-dependent signals. A variable temperature experiment on a similar sample revealed that the resonances of the "symmetric" complex are very temperaturedependent in comparison to the other two major Rh species resonances which are comparatively invariant. The same, perhaps paramagnetic, species is found in small amounts immediately after addition of Et3N. The combined ortho-methyl resonance region data for the species are plotted in Figure 4.10. Fitting straight lines to the two sets of data using a linear least squares calculation indicates that the two resonances became coincident at -19 °C, about the same temperature that the data of Figure 4.9 were collected. Unfortunately only three resonances are discernable, others likely being obscured by more intense signals. In particular, para-methyl resonances of different complexes are often nearly coincident. The variations with temperature could be accounted for by chemical exchange, although within the context of this thesis, such a 'crossing' of TMP orthomethyl resonances of the same complex is never observed. Para-magnetism is a real possibility because Rh species are clearly involved (i.e., in the OEP system) and a diamagnetic [Rh(por)]2 11  complex is unlikely for por = TMP . A likely possibility is monomeric Rh (TMP), but the 2-  n  detailed assignments cannot be made on the basis of the limited data. 2.4  1.8 -20  Figure 4.10.  i  |  -10  i  |  i  |  0 10 temperature (°C)  i  |  20  i  30  Plot of the H nmr shifts of the ortho-methyls of the unknown complex vs. J  temperature. (•)o-H, ( B ) O ' - H .  The visible spectra of the nmr solutions containing mixtures of Rh(TMP)(Cl)(Et2NH) and Rh(TMP)(CH(Me)NEt2), just described, show two maxima probably corresponding to two overlapped P bands. The one at 536 nm is the same as that previously obtained for Rh(TMP)(Q)(Et2NH), formed in situ from Et2NH and Rh(TMP)(Cl)(iPrOH); a broader band at -520 nm presumably belongs to Rh(TMP)(CH(CH3)NEt2). Addition of O2 to a "day-old" nmr sample containing principally Rh(TMP)(CH(CH3)NEt2) and Rh(TMP)(Cl)(Et2NH) causes an immediate disappearance of the resonances of Rh(TMP)(CH(Me)NEt2) and putative Rh species from the H nmr spectrum n  l  (Fig. 4.11). A species whose resonances are close to those of Rh(TMP)(CH2CHO) (Table 4.3), and is in the same relative proportion to the total Rh as was Rh(TMP)(CH(Me)NEt2) before addition of O2, can be found in the new spectrum, and resonances of coordinated Et3N are at -1.74 (t, -CH3) and -2.40 (q, -CH2-). The integration of the Et2NH ligand resonances is more than can be accounted for by just RhCTMP)(Cl)(Et2NH), but the coordinated Et2NH and Et3N resonances together are approximately equivalent to the total equivalents of RhTMP(Cl)(Et2NH) plus the "Rh(TMP)(CH2CHO)" species (assigning the 8.67 ppm peak to the latter). On this basis, the "Rh(TMP)(CH CHO)" species is a mixture of Rh(TMP)(CHCHO)(Et3N) (-30%) and 2  2  Rh(TMP)(CH2CHO)(Et2NH) (-70%). Theresonancesof the -CH2CHO ligand are broadened and the couplings notresolved,consistent with some degree of exchange, probably with Et3N and Et2NH as ligands,resultingin only an average pyrroleresonancefor the two complexes. In confirmation, careful exarriination of theresonancesof the coordinated Et2NHrevealed2 sets of resonances, the new set slightly offset from those of Rh(TMP)(Cl)(Et2NH). Theresonancesat 2.25 and 1.88 ppm are assigned to the ortho-methyl protons of the Rh(TMP)(CH2CHO)(Et2NH) complex and those of the Et3N complex at ca. 2.48 (partially obscured by para-methyl proton resonances) and 1.64 ppm. At least 3 other minor species account for -38% of the total Rh, based on pyrrole integration, and a number ofresonancesup-field of TMS are seen but not assignable at present.  1 = Rh(TMP)(Q)(Et NH) 2  p-Me  o,o'-Me  2 ="Rh(TMP)(CHCHO)* see text 2  f = free amine  -CH=  s=C D 7  8  free iPrOH  —i 8.8  i ,  r  1  8.6  -A-Jt  8.4  \  0  -1  ~T~ -3 -3  -2  8ppm  ^  T-5 -5  -6  -7  Figure. 4.11. The 300 MHz iH nmr spectrum of a C D solution of Rh(TMP)(Cl)(iPrOH) with Et N, after addition of 0 . [Rh] = 3 x 10" M, 3  7  [Et N] - 1 x IO" M, at 18 °C. 2  3  8  3  2  In summary, the reaction of Et3N with Rh(TMP)(Cl)(iPrOH) or Rh(OEP)(Cl)(H20) leads to the same products (ignoring the minor species for the present) with the notable exception of a dimeric RhfTI) species being found only in the reaction with the OEP system. Also, the initial Et3N redox reaction with Rh(TMP)(a)(iPrOH) is slower than with the OEP analogue at similar stoichiometries and concentrations, but the difference is not due torate-limitingdissociation of iPrOH because Rh(TMP)(Cl)(Et3N) rapidly forms and both the TMP and OEP complexes rapidly form Rh(por)(Cl)(Et2NH). The redox reaction of Rh(OEP)(Cl)(H20) with Et3N is rapid but is inhibited by CH3CN, the implication being that coordination of Et3N is required for the reduction to occur. These observations support the TMP ligand inhibition of the formation of a Rh-Rh metal-bonded species and also lead to the idea that under anaerobic conditions the reduction of Rh(HI) to Rh(H) involves equilibrium processes that lie to the Rh(H) side in the OEP case because  of the formation of [Rh(OEP)]2. A possible reaction sequence is shown by reactions (4.1-4.4). Rh (por)(Cl)(L) + Et N ^===- Rhni(por)(Cl)(Et3N) + L  (4.1)  Rhni(por)(Cl)(Et3N) ^=  (4.2)  m  3  Rh (por) + Et NC HCH3 + HCI n  2  Rhni(por)(Cl)(L) + Et NC HCH3 ^  RhD(por) + Et NCH=CH + HCI  2  2 Rh (OEP)  2  (4.3)  2  [Rh(OEP)]  n  (4.4)  2  The HCI produced by reactions 4.2 and 4.3 is mopped up by the amines present. There is only weak evidence for the presence of a small amount of a Rh (TMP) species. n  The enamine produced in reaction 4.3 can be cleaved by HCI or H2O to produce Et2NH (152). By implication, the formation of Rh(por)(CH(Me)NEt2) is via an initial H-atom abstraction from Et3N by monomelic Rh (por) species, which are in low concentration in both the TMP and OEP n  systems (reaction 4.5 and 4.6). The hydride species has not been detected, even during the lowtemperature nmr experiments and so is presumed to react with amine via Rh (por). Indeed, the n  reaction of Et3N with Rh(OEP)(H) in CD C1 is observed by H nmr to give rapidly a product !  2  2  whose nmr srjectrum is similar to that of Rh(OEP)(CE>2Cl) which is formed by reaction of Rh(II) species with CD2CI2 (sect. 4.2.3).  132 Rhn(por) + Et N  Et NC HCH + [Rh(por)(H)]  3  2  Rh (por) + Et NC HCH  Rh(poT)(CH(Me)NEt )  n  2  (4.5)  3  3  (4.6)  2  4.2.3. Amine reaction with Rh(OEP)(Cl)(H 0) in CH C1 2  2  2  The reaction of EtjN with the Rh(OEP)(a)(H20) species in CH C1 is of interest for 2  2  several reasons. The solvent is more polar than benzene or toluene and it is known to react with Rh(U) porphyrin species (sect. 1.4.1) to form Rh (por)(CH Cl). Just such a side-reaction with m  2  CH C1 is presented in this section and the following one (sect 4.2.4). This reactivity has also 2  2  been discussed in Chapter 3, but that work actually followed on the observations described in this chapter. All the experiments using CH C1 as solvent are under anaerobic conditions, except 2  2  where noted. Reaction under anaerobic conditions, and in the dark, of 1 to 2 equivalents of Et N with 3  Rh(OEP)(Cl)(H 0) can be followed by H nmr in CD C1 , and Rh(OEP)(Cl)(H 0) is seen to be J  2  2  2  2  completely consumed within minutes, yielding a mixture of products which underwent slower reactions, over longer periods of hours and days. The "immediate" products of a typical sample examined by H nmr (Fig. 4.12) include Rh(OEP)(Cl)(CH CH=NEt ) in 40% yield. The nmr l  2  2  resonances of Rh(OEP)(Cl)(CH CH=NEt ) are assigned by integration, selective decoupling and 2  2  by comparison to the data for the TMP analogue (sect. 4.2.4) whose ligand ethyl proton resonances are better resolved. The porphyrin ethyl side-chain resonances are overlapped by those of other species, but the meso proton resonance at 10.12 ppm (s, 4H) is typical of a diamagnetic Rh (EI) species. The ligand resonances are listed in Table 4.5 and the assignments are illustrated by the diagram following the Table. The ligand is considered to be an neutral T^-ylidic enamine such as in RhCl (dmso) (ri -CH CH=NEt ) (153), and the trans-ligand is assumed to be CI" to 1  3  2  2  2  balance the charge, and to be consistent with a subsequent reaction product (see below).  133  -CH=  -CH,  1 3  1 = Rh(OEP)(Cl)(CH CH=NEt ) 2 = [Rh(OEP)] 3 = Rh(OEP)(CD Cl) 4 = Rh(OEP)(CH(CH )NEt ) f = free amine 2  2  2  2  3  r^nrrirTnjiiiT i'nf!jniij/Tii]Tin!"i;'i;|Tirr)  2  i  »'.4  10.3  t.B  10.0  -CH,  «.'«  FT —r  T" 6  10  12  Figure 4.12.  LL "T"  4 8 ppm  Jl  LJL  T  0  l  —2  -6  2  The 300 MHz H nmr spectrum of a CD2CI2 solution of Rh(OEP)(Cl)(H20) and EtsN, 2 h after addition of Et3N. [Rh] => 8 x 10" M, [Et3N] = 1 x IO" M, at 18 °C, sealed in vacuo. l  3  2  Table 4.5. Ligand H nmr spectral data for Rh(OEP)(Cl)(CH CH=NEt2). ]  a  2  proton  8(ppm)  integral  H3'(3) H  1.18 t  2H  0.58 t  IH  H4'(4)  -0.04 t  3H  -0.70 m  5H  -5.81 dd  2H  2  Hi  a. 300 MHz; measured in CD2CI2 solution at ca. 20°C.  The two other initially formed major species are [Rh(OEP)]2 (~5%, based on the meso proton resonance at 9.20 ppm) and another new species with a meso proton resonance at 10.15 ppm (~35%). The species associated with this resonance has no discernable ligand resonances and is believed to be Rh(OEP)(CD2Cl) by analogy to data for the TMP system (sect 4.2.4). A very small amount of Rh(OEP)(CH(Me)NEt2) is also present, as judged by a doublet resonance at -4.2 ppm, and two triplets at —0.8 ppm. Over the next few hours, the Rh dimer and the enamine complex are consumed with a n  concomitant increase in the relative amount of Rh(OEP)(CD2Cl) and Rh(OEP)(Cl)(Et2NH) (Table 4.1). In addition, a new meso-proton resonance (initially at 10.18 ppm) grew in as the resonances of the dimer and enamine complexes decrease. This resonance, and that of Rh(OEP)(CD2Cl) (initially at 10.15 ppm), shifted down-field over a few days to -10.16 and -10.12 ppm, respectively (Fig. 4.13). The new species associated with this resonance also has no discernable ligand resonances and is proposed to to be "Rh(OEP)(R)(amine)'\ where R is unknown, derived from the solvent because it apparendy contains no protons (i.e., is probably deuterated) and the amine (Et2NH or Et$N) is in rapid exchange with free arnine. The "free" amine resonances in the "three-day old" sample spectrum (Fig. 4.13) are at 2.36 ppm (q) and 0.75 ppm (t), the negative shift from the position of the free amine suggesting that the free amine is in rapid exchange with a Rh(por) species. Generally, Rh(OEP)(R)(L) species have labile ligands (sects. 1.4.1,1.5.1 and 4.2.4) due to the trans effect of the alkyl group.  135  -CH,  1 = Rh(OEP)(Cl)(Et NH) 2 = Rh(OEP)(CD Cl) 3 = 'Rh(OEP)(R)(amine)" f = free amine 2  2  ,  -CH,tt.*  ~l T l 10.1  1  [ 1  1  1  10.t  1  1  10  8  Figure 4.13.  1  I  1  I I I [  1  lO'.l  1  1  1  6  4  2  g  1 p  p  m  0  1 -2  1 -4  1  1—  -8 .  -6  The 300 MHz *H nmr spectrum of a CD2CI2 solution of Rh(OEP)(Cl)(H20) and Et3N, 3 days after addition of Et3N. [Rh] » 8 x 10" M, [EtjN] ~ 1 x IO" M, at 18 °C, sealed in vacuo. 3  2  During the course of the reaction, the amine resonances shift from positions more positive than the those of free amines (Et^N and Et2NH) through the positions of the free amines and then to more negative values (Fig. 4.14). At the sametimea broad peak movesfrom~11.6 ppm to -8.4 ppm and is probably H , as amine-HCl. The down-field shift of Et3N upon +  protonation is documented (154). Rapid exchange of amine between the amine-HCl species and "Rh(por)(R)(arnine)" in changing proportions during the course of the reaction would account for the variation of the free amine resonances and the apparent lack of amine ligand resonances for "Rh(por)(R)(amine)'\  amine-HCl  1.2  -CH  3  DO  1.1. 11.0." O-  E &  0.90.80.7,  •  Time (h)  i  i  i  100  50 70 Time (h)  Figure 4.14. Plot of the *H nmr shifts of selected arnine resonances: (O) run 1, ( ® ) run 2, (—) average position of methyl proton resonances of Et2NH and Et N . [Rh] 8 x IO" M, [Et N] = 1 x IO" M, at 18 °C, sealed in vacuo. 3  3  2  3  4.2.4. Amine reaction with Rh(TMP)(Cl)(L) in C H C 1 2  2  In contrast to the system in aromatic solvents, Rh(TMP)(Cl)(Et N) is not the initial 3  product of the reaction of Et N with Rh(TMP)(Cl)(iPrOH) in CD C1 or CH C1 . The major 3  2  2  2  2  products observed by *H nmr immediately after addition of ~3 equivalents of Et N to a CD C1 3  2  2  solution of Rh(TMP)(Cl)(iPrOH), under anaerobic conditions, are (e.g., Fig. 4.15): Rh(TMP)(CD Cl) (or Rh(TMP)(CH Cl)) in 30 to 50 % yield, Rh(TMP)(Cl)(CH CH=NEt ) in 20 2  2  2  2  to 30% yield, and that of Rh(TMP)(CH(Me)NEt ) in 8 to 20%, based on nmr integration of the 2  pyrrole resonances. Other products included Rh(TMP)(Cl)(CH CH=N(H)Et) and 2  [Rh(TMP)(Et N)fJit NH)] (see below). The porphyrin ligand assignments are in Table 4.6 and +  3  2  are based on correlations from many different experiments and extents of reaction. The nmr based yields were variable from sample to sample but the ratios of the complexes to each other were always similar. The variability was traced to the presence of other pyrrole resonances overlapping the major peaks at ca 8.5 ppm These could total as much as 36% yield. Realistically the major product yields are considered to be at the low end of the reported ranges.  1 = Rh(TMP)(Cl)(CH CH=NEt ) 2  -CH= 4  o,o'-Me  p-Me  2  2 = Rh(TMP)(Et N)(Et NH)  +  3  2  3 = Rh(TMP)(CH(CH )NEt ) 3  2  4 = Rh(TMP)(CD Cl) 2  f = free amine  JLL p m i T i m j i T r r p T r n mT[ii;:; 111:;nn111111ITTT|  ).o  e.e  e.e  B.'<  8.2  BO  • i — i — j - -  v — r -  0.5  13  1  ii 1- i 10  4  T"  0  8 ppm  0.0'  2  J  K  T  —r  -2  -6  l  -8  Figure 4.15. The 300 MHz H nmr spectrum of a CD2CI2 solution of Rh(TMP)(Cl)(iPrOH) and Et3N, 10 min after thawing a sample frozen l  in liquid nitrogen. [Rhl = 3.8 x 10"3 M, [Et^N] = 1 x IO" M, at 18 °C, sealed in vacuo. 2  138 Table 4.6. The H NMR spectral data for various Rh(TMP) complexes in the *H nmr spectrum ilustrated in Fig. 4.15. ]  a  complex  -CH= m,m'-H P-CH3 o,o'-CH3  other  b  Rh(TMP)(CD2a)  8.53  2.60C  1.92,  Rh(TMP)(Cl)(CH CH=NEt )  8.50  2.60C  2.12, 1.67 <*  Rh(TMP)(CH(Me)NEt2)  8.31  2.57  2.23,1.53 -3.39 d (Hp),-1.30 m  2  2  e  1.81  (H ), -0.60 t (H ), a  3  -0.5 t (H .)  c  3  -5.17 dd (Rh-CHH  Rh(TMP)(Cl)(CH CH=N(H)Et) 8.63 f  2  [Rh(TMP)(Et N)(Et NH)]+ 3  2  8.73  2.62  2.00,1.77 Et N: -1.66 t (-CH3), 3  -2.33 q (-CH2-)  Et NH: -1.82 t (-CH3), 2  -2.91/-3.15 m (-CH ), 2  -6.31 s (NH)  a. In situ at 300 MHz; all singlets unless noted otherwise; integrations match assignments. b. The resonances of all the complexes overlap at ~7.3 ppm. c. Resonances overlapped by those of other species. d. Ligand assignments listed in Table 4.7. e. See Table 4.4 for labelling. f. Partial assignment only. The assignment of the Rh(TMP)(CD Cl) and Rh(TMP)(CH Cl) resonances is based on 2  2  comparison of their nmr spectra in CD C1 and CH C1 . A resonance at -2.72 ppm is observed in 2  2  2  2  the nmr specturm of the sample in CH C1 but is absent in that of the deuterated sample; this -2.72 2  2  resonance is assigned as the "-CH C1" ligand fragment (cf., sect. 3.2.2.1.1.). The same ligand 2  resonance of Rh(TPP)(CH Cl)(py-d5) is reported to be at -2.82 ppm (100). The JRh-H coupling 2  2  is not observed because the ligand site trans to -CH C1 in Rh(TMP)(CH Cl) is occupied by Et3N, 2  2  or Et NH, which is in exchange with free amine. This was apparent from low temperature nmr 2  spectra obtained at longer reactiontimesbut not always apparent at short reactiontimes(see later discussion). The porphyrin ligand assignments are given in Table 4.6.  139 The assignments of the ligand resonances for Rh(TMP)(Cl)(CH2CH=NEt2) are based on integration and selective decoupling and are listed in Table 4-7, using the same labelling as shown in the diagram attached to Table 4.5. The porphyrin assignments are given in Table 4.6. During the course of the decoupling experiments on the enamine ligand, a nearly identical but less intense set of resonances is found underlying the enamine ligand resonances. This set appears more clearly at later points in the reaction. Resonances at -5.17 ppm (dd) and the pyrrole at 8.63 ppm are believed to be part of the same complex. The former resonances are consistent with a Rh-CH2-CH= fragment as in the enamine complex, and on the basis of integration the complex is proposed to be a mixture of cis- and trans-Rh(TMP)(Cl)(CH2CH=N(H)Et). The resonances of the cationic Rh(TMP)(Et3N)(Et2NH) complex grow in as those of +  Rh(TMP)(CH(Me)NEt2) decrease over thefirst10 to 30 min of reaction (Fig. 4.16). The pyrrole resonance is at 8.73 ppm and the resonances at 2.00 and 1.77 ppm are assigned to the inequivalent ortho-methyls. The assignments for the ligands are in Table 4.6.  Table 4.7. LigandH nmr spectral data for Rh(TMP)(Cl)(CH2CH=NEt2).  a  l  6  integral  H3'(3)  1.53 t 1.34 q  IH 2H  H4'(4)  0.08 t  3H  H3(3")  -0.02 m  H4(4")  -0.52 t  2H 3H  Hi  -4.92 dd  2H  proton H  2  a. 3(X) MHz; measured in C D 2 C I 2 solution at ca.20°C.  1 = Rh(TMP)(Cl)(CH CH=NEt ) 2  2  -CH= 2 = Rh(TMP)(Et N)(Et NH)  +  3  2  3 = Rh(TMP)(CH(CH )NEt )  4  3  Time (min)  4  = Rh(TMP)(CH Cl)(L) 2  2  Figure 4.16.  2  5= cis & trans Rh(TMP)(Cl)(CH CH=NHEt) 2  The 300 MHz H nmr spectrum of a C H 2 C I 2 solution of Rh(TMP)(Cl)(iPrOH) and Et3N, at various times after thawing a sample J  frozen in liquid nitrogen. [Rh] - 3.0 x 10 M, [Et^N] = 1 x IO M, at 18 °C, sealed in vacuo. 3  2  The resonances of PJi(TMP)(CH(Me)NEt2) are partially obscured but still distinguishable and are listed in Table 4.6. The separation of the ortho-methyl resonances was 0.70 ppm which is comparable to the 0.72 ppm separation observed in C7D8 solution. Like its OEP analogue, PJi(TMP)(Cl)(CH2CH=NEt2) is not stable and further reaction occurs but at a much slower rate than for the decomposition of Rh(TMP)(CH(CH3)NEt2) (Fig. 4.17). As the Rh(TMPXCl)(CH CH=NEt2) resonances decrease, those of Rh(TMP)(Cl)(Et NH) 2  2  increase; this is seen, for example, by examining the respective pyrrole resonances (8.53 and 8.62 ppm) and the respective axial ligand resonances: Et2NH (-1.83, -2.90, -3.32 and -5.96 ppm) and :CH2CH=NEt2 (-4.92 ppm). The [Pvh(TMP)(Et3N)(Et2NH)]+ spectra remain roughly constant. The pyrrole resonance of Rh(TMP)(CD2Cl) shifts slightly to 8.52 ppm and increases in intensity somewhat as well. Spectra taken of sealed samples at longertimes(2 days to several weeks) show only two pyrrole resonances (8.62 and 8.51 ppm) in about a 1:1.7 ratio (trace for 23 °C in Fig. 4.18). The pyrrole proton resonance at 8.62 ppm is that of Rh(TMP)(Cl)(Et2NH) (vide supra). The other pyrrole resonance is temperature dependent and splits into two resonances (8.55 and 8.48 ppm) at -53 °C; there is a coalescence temperature at about -20°C (Fig. 4.18). Only resonances due to coordinated Et2NH and Et3N are present in the ligand region. At -53 °C, the integrations relative to the pyrrole region are consistent with one Et2NH coordinated as Rh(TMP)(Cl)(Et2NH) and the remaining Et2NH being associated with the larger resonance at 8.48 ppm. The coordinated Et3N resonances match the smaller 8.55 ppm resonance. When a sample in CH2CI2, showing a similar composition by ambient temperature nmr, is then taken to -53 °C, the spectrum had two peaks at -2.85 and -3.44 ppm in the region expected for the -CH2CI ligand (Fig. 4.19). The smaller peak, at -2.85 ppm, roughly integrates to 2 protons relative to the integration of the ethyl groups of the coordinated Et3N and is therefore assigned to Rh(TMP)(CH2Cl)03t2NH), while the integration of the -3.44 ppm resonance integrates as 2 protons relative to the coordinated Et2NHremainingafter accounting for the Rh(TMP)(Cl)(Et2NH) present. Thus the room temperature pyrrole resonance at 8.51 ppm (Fig. 4.18) is the fast exchange average of the pyrrole resonances for Rh(TMP)(CD Cl)(Et3N) and Rh(TMP)(CD2Cl)(Et NH). 2  2  1 = Rh(TMP)(Cl)(CH CH=NEt2) 2 = Rh(TMP)(Et N)(Et NH) 3 = Rh(TMP)(CH(CH )NEt ) 4 = Rh(TMP)(CD Cl)(L) 5= Rh(TMP)(Cl)(Et NH) 6 = cis & trans Rh(TMP)(Cl)(CH CH=NHEt) 2  +  -CH=  3  2  3  4  2,5  Time (min)  2  2  2  2  2,4  1  2,4  +455  2.5  1 6  5  2,5 +155  L...  2,52 5  ±  +35  +10  2  2 2  2  2 2  A S  ^  2  It  3 +7 8.7  ure 4.17.  —r8.6  I  8.5  8.4  —F— 8.3  i  i  -1.0  8.2  r  s  5 ppm  -r -3.0 -  -2.0  -4.0  The 300 MHz H nmr spectrum of a CD2CI2 solution of Rh(TMP)(Cl)(iPrOH) and Et N, at various times after thawing a sample !  3  frozen in liquid nitrogen. [Rh] « 3.0 x 10 M, [Et-$N] ~ 1 x IO* M, at 19 °C, sealed in vacuo. 3  2  Figure 4.18.  The 300 MHz *H nmr spectrum of a C D 2 C I 2 solution of Rh(TMP)(a)(iPrOH) and Et3N, 14 days after after thawing a sample frozen in liquid nitrogen, at various temperatures. [Rh] - 3.8 x 10" M, [Et^N] - 1 x IO' M, at 19 °C, sealed in vacuo. 3  2  CH C1 solution 2  2  (a)  WW  CD C1 solution 2  T 0  - r  -l  T"  —r  -  -3  -2  8 ppm  2  —r  (b)  -~r~  -4  —I  -5  -7  Figure 4.19. The comparison of 300 MHz H nmr spectra of solutions of Rh(TMP)(Cl)(iPrOH) l  with added Et3N in (a) C H 2 C I 2 at -53 °C and (b) C D 2 C I 2 (the -53 °C trace from Fig. 4.18).  For the most part, the reaction of Et3N with Rh(TMP)(Cl)(L) in CH2CI2 parallels that with the OEP analogue, the absence of [Rh(TMP)]2 species being expected for the more hindered TMP complex. Reaction with CH2CI2 occurs and Rh(por)(Cl)(CH2CH=NEt2) is the other initial major product The similar reactivity for both types of Rh(por)(Cl) complexes in CH2CI2 contrasts with the slowness of reaction found for the TMP complex in aromatic solvents. The increased stabilisation of polar or ionic species such as might occur in reactions 4.2 and 4.3 (i.e., loss of HCI, see p. 131) presumably will promote the formation of Rh 0por), the amine adduct of which n  reacts with CH2CI2 to give Rh(rx)r)((rHQ)(aimne) and Rh(por)(Cl)(ainine) (by analogy to the 2  PPh3 complex reactions (3.80 and (3.9)), and the enamine; the imine isomer of this then coordinates to Rh(por)(Cl) to form Rh(por)(Cl)(CH2CH=NEt2). The lack of Rh(por)(Cl)(CH2CH=NEt2) found in benzene is due to the low proportion, relative to that in CH2CI2, of the polar imine isomer in the aromatic solvent (equilibrium 4.7).  145  CH =CH-NEt ^= 2  2  :CH CH=NEt 2  (4.7)  2  The enamine complex Rh(por)(Cl)(CH CH=NEt ) decomposes and Rh(por)(Cl)(Et NH) 2  2  2  concentration concomitantly increases. The decomposition of Rh(por)(Cl)(CH CH=NEt ) 2  2  probably occurs via dissociation of the enajnine because retention of an alkyl fragment (i.e. Rh(por)(CH CHO)) was not observed. Dissociation of the enamine and its hydrolysis to 2  CH3CHO and Et NH (152) followed by complexation of Et NH would explain the findings; 2  2  however, CH3CHO has not been detected. In the OEP system, another uncharacterized complex also forms, and is formulated as Rh(OEP)(R)(Et3N). The origin of the Rh(OEP)(R) fragment of the new complex is unclear because the R ligand is silent in the H nmr. Because the formation of l  Rh(OEP)(Cl)(Et NH) appears to be stoichiometric with the decrease of the enamine complex, other 2  uncharacterized species in solution (~25% initial products) and solvent are possibly involved. 4.3.  Results and discussion of kinetic studies The results of the *H nmr studies suggest that the first and critical step in the reaction of  Et3N with Rh(por)(Cl) is probably the coordination of Et3N. In toluene and benzene solution, a labile Rh(TMP)(Cl)(Et3N) complex is observed but the OEP analogue has not been detected. The aim of the kinetic studies was to investigate the system back to the point where the Rh(OEP)(Cl)(Et3N) complex could be detected. (Visible spectroscopy was used because of convenience and the accessibility of a stopped-flow apparatus.) The reactions were followed in CH C1 rather than toluene or benzene because the both the TMP and OEP complexes react at 2  2  similar rates in CH C1 and give similar products and thus the systems could be usefully 2  2  compared. In addition to the H 0 complex, the Rh(por)(Cl)(CH3CN) complexes were used. 2  Spectra covering the initial reaction in CH C1 under anaerobic conditions were obtained 2  2  by "scanning" with a Durrum single beam, stopped-flow instrument (sect. 2.2.8). The Rh(por)(Cl)(CH3CN) concentrations, after mixing, were ~2 x IO" M and about 150 equivalents of 5  Et3N were used. An initial period of rapid exponential change, complete in 2 to 10 s, was observed, followed by a very much slower change (Fig. 4.20). First, the whole spectra will be  146 considered, and then rates obtained from these stopped-flow data and data obtained at other concentrations will be discussed.  Figure 4.20.  Typical stopped-flow traces (2 sets of 3 superimposed runs) of the change of absorbance at 552 nm of Rh(OEP)(a)(CH3CN) during the reaction with Et3N in CH C1 . [Rh] = 2.41 x 10-5 M , [Et N] = 3.33 x 10-3 M , at 25°C, under Ar. 2  2  3  The absorbances measured during the reaction of Et3N with Rh(OEP)(Cl)(CH3CN) or Rh(TMP)(a)(CH3CN) in CH C1 are summarized in Figures 4.21 and 4.22, respectively. The 2  2  stopped flow data at twotimes,4 and 10 s for the reaction with Rh(TMP)(Q)(CH3CN) and at 0.5 and 2 s for that of Rh(OEP)(Cl)(CH3CN) are overlaid on the data graphically extrapolated back to t = 0 C V . see below); spectra of the initial Rh(por)(a)(CH3CN) complexes are also shown. The wavelength resolution of these stopped-flow spectra is low and variable (2 to 10 nm between points) and subject to interpolation errors as the lines were sketched in by hand. The accuracy of the absorbance scale is discussed in section 22.8 and for these spectra is considered to be ± 0.03 units; that of the wavelength scale is ±1 nm. The 'Tinal" spectra are similar to those obtained using the same solutions and a PE 552A scanning spectrophotometer (~2.5 min to scan to mid-point of  . 0.0 sec (a) • (b) © +0.5 sec (c) O + 2.0 sec (d) Rh(TMP)(Cl)(CH CN)  • // V / / V.  3  / b\ i€  .  <  \|  Ppo  / < &  () © /© a  Q\V  VvvgCb) / /  M  \ y© \jj  \|  / •  \4  (c) Z '  O  © 1  1  Figure 4.21.  1  500  1  I  1  I  , 550 wavelength (nm)  I  $  x  Changes of the visible spectrum during the first 2 seconds of the reaction of Et3N  with Rh(OEP)(Cl)(CH CN) in CH2CI2: (a) the spectrum at "to", (b) after 0.5 s, (c) 3  after 2.0 s and (d) Rh(OEP)(Cl)(CH CN). [Rh] = 2.41 x I O M , [Et N] = 3.33 x -5  3  3  10-3 M, at 25°C, under Ar.  (a) • 0.0 sec (b) © + 4.0 sec (c) O + 10.0 sec (d) Rh(TMP)(Cl)(CH CN) (e) Rh(TMP)(Cl)(Et NH)  > 1  3  2  / >cx (e]  \ \ \ \  x  /(d)  V  (a)  \ \  #  \  % ...(b)" ©,.\ © (c) 0 %  V-^ltx 550 Figure 4.22.  560  570 580 wavelength (nm)  590  600  Changes of the visible spectrum during the first 10 seconds of the reaction of E t N 3  with Rh(TMP)(Cl)(CH CN) in CH2CI2: (a) the spectrum at "to", (b) after 4.0 s, 3  (c) after 10.0 s, (d) Rh(TMP)(Cl)(Et NH), and (e) Rh(TMP)(Cl)(CH CN). [Rh] 2  3  = 2.17 x IO' M, [Et N] = 3.33 x 10" M , at 25°C, under Ar. 5  3  3  148 500-600 nm region after mixing) and a HP 8452A diode array spectrometer (-18 s; 1 s for a scan and -17 s for mixing) and are believed to be of the mixture of initial products observed by *H nmr (i.e., Rh(por)(CH2Cl), Rh(por)(a)(CH CH=NEt2), Rh(por)(CH(Me)(NEt2), etc.). Of more 2  interest is the spectrum obtained by extrapolation to The extrapolation to to is done by linear extension of the smooth curve showing the absorbance change on the photographs of the oscilloscope traces (Fig. 4.20). These V spectra 4  are similar to the spectra of the initial Rh(por)(Q)(CH3CN) complexes, but the differences are believed to bereal.In particular, there are differences between the a bands (~570 nm) of the Rh(TMP)(a)(CH3CN) and of the ' V ' spectrum of the TMP system, and between the p bands (-520 nm) of the Rh(OEP)(Cl)(CH CN) and of the "to" spectrum of the OEP system. The spectra 3  of the Et3N complexes are obviously not available for comparison but the changes indicate that the Rh(por)(Q)(CH3CN) complexes undergoes a very fast initial reaction to give the ' V ' spectrum. This is likely the formation of Rh(por)(Cl)(Et3N). Therelativerate of replacement of the CH3CN from Rh(por)(Q)(CH3CN) is critical because of the extrapolation on which the "to" spectra are based. At the 2.67 s/cmtime-scaleused for the photographs, any change in the first 200 to 300 ms is effectively ignored by the extrapolation to "to". The ti/2 for substitution of CH3CN in Rh(OEP)(a)(CH CN) or Rh(TMP)(Cl)(CH3CN) by CO or PPh is found to be -80 ms (see 3  3  below), with CH3CN loss probably being the rate determining step. On the basis of the dynamics, and the data described above, the "to" spectra are ascribed to Rh(por)(Cl)fJit3N). The data for the change at or near the maximum absorbance of Rh(por)(Q)(Et3N) was examined more closely. For Rh(OEP)(Q)(Et3N) this was at the a band and for Rh(TMP)(Cl)(Et3N) at the p band. The data could be treated as 1 order, the rate being obtained st  from plots of ln(A-Aoo) vs.timeusing an apparent A « , estimated from the absorbances at the end of the period of rapid change (Fig. 420). Table 4.8 summarises theresultsfor the reaction with Et N, and there are several salient features. 3  Table 4.8.  Pseudo first order rate constants for the disappearance of Rh(por)(Cl)(Et3N) in CH Cl2. a  2  run  [Rh] xlfj5M  kobs s-1  tl/2 s  Rh(TMP)(a)(Et3N) data at 540 or 536 nm: 1 2.10 86.0 0.19  3.63  2 3 4 5  3.71 3.40 2.74 1.33  6  0  [Et N] xVfiM 3  0  2.10 1.00  173 345 345 345  0.19 0.20 0.25 0.52  2.17  333  0.23b 3.00 0.18b. c 3.80  Rh(OEP)(Cl)(Et N) data at 552 nm: 3  7 8  2.53 2.41  345 345  0.404 1.72 1.87b 0.372 1.97b. d 0.352  a. The R values for the ln(A-A«) vs. time plots were 0.990-0.999; runs 1-3 at 20 °C; runs 4-8 at 25 b c d  °C. Under argon. Measured from absorbance increase at 520 nm. Measured from absorbance increase at 540 nm. Isosbestics subsequent to formation of Rh(OEP)(Cl)fEt3N) are suggested in Figure 4.21  and comparison of the data for the absorbance decrease at 552 nm with those for the increase at 540 nm supports this (run 8). The support (from the stopped-flow data) for the apparent isosbestics in Figure 4.22 for the TMP case is weaker (run 6). Air apparendy inhibits the OEP system (runs 7 vs. 8) but no such effect is observed for the TMP system (runs 4 vs. 6). Only the TMP system was tested for [Et3N] dependence, because it was difficult and cumbersome to 0  minimize air leakage while using the Durrum stopped-flow apparatus; the data (runs 1-3) show kobs is independent of [Et3N]. The dependence of kobs on [Rh] (run 5 vs. 4,6) is inverse for the 0  TMP system.  For the back-extrapolation to the "to" spectra to be meaningful, the ti/2 of the postulated substitution of CH3CN in Rh(por)(Cl)(CH CN) by Et3N to form Rh(por)(Cl)(Et3N) must be 3  small in relation to the ti/2 of the disappearance of Rh(por)(a)(Et3N). To test the rates of simple substitution of CH3CN at the Rh(IH) center, the reactions of Rh(por)(Cl)(CH3CN) with PPh3 and CO were briefly examined. In the presence of excess ligand L, Rh(por)(Cl)(L) species form (Chapter 5); and Table 4.9 summarises some kinetic data. The experimental stopped-flow data all give good pseudo-first order plots. The PPI13 data from the TMP system in particular gave practically superimposable absorbance values. The kobs values are higher (by a factor of ~50) than those for the disappearance of Rh(por)(Cl)(Et3N) (Table 4.8). As mentioned above, this observation is consistent with coordination of Et3N as the process preceding the disappearance of the Et3N complex. The kobs values (Table 4.9) are also essentially the same, being independent of porphyrin type and, at least in the TMP system, of [PPh3]. Although the lack of dependence on porphyrin type is probably fortuitous, loss of C H 3 C N as the rate determining step of the substitution reaction seems highly likely. The studies described in this kinetic section show that the OEP and TMP systems follow very similar reaction paths with Et3N. The first step seems to be the very fast substitution of CH3CN  in Rh(por)(Cl)(CH3CN) by Et3N, forming Rb(por)(Cl)(Et3N), probably in a S 1 N  process, judged by the data on the reaction of Rh(por)(Cl)(CH3CN) with CO and PPI13. The amine complex then undergoes further transformations that give the products observed by *H nmr (i.e., reduction of RhfTH) to Rh(U), etc.). However, the stopped-flow data indicate that air inhibits the transformation of Rh(OEP)(Cl)(Et3N) to the subsequent products. This observation raises an interesting point that, whereas the products of the reaction of Et3N with Rh(por)(Cl)(L) under anaerobic conditions are a rruxture of Rh(por)(Cl)(Et2NH) and significant amounts of relatively stable organometallic complexes, the samereactionin air givesrelativelyinsignificant amounts of these organometallic species. This suggests that the manifold ofreactionsunder aerobic conditions differs from that under anaerobic conditions.  Table 4.9  Pseudo first order rate constants for the reaction of Rh(por)(Cl)(CH3CN) with PPh a n d C O i n C H 2 C l 2 . a  3  run  [Rh]  [L]  XHPM  XIQSM  0  0  kobs  lip.  S-  S  1  Rh(TMP)(Cl)(CH3CN) data at 536 nm: 9 10 11  2.10 " "  135^ 540b 1080b  9.23  0.075  12  1.00  135b  8.94  0.078  13  2.10  ~360b  9.79  0.071  135  9.09  0.076  ~360b  9.73  0.071  Rh(OEP)(Cl)(CH CN) data at 552 nm: 3  14  2.53  15  "  a  a. The R values for the ln(A-Aoo) vs.timeplots were 0.999; at 25 °C. b. L = PPh . 3  c. L = CO; reagent solution saturated with CO at 1 atm and 25 °C (sect. 2.2.8).  4.4.  General Discussion Under anaerobic conditions, Et3N readily replaces L in Rh (por)(Cl)(L) species to form m  the Rh (por)(Cl)(Et3N) complex. Reduction of R h to Rh follows, although the exact nature of ni  m  n  the electron transfer mechanism has not been elucidated. Certainly an enamine is formed in CH2CI2 indicating that dehydrogenation of the Et3N has occurred, and, at least in CH2CI2, probably via a net two-electron oxidation of the Et3N with concomitant loss of protons (observed by *H nmr spectroscopy). The Et3N would weaken the binding of the trans CI ligand and create -  an incipient electrophilic centre at Rh. The [Rh (OEP)] cation is a potent electrophile (21), and in  +  so a concerted CI* loss and electron transfer from Et3N to [Rh^Xpor)]"" forming Rh (por), arninyl 1  n  radical and presumably ejecting HCI (reactions 4.1-4.3, p. 131) is reasonable. In aromatic solvents, the same mechanism is bebleved to lead to [Rh(OEP)]2 in the OEP system but, in the case of the TMP system, formation of Rh(II) is not favoured because of the low polarity of the solvent  152 and because dimerization of Rh (TMP) is not possible. The formation of [Rh(OEP)]2 is believed n  to stabilize the Rh(U) product relative to the initial Rh(III) complex in aromatic solvents and so drive the reduction of the Rh(in). The Rh(por)(CH(Me)NEt2) product subsequently forms slowly by reaction of Et3N with Rh (por) (reactions 4.5-4.6, p. 131), and these slower reactions n  drive the reduction of Rh(IU) in the TMP system in aromatic solvent A major driving force for both TMP and OEP systems through the reduction step in CH2CI2 is believed to be the formation of Rh-C bonds (le., Rh(por)(CH2Cl)), because both the TMP and OEP systems show comparable reactivity in this solvent in contrast to the situation in aromatic solvents. Formation of a strong Rh-C bond is believed to be a large part of the driving force for other systems involving Rh (por) reactants (sect. 1.5.2 and 1.5.4). n  The dealkylation of Et N to give Et2NH is inferred to occur principally by acid 3  hydrolysis of the free enarnine (152) formed by the net oxidative dehydrogenation of Et2N during the reduction of RhODT) to Rh(H), rather than via a metal-centered process observed in nonporphyrin systems (148,155,156). The dealkylation appears to be stoichiometric and not catalytic under the conditions used, due to the preferential coordination of Et2NH to Rh(por)(Cl) relative to coordination of Et N; thus, further reduction cycles are inhibited. In aromatic solvents, a 3  secondary source of Et2NH is the oxidation of Rh(por)(CH(Me)NEt2) but the Rh(por)(CH2CHO) co-product is stable, and this source evidendy is not important when Et N and Rh(OEP)(Cl)(H20) 3  are reacted together in the presence of air in benzene, this forming principally Rh(0EP)(Cl)(Et2NH). The low yield of Rh(por)(CH2CHO) in this srobic reaction, and the inhibition by air of the decomposition of Rh(OEP)(Cl)(Et N) indicated by the stopped-flow data, 3  suggest that the Rh-centered reactions studied under anaerobic conditions do not directly relate to the mechanism of the aerobic reaction. In the absence of O2, Rh(por)(CH(Me)NEt2) is stable in aromatic solvents. Admission of O2, or air, causes its rapid removal and formation of Rh(por)(CH2CHO) (reaction 4.8). The mechanism is not obvious, and [O] is used to represent the unknown oxidant species. RhDI(por)(CH(CH )NEt2) + [O] 3  — Rh (por)(CH CHO) + HNEt m  2  2  (4.8)  The ultimate source of aldehydic oxygen must be O2, and a RhH(por) species is probably involved as the "carrier". The [Rh (OEP)J2 dimer, and a probable Rh complex in the TMP n  n  system, were present before reaction with O2. The [Rh (TPP)]2 dimer is known to react with dry n  O2 in toluene to form Rh(TPP)(02) (42,151) and similar species may be involved here; however, in the presence of excess H2O the total amount of [Rh (OEP)]2 present was unchanged while the n  oxidation still proceeded. This latter observation is consistent with the synthetic route to [Rh(OEP)] , which involves reacting arefluxing toluene solution of Rh(OEP)(H) with air (78), 2  and appears to depend upon the presence of H2O (sect 3.3). This investigation of the reaction of amines with Rh(por)(Cl)(L) has revealed several novel organometallic products as well as information on mechanistic aspects. At the sametimeit is clear that many components of the mechanism are not known. The trialkylamines, triethylamine and tributyhmine, are capable of rapidly reducing Rh(OEP)(a)(H20) to [Rh(OEP)]2, and the investigation has focused on the triethylamine reaction, but dimethylamine (Chapter 2), diethylamine, aniline, N-methyl-diphenylamine and N-ethyl piperidine all form complexes of the type Rh(OFJ )(a)(amine) (Table 4.1). The secondary amines and aryl substituted amine >  complexes do not rapidly undergo intramolecular redox processes, although Proton Sponge™, an arylamine, does reduce the Rh(HI) to Rh(JJ); this reaction might be driven by formation of the cyclised oxidized amine product, the trimethyldihydroperiruidinium cation (155), although this possibility was not investigated. The range of complexes studied is too narrow to detect meaningful trends, although it is evident that, except for Proton Sponge, only tertiary amines with a N-CH2- moiety, which is required for formation of the imme/enamine product were effective reductants (157). As judged by oxidation potentials (157a) and photoelectron ionization potentials (157b) the aliphatic tertiary amines should be more easily oxidised in reversible one-electron systems than the corresponding secondary amines. This is in contrast to an Fe(por)(Cl) system where the presence of a secondary amine functional group is required for the oxidation (158).  154  Chapter 5 Characterization and chemistry of Rh (por) phosphine complexes ni  5.1.  Introduction In Chapter 3 of this thesis, PPI13 was used as a ligand and substrate to probe the reaction  of Rh(OEP)(H) with O2. In addition, the investigation and development of metaUoporphyrin chemistry (often utilising tertiary phosphine ligands) as it relates to catalysis involving small molecules such as Q2, CO and H2, are of particular interest to our group, although much of our focus involving mono- and bidentate phosphines has been on ruthenium porphyrin chemistry (138,139,159-164). At the inception of the work described in this chapter, coordination of tertiary phosphine to a RhfXfl) porphyrin superoxide complex at low temperature (76), and the reaction of P(OMe)3 with [Rh(OEP)]2 had been reported (42). During the course of the present work, electrochemical and ligand substitution studies of the superoxide complex (44) and some Rh (TPP)(R)Q?R3) complexes have appeared (77), as well as the syntheses of some cationic ni  Rh(ni) bis-phosphine and phosphite complexes (32). In this chapter, the characterization of Rh(OEP)(Cl)(PPh3) and its solution molecular structure are presented, as well as preliminary solution data on the bis-phosphine cations [Rh(OEP)(L)2] , where L is PPI13 or PCBute. The latter complexes are of interest because +  isoelectronic ruthenium (IT) porphyrin complexes containing tertiary phosphines as axial ligands have a key role in catalytic decarbonylation of aldehydes (162), and oxidation of phosphines by molecular oxygen (139). The in situ formation of Rh(OEP) complexes of some diphosphines (dppm, dppe, dppp and dppb) is also discussed, while some data on corresponding complexes of Ru(H) porphyrins (161,165) are reinterpreted. Some of the data on the Rh(OEP)(Cl)(PPh ) and [Rh(OEP)(L)2] (L = PPh or P( Bu) ) n  +  3  3  systems have been published (75). The chloride complex was isolated by Dr. T. Leung of our group and limited *H and P{H) nmr and visible spectral data collected by he and K. Menon. 31  l  3  155 The chloride complex was characterized by S. Ariel using X-ray crystallography. An alternative preparation (see sect. 2.1.5.3., method A inref.75) and the solution studies were performed by myself. 5.2.  Results and Discussion  5.2.1. Reaction of Rh(OEP)(CI)(PPh ) with monophosphines 3  The non-ionic cMorotriphenylphosphine complex Rh(OEP)(Cl)(PPh3) remains 6-ccordinate in solution. Beefs Law was obeyed over the range (0.9-8.0) x 10 M in benzene -4  solution, in the dark. The *H nmr spectra of solutions at 10" -10- M (Table 5.1) are consistent 3  2  with the presence of a diamagnetic Rh (OEP) species, that is asymmetrically substituted with m  regard to the porphyrin plane, i.e., two different axial ligands are present causing the - C H 2 resonances to appear as an ABX3 multiplet (138-141). There is no evidence for free phosphine in solutions of Rh(OEP)(Cl)(PPh3), and the visible spectrum (Table 5.2) is unaffected by addition of CP. Coordination of a single PPh3 is shown by integration of the o-, m- and p-protons which are shifted upfield from their normal positions by the strongring-currentof the porphyrin (164,166). Further, the solid-state visible spectrum (Nujol, Table 5.2) shows absorption maxima that correspond closely to those measured in solution. Addition of PPh3 or P Bu3 to the complex in polar solvents ( C H 3 C N , CH2CI2, diethyl n  ether, DMA)resultedin formation of cationic bis-phosphine complexes,reactions(5.1) and (5.2). K  Rh(OEP)(Cl)(PPh ) + PPh === [Rh(OEP)(PPh )2]+ + CP 3  (5.1)  3  3  Rh(OEP)(Cl)(PPh3) + 2P Bu —»~ [Rh(OEP)(PnBu3)2] + CP + PPh +  n  3  3  (5.2)  The nmr spectroscopic evidence was cleanest for the reaction with P Bu3. Upon addition n  of two equivalents of phosphine to CD3CN or CD2CI2 solutions of Rh(OEP)(Cl)(PPh3), theH l  nmr spectrum of Rh(OEP)(Cl)(PPh3) wasreplacedby a new set of signals due to [Rh(OEP)(P Bu3)2] (Table 5.1). The methylene protons of the ethyl side chains appear as the n  +  expected quartet, due to coupling with the adjacent - C H 3 group, while the upfieldresonancesdue to coordinated P°Bu3 were in a 2:1 equivalent ratiorelativeto the porphyrin.  156 Table 5.1. NMR spectral data for Rh(OEP) complexes of monodentate phosphines and other axial ligands. 3  complex  *H  -CH2-  meso-H  Rh(OEP)(Cl)(PPh )  9.96 s  [Rh(OEP)(PPh ) ]  9.93 sb 10.06 sb 9.74 s  3  +  b  b  3 2  -CH3  o-  3.58 m 6.42 m 6.84 m  4.09 m, 3.95 m 1.94 t 3.93 m 1.901 3.96 q 1.88 1  3.62 m 6.39 m 6.82 m -3.9 m^ 6.28 m 3.45 m 6.38 m 6.85 m 2  [Rh(OEP)(P Bu ) ] 10.31 sb +  3 2  10.24 s  c  Rh(OEP)(Cl)(CO) 10.36 s Rh(OEP)(Cl)(THF) 10.31 s.g f  f  31  P{ H}  r>  4.10 m, 3.97 m 1.91 t  -CH n  m-  - C H - - C H - -CH 2  2  4.17 q  1.921  -3.51m  -1.93 m  0.06 m  0.181  4.15 q  1.941  -3.55 m -1.92 m  0.07 m  0.2 m  4.22 m 4.20 m  2.001 1.941  5(lJ .p)  ]  Rh  Rh(OEP)(Cl)(PPh )  9.56d(124)b 9.61 d (124)c 9.05 d(116)  3  h  [Rh(OEP)(PPh ) ]  -2.32 d (86) -2.1 d (83)'  +  c  3 2  [Rh(OEP)(P Bu ) ] n  3.76 d (81)b  +  3 2  a. 300 MHz for H ; 121.421 MHz for P{ lH} and at 20 °C unless otherwise noted. b. InCD CN. ]  31  3  c. d. e. f. g. h. i.  InCD Cl . In C6D ; 80 MHz for H, at 30 °C. Overlaps with - C H - proton shifts. Formed in situ (see text) in THF-d8Formed in situ by dissolving Rh(OEP)(Cl)(H 0) in THF-dg. In C H8; 32.21 MHz for 3lp{ lH}, at 30 °C. In DMA; 32.21 MHz for P{ H}, at 30 °C. 2  2  l  6  2  2  7  31  1  3  Table 5.2. Visible spectral data at 25 °C for Rh (OEP) complexes. m  complex  solvent  Rh(OEP)(Cl)(PPh ) 3  [Rh(OEP)(PPh ) ]+c 3 2  Rh(OEP)(Cl)(C»)d  Soret  (e)*  (nm)  (rvHcm' )  (nm) (M^cnr ) (nm) (M^cnr )  CoHe  422  158 000  533  21 000  563  24 000  CH2CI2  417  135 000  529  19 000  560  23 400  Nujol THF DMA  418  Rh(OEP)(a)(THF)  (e)  a  1  1  b  529 20 000  562  b  530  561  CH3CN  b  528  17 800  560  22 500  CH2CI2  430  537  18 500  568  13 000  C6H6  409 411 b  CH CN  10 600  526 158 000  525  d  3  400 b  CH2CI2 d  alpha  3  564  THF  3  1  (e)  535  CH2CI2  Rh(OEP)(Cl)(CH CN)  beta  THF  22 000  557 16 500  557  526  557  521 518 517  552 550 549  14 800  27 400  26 300  a. ±5%.  b. Soret region not exarnined. c. In situ formation, in the presence of added 6.75 x 10 M [Rh] and 1.96 x IO M -4  -2  [ Bu4N][C10 ]. n  4  d. In situ formation from Rh(OEP)(Cl)(H20). Reaction (5.2) was also monitored by P{ to} nmr spectroscopy, free PPh being 31  3  clearly observed. An excess of PPh (to ~10 M) was required for in situ formation of _1  3  [Rh(OEP)fJPPh )2] , which was observable by to and P{ to} nmr spectroscopy of CD2CI2 +  31  3  solutions (Table 5.1).  The conductance of a CH CN solution of Rh(OEP)(Cl)(PPh ) after 3  3  addition of PPh rose to a limiting value of 125 Q" cm mol , consistent with formation of a 1:1 1  2  -1  3  electrolyte (167). Stronger binding of P"Bu relativeto triarylphosphines has beenreportedfor 3  158 Ru (0EP) and Ru (TPP) complexes (166) and was accounted for by the higher basicity of the n  n  trialkylphosphines (169). Formation of mixed PPI13 /P Bu3 or Rh(OEP)(Cl)(P Bu3) complexes was not evident by n  n  nmr. Also, the ionic bis-phosphine complexes were not formed at all in toluene or benzene solution. The more polar CH2CI2 (e » 9) or CH3CN (e « 36) were required to promote reactions (5.1) or (5.2). Reactions (5.1) and (5.2) could also be monitored by visible spectroscopy. Addition of phosphine resulted in aredshift of the Soret and visible bands (Table 5.2) with a marked diminution of the a band (Fig. 5.1). On the basis of theresultsin this chapter, these fmdings are to be consistent withreplacementof chloride by an additional phosphine ligand. A corresponding reverse blue shift of the spectrum of Ru(OEP)(P Bu3)(S) (S = DMSO or CH3CN) compared with n  that of Ru(OEP)(P Bu3)2 has been noted previously (166). n  5.2.2. Solution equilibrium measurements Equilibrium (5.1) was studied quantitatively using visible spectroscopy, following qualitative observations on the inhibition of the forward reaction in the presence of added chloride. The same isosbestic points (Fig. 5.1) were observed during a spectrophotometrictitrationwith PPh3 at a given temperature, or during variation of temperature over the range 10-30 °C at any chosen [PPh3]. Indeed the latter type of experiment allows for a rapid estimation of Kob as a S  function of temperature using just a single solution; such values were used to calculate Kob . S  Ambient light was excluded during sample manipulations by using dimmed room lighting and by covering all exposed surfaces with black plastic tape. Aliquots (uL) of IO* M PPh3 in 1  CH2CI2 (alternatively solid PPh3) were added to dilute solutions (~5 x 10 M) of -4  Rh(OEP)(Cl)(PPh3) in CPPiCh- Formation of [Rh(OEP)(PPh3)2] within seconds was evidenced +  by a red shift of the Soret from 419 nm to 429 nm, and the P and a bands from 529 nm to 537 nm and 560 nm to 568 nm,respectively,with a concomitant decrease in the intensity of the a band relative to the P band (Fig. 5.1). Measurements were also performed on solutions containing various amounts of [Ph4As]Cl, [ Bu4N]Cl or [ Bu4N][C104] to exainine the effect of ionic n  n  500  550  600  Wavelength (nm.)  Figure 5.1.  Spectroscopic titration of Rh(0EP)(Cl)(PPh3) with added P P h in CH2CI2 at 3  25 ° C , [Rh] = 8 x IO" M ; curves 0-5 result from added [PPh ] of 0.0, 0.38, 4  3  1.09, 2.69, 5.01 and 7.18 x I O M , respectively. 6 shows the spectrum of - 2  [ R h ( O E P ) ( P P h ) ] (formed at [PPh ] = 5 x I O ' M and (I = 0.02 M ) . +  3  2  2  3  strength and [CI]. No changefromthe initial spectrum of the complex was noted on addition of -  the chloride salts to Rh(OEP)(Cl)(PPh3). The value of K was found using visible data (at 560 nm) obtained using different combinations of initial concentrations of Rh(OEPXCl)(PPh3) (Co), and added CI" (CLj) and PPI13 (Po)- By defining A and A Q as the absorbances measured at 560 nm with and without added PPh , and eo and e« as the extinction coefficients of Rh(OEP)(Cl)(PPh ) and [Rh(OEP)(PPh )2] , +  3  3  3  equation 5.3 may be derived (see Appendix C for derivation, 1 = pathlength):  (5.3)  The £o (23 400 M" cm ) and e« (6 500 M" cm ) values were available experimentally 1  -1  1  -1  because the limiting spectra of Rh(OEP)(Cl)(PPh3) and [Rh(OEP)(PPh3)2] for the equilibrium +  could be measured under readily attainable conditions (high [CI"] with no added phosphine, and high [PPI13] and ionic strength with no added CI", respectively). Because ionic species are involved, the thermodynamic equilibrium constant (K) will be a function of the mean ionic activity coefficient (y±) and the experimental equilibrium constant (Kobs, see Appendix D for raw data)  (5.4)  where y± is defined by the Debye-Huckel limiting law logio Y± Az+z. =  (5.5)  The value of K was deterruinedfromthe intercept of login Kobs plotted vs. u*/ at a 2  particular temperature. Figure 5.2 shows such a plot for the data at 25 °C (Table 5.3), and, for the data at  < 0.07 M ^ , the line drawn gives an intercept corresponding to login K = -1.75 (K = 1  2  1.74 x IO ). The slope of the least squares line drawn (of slope -2Az+z. or +2A for this -2  particular equilibrium) is 26.88. The calculated value for the slope using the standard expression (eq'n (5.6)) for A is 26.7, showing remarkably good agreement. (2TW)1/V  e  2  (5.6)  2.303 ^lOafcT^  where N = Avogadro's number, e = electronic charge, £ = dielectric constant (8.90 for CH2CI2 at 25 °C), = the Boltzmann constant, and T = absolute temperature. 0300  -2.000  l1 1 1 l1 0.020 0.040  1 1 1  0.000  1  l1 1 1 l1 1 1 l1 0.060 0.080 0.100 0.120 l/2 l / 2 1 1 1 1 1 u  Figure 5.2.  1  l1 1 1 0.140 0.160 1  M  Plot of logio Kobs vs. (ionic strength)^ for data in Table 5.3. 1  2  Thennodynamic parameters for equihbrium (5.1) were obtained repeating the equilibrium measurements Gogio Kobs vs. \L fy l  at four other temperatures over the range of 10-20 °C. Values  of K (temp) are 3.27 x IO" (10 °C), 2.62 x IO" (15 °C), 2.02 x IO" (20 °C), and 1.28 x IO 2  2  2  -2  (30 °C) (see Appendix D for raw data). The data give a good van't Hoff plotfromwhich values of AH (-33 ± 2 kJ mol") and AS (-146 ± 8 J K^moH) were estimated. 0  1  0  162  Table 5.3. Variation of Kobs for reaction 5.1 in CH2a2 at 25 °C. Hx lO^M  Kobs x 10  2.16  3.91  2.26  4.06  2.97  4.77  3.11  6.29  3.45  6.06  4.05  6.65  4.50  6.44  4.88  5.83  5.94  8.53  6.49  8.28  6.74  8.13  64.8  a  2  49.9^  179.1  114c  181.5 195.9  136 86.2e  202.6  239  d  f  a. Up to u\ = 6.74 x IO" M, the ionic strength results solely from the ions generated by reaction 4  5.1, i.e., no salt has been added. Initial [Rh(0EP)(Cl)(PPh3)] between (4.0-8.0) x IO" M. 4  The estimated uncertainity in Kobs is ± 5% or better and in \i is ± 2.5% or better unless otherwise noted. b. Added 6.48 x 10-3 M [Ph4As]Cl-H 0. 2  c. Added 1.79 x IO M [Ph4As]Cl-H 0; Kobs ± 7%. -2  2  d. Added 1.82 x IO" M [Ph4As]Cl-H20; addition of H2O to 2 x IO" M had no measurable effect 2  2  on the equilibrium reaction. e. Added 1.96 xl0- M[ Bu4N][ClO ]. 2  n  4  f. Added 2.03 x l(r M [Ph4As]Cl-H 0. 2  2  The net rapid substitution reaction (5.1) almost certainly occurs via a dissociative process and a 5-coordinate intermediate, reactions (5.7), (5.8). The overall K value (= K1K2) shows that a  The netrapidsubstitution reaction (5.1) almost certainly occurs via a dissociative process and a 5-coordinate intermediate, reactions (5.7), (5.8). The overall K value (= K1K2) shows that a [PPh ] of-0.2 M is required to convert 90% of Rh(OEP)(Cl)(PPh3) (initially at - 5 X 1 0 " M) into 4  3  [Rh(OEP)(PPh ) ] at 25 °C. +  3 2  K,  Rh(OEP)(Cl)(PPh ) =  [Rh(OEP)(PPh)]+ + CP  3  (5.7)  3  K  2  [Rh(OEP)(PPh )]+ + PPh 3  [Rh(OEP)(PPh ) ]  (5.8)  +  3  3 2  The stoichiometric conversion with P Bu implies that the equilibrium constant for (5.2) n  3  is > 10 at coiresponding conditions. The large negative AS value (-146 J mol" K" ) for reaction 3  0  1  1  (5.1) is reasonable for transformation of neutral species into solvated charged ones. Chloride is expected to form a stronger bond than PPh to Rh(III), and thus the overall exothermicity (-33 kJ 3  mol ) of the forward reaction presumably results from contributions of the solvation enthalpies of -1  the product ions. 5.2.3. Reactions of Rh(OEP)(Cl)(PPh ) with CO 3  Under dark (thermal) conditions (see below), CH C1 solutions of Rh(OEP)(Cl)(PPh ) 2  2  3  do not react with 1 atm CO (~5 x 10" M), implying that CO at this concentration cannot compete 3  for [Rh(OEP)(PPh )] with the back reaction of equilibrium (5.7), even though the [CI"] must be +  3  very low since Ki is immeasurably small. At an added [PPh ] of about 5 x 10" M, reaction (5.1) 3  3  with Rh(OEP)(Cl)(PPh ) (-5 x 10 M) would generate -35% of the bis-phosphine cation. This 4  3  implies that K (reaction (5.8)) is much smaller for CO addition than for PPh . Isoelectronic with 2  3  [Rh(OEP)(PPh )] , the neutral isolated Ru(OEP)(PPh ) species reacts more readily with CO +  3  3  (139,162,164,166), presumably because the better 7t-acceptor properties of CO (vs. PPh ) (170) 3  are more compatible with the lower oxidation state of Ru(IT). The lack of reaction with CO also indicates negligible dissociation of PPh under these conditions to form Rh(OEP)(Cl), which is 3  known to react with CO to form Rh(OEP)(Cl)(CO) (82) (see below), reactions (5.9) and (5.10): Rh(OEP)(Cl)(PPh ) 3  Rh(OEP)(Cl) + CO  Rh(OEP)(Cl) + PPh  3  Rh(OEP)(Cl)(CO)  (5.9) (5.10)  164  The Rh(0EP)(Cl)(PPh3) complex in benzene, THF or C H 3 C N , however, is photochromic in the presence of 1 atm CO, and reacts according to reactions (5.9) and (5.10). Exposure to light or sunlight yields within minutes an in situ carbonyl ( v c o = 2087 cm in THF) -1  with concomitant release of PPI13, and the nmr data (Table 5.1) are consistent with the presence of Rh(OEP)(Cl)(CO). Quantitative re-formation of Rh(OEP)(Cl)(PPh3) occurs in the dark (under CO) over a few hours via the intermediate Rh (OEP) (CI) (solvent) species (as judged by comparison with the visible spectrum of Rh(OEP)(Cl) dissolved in the appropriate solvent). Solutions of Rh(OEP)(Cl)(PPh3) in THF or C H 3 C N on exposure to hght in the absence of CO also yield the  Rh(OEP)(Cl)(solvent) species. The visible spectral data are given in Table 5.2. The noted reversible carbonylation-decarbonylation reaction, in the daylight and dark, respectively (somewhat atypical in that the decarbonylation process is often photo-assisted), is of potential interest as a further model for solar energy storage in biological systems (171). The *H and P{ H} nmr data for all the species (Table 5.1) show shifts that are typical 31  }  for diamagnetic, octahedral, metallo-porphyrin complexes (161,165,166), and the magnitudes of the JjRh-p coupling constants are appropriate for octahedral Rh(IIT) products (172). 5.2.4.  Reactions of Rh(OEP)(Cl)(H 0) with diphosphines 2  Diphosphines (PP) are known to bind to Ru(II) porphyrins in (i) a monodentate dangling fashion, (ii) a bridging mode between two metal centers, or, (iii) more speculatively, in a bidentate mode on one metal center to form a "seven-coordinate" species (161,165). The data presented below for similar Rh(ffl) species are obtained on in situ samples usually formed bytitrationof a solution of Rh(OEP)(Cl)(H20) with aliquots typically containing -0.2 equivalents of dppm, dppe, dppp or dppb, or by preparation of solutions containing various ratios of diphosphine to Rh(0EP)(Cl)(H20). The solubility of the systems decreased with increasing diphosphine carbon chain length and as the ratio of [diphosphine] to [Rh] increased; presumably oligomeric and polymeric [(-PP-[Rh(OEP)] -PP-) ]Cl complexes are formed and some data on such species are +  n  n  presented below. The diphosphines acting as monodentate ligands readily form Rh(OEP)(Cl)(PP) and [Rh(OEP)(PP)2] complexes, analogous to those formed by PPh3. The H nmr spectra of +  J  solutions of Rh(OEP)(Cl)(PP) at 10-3. io-2 M (Table 5.4) are consistent with the presence of a diamagnetic metaUo-octaethylporahyrin complex, that is asymmetrically substituted with regard to the porphyrin plane. The -CH2- *H nmr resonances of the free diphosphine ligands on coordination are shifted up-field by the porphyrin ring current (Table 5.4), as are the resonances of phenyl protons (Table 5.5), the phenyl protons of the free end of the dangling PP being less affected as the carbon chain lengthens. The 3lp{ lH} nmr resonances (Table 5.4) of the free end of the dangling phosphine are found at higher fields than the free ligand. However, the influence of the ring-current is perhaps obscured by superposition of a variation of 8 values that may be related to the carbon backbone chain length (Fig. 5.3). The 31p{ lH} nmr spectra of the dppm and dppe ligands show AMX patterns for the Rh bound end but the4JRh-p coupling for the angling end of dppe was too small to observe,resultingin an AX pattern although that of dppm was AMX. Phosphorus-phosphorus coupling is not observed for dppp or dppb, and thus only an AX pattern is observed for the Rh bound ends. The ^Rh-p couplings of all four PP complexes are close to that of Rh(OEP)(Cl)(PPh ). 3  The methylene protons of the ethyl side chains of the symmetrically substituted [Rh(OEP)(dppm)2] complex appear as the expected quartet and the dppm *H nmr ligand +  resonances are in a 2:1 ratiorelativeto the porphyrin (Tables 5.4 and 5.5). The *H nmr spectral resonances of the dangling diphosphine ligands are similar to those of the Rh(OEP)(Cl)(PP) complexes but the 31p{lH} nmr spectrum shows more complex AA'MM'X sph'ttings (Fig. 5.4). This partem is believed to arise because of virtual coupling between the Rh bound phosphorus on one side of the metal center and the dangling phosphorus on the opposite side (i.e., A with M'), making the chemically equivalent Rh bound phosphorus nuclei magnetically inequivalent. The neutral, isoelectronic, Ru (TPP)(dppm)2 complex displays arelatedAAXX' pattern of two n  triplets at 11 ppm (Ru-P) and -29 ppm (-P) in CDCI3 (161), and thus the Rh-P inequivalence of the Rh(III) complex is not believed to be due to ion-pairing. The cationic [Rh(OEP)(dppm)2]  +  complex can be observed by nmr in CfPs (Table 5.4 and Fig. 5.5) where it must exist as a tight ion-pair and this, in principle, could introduce asymmetry into the complex, but the P{ fH} 31  spectra in C6D6 and CDQ3 are nearly identical and thus effects due to ion-pairing are not obvious.  166  Table 5.4. Various H and P{ *H} nmr spectral data for Rh(OEP) complexes of monodentate diphosphines. 31  l  8  complex  *H  meso-H  Rh(OEP)(Cl)(dppm) Rh(OEP)(Cl)(dppe) Rh(OEP)(Cl)(dppp)  -CH-?  -CH 2  10.00 s 3.92 m, 3.73 m 1.811 9.99 s 3.94 m, 3.82 m 1.861 10.05 s 3.97 m, 3.83m 1.88 t 10.01 s 3.93 m, 3.77m 1.84 t  Rh(OEP)(Cl)(dppb) [RhCOEPJCdppm^]* [RhtOEPXdppm)^ 4  31P{1H)  9.70 s  3.88 q f  10.05 s  1.75 t f  P-CH - -CH -  -CH - - C H -  b  2  2  2  2  -2.22 d -2.75 m -0.75 m —2.7 m --1.3 m ~0.6 m -3.00 m -1.44 m 0.01 m 0.68 m -2.87 t  5  -2.48 te  8(J): Rh-P  dangling-P  Rh(OEP)(Cl)(dppm)  16.00 dd (^Rh-p = 117; J . = 35)  -31.50 dd ( JRh-p - 3; 2jp. = 35)  Rh(OEP)(Cl)(dppe)  18.64 dd (^Rh-p = 118; J . = 33.3)  -14.22 d ( J . = 33.3)  Rh(OEP)(Cl)(dppp) Rh(OEP)(Cl)(dppb) [Rh(OEP)(dppm) ]« [Rh(OEP)(dppm) ]+d  14.62 d ( JRh-p = 116) 15.03 d( JRh-p= 117) 6.05 dtg 6.68 dt  -22.54 s -18.18 s -31.69tS -30.551  2  P  P  3  P  3  P  P  !  1  2  2  3  P  P  a. The Rh(OEP)(Cl)0?P) complexes were made in situ by mixing 1:1 ratio of PP to Rh in C6D6 (see text); 300 MHz for *H; 121.421 MHz for P{ *H} at 20 °C. 31  b. Only the diphosphine methylene resonances are listed; see Table 5.5 for phenyl proton resonances. c. InCDCl3. d. Prepared in situ by rnixing 3:1 ratio of PP to Rh. e. Triplet is barelyresolvedas shoulders on central signal. f. Overlapped by otherresonances(see text). g. Estimated coupling constants: 2  JPA-PM  (PM-C-PA-RII-PA'-C-PM') ^Rh-Px ~  ~ 34 Hz, 2 J . . ~ 100 Hz, 'jp^p* ~ 20 Hz. Pa  Pa  120 Hz, JRh-PM ~ -2 Hz, 3  167  Table 5.5. Various H nmr spectral data for the phenyl protons of monodentate diphosphine ligands in RJh(OEP) complexes. ]  3  complex  Rh-P(Ph)2-  dangling-P(Ph)2  p-  m-  o-  Rh(OEP)(Cl)(dppm)  6.34  6.01  3.65  Rh(OEP)(Cl)(dppe)  6.48  6.14  3.68  Rh(OEP)(Cl)(dppp)  6.47  6.15  6.50  6.22  3.7b c  6.68  5.88  3.23  Rh(OEP)(Cl)(dppb) [Rh(OEP)(dppm) ]  +e  2  p_-  m6.70  b  6.84  f> 6.20  6.74  6.48 c  d  d  d  6.96  6.81  6.13  -6.8  a. In C6D6, unless otherwise stated; 300 MHz at 20 °C; all resonances are multiplets. b. Overlapped by - C H 2 - resonances of ethyl side chains, assigned using COSY. c. Overlapped by other resonances. d. Overlapped by free dppb. e.  IJ1CDCI3.  1  2  3  Number of carbons Figure 5.3.  Variation of P{ H} nmr 5-Ofree shifts for the PP ligand of Rh(OEP)(Cl)(PP) with 31  !  the chain length of the diphosphine backbone. Data for Rh bound P( • ) and dangling P (Q) are shown.  168  free dppm  -i  1  —r~  -30  -P:  -31  Rh-P  20  10  Figure 5.4.  0  T 8p  r  -10  p m  T  -20  T  -30  The P{ H} nmr spectrum of [Rh(OEP)(dppm)2] in CDCI3 at 20 °C. Prepared 31  l  +  in situ under Ar, [Rh] = 10" M, [dppm] « 3 x IO" M. 2  2  1 = [Rh(OEP)(dppm)]X 2 = Rh(OEP)(Cl)(dppm) 2  Rh-P 2  free dppm  Rh-P  -P:  1  -1  18  80  Figure 5.5.  1 1 1  r T9  15  T  60  The P{ 31  1 1  T  r  7  T  5  T  T  40  r  20 8ppm  0  1 1 1 r  -30  -20  -40  -32  T  -60  nmr spectrum of a C6D6 solution of Rh(OEP)(Cl) in the presence of  -2.4 equivalents of dppm at 20 °C. Prepared under Ar.  Clear identification of cationic bis-phosphine complexes with dppe, dppp or dppb in C5D6  is obscured by the increasing complexity of the nmr spectra during thetitrationsin this  solvent, and only for dppm is simple formation of mono- and bis-phosphine complexes observed as [PP] is increased. In some of these solutions (e.g., with ~1 equivalent dppb), P{ H) nmr 31  l  resonances indicative of Rh-bound phosphine similar to the bis-phosphine cations were found in conjunction with other P{ H) and *H nmr resonances corresponding to those of the bridging 31  l  species discussed below, but without evidence for the corresponding dangling phosphine. This is suggestive of ion-paired species such as "[Cl-Rh(OEP)-ndppb-Rh(OEP)-^dppbRh(OEP)(Cl)]Cl". Addition of 0.5 equivalents of diphosphine to solutions of Rh(OEP)(Cl) usually leads to formation of [Rh(OEP)(Cl)]2-|iPP complexes as the major species. The *H and P{H} nmr data 31  1  on the complexes are summarized in Table 5.6. The P{ ^H} nmr spectra are characterized by a 31  lack of resonances for a dangling phosphine. The spectra of the dppm and dppe systems show similar 6-line AA'XX' patterns, because of magnetic inequivalence of the phosphorus nuclei due to coupling across the bridging phosphine and so an AX pattern is observed. The chain length of the dppp is too long for P-P or Rh-P coupling across the backbone. The cumulative effect of the ring currents of two porphyrins causes the -CH2- *H nmr resonances of the diphosphines to be shifted further up-field than those observed for the dangling phosphine complexes. The meso resonances are also slightly shifted from the values for the dangling species, and the methylene resonances of the ethyl side-chains (at least within the puippm species) are well separated as expected for a species with cofacial porphyrins (e.g. like [Rh(OEP)]2) (78). The dppm phenyl proton resonances are particularly affected by steric crowding enforced by the close proximity of the porphyrins. At -10 °C, a number of small broad *H nmr resonances in the 7 to 0 ppm range are shown by a COSY experiment to be two sets offiveinterrelated resonances (Fig. 5.6). These are assigned as p>dppm phenyl protons, each multiplet being 2H based on integration of the I D spectrum, and are in a 1:2 ratio with the set of shifted porphyrin resonances just mentioned. The ligandH nmr resonances l  are broad above room temperature but the P{H} nmr AAXX' pattern remains at temperatures 31  l  up to 44 °C and the respective 'JRH-P couplings in mixtures of Rh(OEP)(Cl)(dppm) and  170 Table 5.6. Various *H and P{ ^H) nmr spectral data for Rh(OEP) complexes containing bridging diphosphines. 31  8  complex  *H  [Rh(OEP)(Cl)]2-udppm [Rh(OEP)(Cl)] -udppe [Rh(OEP)(a)] -Hdppp 2  2  [Rh(OEP)(Cl)]-^idppb 2  31p{lH)  -CH -  meso-H 9.73 s 9.29 s 9.77 s 9.64 s  2  -CH  P-CH - -CH - -CH - -CH b  3  4.07 m, 3.88 m 1.76 t 3.44 m 1.55 t 3.81 m 1.76 t 3.66 m, 3.49 m 1.46 t  2  2  2  2  -5.37 t -5.60 s -4.26 m c -4.27 m -2.85 m  S(J): Rh-P  [Rh(OEP)(Cl)]2-udppm  11.41 m*  [Rh(OEP)(Cl)] -udppe  17.56 m  [Rh(OEP)(Cl)] -udppp  16.67 d (jRh-p = 117)  2  2  1  d  a. C6D ; 300 MHz for *H; 121.421 MHz for 31p{ lH} at 20 °C. 6  b. Only the diphosphine methylene resonances are listed. c. Overlapped by P-CH2-.  d. 6 fines. Estimated coupling constants: (Rh-PA-C-PA'-Rh) 2  ^Rh-Px  ~ 120 Hz, JRJ,.P . ~ -2 Hz, 3  a  JPA-PA~34HZ.  [Rh(OEP)(Cl)]2-ltdppm remain at 84 °C; thus dppm is only slowly exchanged between the two species. However, the ratio of their respective meso proton integrations varies reversibly with temperature, consistent with an equilibrium involving the two species. A possible conformation that satisfies two sets of pair-wise equivalences of phenyl protons is shown in Figure 5.7, where the porphyrins are nearly parallel. The Aringprotons show shifts to more higher field than the corresponding dangling phosphine complex (Table 5.5) due to the effect of two porphyrin ringcurrents, and the Bringprotons show both up- and down-field relative shifts due to their additional mutualring-currenteffects. The rxjrphyrin - C H 2 - proton resonances of the (Xdppm species appear as two multiplets. The lowerfieldmultiplet broadens more than the higher field multiplet as temperature increases and probably represents the "inside" environment between the porphyrins.  Figure 5.6.  The COSY spectrum of a C7D8 solution of [Rh(OEP)]2-p:dppm at -10 °C. The long and short dashed lines connect the two sets of udppm phenyl protons (i.e: 2 sets of 5 multiplets of 2H per multiplet labelled as in Fig. 5.7).  172 porphyrin planes ; nearly parallel,  Figure 5.7.  Sketch of a possible conformation for dppm in [Rh(OEP)]2-p.dppm.  Thetitrationsof Rh(OEP)(Cl)(H20) with the diphosphines could be monitored also by visible spectroscopy, at [Rh] = 5 x 1(H M. Figure 5.8 illustrates the changes of the P and a bands after addition of 0.54,0.9 and 2.0 equivalents of dppm to Rh(OEP)(Cl) in CH2CI2. The spectra of  CH2CI2  solutions after addition of 0.9 and 2.0 equivalents are very similar to those of  Rh(OEP)(Cl)(PPh3) and [Rh(OEP)(PPh3)2] , respectively, and are most probably those +  corresponding to the respective diphosphine analogues. The spectrum of the Rh(OEP)(Cl)(H20) complex is completely removed by addition of ~0.5 equivalents of dppm, and the resulting spectrum is different from those of the mono- and bis-diphosphine complexes, being therefore attributable to the [Rh(OEP)]2-|idppm complex. A similar progression is observed in C6H6 but only to the mono-bisphosphine. The relatively clean step-wise progression through the |idppm, mono- and bis-dppm species is in accord with the nmr data. Isosbestics at 530, 548 and 563 nm are observed in the 500-600 nm region during the addition of the first to second equivalent of dppm, but varying the temperature of an intermediate spectrum (i.e., 1.4 equivalents; presumably giving a mixture of Rh(OEP)(Cl)(dppm) and [Rh(OEP)(Cl)(dppm)2] ) gave a different set of isosbestics at 559, 562,569 and 578 nm, the +  a band intensities of the equilibrated species diminishing together as the temperature increases.  0—\  1  i  i  i  500  i  1  1  i  1  550  600  wavelength (nm)  Figure 5.8.  Spectroscopic titration of Rh(OEP)(Cl)(H20) with added dppm in CH2CI2 at 25 °C, [Rfi] = 7.25 x 1(H M; curves 0-3 result from added [dppm] of 0.0, 0.5, 0.9, 2.0 equivalents, respectively.  The a band of the [Rh(OEP)(Cl)]2-p-dppm complex is at 560 nm and thus the changes observed are probably due to a equilibrium between the ndppm, mono- and bis-dppm complexes (reactions (5.11) and (5.13)). [Rh(OEP)(Cl)(dppm)2] + Ch +  Rh(OEP)(Cl)(dppm) + dppm  Rh(OEP)(Cl)(dppm) = ^ Rh(OEP)(Cl) + dppm Rh(OEP)(Cl)(dppm) + Rh(OEP)(Cl) =  (5.11) (5.12)  [Rh(OEP)(Cl)] -ndppm 2  (5.13)  The observation of nmr coupling across the dppm and dppe bridges, but not dppp, provides a useful probe of communication between the porphyrins of the bridged species. A related question is whether the length of the bridge also affects the electronic spectrum of the chromophore, i.e., the porphyrin, in comparison to the spectrum of the mono-PP species, and indeed the visible spectrum of the p:dppm and mono-dppm complexes differ (vide infra). Data in the 500-600 nm region taken duringtitrationsof Rh(OEP)(Cl)(H20) with dppe or dppp reveal that the visible spectra of the solutions after addition of 1 equivalent of PP are very  174 similar for both systems and are similar to that of the Rh(OEP)(Cl)(dppm) species; all are probably Rh(OEP)(Cl)(PP) species, the 3 species having P bands at ~530 nm and the a bands -560 nm in C6H6. However, although the nmr data show fairly clean step-wise addition of dppe to Rh(OEP)(Cl)(H20) to form the udppe species with addition of up to 0.5 equivalents of dppe, and then the mono-dppe species at -1 equivalent added dppe, the visible data show only the superposition of the spectra of Rh(OEP)(Cl)(H20) and Rh(OEP)(Cl)(dppe) over the whole range of added dppe. In the dppp system, the visible spectrum of Rh(OEP)(Cl)(H20) is completely removed by the addition of 0.5 equivalents of dppp, being replaced by a spectrum similar to that of the Rh(OEP)(Cl)(dppp) species (531 nm p band, 561 nm a band). Addition of a further 0.5 equivalents resulted in little change to the spectrum This suggests that the spectrum of [Rh(OEP)(Cl)]2-udppp is the same as that of Rh(OEP)(Cl)(dppp) and that there is no effect on the chromophore at that chain length. The visible data for the dppe system do not reveal the spectrum of the udppe species because it appears that such a species is not detectably formed at the concentration used for the visible titration ([Rh] = 2.38 x 10" M) which is -10timesmore dilute 4  than that used for the nmr titration experiments. Attempts were made to isolate the u-dppm complex, as its spectroscopic data suggested that it was the most stable and cleanly formed in the series. Unfortunately, attempts to precipitate the complex from its solutions gave mixtures of free diphosphine (as colourless crystals), starting material and the bridged complex. Isolation byfreeze-dryinga benzene solution of the u-dppm complex prepared by careful titration gave an impure material. 5.3.  General Discussion The findings on reactivity of the PPI13 complexes can be summarized as shown in  Scheme 5.1. Phosphine ligation of Rh(OEP)(Q)(PPh3) with loss of CI in a thermal reaction is -  mermodynamically favoured relative to ccrasponding CO ligation. However, reactivity toward CO with loss of PPh3 (even in the presence of excess PPh3) is enhanced by "forcing" the system through an unsaturated intermediate generated photochemically. These equilibria are of particular relevance to the reactions of M(por)L,2 complexes (M = Fe, Ru; L = phosphine, CH3CN, THF  175 etc.) with gas molecules such as CO and O2, that also go via a dissociative mechanism (159,160, 162,173-182). M(por)(L)2 i M(por)L S M(por)(gas)(L) +L -gas  (5.14)  Enhancement of the concentration of the 16-electron, 5-coordinate complexes is probably important in a catalytic context, such as decarbonylation of aldehydes which might proceed via the M(por)(CO)L species (159,160,178-180). In this regard, preliminary data indicate that phenylacetaldehyde can be used as a carbonyl source, instead of CO gas, to form Rh(OEP)(Cl)(CO) from Rh(OEP)(Cl)(PPh ). For example, a THF solution containing 7 x 10- M Rh(OEP)(Cl)(PPh ) 4  3  3  and excess aldehyde (~0.2 M) slowly generates at 20 °C a solution of Rh(OEP)(Cl)(CO) as judged by visible spectroscopy data, although organic co-products were not tested for.  Rh(OEP)(Cl)(solvent)  -solvent , +solvent  +CO , -CO  Rh(OEP)(Cl) -PPh  Rh(OEP)(Cl)(CO)  +PPh  3  Rh(OEP)(Cl)(PPh ) 3  -PPh,  [Rh(OEP)(PPh )2] „ +PPh 3  +  -CT  +cr  +2P Bu [Rh(OEP)(PPh )] — [Rh(OEP)(P Bu ) ] n  3  +  w  n  3  +  3 2  3  Scheme 5.1. Reactivity scheme for solutions of Rh(OEP)(Cl)(PPh ). 3  The use of diphosphines introduces novel possibilities besides the formation of monodentate complexes analogous to the PPh and P Bu species. Scheme 5.2 summarizes the n  3  3  transformations observed during thetitrationexperiments. In particular, the formation of udiphosphine inetaUo-porohyrin complexes is established, although this finding is not unprecedented, a singlet at 3.7 ppm in the P{ 41} nmr spectrum of a CDC1 solution of a 1:1 31  3  176  Ru(OEP)(CO)(EtOH)/dppe mixture at -20 °C being ascribed to a u-dppe species (165). The correspondingH nrnr spectrum contained a peak at -5.76 ppm which was tentatively ascribed to l  the -CH2- group of the dppe ligand of a seven-coordinate species; thisH resonance is probably l  better assigned to the udppe ligand by comparison to data for the Rh analogues (Table 5.6).  Rh(OEP)(Cl)(H 0) t ° * - 0.5 PP 5  Rh(OEP)(Cl)-uPP-Rh(OEP)(Cl)  P  2  0.5 PP  + 0.5 PP  Rh(OEP)(Cl)(PP) + oligomers [Rh(OEP)(PP) ] y + oligomers + polymers +  2  Scheme 5.2.  - PP  +  p o l y m e r s  + (-PP-[Rh(OEP)]-PP-) Cl n  n  Formation of various rhodium diphosphine complexes.  The propensity of the longer chain diphosphines to form oligomers and polymers has been noted before with Ru(II) porphyrins (161). The benzene solubility of some of the cationic Rh(III) species is surprising. The solubilizing ability of the diphosphines perhaps Hes in stabilization of ion-pairs because the dangling diphosphines, or porphyrin oligomer, contain a suitably dimensioned pocket, for the CI' anion, containing the positively charged Rh center. Additionally, dangling phosphines may simply enhance the solubility of the porphyrin species sufficiently to compensate for the unfavourable solvation energetics. Tertiary phosphines with long chain alkyl substituents are used to enhance the solubility of Rh, Pd or Pt organometallic species in organic solvents (119).  Chapter 6 General conclusions and suggestions for further work  The work in this thesis comprised research into the reactions of some small molecules with various Rh(por) species. The original motivation was to probe the formation of MOOH from the reaction of a metal hydride with O2, the metal in this instance being Rh. Some comments as to the direction of future work are also presented. The reaction of Rh(OEP)(H) with O2 in organic solvents was examined by visible, *H and P{ H] nmr spectroscopy as a candidate system for the net insertion of O2 into the metal31  l  hydride bond. The products of the room temperature reaction in dry benzene were [Rh(OEP)]2 and H2O, but nmr data for a thermally unstable Rh (OEP)(OOH)(H20) intermediate were m  obtained at -40 °C in CD2Q2. Under other conditions, uncharacterised species were observed along with some Rh(OEP)(OH). The system was clearly too sensitive to impurities under the conditions used. The more hindered TMP may be a better possibility, principally because formation of Rh-Rh bonded dimers is prevented. Because of synthetic difficulties only small quantities of Rh(TMP)(H) were prepared, and preliminary studies of the reaction of O2 with the hydride gave contradictory results. The addition of PPI13 to CH2CI2 solutions of Rh(OEP)(H) promoted a rapid minor reaction involving the solvent giving Rh(OEP)(Cl)(PPh ), Rh(OEP)(CH Cl)(PPh3) and 3  2  [Rh(OEP)(PPh3)2] in -20% yield, the other major reaction product being the hydride +  Rh(OEP)(H)fPPh3). Addition of O2 to these solutions appeared to promote further the solvent reaction to the extent that the Rh(OEP)(Cl)(PPh3) and Rh(OEP)(CH2Cl)(PPh3) became the major species (in equimolar amounts) in solution, without concomittant formation of OPPh . The 3  formation of Rh(OEP)(CH2Cl) by reaction with the solvent appears to involve a Rh (OEP)(PPh3) n  species because [Rh(OEP)]2 and, by implication, Rh (OEP) do not react with CH2CI2 at n  comparable rates. In benzene solution there was evidence that attack by the Rh center on the phenyl ring of the P P h 3 occurred.  178 The sensitivity of the reaction of Rh(OEP)(H) with O 2 to initial conditions, and the observation of products containing Rh(TJ) and Rh-CH C1, suggest a radical mechanism, which is 2  consistent with known Rh-H chemistry. MtiationAermination: 2Rh(OEP)(H) ^  [Rh(OEP)] + H 2  [Rh(OEP)] ^  (6.1)  2  2Rh(OEP)-  2  (6.2)  and in the presence of PPI13 [Rh(OEP)] + PPh 2  -Rh(OEP)(PPh ) + Rh(OEP)-  3  (6.3)  3  Propagation: Rh(OEP)- +  *s=^ Rh(OEP)(0 )  (6.4)  2  Rh(OEP)(02) + Rh(OEP)(H)  ^ Rh(OEP)(OOH) + Rh(OEP)-  (6.5)  [Rh(OEP)] + H 0 + \ O2  (6.6)  Termination: Rh(OEP)(OOH) + Rh(OEP)fH)  2  2  and in the presence of PPh  3  •Rh(OEP)(PPh ) + CH C1 3  2  2  Rh(OEP)(Cl)(PPh ) + -CH C1 (6.7) 3  2  Rh(OEP)- + -CH C1 - r — - s - Rh(OEP)(CH Cl) 2  (6.8)  2  Of interest was the effect of H 0 on the reaction of Rh-H with O2 and the formation of 2  [Rh(OEP)] as a product A stabilising effect on [Rh(OEP)] by excess H 0 when 0 was present 2  2  2  2  was also observed during the investigation of the reaction of Et N with Rh(por)(Cl). The presence 3  of PPh , a Lewis base, did not promote formation of the dimer under similar conditions. Clearly 3  the preliminary mechanism presented does not adequately address the effect of Lewis bases and H 0 on the mechanism. The equilibrium behaviour of Rh(H) species (monomeric and dimeric) is 2  central to the chemistry of rhodium porphyrins, and investigation of the effects of steric hindrance (i.e., using TMP to prevent (limerisation), Lewis bases and protic reagents (i.e., H 0) is of 2  interest.  The mechaxiisms of the reactions of some tertiary alkylamines (principally Et N) with 3  Rh (por)(a)(L) (por = OEP or TMP, L = H2O or iPrOH) were explored. The formation of m  [Rh (OEP)]2 species under mild conditions was observed with some amines, and several novel n  organometallic derivatives of Et N have been found. A portion of the tertiary amine was 3  oxidatively dealkylated to the dialkylamine. Detailed spectroscopic examination of the interaction of Rh(por)(Cl)(L) with Et3N revealed a complex manifold of reactions. The interaction gave products, identified by visible spectroscopy (scanning and stopped-flow) and H nmr J  spectroscopy to be Rh(por)(CH(Me)NEt2), EtsNH as Rh(por)(Cl)(Et2NH), and PJi(por)(CH CHO). This indicated amine C-H and C-N bond cleavages and net 1-electron 2  reduction of RhfJH) to Rh(TJ) species ([Rh(OEP)J2). Of other amines examined, aniline, Nmemyl-diphenylamine and N-ethyl piperidine all formed complexes of the type Rh(OEP)(Cl)(amine), although the N-ethyl piperidine complex decomposed within 24 h. Proton Sponge and tributylamine gave [Rh(OEP)]2 as a major product under anaerobic conditions and, with the latter amine, the Rh(OEP)(Cl)( Bu2NH) complex was also observed. n  Stopped-flow data showed that EtsN initially replaced L of the Rh (por)(Cl)(L) species m  to form a Rh (por)(Cl)(Et3N) complex. An equilibrium involving reduction of R h to Rh m  m  n  resulted and in aromatic solvents, under anaerobic conditions, slow reaction of Rh (por) with Et N n  3  proceeded to give Rh(por)(CH(Me)NEt ). The formation of Rh(H) was inhibited in the presence 3  of the competing donor ligand CH CN, and also when the porphyrin was TMP. Thus it appears 3  that formation of [Rh(OEP)]2 provids the driving force in the OEP systems, while there is no comparable driving force in the TMP system because steric hindrance prevented dimer formation. In CH2CI2, reaction of EfjN with Rh(por)(Cl)(L) was fast, giving a mixture principally of Rh(por)(CH2a)(amine) and the T^-ylidic enamine complex, Rh(rx>r)(Cl)(CH2CH=NEt2) with minor mounts of Rh(por)(CH(Me)NEt ) being formed, irrespective of the porphyrin used. The 3  formation of Rh(por)(CH d) species for both TMP and OEP could provide a similar driving force 2  for both systems unlike for the chemistry of aromatic solvents. The solutions containing Rh(por)(Cl)(CH CH=NEt2) or Rh(por)(CH(Me)NEt ) complexes, ultimately form 2  3  Rh (por)(Cl)(Et2NH). The bulk of the Et2NH formed was probably from the acid hydrolysis of ffl  180 the free enamine, itself formed from the net 2-electron oxidation of Et3N via an aminyl radical. The data also show that there was a requirement for an oxidant (i.e., air or O2) to produce at least some of the C-N cleavage products (Et2NH and Rh (por) (CH2CHO)), while oxidation after formation of Rh(OEP)(CH(Me)NEt2) led to more Rh(OEP)(CH2CHO) than when air was present initially, when Et3N reacted with Rh(OEP)(Cl)(H20). Thus the reaction sequence suggested from the investigation of the anaerobic systems is believed not to be the same as that of the purely aerobic system. The O atom in the stable Rh (OEP) (CH2CHO) species appeared to be from the added O2. Coordination of the Et2NH product to Rh (por)(Cl) to form Rh(OEP)(a)(Et2NH) probably m  prevented catalytic dealkylation under the conditions used. Enough mechanistic information about the alkylamine reaction has been extracted to provide a useful framework from which more definitive studies can be undertaken in the future. The non-metal containing products need defining, as well as the less well characterised Rh-R and Rh(H) species, before kinetic analysis. There is potential for a number of interesting VT nmr spectral studies of the conformations (and associated thermodynamics) of ligands bound to Rhffl(TMP). The to nmr spectra of Rh(TMP)(Cl)(Et NH), Rh(TMP)(Cl)(CH Cl2) and 2  2  Rh(TMP)(CH(Me)NEt2) were particularly temperature dependent, and the activation parameters for the associated processes need determiiiing. The solution behaviour of Rh(TMP)(Cl)(L) and Rh(TMP)(Cl)(solvent) versus the less hindered corresponding OEP complexes is interesting from the point of view of possible local modification of solvent structure by formation of a "solvent-free cavity" if twofive-coordinateRh (TMP)(L) species associate in solution. In addition, the effects m  of size and/or Lewis acid/base behaviour may be distinguishable (Table 2.8, p. 66). The solvation data will be particularily important in the context of the direct reaction of H2 with Rh(por)(Cl) species to give Rh(por)(H), possibly via a dihydrogen complex precursor, reaction in both solution and solid state has been observed and it will be interesting to see if die hydride formation occurs via an intermolecular or intramolecular (Le., H-atom tunnelling) process. The synthesis, along with characterisation by visible, to and P{ to) nmr 31  spectroscopy, of the mono-phosphine complex Rh(OEP)(Cl)(PPh3) are presented. Additionally, spectroscopic evidence is presented for solution equilibria of Rh(OEP)(Cl)(PPh3) involving  formation of Rh(OEP)(L)2 (L = PPI13, P Bu3> via thermal reactions, and Rh(OEP)(Cl)(L') (L = +  1  n  CO, THF, CH3CN) via photochemical processes. Thermodynamic data (AH = -33 ± 2 kJ mol" 0  1  and AS = -146 ± 8 J K^mor ) have been estimated for the formation of the 0  1  bis(triphenylphosphine) species in CH2CI2 (reaction (6.9)). K  Rh(OEP)(Cl)(PPh3) + PPh ==^ [Rh(OEP)(PPh3)2]+ + CI"  (6.9)  3  Some complexes of Rh (OEP) containing dppb, dppe, dppm and dppp have been ffl  characterised in situ using visible, to and P{ to} nmr spectroscopy. The (phosphines bind to 31  Rh(DT) porphyrins in a monodentate dangling fashion (Rh (OEP)(Cl)(PP) and m  [Rh (OEP)(PP)2] ), or in a bridging mode between two metal centers ([Rh (OEP)(Cl)]-uPP+  m  m  [Rh (OEP)(Cl)]). 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Ch. 16.  Appendix A Rhodium porphyrin organometallics literature data summary Table A.l. Rh (por)(R) species (R = hydrocarbyl), and methods of their synthesis. m  3  -R  precursor  0  OCC H 6  alkylating reagent  Rh(IH) Rh(IH)  5  C6H5  Rh(ni)  P-C6H4CH3  Rh(ni)  CH=CH2 U-(-CH=CH-) cis-CH=CHC6H5 trans-CH=CHC6H5 U-(-CH=C(C H )-)  Rh(I) Rh(U) Rh(I) Rh(I) Rh(H)  CH3  Rh(?)  6  +  Rh(IU)  fi  5  LiOCC6H5 C6H5L1 C6H6  +  P-CH3C6H4U C6H5CH3 HCsCH ti  HC=CC6H5 trans-BrHC=CHC6H5 ti  ?  d  CH3I  Rh(I)  e  ti  Rh(ffl)  CH3Li  Rh(I) Rh(IIT) Rh(?) RhCT/ Rh(m) Rh(HI) Rh(IH) Rh(m) Rh(IH) Rh(II) Rh(U) Rh(II) Rh(I) Rh(H) Rh(H) Rh(II) Rh(U) Rh(H) Rh(H) Rh(I) Rh(U) Rhfl) Rh(II) Rh(I) Rh(II) Rh(I) Rh(U) Rh(I) Rh(H) Rh(I)  CH3I C2H5U  f  f  C2H5 ti  U-(-CH CH -) 2  1  2  11-C3H7 n-C4H9  11-C5H11  n-C Hi3 6  11-C9H19  CH CH=CHC6H CH2CH=CHC3H 2  5  7  CH2C6H5 11  P-CH2C6H4CH3 IT1-CH2C6H4CH3  CH2CH(CH3)C6H5 ft  CH2CH2C6H5 "  CH2CH2CH2C6H5 rt  CH(C6H )CH n 5  3  CH(C H )CH CH3 6  5  2  ft  CH(CH3)CH2C6H5 ti  C7H9 C7H11  ?  d  Rh(I)  BrCH2CH2Br  n-C3H7Li n-C4H9Li  n-C5HnLi  n-C6Hi Li n-C9H]9Li CH2=CHCH2C6H CH2=CHC4H9 BrCH2C6H5 3  5  CICH2C6H5 C6H5CH3 P-CH3C6H4CH3 IT1-CH3C6H4CH3  CH CH2(CH3)C6H CH =C(CH3)C H 3  2  6  5  5  CH3CH2C6H5 CH2B1CH2C6H5 CH3CH2CH2C6H5  CH2BrCH2CH2C6H  5  CH3CH2C6H5 CH3CHB1C6H5 CH3CH2CH2C6H5 CH3CH2CHB1C6H5 CH3CH2CH2C6H5 CH3CHB1CH2C6H5 CH3CH=CHC6H5 quadricyclane  [4.1.0.0 '7]tricycloheptane 2  product ref 0  y,F  1 1  y,s y.F y.s y,F y,F y.F y.s y.F y.s y.F y.F y.F y.F y.s y.s y.F y.F y.F y.F y.F y.F y.F y.F y.s i.S i.S i.S i.S i.S i.S y.s i.S y.s i.S y.s i.S y.s i.S y.s i.S y.F y.F  2 1 2 1 3 1 1 3 4 5 1 1 1 4 4 1 1 1 1 1 3 3,6 3 7 7 7  7 7 7  7 7 7 7  7 7 7 7 7 7 7 8  8  193 a.  OEP, unless stated otherwise.  b.  Rh(I) = [RtfCpor)]-; Rh(JJ) = [Rh (por)] ; Rh(JJr) = Rh (por)(X), Rh(III) = n  m  +  2  [Rh (por)]+; Rh(H) = Rh(por)(H). m  c.  y = isolated; i = prepared in situ; F = fully characterised (spectroscopy and elemental analysis); S = spectroscopically characterised.  d. TPP. e.  MeDME.  f.  Also isolated as Rh (OEP)(CH3)(B), B = 4-CH3-py, py, 4-CN-py (ref. 1).  1.  H. Ogoshi, J. Setsune, T. Omura and Z. Yoshida. J. Am. Chem. Soc. 97, 6461 (1975).  2.  Y. Aoyama, T. Yoshida, K. Sakurai and H. Ogoshi. Organometallics, 5,168 (1986).  3.  H. Ogoshi, J. Setsune and Z. Yoshida. J. Am. Chem Soc. 99, 3869 (1977).  4.  B.B. Wayland, S.L. Van Voorhees and C. Wilker. Inorg. Chem. 25,4039 (1986).  5.  Y. Aoyama, K. Aoyagi, H. Toi and H. Ogoshi. Inorg. Chem. 22, 3046 (1983).  6.  Z. Yoshida and H. Ogoshi. Japan. Kokai 77 59,199 (1977).  7.  K.J. Del Rossi and B.B. Wayland. J. Am. Chem. Soc. 107, 7941 (1985).  8.  H. Ogoshi, J. Setsune and Z. Yoshida. J. Organomet. Chem. 185, 95 (1980).  m  Table A.2. Rh (por)Q^) species containing heteroatoms, and methods of their synthesis. m  3  -R  precursor  15  CH2CH2NH2HCI CH2CH=CHCN CH2CH2CN CH=NBu tl  CH2OH  Rh(I) Rh(II) Rh(I) Rh(H) Rh(II) Rh(H) Rh(H) Rhcirr/ RbfJDO) RhCQT/ d  ti  CH2OCH3 CH(OCH3)C02C2H5 n CH(OCH2C6H5)C02C2H5 CH(OAc)CX>2C2H5 C(CX)2C2H5)=CH2 CO2C2H5 C(C02CH3)=CH 2  it  Rhcnr/  3  tt  1  It  1  RhCDT/ Rh(m)  d  N2CHCO2C2H5; bzOH N2CHCO2C2H5; AcOH N2C(C02C2H5)CH3 N2C(C02C2H5)CH3 N C(C02CH3)CH3 N C(C02CH3X:H3 N2C(C02CH3)CH3 N2C(CO2CH3)CH2C02CH3 (CH2CH2P CH3CHO CH3CH2CHO C6H5CHO e  1  Rh(m)  2  Rhorr/ RhCDT/ Rh(m) Rh(I) Rh(H) Rh(H) Rh(H)  1  d  product  ref  y.F y.F y.F  l 2,3 4 5 5 6 7,8 9 9 9 9 9 9 9 9 9 9 9 1 10 10 10  2  y.s y.s  CH2N2; MeOH N2CHCO2C2H5; MeOH  1  CO2CH3 C(C02CH3)=CHC02CH3 CH2CH2OH CH(CH )OH CH(C2H5)OH CH(C6H5)OH  (CH2CH2)NH CH2=CHCH2CN CH2=CHCN BuNC BuNC, H2O CH2O  1  1  RhfW  alkylating reagent  2  e  y.s y.s y.F y.F y.F y.F y.F y.F y.F y.F y.F y.F y.F y.F y.s i.S i.S  194 precursor  2 (cont'd) -R CH2CH(OC2H )2 5  rt  CH2CHO  f  rt ti n  CH2C(0)CH3 rt  CH(C(0)CH3)2 CH(C(0)CH3)C(0)C2H CH2CH2CH2C(0)CH3 C7H90-exo C7H10CO2CH3 CH2CH2CH2CO2CH2CH3 m-C6H4C02CH3 P-C6H4CO2CH3 P-C6H4OCH3 5  ti  CH2I  alkylating reagent  0  Rh(I) Rh(IU) Rh(U) RhCQT)  C1CH2CH(0C2H5)2 CH2=CHOC2H5, NEt CH2=CHOC H CH2=CHOC2H5, NEt3; H  Rh(I) Rh(H) Rh(ni)+ Rh(IH)g  C1CH2CH(0C H5)2; H HOCH2CHO; H+ CH3C(0)CH3 CH C(0)CH  Rh(ni) Rh(nr) Rh(I) Rh(T) Rh(I) Rh(I) Rh(ni)  CH (C(0)CH )2 CH (C(0)CH )C(0)C2H5 C H C(OX:H3 nortricyclanone h C3H5CO2CH2CH3 C6H5CO2CH3  3  2  3  +  Rh(ni)+ Rh(]U) RhG or II?) Rh(HI)  C(0)C Hn 5  5  n  Rh(IU) Rh(IU)  C(0)CH2CH2CH20H CHO  3  3  +  Rh(ni) Rh(IH) Rh(IU)  5  3  2  ti  P-C6H4CI CH=CHC1 CH=C(C6H5)C1 C(0)CH C H 6  +  +  3  2  +  d  2  5  2  d  tt  product  +  "  C6H5OCH3 LiC6H50CH3 CH I CH2N2 C6H5CI HC^CH HC=CC6H5 "; H 0 HC=CC4H9; H2O HC=CCH2CH20H; H2O CO, KOH 2  2  2  Rh(m)  Rh(IU) Rh(U)  d  ti  ti  CO, H2O CO, H CO CO.H2 CO, H2 2  Rh(H) Rh(H) Rh(H)  d  d  0  y.s y.F y.F y.F y.F i.S y.s y.s y.s y.s y.F y.F y.F y.F y.F y.F y.F y.F y.s y.F y.F y.F y.F y.F y.F y.F i.S i.S y,s y.s y.s i.S i.S J  ref 11 11 11, 12 11 11 13 14 15 14 •14 1 1 1 1 16 16 16 17 6 9 16 11 11 11 11 11  18 18 5 5 19 20 20  a-d. As in Table A.2. e.  Excess reagent  f.  Also isolated as Rhni(OEP)(CH CHO)(B) (B = py, PPh ); ref. 13.  g.  por = cis- and trans-5,15-bis(2-hydroxy-l-naphthyl)-octaethylporphyrin, tetrakis(2-hydroxy-  2  3  phenyl)porphyrin, trans-5,15-di(8-quinolyl)octaethylporphyrin. h.  l-methoxycarbonyl[4.1.O.O^ltricycloheptane.  i.  Including single-crystal X-ray diffraction.  1.  H. Ogoshi, J. Setsune and Z. Yoshida. J. Organomet. Chem. 185, 95 (1980).  2.  H. Ogoshi, J. Setsune and Z. Yoshida. J. Am. Chem. Soc. 99, 3869 (1977).  195 3.  Z. Yoshida and H. Ogoshi. Japan. Kokai 77 59,199 (1977).  4. 5. 6. 8. 9.  H. Ogoshi, J. Setsune, T. Omura and Z. Yoshida. J. Am. Chem. Soc. 97 6461 (1975). B.B. Wayland, B.A. Woods and R. Pierce. J. Chem. Soc. 104, 302 (1982). B.B. Wayland, S.L. Van Voorhees and C. Wilker. Inorg. Chem. 25, 4039 (1986). S.L. Van Voorhees and B.B. Wayland. Organometallics, 4, 1887 (1985). HJ. Callot and E. Schaeffer. Nouv. J. Chim. 4, 311 (1980), HJ. Callot and E. Schaeffer. J. Chem. Soc. Chem. Commun. 937 (1978). 10. B.B. Wayland, B.A. Woods and V.M. Minda. J. Chem. Soc. Chem. Commun. 634 (1982) . 11. H. Ogoshi, J. Setsune, Y. Nambo and Z. Yoshida. J. Organomet. Chem. 159, 329 (1978). 12. Z. Yoshida and H. Ogoshi. Japan. Kokai 77 59,200 (1977). 13. B.B. Wayland, S.L. Van Voorhees and K.J. Del Rossi. J. Am. Chem. Soc. 109, 6513 14. 15. 16. 17. 18.  19. 20.  (1987). Y. Aoyama, T. Yoshida and H. Ogoshi. Tet. Lett. 26, 6107 (1985). Y. Aoyama, A. Yamagishi, Y. Tanaka, H. Toi and H. Ogoshi. J. Am. Chem. Soc. 109, 4735 (1987). Y. Aoyama, T. Yoshida, K. Sakurai and H. Ogoshi. Organometallics, 5, 168 (1986). J. Setsune, T. Yazawa, H. Ogoshi and Z. Yoshida. J. Chem. Soc. Perkin I, 1641 (1980). B.B. Wayland, A. Duttaahmed and B.A. Wood. J. Chem. Soc. Chem. Commun. 142 (1983) . B.B. Wayland and B.A. Woods. J. Chem. Soc. Chem. Commun. 700 (1981). B.B. Wayland, S.L. Van Voorhees and C. Wilker. Inorg. Chem. 25, 4039 (1986).  Table A.3. Rh (EP)(R) species prepared from the "out-of-plane" Rh(I) complexes. m  -R  alkylating reagent  product  CH3I CH3SO2F  y.F y.F y.F y.F y.F y.F y.F  CH3 II  CH2CH3 TI  CH2CH2CH2CH3 C6H5 n  CH3CH2I CH3CH2SO2F CH3CH2CH2CHCHO C6H5CHO (C6H C(0))20 5  n  C6H Br  Tt  C6H5I p-BrC6H4CN p-BrC6H4F  y.s y.s  5  P-C6H4CN P-C6H4F  CH(CH )C(0)C6H5 CH C(0)C H CH2CH CH2C(0)-p-C6H4F CH C(0)C6H CH2C(0)-2-furyl 3  2  3  5  2  2  5  CH CH C(0)C6H5 CH C(0)C H p-FC H4C(0)C3H5 CH C(0)C6H CH3C(0)-2-furyl 3  2  3  3  5  6  3  3  5  y.F y.F y.F y.F y.F y.F y.F  ref 1, 2 1 1 1 3,4 3,4 5, 1 4 3 3 3 3,5 3, 5 3,5 3, 5 3  196 A.3 (cont'd)  -R  C(0)CH3 n n tt C(0)CH2CH3 tt tt C(0)CH2CH2CH3 C(0)C6H5 tt ft n tt n C(0)-p-C6H4F CO2CH2CH3 tt CO2CH2CH2CH2CH3 CO2C6H5 tt  alkylating reagent  product  CH3I CH3SO2F CH3CO2H (CH CO)20 CH3CH2I CH3CH2SO2F (CH3CH2CO)20 (CH3CH2CH2CO)20 C6H5CHO C6H5CHO C6H5C(0)C1 (C6H5C(0))20 C6H5Br C6H5I p-BrC6H4F CH3CO2CH2CH3 BrCH2C02CH2CH3 HCO2CH2CH2CH2CH3 HCO2C6H5 CH3CO2C6H5  y.F y.F y.s y.F y.F y.F y.F y.F y.F y.F y.F y.F y.s y.s y.F y.F y.F y.F y.F y.F  3  8  ref 1.2 1 1 5, 1 1 1 5,1 5,1 3,2 3 5, 1 5,1 4 3 3 3 3 3 3 3  a.  y = isolated; i = prepared in situ; F = fully characterised (spectroscopy and elemental analysis); S = spectroscopically characterised.  1.  A.M. Abeysekera, R. Grigg, J. Trocha Grimshaw and V. Viswanatha. J. Chem. Soc.  2. 3. 4. 5.  Perkin I, 36 (1977). R. Grigg, J. Trocha Grimshaw and V. Viswanatha. Tetrahedron Lett. 4, 289 (1976). A.M. Abeysekera, R. Grigg, J. Trocha Grimshaw and V. Viswanatha. J. Chem. Soc, Perkin 1,1395 (1977). A.M. Abeysekera, R. Grigg, J. Trocha Grimshaw and V. Viswanatha. Tetrahedron Lett. 36, 3189 (1976). A.M. Abeysekera, R. Grigg, J. Trocha Grimshaw and V. Viswanatha. J. Chem. Soc. Chem. Commun. 227 (1976).  197  Table A.4. Rh (TTP)(R) species electrcchernically prepared from Rh (TPP). m  n  -R  n  alkylating reagent  C H2n+l  1 2  CH3I CnH2n+lX(X=Br,I)  n  n  n ti  J ti  «  ft  ti  4 tl  a  ref  tt  H2C=CHC3H7 HOCC3H7 C H2n+lX (X=C1. Br, I) H C=CHC4H9 HC=CC4H9 C H2n+lX (X=F, CI, Br, I) H2C=CHC5Hn HCsCCsHu C H lX(X=?) HOCC Hi3 CH3CH2CH(CH3)C1 (CH3)3CC1 C H2nX2 (X=C1, Br, I) n  2  tl ti  5 n  ti ti  6  ti  it  n  n  2n+  6  CH(CH3)CH2CH3 C(CH ) C H nX (X=C1, Br, I) 3  n  3  2  ti ii  CnH2nI CHX2 (X=C1,1) CX3 (X=C1,1)  a.  1 3 4 5 6  n  n  ti ti  Cn.H2n.l2 CHX3 (X=C1,1) CX4 (X=C1,1)  1 1 1 1 2 2 1 2 2 1 2 2 3 2 1 1 1 3 3 3 3 1 1  Rh (TPP) prepared in situ from le- reduction at -1.20 V (vs. SCE) of n  [Pvh (TPP)(NHMe2)2]Cl in THF, 0.2 M TBAP; products isolated from bulk electrolysis and m  characterized by H nmr in CgE^. }  1.  J.E. Anderson, C. Yao and K.M. Kadish. J. Am. Chem. Soc. 109 1106 (1987).  2.  J.E. Anderson, C. Yao and K.M. Kadish. Organometallics, 6, 706 (1987).  3.  J.E. Anderson, Y.H. Liu and K.M. Kadish. Inorg. Chem. 26, 4174 (1987).  Appendix B Spectral data for Rh(TMP)(Cl)(phosphine)  complexes  Table B.l. The H NMR spectral data for Rh(TMP)(Cl)(phosphine) complexes in !  phosphine -CH= 8.756  PPI13  m,m'-H 7.241,6.879  P-CH3  o,o'-CH3  CoD6.  a  coordinated phosphine  2.391 2.193,1.279  6.377, 6.186, 4.371  2.424 2.637,1.448  -CH - - C H 2 - - C H 2 - -CH -2.440, -1.164, (0.264), 0 . 8 1 4 2  P Bu n  3  ^PQH)  PPh P Bu 3  n  a.  3  8.804  7.273,6.929  3  5(lJ . ) Rh  P  3.2 d (115) 17.8 d (117)  Prepared in situ from Rh(TMP)(Cl)(iPrOH) plus excess phosphine; all singlets and at otherwise, integrations matching assignments, at 300 MHz.  19°C  except where  noted  i99  Appendix C The derivation of equation 5.3  In addition to the existing variables defined for equation (5.3), the following are used in this derivation: C+ = [[Rh(OFJ?)(PPh )2J ], G = [ C P ] , C = rRh(OFJ?)(Cl)(PPh )] and P = [PPh ] +  3  3  3  The expression for Kobs based on equilibrium (5.1) is C+-C1  Kobs  £.p »  =  (C.l)  which can be written in terms of initial concentrations and C, . (C - C)-(C1 + C p - C) obsC - ( P o - C o - C ) The property actually measured is the absorbance at 560 nm, v K  A  0  0  = EolC + EoolC+ ,  r  (  r  9  ^  v }  (C.3)  which again can be written in terms of initial concentrations and C, A = eolC + Eool(Co-C),  (C.4)  and rearranging to obtain the equation C+  =  (A (e  0  (C.5)  A o o )  - Eoo)l  Substitution of equation (C.5) into (C.2) gives the equation used to calculate the values of Kobs,  v  I  L(e - eoo)lJJ I '  L(e -eoc)ljJ  0  l(eo-Eoo)lJl °  0  °  L(e -eoo)lJJ 0  200  Appendix D Tables of K b s for reaction 5.1 at various ionic strengths and temperatures 0  Table D.l. u x 10 M 4  2.76 3.20 3.57 3.89 4.93 5.49  Variation of Kobs Kobs x 10  8.86 10.9 11.6 14.0 16.5 13.0  2  reaction5.1 in CH2CI2 at 10 ° C  f o r  Absorbance 560 nm I baseline  [RbJo x 10  4  a  [PPh ]o x 10 [ C T ] 4  3  0.661 1.038 0.513 0.463 0.745 0.653  0.092 0.109 0.079 0.083 0.108 0.109  4.43 6.29 4.43 4.43 6.29 6.29  54.5 33.5 130 203 114 295  0.704 0.565 0.507  0.083 0.090 0.083  4.66 4.66 4.66  1.404 0.975 0.756 0.625  0.044 0.043 0.055 0.053  0.674 0.550 0.481  b 0  x 10  —  4  [salt] x 10 c  —  — —  —  90.4 220 337  64.8 64.8 64.8  —  8.05 7.67 7.17 6.47  56.8 162.6 303.7 502.1  179.1 179.1 179.1 179.1  0.031 0.032 0.035  5.37 5.37 5.37  127.2 277.3 666.7  181.5 181.5 181.5  64.8 64.8 64.8 avg  107 107 107  179.1 179.1 179.1 179.1 avg  211 232 258 232  181.5 181.5 181.5 avg  312 280 236 282  195.9  157  0.473  0.045  5.15  30.0  202.6 202.6 202.6 avg  473 513 516 501  0.914 0.684 0.518  0.053 0.041 0.053  5.15 5.15 5.15  30.0 76.3 232.8  4  0  107  _ —  233 e  —  e  —  e  —  d  —  202.6 202.6 202.6  195.9  — —  a. Up to n = 6.74 x IO" M, the ionic strength results solelyfromthe ions generated by reaction 5.1, i.e., no salt has been added. Initial [Rh(OEP)(Cl)0?Ph3)] between (4.0-8.0) x lO^M. Pathlength of cell = 0.1 cm. The estimated uncertainity in Kobs is ± 5% or better and in n is ± 2.5% or better unless otherwise noted. b. Added [Ph4As]Cl-H 0. 4  2  c. Added FBu4N][C104]. d. Kobs ±9%. e. Addition of H2O to 2 x 10" M had no measurable effect on the equilibrium reaction. 2  201  Table D.2. U x 10 M 4  Variation of Kobs for reaction 5.1 in CH2CI2 at 15 ° C . Kobs x 1 0  2.59 2.84 3.38 3.77 4.65 5.31 64.8 64.8 64.8  avg  Absorbance 560 nm I baseline  [Rb] x 10 0  4  [PPh ] x IO {Cl-] 4  3  6.98 7.65 8.62 10.8 12.1 10.0  0.689 1.099 0.544 0.482 0.792 0.680  0.091 0.110 0.079 0.083 0.107 0.107  4.43 6.29 4.43 4.43 6.29 6.29  54.5 33.5 130 203 114 295  81.6 84.6 83.1  0.754 0.593 0.535  0.082 0.085 0.083  4.66 4.66 4.66  1.542 1.045 0.796 0.641  0.040 0.039 0.046 0.040  avg 179.1 179.1 179.1 179.1  2  a  0  b 0  x 10  4  [salt] x 1 0 c  _ —  —  — —  —  —  —  —  90.4 220 337  64.8 64.8 64.8  —  8.05 7.67 7.17 6.47  56.8 162.6 303.7 502.1  179.1 179.1 179.1 179.1  —  83.1 128 180 202 188 175  — — —  d  181.5  238  0.729  0.031  5.37  127.2  181.5  f  181.5  230  0.032  5.37  —  195  0.035  5.37  277.3 666.7  181.5  181.5  0.588 0.499  f  181.5  f  —  avg  221  —  e  195.9  128  0.485  0.037  5.15  30.0  202.6 202.6 202.6  372 388 401  0.958 0.739 0.538  0.050 0.040 0.043  5.15 5.15 5.15  30.0 76.3 232.8  avg  4  0  —  202.6 202.6 202.6  195.9  — —  387  a. Up to |i = 6.74 x lCr M, the ionic strength results solelyfromthe ions generated by reaction 5.1, i.e., no salt has been added. Initial [Rh(OEP)(Cl)(PPh3)] between (4.0-8.0) x 10: M. Pathlength of cell = 0.1 cm. The estimated uncertainity in Kobs is ± 5% or better and in u; is ± 2.5% or better unless otherwise noted. b. Added [Ph4As]Cl-H 0. 4  4  2  c. d. e. f.  Added [ Bu4N][C104]. Kobs ±13%. Kobs ±7%. Addition of H2O to 2 x 10" M had no measurable effect on the equilibrium reaction. n  2  202  Table D.3. u x 10 M 4  Variation of Kobs for reaction 5.1 in CH2CI2 at 20 ° C . Kobs x 10  5.24 5.55 6.43 9.02 7.62 8.02  2.37 2.54 3.19 3.61 4.36 5.11 64.8 64.8 64.8  62.4 65.3 64.5  avg 179.1 179.1 179.1 179.1 avg  2  Absorbance 560 nm I baseline  [Rh] x 10 0  4  a  [PPh ] x 10 [ Q - ] 4  3  0  b 0  x 10  4  [salt] x 10 c  4  0  0.724 1.149 0.577 0.508 0.841 0.722  0.089 0.109 0.079 0.082 0.108 0.107  4.43 6.29 4.43 4.43 6.29 6.29  54.5 33.5 130 203 114 295  —  —  0.805 0.635 0.568  0.083 0.086 0.083  4.66 4.66 4.66  90.4 220 337  64.8 64.8 64.8  _ —  1.577 1.117 0.842 0.674  0.038 0.037 0.036 0.036  8.05 7.67 7.17 6.47  56.8 162.6 303.7 502.1  179.1 179.1 179.1 179.1  0.787 0.631 0.523  0.031 0.032 0.035  5.37 5.37 5.37  127.2 277.3 666.7  181.5 181.5 181.5  —  64.1 111 142 158 149 140  181.5 181.5 181.5 avg  182 178 156  195.9  104  0.507  0.038  5.15  30.0  202.6 202.6 202.6 avg  296 300 310  0.994 0.793 0.574  0.044 0.040 0.043  5.15 5.15 5.15  30.0 76.3 232.8  172  —  d  f  —  f  —  f  —  e  —  202.6 202.6 202.6  195.9  — —  302  a. Up to u = 6.74 x 10" M, the ionic strength results solely from the ions generated by reaction 5.1, i.e., no salt has been added. Initial [Rh(OEP)(a)(PPh3>] between (4.0-8.0) x IO" M. Pathlength of cell = 0.1 cm The estimated unceitainity in Kobs is ± 5% or better and in u is ± 2.5% or better unless otherwise noted. 4  4  b. Added [Ph4As]Cl-H20. c. Added [ Bu4N][C10 ]. n  4  d. Kobs ±10%. e. Kobs ±6%. f. Addition of H2O to 2 x IO* M had no measurable effect on the equilibrium reaction. 2  Table D.4.  Variation of Kobs forreaction5.1 in CH2CI2 at 25 °C.  a  U x 10 M  Kobs x 10  4  2.16 2.26 2.97 3.11 3.45 4.05 4.50 4.88 5.94 6.49 6.74 64.8 64.8 64.8 avg 179.1 179.1 179.1 179.1 avg 181.5 181.5 181.5 avg 195.9 202.6 202.6 202.6 avg  Absorbance 560 nm I baseline  2  3.91 4.06 4.77 6.29 6.06 6.65 6.44 5.83 8.53 8.28 8.13 48.8 50.6 50.2 49.9 99.0 114 125 119  [Rh] * 10 [PPh ] x 10 4  0  4  3  0.724 1.149 0.577 1.269 0.508 0.841 , 1.035 0.722 0.792 0.700 0.659  0.089 0.109 0.079 0.037 0.082 0.108 0.037 0.107 0.037 0.037 0.037  4.43 6.29 4.43 7.52 4.43 6.29 7.52 6.29 7.52 7.52 7.52  54.5 33.5 130 38.0 203 114 109 295 269 501 718  0.850 0.678 0.605  0.083 0.085 0.083  4.66 4.66 4.66  1.604 1.186 0.902 0.716  0.038 0.037 0.036 0.036  0.843 0.678 0.550  0  [a-]  b  0  x 10  4  [salt] x 10 c  4  0  _  — —  —  _ — . —  —  —  —  —  —  —  —  90.4 220 337  64.8 64.8 64.8  —  8.05 7.67 7.17 6.47  56.8 162.6 303.7 502.1  179.1 179.1 179.1 179.1  0.032 0.033 0.035  5.37 5.37 5.37  127.2 277.3 666.7  181.5 I81.5 181.5  0.530  0.041  5.15  30.0  1.031 0.844 0.613  0.046 0.040 0.043  5.15 5.15 5.15  30.0 76.3 232.8  —  — — —  114  d  142 139 126 136 86.2 237 236 243 239  —  202.6 202.6 202.6  e  —  e  —  e  —  195.9 — —  a. Up to n = 6.74 x 10" M, the ionic strength results solely from the ions generated by reaction 5.1, i.e., no salt has been added. Initial [Rh(OEP)(Cl)(PPh3) between (4.0-8.0) x lO^M. Pathlength of cell = 0.1 cm. The estimated uncemdnity in Kobs is ± 5% or better and in \i is ± 2.5% or better unless otherwise noted. 4  b. Added [Ph4As]Cl-H 0. 2  c. Added [ Bu4N][C10 ]. d. Kobs ± 7 % e. Addition of H2O to 2 x 10* M had no measurable effect on the equilibrium reaction. n  4  2  204  Table D.5. u x 10 M 4  Variation of Kobs for reaction 5.1 in CH2CI2 at 30 °C.  a  Kobs 10 x  3.04 3.18 3.63  1.98 2.06 2.77 3.28 3.74 4.65  4.69 5.00  4.54  2  Absorbance [Rh] x 10 [PPh ] x 10 [Cl-] x 10 560 nm I baseline 4  0  4  3  0.786 1.228 0.646 0.561 0.943 0.791  0.085 0.107 0.078 0.079 0.106 0.106  4.43  6.29 6.29  54.5 33.5 130 203 114 295  6.29  4.43 4.43  b  0  4  0  —  —  —  —  _  — —  —  —  0.884 0.718 0.644  0.082 0.084 0.083  4.66 4.66 4.66  90.4 220 337  64.8 64.8 64.8  179.1 179.1 179.1 179.1 avg  93.2 93.7 99.2 94.3 95.1  1.617 1.246 0.964 0.762  0.037 0.036 0.036 0.036  8.05 7.67 7.17 6.47  56.8 162.6 303.7 502.1  179.1 179.1 179.1 179.1  0.895 0.732 0.583  0.032 0.033 0.036  5.37 5.37 5.37  127.2 277.3 666.7  181.5 181.5 181.5  0.543  0.033  5.15  30.0  1.048 0.891 0.655  0.040 0.040 0.042  5.15 5.15 5.15  30.0 76.3 232.8  195.9 202.6 202.6 202.6 avg  71.2 204 188 191 194  —  202.6 202.6 202.6  4  —  _  40.0 40.4 39.5 40.0  112 107 100 107  c  0  —  64.8 64.8 64.8 avg  181.5 181.5 181.5 avg  [salt] x 10  —  — — —  d  —  d  —  d  —  195.9  — —  a. Up to u = 6.74 x IO M, the ionic strength results solely from the ions generated by reaction 5.1, i.e., no salt has been added. Initial [Rh(OEP)(a)(PPh3)] between (4.0-8.0) x 1(H M. Pathlength of cell = 0.1 cm. The estimated uncertainty in Kobs is ± 5% or better and in |i is ± 2.5% or better unless otherwise noted. -4  b. Added [Ph4As]Cl-H 0. 2  c. Added [ Bu4N][C10 ]. d. Addition of H2O to 2 x IO* M had no measurable effect on the equilibrium reaction. n  4  2  205  Appendix E Assignment of the ligand *H nmr resonances of Rh(OEP)(CH(Me)NEt ) 2  The data shown in Table E.1 (and Table 4.2) were determined from selective decoupling and COSY *H nmr experiments performed on various nmr samples containing Rh(OEP)(CH(Me)NEt2). The spectra illustrated in Figures E.1 and E.2 are representative examples. These spectra were obtained on the same sample as illustrated in Figure 4.4b (page 116). The selective decoupling experiments linking H2* with H3', and HQ with Hp were done but are not illustrated. The Ha with Hp linkage is also shown by COSY data (Fig. E.2). In addition, off-resonance effects on Hp due to irradiation of the Hi' resonance can be seen in Fig. E.ld.  206  Table E. 1. Ligand *H nmr spectral data for Rh(OEP)(CH(Me)NEt2).  a  proton  5  integral  H2  -0.61 m  IH  H  3  -0.811  3H  H' H2(i)  -0.95 t  3H  -1.60 m  IH  Hi( ) Hr  -1.87 m  IH  -2.28 m  IH  H Hp  -2.30 m  IH  -3.96 d  3H  3  2  a  a. 300 MHz; measured in C7D8 solution at ~20°C.  Figure E.2.  Atom labelling scheme for the -(CH(Me)NEt2) ligand of Rh(OEP)(CH(Me)NEt ). 2  207  x = Rh(OEP)(a)(NEfcH)  i -|—r—r—r—t—|—; -0.5 -i'. 0  i i I j I I ) I | I I i i | i i -1.5 -2.0 -2.5  i i [ 1 i i : • i i i i| — r -3.0 -a',5 PPM - 4 . 0  i  Figure E.2.  ii  The 300 MHz partially decoupled *H nmr spectra of the -(CH(Me)NEt2) ligand of Rh(OEP)(CH(Me)NEt2), prepared in situ in C7D8 solution at 20°C, in vacuo in a sealed nmr tube. Labelling as shown in Figure E.l.  (a) undecoupled, (b-d)  location of irradiation shown by the appropriate arrow.  208  F2 (PPM)  x = Rh(OEP)(Cl)(NEt2H)  -4.0-f  -3.5-  -3.0-  •2.5-  -2.5 -3.0 F l (PPM) Figure E.3.  -4.0  The 300 MHz *H COSY spectrum of part of the -CH(Me)NEt2) ligand of Rh(OEP)(CH(Me)NEt2), prepared in situ in C7D8 solution at 20°C, in vacuo in a sealed nmr tube. Labelling as shown in Figure E.1.  

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