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Reactions of CpW(NO)(CH₂SiMe₃)₂ with Lewis acids : characteristic chemistry of CpW(NO)(CH₂SiMe₃)(CH₂CPh₃) Brunet, Nathalie 1988

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REACTIONS OF CpW(NO)(CH2SiMe3)2 WITH LEWIS ACIDS. CHARACTERISTIC CHEMISTRY OF CpW(NO)(CH2SiMe3)(CH2CPh3) by NATHALIE BRUNET B.Sc. (Hons.), University of Ottawa, 1985 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1988 © Nathalie Brunet, 1988 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 be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia Vancouver, Canada Department DE-6 (2/88) i Abstract The nitrosyl complex CpW(NO)R2 (R = CH2SiMe3) forms 1:1 adducts via isonitrosyl linkages to Lewis acids such as AlMe^ and Cp^Er, i.e. CpVfl^ CNO-iA) (A = AlMe^, ErCp^). These adducts regenerate the starting dialkyl complex when treated with water. Protonation of CpW(N0)R2 by HBF^»0Me2can also be effected. Whether the site of protonation is the nitrogen or the oxygen atom of the nitrosyl ligand is not known with certainty, although O-protonation is postulated by analogy with the other Lewis-acid adducts of CpW(N0)R2. In these adducts, the nitrosyl stretching frequency is shifted to lower wavenumbers relative to that of the parent dialkyl, to an extent which increases as harder Lewis acids are employed. The colour of the adducts also ranges from red to orange to yellow as progressively harder acids are used. Treatment of CpW(NO) (C^SiMe.^ with [Ph3C]+ PFg" in Ch^C^ results in electrophilic cleavage of a carbon-silicon bond to yield the mixed dialkyl CpW(NO)(CH2SiMe3)(CH2CPh3), which has been fully characterized by spectroscopic methods and by a single-crystal X-ray crystallographic study. The formation of Me3SiF and PF^ (coordinated to Lewis bases in the reaction mixture) as by-products of this reaction has been confirmed by 3 1P and 1 9F NMR spectroscopy of the reaction mixture in CD2CI2. Preliminary attempts to extend this novel reaction of a silicon-containing ligand by using other carbocations were unsuccessful. This is attributed to the high reactivity of the required carbocations and the large number of possible reaction sites on the metal complex. Some reactions of the mixed dialkyl CpW(NO)RR' (R = Cl^SiMe^ R' = CH2CPh3) were found to be analogous to those of the parent CpW(NO)R2, while other reactions followed a different course because of the ability of the CH2CPh3 ligand to orthometallate. Thus, CpW(NO)RR' is much less thermally stable than CpW(NO)R2. As a solid or a solution in non-coordinating solvents, i t decomposes in a matter of days at room temperatures to a mixture of products which were not identified. In acetonitrile solution, an orthometallated complex derived from CpW(NO)RR' can be trapped by coordination of solvent. The product Cpft(NO)(CH2C(C5H4)Ph2)(NCMe) has been isolated and crystallographically characterized. Cyclic voltammograms of CpW(NO)R2 and CpW(NO)RR' show that both complexes undergo an apparently chemically reversible reduction and an irreversible oxidation. The mixed dialkyl CpW(NO)RR' is somewhat easier.both to reduce and to oxidize than CpW(NO)R2. Like CpW(NO)R2, CpW(NO)RR' reversibly forms a 1:1 adduct with PMe3. Also analogously to CpW(NO)R2> i t reacts with 0^ to form a 5:1 mixture of dioxoalkyl complexes CpW(0)2R and CpW(0)2R', and with NO(g) to form 2 CpW(NO)R'(n -02N2R). In this product, insertion of NO has occurred exclusively in the W-CH2SiMe3 bond. Upon photolysis, both complexes CpW(NO)R"(n2-02N2R) (R" = CH2SiMe3 or CH"2CPh3) form dioxo alkyls CpW(C»2R" in an unprecedented reaction. The ability of CpW(NO)RR' to orthometallate also results in the i 1 formation, when this complex is treated with sulphur, of CpW(O)(CH2C(CgH^)Ph2)-(SR). No analogue to this compound can be obtained from reaction of CpW(NO)R_ i i i with sulphur. The sequence of reactions leading to the formation of this product is not known. iv Table of Contents Page Abstract i Table of Contents iv List of Tables v i i List of Figures v i i i List of Schemes xi List of Abbreviations x i i Acknowledgements xiv Chapter I - Introduction 1 I-A Reactions of Organometallic Complexes with Electrophiles . . 1 I-A-l Adduct Formation 2 I-A-2 Electron Transfer 6 I- A-3 Reactions at a Ligand 6 I- B Reactivity of CpW(NO)R2 Complexes 10 References 15 Chapter II - Reactions of CpW(NO)(CH2SiMe3)2 with Lewis Acids 18 Experimental Section 19 Results and Discussion 27 II- A Formation of Adducts 27 II- A-1 Al^Me and ErCp3 Adducts 27 II-A-2 Protonation of CpW(NO)(CH2SiMe3)2 30 II-A-3 Spectroscopic Properties of the Adducts 31 V Page II- B Electrophilic Cleavage of a Silicon-Carbon Bond of CpW(NO)(CH2SiMe3)2 32 II-B-1 Synthesis and Properties of CpW(NO)(CH2SiMe3)-(CH2CPh3) (12) 32 II-B-2 By-products in the Synthesis of 12 38 II-B-3 Precedents for Electrophilic Cleavage of Silicon-Carbon Bonds 44 II-B-4 Mechanistic Considerations 45 II- B-5 Attempted Extension to Other Electrophiles 46 References 50 Chapter III - Reactivity of CpW(NO)(CH2SiMe3)(CH2CPh3) 53 Experimental Section 53 Results and Discussion 62 III- A Thermal Behaviour 62 III- A-1 Decomposition in the Absence of a Coordinating Solvent 62 III-A-2 Decomposition in a Coordinating Solvent: Formation of CpW(NO)(CH2C(C6H4)Ph2)(NCMe) 64 III-A-3 Cyclic Voltammetry of CpW(NO)(CH2SiMe3)(CH2CPh3) . . 70 III-B Reactivity of CpW(NO)(CH2SiMe3)(CH2CPh3) with Small Molecules 72 III-B-1 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) with PMe3 . . 72 III-B-2 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) with 0 2 . . . 74 III-B-3 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) with N0(g). . 75 vi Page III-B-4 Photolysis of CpW(NO)(CH2CPh3)(n2-02N2CH2SiMe3) and CpW(NO)(CH2SiMe3)(p2-02N2CH2SiMe3) 80 III-B-5 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) with Sg . . . 83 Conclusions 95 References 97 Spectral Appendix 98 vii: List of Tables Table Page II-l IR and Colour Data for CpW(NO)(CH2SiMe3)2 and its Adducts with Lewis Acids . . . . . 29 II-2 Selected Bond Lengths and Angles for CpW(NO)(CH2SiMe3)2 and CpW(NO)(CH2SiMe3)(CH2CPh3) 35 II- 3 3 1P and 1 9F NMR Data for the Reaction Mixture of CpW(NO)(CH2SiMe3)2 and [Ph3C]+ PF6~ in CD 2Cl 2 A3 III- l Selected Bond Lengths and Angles for CpW(NO) (CH2C(C^^)Ph2)-(NCMe) • 67 III-2 Cyclic Voltamraetric Data for CpW(NO) (CH2SiMe3)a and CpW(NO)(CH2SiMe3)(CH2CPh3) 72 III-3 Selected Bond Lengths and Angles for CpW(NO) (Ch^CCC^)Ph2)-(SCH2SiMe3), CpW(NO)(CH2SiMe3)(SCH2SiMe3) and CpW(NO) (CH2C(C6H4)Ph2)(NCMe) 92 v i i i List of Figures Figure Page I- 1 Partial Solid State Molecular Structure of [CpMo(NO) (CH2SiMe3)2l2»MgI2 4 II- 1 Solid State Molecular Structure of CpW(NO)(CH2SiMe3)(CH2CPh3) 34 II-2 270 MHz iH NMR Spectrum of CpW(NO)(CH2SiMe3)(CH2CPh3) in C&D6 37 II-3 75 MHz ^CPH} NMR Spectrum of CpW(NO) (CH2SiMe3) (CH2CPh3) in CD2C12 39 II-4 121.4 MHz 3 1P NMR Spectrum of the Reaction Mixture of CpW(NO)(CH2SiMe3)(CH2CPh3) and [Ph3C]+PF6~ in CD2C12 41 II- 5 282 MHz 1 9F NMR Spectrum of the Reaction Mixture of CpW(NO)(CH2SiMe3)2 and [Ph3C]+ PFg" in CD 2Cl 2 42 III- l Solid State Molecular Structure of CpW(NO)(CH2C(CgH^)Ph2)(NCMe) 66 III-2 Cyclic Voltammograms of CpW(NO)(CH2SiMe3)(CH2CPh3) in CH2C12 71 I X Figure Page III-3 400 MHz iH NMR Spectrum of CpW(NO)(CH2CPh3)-(n2-02N2CH2SiMe3) in CDC13 77 III-4 75 MHz "CI1!!} NMR Spectrum of CpW(NO) (CH2CPh3) (n2-02N2CH2SiMe3) in CDC13 78 III-5 80 MHz iH NMR Spectra of the Photolysis of CpW(NO)(CH2CPh3)-(n2-0.N„CH„SiMeo) in C,D, 82 2. 2. Z 5 D O III-6 a) 80 MHz JH NMR Spectrum of the Dried Residue from the Reaction Mixture of CpW(NO) (CH2SiMe3) (CH2CPh3) with C>2, in C,D, o o b) 80 MHz *H NMR Spectrum of CpW(O)2(CH2CPh3) from Photolysis of CpW(NO) (CH2CPh3) (n2-02N2CH2SiMe3) in CgDg 84 III-7 80 MHz *H NMR Spectrum of the Dried Residue from the Reaction Mixture of CpW(NO)(CH2SiMe3)(CH2CPh3) with Sg, in C6D& . . . . 86 III-8 75 MHz "CpH} NMR Spectrum of CpW(O) (CH2C(CgH^)Ph2) (SCH2SiMe3) i n C6°6 ' ' ' ' ' 8 8 II1-9 80 MHz iH NMR Spectrum of CpW(O)(CH2C(CgH^)Ph2)(SCH2SiMe3) in CgDg 89 X Figure Page 111-10 Solid State Molecular Structure of CpW(O)(CH2C(C6H4)Ph2)-(SCH2SiMe3) 90 III-ll Simplified ORTEP Diagram Showing the Arrangement of the Four "Piano-Stool Legs" of CpW(O)(CH2C(C6H4)Ph2)(SCH2SiMe3) . . . . 94 X I List of Schemes Scheme Page 1-1 I I I - l I I I - 2 12 63 69 x i i List of Abbreviations cp - n^-cyciopentadienyi Cp' - n^-methylcyclopentadienyl CP - centroid of a Cp ring Fp - CpFe(CO)2 trityl - (trivial name) Ph^ C, triphenylmethyl Me - CH3> methyl Et - CH3CH2, ethyl Bu - C 4 H 9 » butyl -Bu - Me3C, tert-butyl Ph - C 6 H 5 » phenyl THF - C 4 H 3 ° > tetrahydrofuran dppe - Ph2PCH2CH2PPh2 TMS - Me^Si, tetramethylsilane Ln - lanthanide eq - equatorial ax - axial v:v - volume: volume IR - infrared \JNO - nitrosyl stretching frequency - carbonyl stretching frequency v_ - hydroxyl stretching frequency UH \J^ =Q - tungsten-oxo stretching frequency TT (Cp) - frequency of out-of-plane bending of C-H bonds in Cp ring NMR - nuclear magnetic resonance x i i i s - singlet d - doublet t - triplet q - quartet p - pentet ppm - parts per million 13C{1H} - proton-decoupled carbon-13 m/z - mass-to-charge ratio (in the mass spectrum) p + - molecular ion (in the mass spectrum) mp - melting point dec - decomposes C.V. - cyclic voltammogram M.O. - molecular orbital HOMO - highest occupied molecular orbital LUMO - lowest unoccupied molecular orbital xiv Acknowledgement This thesis would never have seen the light of day without the help and encouragement of a great many people in the Department. My very sincere thanks go to my supervisor, Peter Legzdins. Our relations weren't always easy, yet he always believed in me, encouraged me, and allowed me to work much on my own. I also learned and received a great deal of help from my co-workers, past and present: Allen first of a l l , who first taught me the ropes and remains a valued friend and mentor, Be, Luis, Jeff, George, Nancy, Everett, Neil, Teen, Lillian, Jacquie and Mike. Peter, Neil, Teen and George also deserve my thanks for reading a l l or parts of this thesis in painstaking detail and making many helpful comments. Vivien Yee solved a l l three crystal structures in this work, and answered cheerfully many an anguished call for help. I could also never have done this without the staff in the NMR lab; Tilly Schreinders typed this manuscript, and Steve's and Andy's help in proofreading i t is much appreciated. I also wish to thank Dr. W. Beck for sending us a copy of his review prior to publication, and NSERC and the University of British Columbia for financial support. Finally, I would like to thank my Vancouver "family", the people who put up with me and kept me sane while I was doing this work: my friend Leslie; St.-Jacques de Compostelle; my housemates Claire, Bev, John, Richard and Ti-Nours; numerous friends within the Department, who have understood my miseries and cheered my successes; and my recorder quintet. X V "Cottleston, Cottleston, Cottleston Pie, Why does a chicken, I don't know why. Ask me a riddle and I reply: Cottleston, Cottleston, Cottleston Pie" A.A. Milne 1 CHAPTER I Introduction I-A Reactions of Organometallic Complexes with Electrophiles A Lewis acid, or electrophile, is a species capable of accepting electronic density, while a Lewis base, or nucleophile, can donate electronic density.''' Lewis acids and bases can be described as hard or soft; a soft acid or base is one whose valence electrons are easily polarized or removed, and a hard acid or base holds its electrons tightly and is not easily distorted. Hard acids preferentially coordinate to hard bases, and soft acids to soft . 1 bases. Heavier atoms in low oxidation states behave as softer acids than lighter, more highly oxidized atoms. The hardest acid is H+, since i t has no electrons to be polarized. Other typical hard acids are cations of the alkali and alkaline-earth metals, BF^, AlMe3, A1C13, C02> HX (X = halide). Acids such as SO^ , N0+, or R3C+ are intermediate, and T l + , Hg+, I + or Br +, for example, are soft.''' Reactions of organometallic complexes with such acids are many and 2 varied. The following discussion is restricted to those reactions that might be applicable to monometallic complexes containing Cp, nitrosyl and alkyl ligands, such as CpW(NO)(CH2SiMe3)2, which is the object of some of the work presented in this thesis. 2 1-A-l Adduct formation Organometallic complexes having a site of electronic density, either metal- or ligand-based, may form simple Lewis acid-base adducts with electrophiles. 3 a) Metal-based lone pair of electrons H + + Ex 1: Cp2M — • Cp2MH (1) (ref 4) M = Fe, Ru, Os Ex 2: CpCo(CO)2 + HgCl2 • CpCo(CO)2(HgClg) (2) (ref 5) 1 In such reactions, donation of electron density from the transition-metal centre to the acid reduces back-bonding from the metal to any n-acid ancillary ligand which may be present. For example, in the case of compound 1, this results in an increase of the carbonyl stretching frequency of — 1 6 about 50 cm compared to the parent. b) Ligand-based electron pair. Adduct formation at the oxygen atom of a carbonyl ligand is well known^ : 3 H>Ph3 <^7^P p h3 I MO + AIMe3 — MO (3) (ref 8) o o 3 Fewer examples are known of analogous coordination to a terminal nitrosyl ligand: CpM(CO)2(NO) + R3Ln • CpM(C0)2(N0-LnR3) (A) (ref 9) 2 M = Cr, Mo, W Ln = Sm, Ho, Yb, Er R = Cp or Cp1 More recently, a 2:1 adduct of CpM(NO)(CH2SiMe3)2 (M = Mo.W) with Mgl2 has been isolated.^'^ A partial X-ray crystallographic analysis of this adduct has been done, and the arrangement of the atoms that could be located is shown in Figure I - l . ^ In these cases, the stretching frequency of the CO or NO ligand to which the acid is coordinated is shifted to lower wavenumbers, as the C-0 or N-0 bond is weakened by donation of the electrons of the oxygen atom to the acid. For example, the nitrosyl stretching frequency in adducts 2 -1 9 decreases by 57 to 78 cm relative to the parent. Concomitantly, the stretching frequencies of the remaining carbonyls increase by about 20 and Fig. 1-1 Partial Solid State Molecular Structure of [CpMo(NO)(CH2SiMe3)2]2»MgI2 5 -1 9 30 cm , as electronic density is drained away from the metal centre. The TT-electrons of a coordinated Cp or arene ligand can also serve as a 12 site of Lewis basicity, as in the general equation (5): M A+ -M (5) Such examples are rare, however, since spontaneous deprotonation usually 12 follows to give the electrophilic substitution product. However, the product resulting from trityl cation addition to 3 can be isolated, then treated in a separate step with Et^N to give the neutral substitution product: 13 6 I-A-2 Electron transfer A simple redox reaction, 1-electron transfer from the metal to the acid, is also possible: Subsequent reaction of the oxidized organometallic product is frequently-observed. Reactions that may be oxidatively induced include ligand substitution,^ insertion,^ and reductive elimination.^ I-A-3 Reactions at a ligand 18 a) Removal of an anionic ligand from the metal centre A proton is most often used to remove an organic ligand from a transition metal: (n7-C7H7).Mo(dppe) (-CECR) + [Cp2Fe]+BF4 • [ (n7-C?H7)Mo(dppe) (-CECR) ] +BF + Cp2Fe (7) (ref 14) 3' (8) (ref 19) Fp = CpFe(CO), Deuterium labelling, using DC1 in reaction (8), has shown that the cleavage 19 proceeds with retention of stereochemistry at carbon. Carbon electrophiles can also effect the same reaction: 7 (CO)4(PPh3)Mn-Me + [CPh 3] + BF wet CH 2C1 2 [(CO) 4(PPh 3)Mn(OH 2)] + BF^ + MeCPh3 (9) (ref 20) b) Insertion in the metal-carbon bond Some electrophiles such as N0 + insert into the metal-carbon bond: Reaction (10) apparently proceeds by direct attack of the M-C bond by the electrophile. c) E l e c t r o p h i l i c substitution at Cp 12 Aromatic substitution on a coordinated Cp group i s similar to 23 that known to occur on benzene (Friedel-Crafts alkylation). (10) (ref 21,22) MLn O MLn (11) (ref 24) MLn = FeCp, RuCp, Mn(CO)3> OsCp, Cr(CO)2(NO), V(CO) A, Re(C0) 3 8 The degree of reactivity can be related to the electron-richness of 24 the metal centre. In a series of competitive acetylation reactions, the reactivity of metallocenes was found to be generally higher than that of CpM(CO)m(NO)n complexes; this was attributed to the greater overall electron-withdrawing abilities of CO and NO compared to Cp, which destabilize the transition state for E + addition: E + -(12) d) Hydride abstraction from alkyl ligands These processes are most commonly done using trityl cation (Ph3C+). A hydride can be removed from either the a or B position of an alkyl group, giving rise to either an alkylidene (equation (13)) or an olefin complex (equation (14)): [Ph„C]+ PF " CpRe(NO) (PPh3)-CH2Ph 2 • Ph3CH + [CpRe(NO) (PPh3)=CHPh] PFg (13) (ref 25) ,+ „,„- THF r „ ti 2 n + Fp-CH2CH2CH3 + [Ph3C] ClO^ ± i i^- [Fp-|| ] ClO^ + Ph3CH (14) (ref 26) Fp = CpFe(C0)2 CIS:H3 9 27-29 31 30-32 Work has been done by several groups, led by Cooper, ' Gladysz and 33 Bly, to study the mechanisms of these reactions, in an effort to understand the reasons for a- vs B-hydride selectivity. The results were found to depend on both the alkyl group and the metal centre. Thus, the tungsten akyl 27 28 29 complexes Cp2WRR' (R = Me, R' = Me ' or Ph ) underwent a-abstraction by an electron-transfer mechanism; the intermediate 17e radical cations [CP2WRR'] +have been isolated and shown to transfer H» to trityl radical to give the expected products: ,Me - Me Ph C ,CH Cp W [Cp Wx ] — • Cp w' Z + Ph CH (15) R1 R' R' The rhenium alkyls CpRe(NO)(PPh.j)R, on the other hand, were shown to 30 undergo either a-or B-hydride abstraction depending on the nature of R. Unbranched aliphatics undergo exclusively a-abstraction; B-abstraction competes or dominates in the case of branched aliphatics substituted in the CD P position, and is the exclusive pathway i f branching is in the C^  position. The reaction was shown to proceed by electron-transfer followed by H-abstraction in this case also, for both a and B abstraction. 23 In contrast, Bly's work on Fp-alkyls (Fp = CpFetCO^)) showed that a-abstraction could not be obtained at a l l for the complexes studied. Although there was some evidence for a small concentration of [Fp-R]+ and 10 Ph^ C* in the reaction mixture, there was no indication of whether or not these were implicated in the production of the final olefin complexes. I-B Reactivity of CpW(N0)R2 complexes (R = alkyl) The second portion of the work described in this thesis, covered in Chapter III, concerns the reactivity of CpW(NO)(CH2SiMe3)(CH2CPh3). This work was undertaken with the goal of comparing the results with those obtained using CpW(NO)(CH2SiMe3)2 (4) f which are summarized here. (For the rest of this discussion, R = CH2SiMe3.) The dialkyl complex 4 was prepared in our laboratories by Luis Sanchez.^'^ Et-0 [CpW(NO)I2]2 + 4RMgCl Q„ » [CpW(NO)R2]2MgI2»Et20 + 3MgX2(Et20)n (X = CI,I) (16) Et„0 [CpW(NO)R2]2MgI2«Et20. + 6H20 » 2 CpW(NO)R2 + [Mg(0H 2) 6] 2 + + 21 + Et 20 4 (17) The product is obtained initially in the form of an adduct to Mgl2 which has been described above. The desired product 4 is released by treating the adduct with water. Complex 4 is a deep violet, diamagnetic solid, very soluble in al l common organic solvents. It can be handled in air as a solid for short 11 periods of time, without appreciable decomposition, though i t is quite air-sensitive in solution. The molecular structure, which has been determined by a single crystal X-ray crystallographic analysis, is that of a monomeric, 16-electron, "three-legged piano stool": 4 In spite of the formal electronic unsaturation, the very low (1603 cm in hexanes) is indicative of considerable M -* NO back-bonding. This has been rationalized in terms of the valence electronic structure of 4 . ^ Fenske-Hall M.O. calculations^ have shown that in complexes of this type the LUMO is metal centered and non-bonding; whether i t is occupied or not has li t t l e effect on M -* NO back-donation. Solutions of 4 are quite thermally and photolytically stable. For instance, thermolysis at 70°C.or photolysis at 20°C in benzene for 1 or 2 days leads to decomposition of only 10% of the starting material to an intractable red-brown solid. Other reactions of 4, with various small molecules, are summarized in Scheme 1-1,^ and those that are relevant to the work described in this thesis are discussed below. Reaction of 4 with oxygen gives the white dioxoalkyl complex 12 I w R / | J N N O — A I M e 3 0 A 0 AIMe, i 0 N PMe3 PMe, vacuum CNR' ^ R O R i w 2 NO N / O 2/eS R=$Bu E = S,Se Scheme 1-1 13 CpW(0)2R in 40-50% isolated yield. The by-products of this reaction are not yet known. In addition to the Lewis base properties of the nitrosyl ligand, the dialkyl complex also has Lewis acid character at its metal centre, as expected for a 16-electron compound. Access to the metal centre, however, is restricted by the steric bulk of the alkyl ligands. Thus, the small Lewis base PMe^  reversibly forms a 1:1 adduct with 4, but bulkier phosphines such as PMe^ Ph or PPh^  do not. Complex 4 in hexanes rapidly inserts two equivalents of N0(g) to form N-alkyl-N-nitrosohydroxylaminato complex 5 as a yellow, crystalline, air-stable solid: CpW(NO)R2 + 2NO(g) • CpW(NO)(R)(n2-02N2R) (18) 5 35 This reactivity is well-known for other diamagnetic alkyl complexes such as Cp 2ZrR 2. 3 6 , 3 7 In non-polar solvents, the and ^ Cf^H} NMR spectra of 5 indicate that i t consists of a mixture of 2 interconverting isomers, which probably differ only in the orientation of the R substituent of the 2 planar n -09N„R group: 14 1 ^ ^ 1 ^ (19) R Finally, 4 also reacts with sulphur or selenium according to the following sequence: W. /E R E R 4 R 6 W^ —ER W. ,ER VER 8 (20) (E = S, or Se) When E = S, both intermediate compounds 6 and 7 can be isolated. The first two steps proceed cleanly and in high yield, and al l compounds are crystalline, diamagnetic solids, fully characterized by conventional methods including single-crystal X-ray crystallographic analyses of 6 and 7. However, attempted kinetic studies have shown that the first two reactions proceed best under heterogeneous conditions, with the sulphur incompletely dissolved, and are accelerated by trace amounts of water. It therefore appears that the mechanisms of sulphur insertion into these W-C bonds may be quite complicated.^' 15 References 1. Jolly, W.L. Modern Inorganic Chemistry; McGraw-Hill: New York, 1984; pp 205-211. 2. Collman, J.P.; Hegedus, L.S.; Norton, J.R.; Finke, R.G. Principles and  Applications of Organotransition Metal Chemistry, 2nd ed.; University Science Books: Mill Valley, CA, 1987, Chapter 8. 3. Interactions of metal centres with Lewis acids have been reviewed: a) Shriver, D.F. Acc. Chem. Res., 1970, 3, 231. b) Kotz, J.C.; Pedrotty, D.G. Organomet. Chem. Rev. A, 1969, 4, 479. 4. Curphey, T.J.; Santer, J.O.; Rosenblum, M.; Richards, J.H. J. Am. Chem.  Soc.. 1960, 82, 5249. 5. Nowell, I.N.; Russell, D.R. J. Chem. Soc, Chem. Commun. , 1967, 817. 6. Cook, D.J.; Dawes, J.L.; Kemmitt, D.W. J. Chem. Soc. (A), 1967, 1547. 7. Horwitz, CP.; Shriver, D.F. Adv. Organomet. Chem., 1984, 23, 219. 8. Kotz, J.C.; Turnipseed, CD. J. Chem. Soc, Chem. Commun., 1970, 41. 9. Crease, A.E.; Legzdins, P. J. Chem. Soc, Dalton Trans., 1973, 1501. 10. Legzdins, P.; Rettig, S.J.; Sanchez, L., Bursten, B.E.; Gatter, M.G., J. Am. Chem. Soc, 1985, 107, 1411. 11. Legzdins, P.; Rettig, S.J.; Sanchez, L., submitted for publication to Organometallics. 12. Watts, W.E. in Comprehensive Organometallic Chemistry; Wilkinson, G.; Stone, F.G.A.; Abel, E.W., Eds; Pergamon: Oxford, 1982; Vol. 8, Chapter 59. pp 1016-1026. 13. Klemarczyk, P.; Price, T.; Priester, W.; Rosenblum, M. J. Organomet.  Chem., 1977, 139, C25. 14. Adams, J.S.; Bitcon, C; Brown, J.R.; Collison, D.; Cunningham, M.; Whiteley, M.W. J. Chem. Soc, Dalton Trans. , 1987, 3049. 15. Ref. 2, Chap. 4, Section C 16. Ref. 2, pp 373-375. 17. Ref. 2, pp 324-326. 18. A review on electrophilic, cationic transition-metal complexes, which can be prepared by such reactions, will appear shortly. Beck, H., Sunkel, K., submitted for publication to Chem. Rev. 16 19. Rogers, W.N.; Baird, M.C. J. Organomet. Chem., 1979, 182, C65. 20. Harris, P.J.; Knox, S.A.R.; McKinney, R.J.; Stone, F.G.A. J. Chem. Soc,  Dalton Trans., 1978, 1009. 21. Legzdins, P.; Wassink, B.; Einstein, F.W.B.; Willis, A.C. J. Am. Chem.  Soc, 1986, 108, 317. 22. Legzdins, P.; Richter-Addo, G.B.; Wassink, B.; Einstein, F.W.B.; Jones, R.H.; Willis, A.C. Manuscript in preparation. 23. Fessenden, R,J.; Fessenden, J.S. Organic Chemistry, 3rd ed.; Brooks/Cole: Monterey, CA, 1986; pp 478-479. 24. Fischer, E.O.; Von Foerster, M.; Kreiter, C.G.; Schwarzhans, K.E. J. Organomet. Chem., 1967, 7, 113. 25. Kiel, W.A.; Lin, G.-Y.; Constable, A.G.; McCormick, F.B.; Strouse, C.E.; Eisenstein, 0.; Gladysz, J.A. J. Am. Chem. Soc., 1982, 104, 4865. 26. Green, M.L.H.; Nagy, P.L.I. J. Organomet. Chem., 1963, 1, 58. 27. Hayes, J.C.; Pearson, G.D.N.; Cooper, N.J. J. Am. Chem. Soc, 1981, 103, 4648. 28. Hayes, J.C. ; Cooper, N.J. J. Am. Chem. Soc 1982, 104, 5570. 29. Jernakoff, P.; Cooper, N.J. Organometallics, 1986, _5, 747. 30. Kiel, W.A.; Lin, G.-Y.; Bodner, G.S.; Gladysz, J.A. J. Am. Chem. Soc, 1983, 105, 4958. 31. Asaro, M.F.; Bodner, G.S.; Gladysz, J.A.; Cooper, S.R.; Cooper, N.J. Organometallics, 1985, 4, 1020. 32. Bodner, G.S.; Gladysz, J.A.; Nielsen, M.F.; Parker, V.D. J. Am. Chem.  Soc., 1987, 109, 1757. 33. Bly, R.S.; Bly, R.K.; Hossain, M.M.; Silverman, G.S.; Wallace, E. Tetrahedron, 1986, 42, 1093. 34. Legzdins, P.; Rettig, S.J.; Sanchez, L. Organometallics, 1985, 4, 470. 35. Middleton, A.R.; Wilkinson, G. J. Chem. Soc, Dalton Trans., 1981, 1898, and references therein. 36. Wailes, P.C.; Weigold, H.; Bell, A.P. J. Organomet. Chem, 1972, 34, 155. 17 37. Fochi, G. ; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Chem. Soc,  Dalton Trans., 1986, 445. 38. Legzdins, P.; Sanchez, L. J. Am. Chem. Soc., 1985, 107, 5525. 18 CHAPTER II Reactions of CpW(NO)(CH,SiMe,), with Lewis Acids The coordinated nitrosyl of CpW(NO)(CH2SiMe3)2 ( 4 ) is known to be a Lewis base site, as shown by the fact that 4 is initially obtained as 1 2 an adduct with Mgl2 ' from reaction between [CpW(NO)I2]2 and the required Grignard reagent. When the work presented in this thesis was begun, a 1:1 adduct between 4 and AlMe^ had also been observed, but not fully 2 characterized. It was of interest to extend the adduct series to other Lewis 3 acids. In particular, since previous work in our laboratories had shown that Cp^Ln complexes (Ln = lanthanide) were capable of forming isonitrosyl linkages to various related nitrosyl compounds, a species of this class seemed an appropriate choice. These adduct formations are considered in the first part of this chapter. Reaction of 4 with trityl cation might have been expected to result in a-hydride abstraction, as discussed in the Introduction. Alkylidene complex 9 would have been the initial product. R J, CHSiMe3 O 9 19 This would have been a cationic analog to oxoalkylidene complex 3, 4,5 which results from thermal decomposition of 4 i CHSiMe3 10 6 Transition metal alkylidene complexes are known to be olefin metathesis and 7 8 polymerization catalysts, and carbonyl olefination reagents. However, hydride abstraction was not obtained; heterolysis of the silicon-carbon was observed instead. The second part of this chapter is devoted to this novel reaction of a silicon-containing ligand in a transition metal complex. All manipulations were performed under anhydrous and anaerobic conditions, under an atmosphere of prepurified nitrogen, either on the bench using conventional techniques for the manipulation of air-sensitive 9 compounds, or in a Vacuum Atmospheres Corp. Dri-Lab Model HE-43-2 dry box. All reagents were of reagent grade or comparable purity and were either purchased from commercial suppliers or prepared according to published Experimental Section 20 procedures. Their purity was ascertained by elemental analysis and/or other suitable methods. Melting points were taken in capillaries (sealed under nitrogen) using a Gallenkamp Melting Point apparatus, and are uncorrected. Hexanes, acetonitrile, and nitromethane were dried with CaR^ ; diethyl ether and THF, with Na/benzophenone ketyl; toluene with Na; dichloromethane with ?2®5' solvents were distilled from their respective drying agents and purged with just prior to use. All reactions described were done at ambient temperatures. Infrared spectra were recorded on a Nicolet 5DX FT-IR instrument (internally calibrated with a He/Ne laser). Proton NMR spectra were obtained on a Bruker WP-80, WH-400, or Nicolet-Oxford HXS-270 spectrometer, and referenced to the residual proton signal of the deuterated solvent employed.^ Chemical shifts are reported in parts per million downfield from Me^Si. Carbon-13 NMR spectra were recorded on a Bruker WP-80 or Varian XL-300 spectrometer, operating at 20 MHz and 75 MHz respectively. Spectra were referenced to the solvent used,^ and chemical shifts are reported in parts 19 per million downfield from Me^Si. The F-NMR spectrum was obtained on a Varian XL-300 instrument operating at 282 MHz and referenced to external CF3C00H. Chemical shifts are reported downfield from CF3C00H. The 31P-NMR spectrum was obtained on a Varian XL-300 instrument operating at 121.4 MHz and referenced to external 0P(0Ph)3. Chemical shifts, however, are reported downfield from 85% H^O^. Mrs. M.T. Austria, Ms. L.K. Darge, Mrs. A. Sallos and Dr. S.O. Chan assisted in obtaining the NMR data. Electron impact mass spectra were recorded at 70 eV on an Atlas CH4B or a Kratos MS50 spectrometer, 21 using the direct insertion method, by Mr. M.A. Lapawa and Dr. G.K. Eigendorf. Elemental analyses were performed by Mr. P.Borda. 22 Preparation of CpW(NO)(CH2SiMe3)2«AlMe3 (11c) To a stirred, colourless solution of AlMe3 (1.6 mL, 2M in toluene, Aldrich; 1 2 3.2 mmol) in hexanes (20 mL) was added purple CpW(NO)(CH2SiMe3)2 ' (4) (0.45 g, 1.0 mmol). The resulting clear red-orange solution was concentrated under vacuum, allowing the temperature to drop as the solvent was evaporated, until the reduction in volume and temperature induced the precipitation of an orange powder. This mixture was cooled to *\. -40°C using a saturated CaCl2/Dry Ice bath to complete the precipitation. The orange precipitate was isolated by filter-cannulating away the supernatant liquid, washing with cold pentane (2 x 15 mL) and drying at 0°C (0.05 torr) for several hours. In this manner, 0.41 g (0.78 mmol, 78%) of analytically pure 11c was obtained as an orange powder. Anal. Calcd for C.,H_.AlNOSiW: C, 36.57; H, 6.90; N, 2.67. Found: C, lo Jo 36.77; H, 7.10; N, 2.52. IR (Nujol) v 1447 (s) cm"1. *H NMR (CgDg) 6 5,42 (s, 5H, Cp_) , 1.95, 0.34 (AB, 4H, CH2, J = 8 Hz) 0.10 (s, 9H, SiMe_3) , -0.31 (S, 9H, AlMe ). isc {*HJ (CgDg) 6 105.1 (Cp.) , 69.9 (CH2) , 1.3 (SiMe_3) , -7.0 (br AlMe3). mp 59-68°C dec. Preparation of CpW(NO)CH2SiMe3)2«ErCpyl.5 CH2C12 (11a) To a stirred, purple solution of CpW(NO)(CH2SiMe3)2 (4) (0.23 g, 0.5 mmol) in CH2C12 (15 mL) was added pink Cp^r 1 1 (0.18 g, 0.5 mmol). The colour of the solution turned immediately from purple to dark red. Hexanes (5 mL) were added, and the solution stored at -10°C for several days. The ruby-red crystals that formed were collected by filter-cannulation to yield 23 0.35 g (0.37 mraol, 75% yield) of 11a. Anal. Calcd for C , r t CH.cCl.ErNOSi_W: C, 37.56; H, 4.80; N, 1.48. 29.5 45 3 2 Found: C, 37.55; H, 5.11; N , 1.62. IR (Nujol) \> Q 1507 cm"1. R e a c t i o n o f C p W ( N O ) ( C H 2 S i M e 3 ) 2 (4) w i t h HBF 4 «0Me 2 To a stirred, purple solution of CpW(NO)(CH2SiMe3)2 (4) (0.23 g, 0.5 mmol) in ether (15 mL) was added HBF4»0Me2 by microsyringe. Aliquots of 0.08 mL (0.05 mmol) were added, the reaction mixture being monitored by its IR spectrum after each addition, until the initial nitrosyl band at 1591 cm ^, characteristic of the starting material, had completely disappeared. The total volume of HBF4»0Me2 needed was 0.24 mL (1.5 mmol). The reaction mixture at this point consisted of a yellow solution and black solid. The solution was filter-cannulated to a new flask, and the solvent removed under vacuum. A yellow oil was obtained. IR (neat oil) : \;ou 3250 cm ^  (br) , \>.T_ 1404 cm ^  (s). When exposed to moist air, this material regenerated purple CpW(NO) (CH2SiMe3)2 (,\>m (solid film) 1541 cm"1). Attempted work-up of the yellow oil led only to decomposition to an intractable black solid. R e a c t i o n o f C p W ( N O ) ( C H 2 S i M e 3 ) 2 (4) w i t h [ P h 3 C ] + : P r e p a r a t i o n o f C p W ( N O ) ( C H 2 S i M e 3 ) ( C H 2 C P h 3 ) ( 1 2 ) : A stirred red-brown solution of CpW(NO)(CH2SiMe3)2 (4) (1.15 g, + - 12 2.5 mmol) and [Ph3C] PFg (1.16 g, 3.0 mmol) in CH2C12 (75 mL) was allowed to react for 2 days at room temperature. The resulting brown solution was concentrated under vacuum to ^15 mL, then chromatographed on a silica gel 24 column (3 x 12 cm, silica gel 60) made up in 1:1 (v:v) Ch^C^: hexanes. The same mixture of solvents was used initially as eluant, then the proportion of C H 2 C I 2 was gradually increased to 100%. A yellow band was eluted first, and yielded a yellow-white residue upon removal of the solvent. This was shown to consist mainly of Ph^ COH by its physical and spectroscopic properties (IR (Nujol) \j_„ 3470 cm"1 *H NMR ( C D C 1 . ) 6 7-7.5 (m, 15H, Ph), 2.20 (s, 1H, OH). Low resolution mass spectrum (probe temperature 120°C) m/z 260, M+. Two red bands were eluted next, and a brown material remained at the top of the column. The first red band yielded a purple eluate which was taken to dryness in vacuo. The glassy, purple residue was treated with hexanes (^  100 mL); the resulting supernatant solution was filter-cannulated away from a hexanes-insoluble beige residue, and the filtrate concentrated under vacuum to ^ 10 mL, inducing precipitation of a purple solid. The mixture was cooled to x -40°C for an hour to complete precipitation. The solid product was isolated by filter-cannulating away the mother-1iquor, and dried overnight under vacuum (0.05 torr, 25°C). These operations afforded 0.30 g of 12 (0.48 mmol, 19% yield). The second red band that followed this down the column was shown to 1 2 contain unreacted starting material by the XH NMR spectrum ' of the residue left after removal under vacuum of the solvent from the purple eluate. Single crystals of 12 were grown by evaporation of an ether-hexanes solution under a slow stream of nitrogen. Anal. Calcd for COQH„-N0SiW: C, 55.86; H, 5.33; N, 2.25. Found: C, 25 56.15; H, 5.21; N, 2.11. IR (Nujol) \>m 1572 cm"1, (CH2C12) M 1580 cm"1. »H NMR (C6Dg) fi A.89 (s, 5H, Cp_) , 7-7.6 (m, 15H, CPh3) , 3.53 (d, 1H, CH^ HgCPh^ , J = 12.8 Hz), 2.AO (d, 1H, CH^ HgSiMe^ , J = 9 Hz) , 1.28 (dd, 1H, qyjgCPh, J = 12.8 Hz, 2 Hz), -0.76 (dd, 1H, CH^ HgSiMe^ , J = 9 Hz, 2 Hz), 0.29 (s, 9H, SiMe3). *3C pH} NMR (CD0C1,) 6 150.5 (C. ), 127.5 (C or C . ), 127.9 (C 2 2 ipso ortho raeta ' ortho or C ^ ), 125.6 (C ), 102.3 (Cp), 86.A (W-CH.-C, 2 J . m = 102 Hz), 58.1 meta ' para —^ — 2 -WH (W-CH -Si), ' J ^ = 81 Hz) 62.8 (CPhg), 2.9 (SiMe_3). mp 96°C dec. Reaction of CpW(NO)(CH2SiMe3)2 (A) with [Ph 3Cj + PFg" in CD2C12; 1 9F and 3 1P NMR spectra of the Reaction Mixture A reddish-brown solution of CpW(NO)(CH2SiMe3)2 (4) (0.023 g, 0.050 mmol) and [Ph3C]+PF6~ (0.03 g, 0.08 mmol) in CD2C12 (% 0.8 mL) was prepared in a small Schlenk tube and filter-cannulated into a nitrogen-filled NMR tube capped with a small septum. 1 9F and 3 1P NMR FID's of this mixture were acquired over the next two hours. The resulting spectra are shown in Figures II-5 and II-6, and the chemical shift and coupling data are summarized in Table II-3. Attempted Reaction of A with [NH4]+PF6~ A purple solution of CpW(NO)(CH2SiMe3)2 (1) (0.23 g, 0.50 mmol) in THF (15 mL) was prepared and [NH^]+PFg (0.086 g, 0.53 mmol) was added. 26 No change in the appearance of the solution was evident, either at that time or over the next 24 hours. An IR spectrum of the solution after that period showed no change in the intensity of the nitrosyl band at 1583 cm Reaction of CpW(NO)(Ch^SiMe,)2 (4) with [C7H73+BF4~ A purple solution of CpW(NO)(CH2SiMe3)2 (4) (0.23 g, 0.50 mmol) and [C7H7]+BFA~ (0.21 g, 1.18 mmol) in CH3N02 (20 mL) was prepared. This solution was stirred overnight, after which time the colour had turned to green-black. Evaporation of the solvent in vacuo yielded an intractable, black, oily residue. Reaction of CpW(NO) (Crt^SiMe,)2 (4) with -BuCl and A1C1 3 A CH2C12 (3 mL) solution containing CpW(NO)(CH2SiMe3)2 (4) (0.23 g, 0.5 mmol), -BuCl 1 3 (0.5 mL, 0.43 g, 4.6 mmol) and A1C13 (0.20 g, 1.50 mmol) was prepared and left to stir overnight in a closed flask. After 12 hours, the reaction mixture was an amber solution, and a slight pressure had built up within the flask. When the flask was opened to the air, the escaping gases fumed and had the characteristic smell of HC1. The solution was treated with a few drops of water to destroy the excess A1C13> and then taken to dryness in vacuo. A NMR spectrum of the brown residue (C^ D^ ) showed broad resonances between 0.5 and 3 ppm (attributed to polyisobutylene), and resonances attributable to a complex mixture of Cp- and SiMe3~ containing products, none of which was CpW(NO)(CH2SiMe3)2>2 27 Attempted Reaction of CpW(NO)(CH2SiMe3)2 (4) with Ph3CBr and A1C13 A reddish-brown solution of A1C13 (0.20 g, 1.5 mmol), Ph3CBr (0.64 g, 1.5 mmol) and CpW(NO)(CH2SiMe3) (4) (0.23 g, 0.50 mmol) in CH2Cl2(15 mL)) was stirred overnight. No change in the appearance of the solution occurred. A portion of the final solution (0.5 mL) was then filtered through Florisil (0.7 x 7 cm) which was then washed thoroughly with ether. An IR spectrum of the combined purple filtrates showed only one \Jnq, at 1593 cm \ attributable to 4 . The rest of the reaction mixture was treated with Na+PF^ (0.17 g 1.0 mmol) and allowed to react further for a day. The solvent was removed in vacuo and a 1E NMR spectrum of the residue, redissolved in cg ug» contained only resonances attributable to the starting material. Results and Discussion II-A Formation of Adducts II-A-1 • AlMe3 and ErCp3 Adducts Treatment of CpW(NO)(CH2SiMe3)2 (4) with Lewis acids such as AlMe3 or Cp3Er results in immediate formation of red-to-orange adducts 11: 28 NO—-A A 11 R = CH2SiMe3> A = AlMe^, ErCp3 11c 11a These adducts can be isolated by crystallization as extremely hygroscopic solids, which upon exposure to trace moisture regenerate purple complex A. The spectroscopic properties of adducts A are consistent with the indicated formulation. Most revealing are their IR spectra; in both cases, the nitrosyl stretching frequency is shifted to lower wavenumber relative to parent compound A, as expected for the formation of an isonitrosyl linkage. These data, as well as those pertaining to the cases where A = H+ are collected in Table II-l. 29 Table II-l IR and Colour Data for CpW(NO) (Ch*2SiMe3)2 (4) and its Adducts with Lewis Acids Compound Lewis Acid UN0" A B  yN0" Colour -1 -1 cm cm 4 1541 purple 11a Cp3Er 1507 34 red lid - MgI2(ON)WR2Cp- 1505 36 red He AlMe 1447 84 orange lid H+ 1404- 137 yellow — Nujol mull, except where indicated " A X ,N0 = \0 W ~ yN0 ( U ) - ref. 2 - R = CH2SiMe3 — neat oil 30 II-A-2 Protonation of CpW(NO)(CH2SiMe3)2 (4) Reaction of 4 with HBF4»OMe2 in ether results in the formation of a yellow, oily product whose spectroscopic properties are consistent with its formulation as an adduct of type 11, where A = H+. Thus, the IR spectrum of the neat oil shows a \>NQ of 1404 cm 1, and a broad absorption in the region characteristic of OH stretches (VQ# 3250 cm . When exposed to moist air, this material quickly regenerates purple 4 (UJJQ (solid film) 1541 cm ^). Unfortunately, its thermal decomposition to an intractable black solid has to date prevented purification and complete characterization of lid. A nitrosyl ligand is, in principle, capable of being protonated at either the N or the 0 atom: 0 + + 11 + M-NO + H • [M-NO - H] or [M - N ] NH 14-17 There are few reports of protonated terminal NO ligands. Only in one case has.the site of protonation been definitely established by a single-crystal X-ray crystallographic analysis: 1 7 the osmium complex Os(PPh3)2 (C0)C12(HN0) is known to be N-protonated. The available data for complex lid do not permit unambiguous determination of the site of protonation. However, by analogy with the other adducts 11, in particular lib which has been crystallographically 2 characterized as an 0-adduct, O-protonation is postulated. 31 Two known cases of 0-protonated NO ligands are [(Cp'Mn(NO))^~ (u -NOH)] and [Ru^(CO)^(u -NOH)], the NOH group being triply bridging in both complexes. II-A-3 Spectroscopic Properties of the Adducts As can be seen from Table II-l, the y N 0 ' s of the adducts are shifted to lower wavenumbers compared to that of the parent 4. The extent of this shift depends on the hardness of the Lewis acid; the proton, the hardest Lewis acid, lowers the by 137 cm \ whereas a softer acid such as Cp^Er only shifts i t by 34 cm This trend is as expected, as harder acids drain the electronic density from the NO ligand more efficiently, and increase back-bonding from the metal to a greater extent, than the softer acids. By this 3 criterion, Cp^Er is a softer acid than AlMe^, as previously shown, and about 1 2 the same hardness as Mgl^ (ON)WR2Cp. ' The colours of adducts 11 are also reported in Table I I - l . A correlation between these and the hardness of the Lewis acid can also be seen: as harder acids are used, the colour shifts from purple in uncomplexed 4 through red for adducts of soft acids to yellow for the protonated species. A similar trend has been reported in the colours of aluminum and 20 gallium alkyl adducts of Mo(phen)(PPh^)(CO)2 (phen = phenanthroline) and related species, which contain analogous isocarbonyl linkages. The absorbance giving rise to the colour of these complexes was attributed to an electronic transition from a ub. orbital centered on the Mo(C0)„ fragment, to a tTb 1 32 orbital located on the phenanthroline ligand. This absorbance is shifted to higher energies when Lewis acids are coordinated to the carbonyl ligands, due to a lowering in energy of the trb^  orbital as a consequence of the drainage of electron density from the CO ligand. A similar reasoning can account for the colours of adducts 11. The HOMO of dialkyls such as 4 has been shown by Fenske-Hall molecular calculations to have components from the metal's d and the nitrosyl's 2TT orbitals. 1 Electronic transitions involving promotion of electrons from this orbital might be expected to be shifted to higher energies as coordination of a Lewis acid to the nitrosyl lowers the energy of the NO's 2TT orbitals. II-B Electrophilic Cleavage of a Silicon-Carbon Bond of CpW(NO)(CH2SiMe3)2 (4) II-B-1 Synthesis and Properties of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) Reaction of 4 with a 30% excess of trityl cation in dichloromethane results initially in formation of an acid-base adduct of type 11. Such adduct formation is indicated by a change in colour of the solution from the purple of 4 to red-brown upon addition of trityl hexafluorophosphate and disappearance of the at 1566 cm 1 characteristic of 4. However, over the course of a few days, a subsequent reaction takes place, resulting in cleavage of a silicon-carbon bond and isolation, after chromatography, of purple complex 12 in low to moderate yield (10-40%). 33 i Me 3Si C H 2 J} C H 2SiMe 3 [Ph3C]+Prf CHJCIJ i Me^Si0"2 K C H 2CPh, 4 12 Mixed dialkyl complex 12 is a crystalline, diamagnetic solid, stable in air for short periods of time and under indefinitely, provided the solid is analytically pure. Solutions, however, are air-sensitive and thermally decompose under inert atmosphere in about a week, the decomposition being accelerated by impurities. The molecular structure of 12 has been established by a single-crystal X-ray crystallographic analysis performed by Ms Vivien Yee and Dr James Trotter of this Department. (All the X-ray analyses discussed in this work were done by Yee and Trotter, and details of the data collection and refinement will be reported elsewhere.) Complex 12 is chiral, and crystallizes with one molecule of each enantiomer per unit cell. There is a close similarity, in the lengths and angles of bonds about the metal centre, between 4 and 12. Selected data are summarized in Table II-2, and Figure II-1 is an ORTEP diagram of 12. Fig. II-l Solid State Molecular Structure of CpW(NO)(CH2SiMe3)(CH2CPh3) (12). a) ORTEP diagram b) Packing diagram. 35 Table II-2 2 Selected Bond Lengths and Angles of CpW(NO)(CH2SiMe3)2 (4) and CpW(NO)(CH2SiMe3)(CH2CPh3) (12)-4 12 Bond Lengths (A) W-N 1.757(8) 1.740(7) N-0 1.226 (10) 1.240(8) W-CH2SiMe3 2.104(9); 2.108(10) 2.132(9) W-CH2CPh3 2.124(8) Angles (deg) W-N-0 169.5(6) 170.3(6) CH2-W-CH2 109.6(4) 106.9(3) Me3SiCH2-W-NO 95.7(4); 97.7(4) 99.0(3) Ph3CCH2-W-NO 99.0(3) — Estimated standard deviation in parentheses. The considerable M-NO back-bonding that was indicated in 4 by the 1 2 short W-N and long N-0 bonds, and the essentially linear nitrosyl ligand, ' is also present in 12. The comparable, low nitrosyl stretching frequencies seen in the IR spectra of 4 and 12 (1566 cm 1 and 1580 cm \ respectively, in CH2C12) support this conclusion. The W-CH2SiMe bond is 0.026 A longer in 12 than the average for the two analogous bonds in 4, suggesting i t may be somewhat weaker in 12; this may account for the fact that this alkyl group is easily lost from 12 by elimination of TMS under differing conditions (see Chapter I I I ) . 36 There are no unusual interactions, either inter- or intra-molecular, between atoms. The ortho hydrogens on the phenyl rings, in particular, might have been expected to interact with the 16e tungsten centre, especially in view of the ready ortho metallation reactions of 12 (see Chapter III). However, the closest ortho hydrogen (that on C29) is well removed at 3.360 A from the metal. The spectroscopic properties of 12 are consistent with the general features of the solid state molecular structure and indicate that the basic monomeric unit persists in solution. The *H NMR spectrum is shown in Figure II-2. Particularly interesting are the resonances due to the methylene protons of the two alkyl ligands (CH^ SiMe^  and CH^CPh^). Each of these constitutes an AX spin system which produces a pair of doublets in the spectrum. The higher field one (6 2.40, -0.76 ppm, J = 9 Hz, in Cgn§) is attributed to the CH^ SiMe^  group, by comparison of the chemical shifts and 1 2 coupling constant with those of the parent compound 4. ' (6 2.31, -0.52 ppm, J = 8.3 Hz in C^Dg). The other pair of doublets (6 3.53, 1.28 ppm, J = 12.8 Hz in Cgng) is correspondingly assigned to the CH^ CPh^  group. An additional coupling of 2 Hz between one of the protons on one alkyl group and one proton of the other is also evident. This feature cannot be easily explained. Such long range, 4-bond couplings of 1-4 Hz are well-known in ^C' C systems that are held rigidly in the indicated coplanar "W" 21 conformation. However, this is not the conformation adopted by 12 in the solid state: < & 2 ? SiSVIe, T | 1 I 1 I I ' I I 7 6 5 4 3 2 1 0 -1 6 ppm Fig. II-2 270 MHz *H NMR Spectrum of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) in C6D6. 38 The angle between the two planes defined by H^ C^ W and WC^ Hp is 69°. Examination of a molecular model shows that arranging the C^ H^  and C^ H^  bonds so that they are coplanar with the CjWC2 unit forces the bulky SiMe^ and CPh^  groups unacceptably close to each other. Perhaps the observed coupling is between H_ and H„ and due to their proximity in space (2.339 A ) . The 13C{1H} NMR spectrum of 12 is shown in Figure II-3, along with the assignment of the various resonances. II-B-2 By-products of the Synthesis of 12 The synthesis of 12 from A can be represented by eq (1) CpW(NO)(CH2SiMe3)2 + [Ph3C]+PF6~ • CpW(NO)(CR^SiMe^(CH2CPh3) (1) A 12 + Me3SiF + "PF5". The formation of Me3SiF and "PF,." (as Lewis-base adducts) as the other products has been demonstrated by 3 1P and 1 9F NMR spectroscopy of the reaction mixture, in CD 9C1„. The resulting spectra are shown in Figures II-A and II-5, Ph I W Me3Si * g CPh3 £jpso Cp W-CH2-C W-CH2-Si Si Me, CPh3 1 | 1 1 1 1 I I' I I | I I I I | I I I I | I I I I | I | | [ | | | | | | | | I I | | I I I | I | I I | I I I I | ' 260 240 220 200 180 160 i i | 111140 l | M l l | ' l l  | l l l l | l l l l | l i i l | I I l l | l I I l | I I I I | I l 120 mo 80 60 40 rryr 20 ' | i ' ' i I 0 PPM • solvent Fig. II-3 75 MHz "Cf^H} NMR Spectrum of (12) in CD 2C1 2. AO respectively. These show resonances attributable to PFg , OPF^  (resulting from 22 hydrolysis of PF,. ), Me^SiF, and two kinds of base-PF,. adducts. The chemical shifts and coupling data for each species are collected in Table I I - 3 ; they 22 23 agree reasonably well with published data. ' The 1 9F NMR resonances due to the base-PF,. adducts are distinctive. They consist of a doublet of doublets (due to A equatorial fluorines, coupled to the phosphorus and one axial fluorine) and a doublet of pentets (due to the axial fluorine, coupled to the phosphorus and four equatorial fluorines) 22 in A:l ratios. These patterns are typical of octahedral base-PF,. adducts. Signals for two such adducts are seen in the 1 9F NMR spectrum, although the 3 *P chemical shifts for the two are apparently too close to permit resolution in the 3 JP NMR spectrum. This is not particularly surprising, as 1 9F chemical 2A shifts are known to be very sensitive to changes in molecular structure. The Lewis bases in these adducts cannot be known with certainty. In view of the basicity of the nitrosyl ligand in CpW(N0)R2 complexes, demonstrated above, A and 12 are likely candidates. Finally, the other product of reaction (1) is Me^SiF. The silicon-25 fluorine bond is known to be extremely strong (565 kJ/mole) and presumably its formation provides the driving force for the reaction. In addition to the assigned resonances the 3 1P NMR spectrum also shows a doublet of quartets (6 -138.8 ppm, J = 1552, 80A Hz), which has no corresponding 1 9F resonance within the spectral width of the spectrum, and whose origin has not been identified. OPF, * PF6" ffl o Base- PF5 • o unidentified (—I—I i H I I I—I | I I I I | 1 I I I I |—I I I I | I—I I I |—I—I i | i |—i—I—I—i—| I I i—r j I T i—i—|—r-- 40 -60 -80 -100 -120 - i — i — | — i — i —r -|—I—I—I—I—|—I—i—i—r-]—' •140 F i g . II-4 121.4 MHz 3 1 P NMR Spectrum of the Reaction Mixture of CpW(NO)(CH 2SiMe 3)(CH 2CPh 3) (4) and [Ph 3C] +PF 6" i n CD 2C1 2. I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 - 20 -AO - 6 0 -BO 6 ppm Fig. II-5 282 MHz 1 9F NMR Spectrum of the Reaction Mixture of CpW(NO)(CH2SiMe3) (4) and [Ph3C]+ PF6~ in CD2C12> Table II-3 S 1 P and 1 9 F NMR Data from the Reaction Mixture of CpW(NO)(CH-SiMe,). (4) and [Ph.C] + PF~ i n CD.C1. Species J 1 P (121.4 MHz) >»F (282 MHz) L i t e r a t u r e Data J (Hz) 6- (ppm) mult. 6- (ppm) mult. J (Hz) a- >ip ppm 6^ »'F ppm J (Hz) P F e" OPF 3 Me 3SiF -143.8 -35.5 br septet q 'J„- 700 3.4 -12.8 -82.2 br d d decet (with S i - s a t . ) l i P F = 704 iJ p F=1065 J 4H = 8 ' ^ S i F * 2 2 0 _ 1 A 522.23b 22 -35 % i o 2 2 - 1 5 . 8 2 2 - 8 2 2 3 a 22 7 1 0 Z Z 22 1 0 8 0 " Base.-PF C -139.6 dp 22 (F ) ax eq Base^-PFj -139.6 dp »J„ =739 ax 'JpF = 8 0 2 eq -6.8 8.7 dp dd i J p F = 7 3 4 ; >J F p=60 i J p F = 8 0 2 ; »J F p=60 l i P F = 7 4 0 M F = 5 5 2 2 (F ) ax > J p F =739 ax -6.4 dp lip F=734; >J p F=60 eq l i P F =802 eq 8.0 dd 1ip F=796; »J F F=60 ? -138.8 dq 1552, 804 — J 1 P chemical s h i f t s i n ppm downfield from e x t e r n a l 85% H^PO - l , F chemical s h i f t s i n ppm downfield from e x t e r n a l CF.COOH. 44 II-B-3 Precedents for Electrophilic Cleavage of Silicon-Carbon Bonds The occurrence of reaction (1) establishes a transformation of a silicon-containing ligand that is, to the best of my knowledge, unprecedented in transition-metal organometallic chemistry. The reaction formally involves the removal of an anionic ligand from a silicon centre by an electrophile: Me3Si-R + E + • E-R + "Me3Si+" (2) where R = CH2W(CH2SiMe3)(NO)Cp E + = Ph3C+ 26 26 + Both nucleophiles and electrophiles, either inorganic (H , metal 27 chlorides such as FeCl 3 > A1C13> HgCl2, BiCl 3) or organic carbocations, are well-known to attack silicon-carbon bonds. This feature has been extensively used in synthetic organic chemistry for the formation of new carbon-carbon 27 bonds. Reaction (1) is the first application of this method to modify a silicon-containing ligand on a transition metal. The reverse approach, using an organometallic cation to remove an alkyl group from an organosilicon 28 compound, was reported in 1980: 45 + R (CO) 3Fe-R 3 PF6 (3) (CO) 3Fe-R. II-B-A Mechanistic considerations At present, the mechanism of reaction (1) can only be the subject of speculation. However, since A does not react with [NH^]+PF^ , i t would seem that attack on the Si-C bond has to be by the Ph3C+electrophile and not by the PF^ anion. Reactions (A)-(6) are therefore proposed to account for the formation of the observed products 6 (A) [Me3Si]+PF6~ • Me3SiF + PF$ PF5 + W-NO • W-NO -PF5 R = CH2W(CH2SiMe3)(NO)Cp W = CpW(CH2SiMe3)2 or CpW(CH2SiMe3)(CH2CPh3) (5) (6) 46 Silyl cations such as [Me^Si] have never been observed in solution, hence, it probably does not persist as a discrete species in this case, but immediately attacks the PFg anion. As outlined in the introduction to this chapter, the anticipated result from the reaction of 4 with trityl cation was hydride abstraction. That this was not observed may be due to the steric bulk of the Cr^SiMe^ ligand. 30 31 It can be noted that both Gladysz and Bly have attempted unsuccessfully to remove an a-hydride from analogous Cr^ CMe^  ligands, and have attributed the failure of the reaction to steric hindrance. II-B-5 Attempted Extension to Other Electrophiles In view of the difficulty experienced by other investigators in 2 synthesizing complexes of type 4 with a broad range of alkyl groups, reactions such as (1) using different electrophiles seemed appealing as a way to modify alkyl ligands already on the metal centre. Some preliminary experiments were therefore made to extend the scope of reaction (1). One approach to the electrophilic cleavage of Si-C bonds often used in 27 organic chemistry involves the use of alkyl halides and aluminum trihalides 32 to generate an incipient carbocation in situ, as shown in eq. (7). (The same reaction is used in the Friedel-Crafts alkylation of benzene and its derivatives.) 47 4 - cat. AIBr3 . or 1 eq AICI 3 r AIX. CI + (7) Si Me, 4 -Me X = Cl or Br Tert-butyl chloride was selected as the alkyl halide for the first 34 attempts since the intermediate cation is relatively stable. The expected product 13 is thermally stable and can be readily recognized by its known 2 spectroscopic properties. I Me3CCHz g C H 2cMe, 13 (To avoid the possibility of a statistical mixture of CpW(NO)(CH^SiMe^)2> CpW(NO)(CH2CMe3)(CH2SiMe3) and CpW(NO)(CH2CMe3) , an excess of alkyl chloride was used.) Unfortunately, the reaction of 4 with -BuCl in the presence of 48 an excess of AlCl^ did not result in the formation of 13, as judged by 1H NMR spectroscopy of the non-volatiles from the reaction mixture. Instead, decomposition of the organometallic reactant to a complex mixture of products was observed. Formation of polyisobutylene was also suggested by an examination of the 1H NMR spectrum, which contained broad resonances between 0.5 and 3 ppm. This is the product expected from the polymerization of 35 ^ 36 isobutylene, produced by elimination of H from the t-butyl cation, as shown in equations (8)-(10) CI -*- AICI3 4 — - 4 * - < -< - i -< + H" polyisobutylene (8) (9) (10) Similarly, reaction of 4 with [C^E-,]+M^ ([C^H^] += tropylium cation) resulted in decomposition. Complex 4 did not react at a l l with Ph^ CBr in the presence of excess AlCl^, either in the presence or the absence of Na+PF ~. o These preliminary investigations suggest that reaction (1) is not of general applicability. The reagent cations needed are highly reactive species 49 susceptible to involvement in side-reactions, and the possible sites of attack on the organometallic starting material are numerous. Clean, high-yield reactions are thus unlikely. 50 References 1. Legzdins, P.; Rettig, S.J.; Sanchez, L.; Bursten, B.E.; Gatter, M.G. J. Am. Chem. Soc, 1985, 107, 1411. 2. Legzdins, P.; Rettig, S.J.; Sanchez, L., submitted for publication to Organometallics. 3. Crease, A.E.; Legzdins, P. J. Chem. Soc, Dalton Trans., 1973, 1501. 4. Legzdins, P.; Rettig, S.J., Sanchez, L. Organometallics, 1985, 4, 1470.' 5. Legzdins, P.; Phillips, E.C., manuscript in preparation. 6. Collman, J.P.; Hegedus, L.S.; Norton, J.R.; Finke, R.G. Principles and  Applications of Organotransition Metal Chemistry, 2nd ed.; University Science Books: Mill Valley, CA, 1987: pp 475-485. 7. Ref. 6, pp 577-584. 8. Ref. 6, pp 811-815. 9. Shriver, D.F.; Drezdzon, M.A. The Manipulation of Air-Sensitive Compounds, 2nd ed.; Wiley-Interscience: Toronto, 1986. 10. Merck Deuterated Solvents for NMR, Catalogue, MSD Isotopes, Montreal, Que., Price List 47c, p 7. 11. Cp-jEr was prepared by A.E. Crease according to the method of Calderazzo, F.; Pappalardo, R.; Losi, S. J. Inorg. Nucl. Chem., 1966, 28, 987. 12. [Ph2C]+PFg~ was purchased-from Aldrich and recrystallized from Ct^C^/hexanes, then stored under N2 at 5°C until use. 13. ^BuCl was distilled from P2O5 before use. 14. Grundy, K.R. ; Reed, C.A.; Roper, W.R. J. Chem. Soc, Chem. Commun. , 1970, 1501. 15. La Monica, G.; Freni, M.; Cenini, S., J. Organomet. Chem, 1974, 71, 57. 16. Enemark, J.H.; Feltham, R.D.; Riker-Nappier, J.; Bizot, K.F.; Inorg. Chem. 1975, 14, 624. 51 17. Wilson, R.D.; Ibers, J.A. Inorg. Chem., 1979, 18, 336. 18. Legzdins, P.; Nurse, CR. ; Rettig, S.J. J. Am. Chem. Soc. , 1983, 105, 3727. 19. Stevens, R.E.; Gladfelter, W.L. J. Am. Chem. Soc, 1982, 104, 6454. 20. Shriver, D.F.; Alich, A. Inorg. Chem., 1972, 11, 2984. 21. Becker, E.D. High Resolution NMR, Theory and Applications; 2nd ed.; Academic Press: New York, 1980; p 104. 22. Schmutzler, R. Adv. in Fluorine Chem., 1965, 5, 31. Note that in this review on fluorides of phosphorus, 3 1P chemical shifts are reported upfield from 85% H3PO4. 1 9F chemical shifts are reported upfield from TFA or CCI3F, as indicated. 23. a) For useful tabulations'of 1 9F chemical shifts, see Emsley, J.W.; Phillips, L. Prog. NMR Spectrosc., 1971, 7, 1. b) For useful tabulations of 3 1P chemical shifts, see Mavel, G. Ann.  Reports NMR Spectrosc, 1973, 5B, 1. 24. Mann, B.E. in NMR and the Periodic Table; Harris, R.K. and Mann, B.E., Eds.; Academic Press: London, 1978; p 99. 25. Greenwood, N.N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 389. 26. Bazant, V.; Chvalovsky, V.; Rathousky, J. Organosilicon Compounds; Academic: New York, 1965, Vol. 1. 27. Parnes, Z.N.; Bolestova, G.I. Synthesis, 1984, 991. 28. Kelly, L.F.; Narula, A.S.; Birch, A.J.; Tetrahedron Lett., 1980, 21, 871. 29. Ponec, R. in Carbon-Functional Organosilicon Compounds; Chvalovsky, V. and Bellama, J.M., Eds.; Plenum: New York, 1984; pp 275-276. 30. Kiel, W.A. ; Lin, G.-Y.; Bodner, G.S.; Gladysz, J.A. J. Am. Chem. Soc, 1983, 105, 4958. 31. Bly, R.S.; Bly, R.K.; Hossain, M.M.; Silverman, G.S.; Wallace, E. Tetrahedron, 1986, 42, 1093. 32. Bolestova, G.I.; Parnes, Z.N.; Latypova, F.M.;, Kursanov, D.N. Zh.Qrg.  Khim., 1981, 17, 1357. Chem. Abstr., 1981, 95, 168 419. Cited in ref. 27. 52 33. Fessenden, R.J.; Fessenden, J.S. Organic Chemistry, 3rd ed.; Brooks/Cole: Monterey CA, 1986; pp 478-479. 34. Ref..33, p 189. 35. Ref. 33, p 437. 36. Ref. 33, pp 198-199. 53 CHAPTER III Reactivity of CpW(NO)(CH.SiMe,)(CH2CPh3) The synthesis of CpW(NO)RR' (12) (for the rest of this chapter, R = CH2SiMe3> and R' = CH2CPh3) provided the first dialkyl complex of the type CpW(NO)R^R2> where R^  f R2» Symmetrical dialkyls of this type (where R^  = R2) show interesting reactivity with a variety of small molecules, studied using 1 2 CpW(NO)(R)2 (A) as a prototypal complex ' and summarized in the introduction to this thesis (see Scheme 1-1). Most of the reagents employed attack one of the W-C bonds but leave the other one intact. Analogous reactions using an unsymmetrical dialkyl such as 12 can therefore in principle yield two different products, depending on which one of the W-C bonds is attacked. Work was directed towards establishing which one of these products, i f any, would be favoured. In the course of this investigation, i t was found that although some reactions proceed analogously for both 4 and 12, other reactions follow unexpected courses. The results of these investigations are presented here. Experimental Section Standard techniques employed were detailed in Chapter II. The starting material, CpW(NO)(CH2SiMe3)(CH2CPh3) (12) was always prepared and chromatographed just before use, as indicated in Chapter II. The eluate from the column was collected, taken to dryness under reduced pressure, and the residue weighed in a tared Schlenk tube. It was then redissolved in an appropriate solvent and transferred, i f necessary, to a reaction flask. On several occasions, lH NMR spectra of the product obtained in this fashion showed i t to be reasonably free of proton-containing impurities. The yield was generally around 40%. Nitric oxide (Matheson, CP.) was purified by passage through a column of silica gel cooled to -78°C. Oxygen (Medigas, USP) was used without purification. KBr pellets were prepared using infrared-grade KBr purchased from Mallinckrodt. Decomposition of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) in CgHg A benzene solution (10 mL) of CpW(NO) (CH2SiMe3) (CH"2CPh3) (12) (0.10 g, 0.16 mmol) was left undisturbed for 5 days. During this time, the colour of the solution changed from purple to amber, and a tan precipitate formed. The solvent was removed in vacuo. The IR spectrum (Nujol mull) of the solid residue showed bands assignable to terminal nitrosyls at 1594, 1578, 1561 and 1547 cm A 1H NMR spectrum of the residue in CgD^  showed resonances attributable to a mixture of several different Cp-containing compounds. These products were not further investigated. Decomposition of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) in C & D 6 A sealed NMR sample of CpW(NO) (CH"2SiMe3) (CH"2CPh3) (12) in C^^, which had been degassed by three freeze-pump-thaw cycles before being sealed, was kept at room temperature for 5 days. The reaction was monitored by XH NMR spectroscopy. After 5 days, the sample consisted of an amber solution and tan precipitate. The lH NMR spectra collected showed that a l l the CH„SiMe_ groups 55 had been converted to TMS (6 0.00, s). Again, there were several different Cp-containing fragments, which corresponded to the ones observed in the reaction in C,H,. Similar results were obtained using CD„Cln or CDCl_. o o z 2 J Decomposition of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) in MeCN: Preparation of CpW(NO)(CH2C(C6H4)Ph2)(NCMe) (14) A solution of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) (0.30 g, 0.48 mmol in CH"3CN (10 mL) was kept, undisturbed, for 3 weeks. This produced an amber solution and transparent, brownish-red crystals, suitable for X-ray crystallo-graphy. These crystals were collected by cannulating away the supernatant liquid, then dried overnight under vacuum (0.05 torr). In this manner, 0.20 g (0.35 mmol, 73% yield) of 14 were obtained. The evolution of TMS as the other product was confirmed by 1H NMR-monitoring of the reaction in CD3CN in a separate experiment. Anal. Calcd for C^H^N^W: C, 56.27; H, 4.20; N, 4.86. Found: C, 56.51; H, 4.30; N, 4.70. IR (KBr pellet) \Jnq 1574, 1559 cm-1. Low resolution mass spectrum (probe temperature 180°C) m/z 535 [M-CH3CN]+. The crystals decomposed gradually without melting when heated, decomposition being first apparent at 150°C. They showed no or very l i t t l e solubility in common organic solvents. Attempts to dissolve them in CgDg, CD3CN, CD3N02 or CD2C12 resulted in pale yellow, very dilute solutions whose lH NMR spectra showed only peaks attributable to a mixture of decomposition products. 56 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) with PMe3: Preparation of CpW(NO)(CH2SiMe3)(CH2CPh3)(PMen) (15) A purple solution (\>NQ 1607 cm"1) of CpW(NO) (CH2CPh3) (CH2SiMe3) (12) 3 (0.08 g, 0.13 mmol) in ether (5 mL) was treated with excess PMe3 (0.2 mL, 2 mmol) added by syringe. The colour immediately changed to yellow, and an IR spectrum of the solution indicated that the had shifted to 1580 cm 1. Addition of hexanes (5 mL) and cooling down to -78°C for 1 hr induced the precipitation of a yellow solid which turned pink in colour when the mother-liquor was removed by filter-cannulation and the solid was subjected to reduced pressure for a few minutes. Redissolution of the solid in C^ Dg or CDCl3 in the absence of excess phosphine led to purple solutions, the colour being characteristic of 12. A 1H-NMR spectrum of CpW(NO)(CH2SiMe3)-(CH2CPh3)(PMe3) (15) in CDC13 in the presence of a large excess of PMe3 was obtained. *H NMR 6 7.0 - 7.5 (m, 15H, Ph) , A.94 (d, 5H, Cp_, 3 J H p = 2.5 Hz),-3.04 (dd, 1H, CH, 2 J R H = 15 Hz, 3 J H p = 2.5 Hz) 1.40 (d, 9H, PMe3> 2 J = 9 Hz), 0.04 (s, 9H, SiMe,). The resonances due to the other three H r J methylene protons are obscured, presumably, by those due to the excess uncoordinated PMe3 (6 1.00, d, J = 3 Hz) coordinated PMe3, and 0PMe3 present as an impurity in PMe3 (6 1.49, d, J = 15 Hz). After being stored for 8 months at room temperature, exposed to ambient light, the same sealed sample's XH NMR spectrum showed, in addition to the resonances listed above, complex new patterns attributed to a mixture of decomposition products. No peak at 0 ppm attributable to TMS was observed. Three new resonances attributed to Cp_W(PMe3) fragments appeared at 5.66, 5.62, and 5.00 ppm (d, J = 2 Hz in a l l cases). The combined intensity of these was 35% of the total intensity of the 57 Cp resonances, including that attributed to CpW(NO)(Cg SiMf* )(C| CPh lPMe3) (15). Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) with 0 2 A purple solution of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) (0.10 g, 0.16 mmol) in CH2C12 (100 mL) was prepared, and 0 2 was bubbled through i t until the purple colour completely disappeared (^  10 min). A clear yellow solution was obtained. The solvent was removed under vacuum, and a XH NMR spectrum of the dried residue in C,D, was obtained. It showed resonances attributable to a o o mixture of CpW(O) (CH2CPh3) (17) and CpW(O) (CH2SiMe3)(18) in 2 12 a ratio of 1:5, ' these being the only two Cp-containing species present. The resonances attributed to 17 were 6 7.0 - 8.0 (m, 15H, Ph), 5.30 (S, 5H, Cp_) , 3.35 (5, 2H, CH,,). Several attempts to separate the two products were unsuccessful. In repeat experiments, the time required for completion of the reaction was found to vary from *» 10 min. to *» 5 hours. However, *H NMR spectra of the dried residue from the reaction mixture in CgD^always showed resonances associated with the same two products in the same ratio as above. Preparation of CpW(NO)(CH2CPh3)(u2-02N2CH2SiMe3) (19) Nitric oxide was bubbled through a hexanes (150 mL) solution of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) (0.62 g, 1.0 mmol) for 10 min. The colour of the solution turned from purple to yellow, and a yellow precipitate was formed. The mixture was cooled to ^  -23°C to ensure completion of precipitation. The solid product was isolated by filter-cannulating away the 58 supernatant liquid, washing with hexanes (3 x 15 mL), and drying under vacuum (0.05 torr) overnight, in a foil-wrapped flask to avoid exposure to light. In this manner, 0.40 g (0.58 mmol, 58%) of 19 was obtained. In a separate experiment, the final reaction mixture was taken to dryness in vacuo, and a XH NMR spectrum of the residue in CgD^  showed that 19 was the only Cp-containing product. Anal. Calcd for C^H^N^SiW: C, 50.90; H, 4.87, N, 6.17. Found: C, 51.17; H, 5.00; N, 5.96. IR (Nujol mull): v 1597, 1582 cm"1, (CH2C12) 1591 cm"1. 400 MHz *H NMR (CDClg). Major isomer 6 7.49 (d, 6H, ortho-H, J = 8 Hz) 7.23 (t, 6H, meta-H, J = 8 Hz), 7.14 (t, 3H, para-H, J = 8 Hz), 5.36 (s, 5H, Cp_) , 3.87, 3.93 (AB, 2H, CH2> J = 15 Hz), 3.26, 3.29 (AB, 2H, CH2, J = 12 Hz), 0.31 (s, 9H, SiMe3). Minor isomer 6 7.56 (d, 6H, ortho-H, J = 8 Hz), 7.23 (t, 6H, ortho-H, J = 8 Hz), 7.14 (t, 3H, para-H, J = 8 Hz), 5.27 (s, 5H, Cp_) 3.82, 3.93 (AB, 2H, CH_2, J = 14 Hz), 3.49 3.46 (AB, 2H, CH_2, J = 13.5 Hz) 0.23 (s, 9H, SiMe3). Major:minor ratio 2.7:1 (In CgDg, this ratio is 2.5:1). ^CpH} NMR (CDC13). Major isomer 6 151.6 (ipso-C) , 130.0 (ortho- or meta-C) , 127.2 (ortho- or meta-C) , 125.0 (para-C) , 104.4 (Cp_) , 61.0 (CPh3) , 47.7 (W-CH2-Si) 41.5 (N-CH2-C) , -2.3 (SiMe_3) . Minor isomer 6 151.6 (ipso-C) , 130.0 (ortho or meta-C) , 127.2 (ortho or meta-C) , 125.0 (para-C) , 104.2 (Cp_) , 48.3 (W-CH2-Si) , 46.7 (N-CH2-C) , -2.4 (SiMe_3) . Due to its low intensity, the signal due to the CPh3 carbon of the minor isomer could not be observed, mp 149°C dec explosively. 59 Photolysis of CpW(NO)(CH2CPh3)(n2-02N2CH2SiMe3) (19). Formation of CpW(0)2(CH2CPh3) (17) A sealed NMR sample of CpW(NO) (CH2CPh3) (r|2-02N2CH2SiMe3) (19) in CgDg, which had been degassed by three freeze-pump-thaw cycles before being sealed, was kept for 17 days at room temperature, exposed to ambient light. The reaction was monitored by 1K NMR spectroscopy. During ths time, the resonances due to 19 in the spectra slowly decreased in intensity and were replaced by another set, attributed to CpW(O)2(CH"2CPh3) (17) (6 7.0 -8.0) (m, 15H, Ph), 5.30 (S, 5H, Cp_) , 3.35 (S, 2H, CH2). This was the only new Cp-containing product observed. A complex pattern of new resonances between -0.2 and 0.6 ppm also appeared. At the end of 17 days, the ratio of 17 to starting material 19, calculated from the relative intensity of the Cp resonances, was ^ 3:7. The sample was then irradiated for 3 1/2 hours, using a medium-pressure mercury lamp, (Hanovia 608A) housed in a water-cooled Pyrex jacket. A *H NMR spectrum of the sample after this treatment showed complete conversion of 19 to 17. The sample's colour had changed from its initial yellow to amber. The sample tube was then broken open and its contents poured into a Schlenk-tube. The solvent was removed in vacuo to yield a light brown residue. IR (Nujol mull) \^_Q 952, 910 cm .^ Photolysis of CpW(NO)(CH2SiMe3)(u2-02N2CH2SiMe3) (5) 2 2 A sealed NMR sample of CpW(NO)(CH2SiMe3)(u -02N2CH2SiMe3) and cyclohexane 60 (as an integration standard) in C^ Dg was irradiated overnight, using a medium-pressure mercury lamp (Hanovia 608A), housed in a water-cooled Pyrex jacket. During this period, the sample's colour went from yellow to brown. The only Cp-containing product was CpW(0)2(CH2SiMe3), identified by its 12 characteristic 1H NMR spectrum. Integration of the Cp resonances against the cyclohexane's showed the yield to be ^ 43%. A spectrum taken after the sample had been irradiated for 1 hour showed a transient species with a Cp resonance at 5.70 ppm. Preparation of CpW(O) (SCI^SiMe,) (Cr^CPh^CgH^)) (20) Sulphur (0.0601 g, 1.9 mmol of S) was added to a toluene (40 mL) solution of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) (1.05 g, 1.7 mmol). The mixture was stirred for a week, after which time a 1H NMR spectrum (C^ D^ ) of the dried residue from a small portion of the reaction mixture showed complete consumption of the starting material. During this week, the colour of the solution changed from purple to dark red-brown. The mixture was filtered through a Florisil column (3x4 cm, supported on a glass f r i t ) , which was then washed with ether (3 x 30 mL). The collected filtrates were taken to dryness in vacuo, the residue redissolved in a 1:2 mixture of CH2C12 and hexanes (15 mL). This was transferred to the top of a silica gel column (3 x 12 cm, silica gel 60), made the same solvent mixture, which was also used as eluant initially. As the chromatography progressed, the proportion of CH2C12 in the eluant was gradually increased to 100%. Four bands separated upon elution. The first two, yellow and salmon-pink in colour respectively, contained very small amounts of material and were discarded. The third band 61 was yellow-orange and gave a yellow-orange residue when the eluate was taken to dryness. This residue was recrystallized from ether to obtain 0.10 g of pale orange crystals of 20 (0.16 mmol, 9% yield). Single crystals, suitable for an X-ray diffraction analysis, were grown from ether at -10°C. Anal. Calcd for C2gH32OSSiW: C 54.38; H, 5.04; N, 0.00; Found: C, 53.94; H, 5.22, N, 0.00. IR (Nujol mull) vTT n 947 cm-1,^.., 1246 cm"1, \j_ J W=0 SiMe_ ' Cp_ J o 849 cm"1 IR (CH2Cl2) v^=Q 949 cm"1. *H NMR (CgDg) 6 7.74 (dd, 1H, Ph, J = 7 Hz, 1.5 Hz) 6.8 - 7.2 (m, 13H, Ph) , 5.12 (s, 5H, Cp_) , 4.30, 3.56 (AB, 2H, S-CH2-SiMe3, J = 14 Hz), 2.57, 2.23 (AB, 2H, W-CH2-C, J = 12.5 Hz), 0.24 (s, 9H, SiMe3). ^CpH} NMR (C6D&) 8 166.9, 164.1, 154.3, 147.9 (ipso C) ; 141.3, 131.3, 129.7, 129.3, 128.4, 126.4, 126.2, 126.1, 125.7 (Ph); 107.2 (Cp); 74.0 (W-CH2-C ! J C W 65 Hz), 71.1 (CPh3) , 28.4 (s-CH2-SiMe3) , -1.4 (SiMe_3) . Low-resolution mass spectrum (probe temperature 120°C) m/z 640 (P +). 184 High-resolution mass spectrum: m/z 640.1455 (C2gH32OSSi W), 642.1483 (C 2 gH 3 2OSSi 1 8 6W). The fourth band on the column was of a darker orange colour; the eluate was taken to dryness in vacuo to give a red-orange residue which decomposed upon attempted recrystallization. 62 Results and Discussion The reactions of CpW(NO)(CH2CPh3)(CH2SiMe3) (12) that were studied in this work are summarized in Scheme III-l. Each of the transformations shown will now be considered in some detail. III-A Thermal Behaviour III-A-1 Decomposition in the Absence of a Coordinating Solvent In non-coordinating solvents such as C,H-, C,D-, CDC1. or CD»C1„, o o o o i z z 12 decomposes in about a week at room temperature to an intractable light brown powder, which appears to consist of a mixture of products. aH NMR spectroscopy of the reaction mixture in deuterated solvents shows that a l l CH2SiMe3 groups have been converted to TMS. The decomposition is accelerated by impurities. Decomposition to a brown powder also occurs in the solid state i f the product is not analytically pure, decomposition being first noticeable after a day at -10°C. Analytically pure crystals of 12, however, can be kept under N2 at -10°C for months without noticeable decomposition. The practical consequence of this decomposition is that preparative-scale isolation and storage of 12 are not practical. Purification of the product is difficult because of concurrent decomposition, and decomposition cannot be halted until purification is achieved. To circumvent this problem, 63 Decomposition Me3Si O non-coordinating solvents 1 wk, RT MeCN-^y^ 1:5 0 N R' Scheme II1-1 64 12 was always prepared and chromatographed just prior to use, by the procedure described in the Experimental Section. III-A-2 Decomposition in a Coordinating Solvents: .Formation of CpW(NO)(CH2C(C6H^Ph2)(NCMe) In an effort to understand the decomposition process, the thermal 4 behaviour of 12 in a coordinating solvent was investigated. It was hoped that coordinatively unsaturated intermediates in the decomposition reaction would be stabilized by coordination of a solvent molecule, so that an isolable product could be obtained. Indeed, a solution of 12 in acetonitrile over about 3 weeks slowly deposits transparent, brick-red crystals of 14 in 73% yield: < 7 > ( i ) W MeCN  r / | \ r H 3wks,RT Me3Si g C H 2 C P h 3 12 SiMe4 ,Ph The evolution of TMS as the other product is demonstrated by 1H NMR spectroscopy of the reaction in CD^ CN. Orthometallated complex 14 is a brick-red crystalline solid, air-stable for short periods of time. It is insoluble in all common organic 65 solvents, a feature which has prevented its characterization by the usual spectroscopic methods. Its IR spectrum (KBr) shows nitrosyl stretching frequencies of 1574, 1559 cm (The presence of two bands in this area may be due to solid state effects or to the presence of isomers (see below)). The only means of establishing the molecular struture of 14 was a single-crystal X-ray crystallographic analysis. Fortunately, the crystals that deposited from the reaction mixture were of suitable quality. An ORTEP diagram of the molecular structure of 14 is shown in Figure I l l - l a . Two isomers, differing in the arrangement of the NO and MeCN ligands relative to the unsymmetrical metallacycle, are possible: Only the isomer where the nitrosyl ligand is trans to the W-Cr^  bond and the acetonitrile group is trans to the W-aryl bond is observed (isomer A). It may be that isomer B is not formed at a l l , or i t may be i t is formed but crystallizes separately from A and i t just happened that a crystal of A was selected for the crystallographic study. The presence of both isomers in a mixture of crystals is one possible explanation for the observation of two nitrosyl frequencies in the IR spectrum of 14. This question cannot be resolved in the absence of more extensive spectroscopic data. 66 C3 Fig. III-l Solid State Molecular Structure of CpW(NO)(CH2C(C5HA)Ph2)(NCMe) (14). a) ORTEP diagram. H-atoms have been removed for clarity b) Packing diagram. 67 Complex 14 is chiral and crystallizes with two molecules of each enantiomer per unit cell, as shown in Figure Ill - l b . Selected bond lengths and angles for 14 are given in Table III-l. Table III-l Selected Bond Lengths and Angles of CpW(NO) (CH"2C(C6HA)Ph2) (NCMe) (14) Bond Lengths ( A ) Bond Angles (deg) W-CP W-NO 1.762 O)- W-N-0 173.8 N-0 1.228 (9) W-CH2C 2.232 (8) W-CH2~C 113.6 (5) W-C,H. 6 4 2.201 (8) • W-NCMe 2.152 (7) W-N-C 178.2 (7) N-CMe 1.140 (10) N-CMe 178.5 (9) MeCN-W-NO 88.6 (3) 0N-W-C,H. 6 4 88.5 (3) CCH.-W-CH0 0 4 z 72.1 (3) CH2-W-NCMe 74.6 (3) - Estimated standard deviation in parentheses The solid state structure shows no unusual features. The acetonitrile ligand is normal compared to that of other transition metal complexes of 68 organonitriles. It is bound end-on and the C-N bond length is similar (within experimental error) to that of free acetonitrile (1.155 A ) . 6 The geometry of the metallacycle is also as expected. The observed insolubility of 14 is puzzling; there are no short intermolecular distances which might account for i t . The formation of 14 by reaction (1) is an orthometallation reaction. These are well-known7 for a wide variety of organometallic complexes. The isolation of 14, together with the observation of TMS as a by-product of both reaction (1) and the decomposition of 12 in non-coordinating solvents suggests that the decomposition process may be as outlined in Scheme III-2. A 16-electron intermediate metallacycle is postulated; i t is apparently unstable and decomposes to a mixture of products in the absence of a trapping ligand. The reason for this instability is not clear, in view of the demonstrated stability of related acyclic, 16-electron 1 2 dialkyls ' such as 4 and 12. Analogous 16-electron diaryl Q complexes have also been synthesized and are stable enough to be isolated, so that decomposition cannot be attributed to any unfavourable feature of the W-aryl bond. In any case, the orthometallation step in the decomposition accounts for the thermal instability of 12 compared to 4. An analogous cyclo-metallation such as (2) is possible for 4: 69 Scheme 111-2 70 / C H 2 WCHjSiMea * W SiMe2 (2) N C H 2 / W = CpW(NO)(CH2SiMe3) g Such reactions of a Cr^SiMe^ ligand are known. However, this reaction is expected to be much more difficult than the orthometallation of a phenyl-containing ligand, as aromatic C-H bonds are known to be easier to activate than aliphatic ones.1*"1 Reaction (2) also leads to a A-membered metallacycle, more strained than the 5-membered cyclic product of the orthometallation reaction. Hence, i t is not surprising that reaction (2) is not observed. III-A-3 Cyclic Voltammetry of CpW(NO)(CH2SiMe3)(CH2CPh3) The electrochemical behaviour of 12 has also been investigated and compared to that of A. George Richter-Addo of our research group obtained the cyclic voltammogram (C.V.) of 12 in CH2C12> at a complex concen-—A n + -tration of •» 1x10 M, using 0.1 M [-Bu^ N] PFg as support electrolyte, a Pt-bead working electrode and an Ag-wire reference electrode. The scan rate was 0.A V«s 1 1 1 The C.V. of A had been previously obtained 1 1 using comparable conditions (same as above, except that the complex concentration -A -1 was 5x10 M and the scan rate 0.15A V»s ). The C.V.'s for both complexes are qualitatively similar; that of 12 is shown in Figure III-2. Both complexes show an apparently chemically reversible reduction and an irreversible oxidation. The potentials for these 71 Volts vs Ag-wire b) I d i Volts vs Ag-wire Fig. III-2 Cyclic Voltammograms of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) in CH2C12. a) Negative potentials b) Positive potentials. 72 processes as well as the reversibility data for the reductions are given in Table III-2. Table III-2 Cyclic Voltammetry Data for CpW(NO)(CH2SiMe3)2 (4) and CpW(NO)(CH2SiMe3)'(CH2CPh3) (12) Complex Oxidation Reduction -pa h/2 ( V ) AE (mV) i / i —pa —pc (V.s l) 4 1.15 -1.61 90 0.97 0.154 12 0.80 -1.50 200 0.99 0.400 Comparison of these values shows that 12 is easier both to oxidize (by 0.35 V) and to reduce (by 0.11 V) than 4. This could be attributed to the presence of the phenyl rings in 12 which might serve as "electron charge reservoirs" and help delocalize both positive and negative charges by resonance. The AE value for the reduction wave of 12 appears to be greater than that of 2; however, no comparison is possible between the two experiments, as the scan rates were different. III-B Reactivity of CpW(NO) (CH"2SiMe3) (CH"2CPh3) with Small Molecules III-B-1 Reaction of CpW(NO) (CR"2SiMe3) (CH"2CPh3) (12) with PMe3 73 Treatment of a solution of 12 in ether or CDCl^ with PMe^  results in a change in colour from purple to yellow which is attributed to formation of the phosphine adduct 15: CpW(NO)RR' + PMe3 ^ ===^ CpW(NO) (PMe3)RR' (3) 12 15 R = CH2SiMe3 R' = CH2CPh3 This reaction is analogous to that undergone by 4 under the same 2 conditions. Although the product 15 was not isolated and.completely characterized because of the ease with which i t loses phosphine, i t is formulated as indicated based on spectroscopic evidence and by analogy with the known CpW(NO)R2(PMe3) (16). Both phosphine adducts 15 and 16 are yellow, diamagnetic crystalline solids, which lose phosphine upon exposure to vacuum; this loss appears more facile for the more sterically congested 15. Infrared spectra show that the of 12 in ether shifts 27 cm 1 to lower wavenumbers upon phosphine coordination (the analogous -1 2 shift for 4 is 21 cm in benzene ). These shifts reflect the increase in electronic density at the metal centre that occurs upon coordination and results in increased M -» NO back-bonding. The 1H NMR spectrum of 15 can only be obtained i f a large excess of PMe_ is added to the sample, as the adduct dissociates in solution in the 74 absence of excess phosphine. Unfortunately, the resonances associated with some of the adduct's methylene protons are obscured in the resulting spectrum by the large peaks due to the free phosphine. However, the spectrum does show clearly resonances due to the SiMe^, phenyl, and Cp protons; the latter signal is split into a doublet (3Jpjj = 2 Hz), which is consistent with coordination of the phosphine to the tungsten centre. Coordination of PMe^  to 12 appears to prevent orthometallation of the CH2CPh.j ligand. The adduct 15 does show evidence for slow decomposition, but this is much slower than for 12 (35% after 8 months at room temperature) and occurs without evolution of TMS. This relative stability is as expected, since oxidative addition of a C-H bond requires a vacant coordination site on the metal. III-B-2 Reaction of CpW(NO) (CH2SiMe0) (CH^Ph,) (12) with 0 2 Treatment of a CH2C12 solution of 12 with 0^ results in formation of dioxoalkyl complexes 17 and 18, in a ratio of 1:5 75 This reaction is analogous to that undergone by 4 under the same conditions (complex 18 was first isolated from the reaction between 4 2 12 and dioxygen ' ). The two products could not be separated. Their presence was revealed by *H NMR spectroscopy of the dried residue from the reaction mixture. The preparation of 17 by another route is reported in Section III-B-4. The ratio of the two products indicates that the W-CR^ CPh^  bond is broken preferentially to the W-CH^ SiMe^  bond, by a factor of 5:1. The reaction rate of reaction (4) has been found to be quite variable, the time for completion of the reaction varying from 10 minutes to 5 hours. Catalysis by trace impurities is a possible explanation for this; since the starting material 12 was not isolated and its purity verified by elemental analysis before use, i t is reasonable to suppose that the amounts and even the nature of any impurities might vary from one preparation to. the next. However, in al l experiments, the identity and the ratio of the two organometallic products of the reaction with 0^ remained the same, as verified by XH NMR spectroscopy of the crude residue from the reaction mixtures. III-B-3 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) with NO (g) Complex 12 also reacts with excess NO (g) in the same manner as 4 to give the N-alkyl N-nitrosohydroxylaminato complex 19: 76 7- W ( 5 ) W + 2N0(g) h e x a n e s . R V N T ° ^ N « R' N 0 o1 N R 12 19 R = CH2SiMe3 R* = CH2CPh3 Complex 19 is a yellow, diamagnetic crystalline solid, which is stable in air and closely resembles complex 5 obtained from the analogous reaction of A with NO (g) 5 The XH and 1 3C NMR spectra of 19 are shown in Figures III-3 and III-4, respectively. They show that 19 in solution consists of a mixture of two Ph B \ B B A B yuW. Fig. III-3 400 MHz *H NMR Spectrum of CpW(NO)(CH2SiMe3)-(n -02N2CH,SiMe3) in CDC13. A and B indicate the resonances due to the major and minor isomers, respectively. o 6 ppm • CpW|0|2|CH2CPh3l Ph vv R - ipso Cp N C H 2 - S i W - C H 2 - C JL C P h 3 X A A A B,,B SiMe, B uiijiiii^ ii|.ni|u»juii|iiu|iii|iiii|m^ im|miii i 11 i i i I I i i i i | i i ! i I i ; i i l i I i I | I i i • | I I I i | i I I : | i i i i | i i i i i i : i i , i i i . | i i ' i | i i i i | i i i i | i i i i ' M 1 1 1B0 r j , , i i i• • I o 6 ppm * solvent 00 ^ 0 1^ 0 " 1 • I 120 BO r Fig. III-A 75 MHz "Ct^H} NMR Spectrum of CpW(NO)(CH2CPh3)(n2-02N2CH2SiMe3) in CDC13. A and B indicate the resonances due to the major and minor isomers, respectively. 79 isomers, in a ratio of 2.7:1 in CDC1_ and 2.5:1 in C,D,. As in the case of ' 3 6 6 5 (see Chapter I), the two isomers are thought to differ only in the orientation of the R substituent on the 0„N,R group: An examination of the 1H NMR spectrum of the crude residue from the reaction mixture reveals that only one such pair of isomers is obtained from reaction (5). It follows then that NO insertion has occurred in one of the two W-C bonds exclusively. Two lines of reasoning suggest that i t is the W-Cr^ SiMe^  bond which is attacked, rather than the W-Cr^ CPh^  bond. The first reasoning is based on the 1 3C chemical shifts of the methylene carbons, compared to the analogous values 2 for complex 5. The data for 5 in CgDg show that a carbon in a W-Cr^ 'SiMe^  group in these closely related systems resonates at about 15 to 2 18 ppm, whereas a carbon in a W(n, -02N2-CH2~SiMe2) group resonates at about 47 ppm. The 1 3C NMR spectrum of 19 in CDC1» does not show any resonance 80 in the area around 15 - 18 ppm, but does show signals at 47.7 (major isomer) and 48.3 ppm (minor isomer), attributable to methylene carbons. Therefore, 19 apparently does not contain a W-Cr^-SiMe^ grouping, but does contain a C^^-Cr^-SiMe^ group. Accordingly, its structure is formulated as indicated in equation (5). Additional evidence for this formulation is provided by the obtention of the dioxo alkyl 17, in which the W-Cr^CPh^ bond persists intact, as a product of the photolysis of 19 (see below). It is unlikely that an alkyl group initially on the 02N2 chelate ring would be transferred to the metal as a result of photolysis, while an alkyl group that was already on the metal was the one that was lost in the reaction. It is postulated instead that the W-Cr^ -CPh^  bond remains intact throughout these reactions and that nitric oxide insertion occurs in the W-Cr^SiMe^ bond. III-B-4 Photolysis of CpW(NO)(R1)(n2-02N2R) (19) and of CpW(NO)(R)(n2-02N2R) (5) 2 During attempts to recrystallize CpW(NO) (R1) (p -O^R) (19), i t was noticed that its *H NMR spectrum showed i t was often contaminated with varying amounts of another organometallic compound. The resonances associated with this product corresponded to those attributed to CpW(0)2R' (17) obtained in the reaction of CpW(NO)RR' (12) with 0 2 (see Section III-B-2). It was suspected that conversion of 19 to 17 had taken place. In order to confirm this hypothesis a sealed NMR sample of 17 in C,Dfi was prepared and left at room temperature, exposed to ambient light, for 81 17 days. The progress of the r e a c t i o n was monitored by 1E NMR spectroscopy. The spect ra obta ined are shown i n F igure I I I - 5 ; they show tha t the resonances due to the s t a r t i n g m a t e r i a l 19 decrease w i t h time and are rep laced by those a t t r i b u t e d to the dioxo complex 17. The convers ion under these cond i t i ons i s slow: at the end of 17 days, on ly *- 30% of the s t a r t i n g m a t e r i a l has been converted. I r r a d i a t i o n of the same sample us ing a mercury lamp then showed that the r e a c t i o n was induced by l i g h t . Complete convers ion was obtained a f t e r 3 1/2 hours, as shown by a 1H NMR of the sample (F igure I I I - 5d ) . 2 The r e l a t e d compound CpW(NO)(R)(n - O 2 N 2 R ) was a l so shown to reac t analogously under the same cond i t i on s . The known dioxo complex CpWtO^R 2 12 (18) ' was obta ined, and i d e n t i f i e d by i t s 1H NMR spectrum. React ion (6) the re fo re occurs p h o t o l y t i c a l l y : R" = CH 2 S iMe 3 , CH 2 CPh 3 0 0 F i g . I I I - 5 80 MHz *H NMR Spectrum of the P h o t o l y s i s of CpW(NO)(CH 2CPh 3)(n 2-0 ?N 2CH 2SiMe 3) (19) i n C f i D 6 . a) At s t a r t of experiment. b) 1 wk exposure to ambient l i g h t . c) 17 days exposure to ambient l i g h t . d) 17 days exposure to ambient l i g h t , f o l l o w e d by 3 1/2 hours i r r a d i a t i o n by mercury lamp • i n d i c a t e s s t a r t i n g m a t e r i a l , t i n d i c a t e s CpW(0) 2(CH 2CPh 3) product, G i n d i c a t e s s i l i c o n e grease. 83 Although time constraints prevented the isolation and complete characterization of CpW(0)2R' (17), i t was identified based on its spectroscopic properties. An IR spectrum (Nujol mull) of the dried residue from the reaction mixture shows two V ^ _ Q bands: 952, 910 cm '. As shown in Figure III-6, 1H NMR spectra show that the same product is obtained from this photolysis and from the reaction of 12 with G^ ; the resonances observed are consistent with the indicated formulation of the dioxo complex. To the best of my knowledge, reaction (6) is unprecedented. Several examples of the formation of oxo complexes by reaction of a transition-metal 13 14 alkyl and N0(g) ' are known, but in al l cases the intermediate, 0 14 13 postulated or isolated, is a M—N—R complex. There are no reported cases /0=N of an isolated organometallic complex of the type M ' undergoing conversion to an oxo complex. The by-products of this reaction are not known. By a simple mass-balance reasoning, i t appears that an NO' and an RN2* fragment have been lost from the metal centre. A radical such as RN2* would of course undergo rapid subsequent reactions. Further experiments, including repeating the photolysis in the presence of a radical trapping reagent,1"* should be performed to elucidate the reaction mechanism. III-B-5 Reaction of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) with Sulphur The reaction of 12 with one equivalent of sulphur in toluene is much slower than the analogous reaction of CpW(NO)(CH2SiMe3)2 (4), 84 a) 5 0 ° PPm . III-6 a) 80 MHz 1H NMR Spectrum of the D r i e d Residue from the R e a c t i o n M i x t u r e of CpW(NO)(CH 2SiMe 3)(CH 2CPh 3) (12) w i t h 0 2 , i n C6 D6-b) 80 MHz *H NMR Spectrum of CpW(0)a(CH 2CPh 3) (17) from P h o t o l y s i s of CpW(NO)(CH 2CPh 3) (n 2-0 2N 2CH 2SiMe 3) (19) i n CgD-g. f i n d i c a t e s CpW(0) 2(CH 2CPh 3) (17), • i n d i c a t e s CpW(N0j(CH 2CPh 3) (n -0 2N 2CH 2SiMe 3) (19). 85 proceeds to completion in 16 hours. ' Complete consumption of 12 under these conditions requires a week, presumably because of the greater steric congestion about the W centre. This is about the same time as required for the thermal decomposition of 12 under the same conditions. As a result, decomposition competes with the reaction with sulphur, and a complex mixture of products is obtained. A 1H NMR spectrum (CgD^ ) of the dried residue from the reaction mixture (Figure III-7) shows that 4 Cp-containing products not obtained from decomposition of 12 are produced in the reaction with sulphur. (The resonances attributed to the Cp rings of these compounds are indicated in Figure III-7). The most abundant of these, complex 20, is isolated in 9% yield by careful chromatography of the product mixture Ph (7) 12 20 Product 20 is a yellow-orange, diamagnetic, air-stable solid. As an ether solution, i t decomposes slowly (over a few weeks) when exposed to air, depositing a crystalline, raspberry-red solid which has not been identified. The identity of 20 was first tentatively established based on its physical and spectroscopic properties. The analytical and mass spectroscopic results (high resolution mass spectrum m/z 640.1455, 0 0 Fig. III-7 80 MHz lH NMR Spectrum of the Dried Residue from the Reaction Mixture of CpW(NO)(CH2SiMe3)(CH2CPh3) (12) with Sg, in & ppm * toluene C6 D6* Cp resonances of products arising from this reaction but not from the decomposition of 12 in the absence of Sg are indicated The it denotes the Cp resonance of 20. 87 2^9^ 32 ^ indicated the empirical formula; the presence of the oxo ligand was shown by the occurrence of a V^=Q band in the IR spectrum, at 949 cm 1 (CH^Cl^. Orthometallation of the CH^CPl^ ligand was suggested by the presence of 4 resonances attributable to ipso carbons in the 1 3C NMR spectrum (shown in Figure III-8). The site of insertion of the sulphur was considered more likely to be the W-C^SiMe^ bond because of the 1 3C chemical shift of the W-CH"2-SiMe3(28.4 ppm in CgDg) which is close to the analogous values for complexes CpW(NO) (R) (S-CH"2SiMe3) (6) and CpW(NO)(S-CH2SiMe3)2 (8) that contain the same grouping (32.84 and 2 30.35 ppm, respectively, in the same solvent). The aH NMR spectrum of 20 in CgDg is shown in Figure III-9. It shows that one of the phenyl protons gives rise to a doublet of doublets at a lower field than the others (fi 7.74 ppm); this set of resonances is attributed to the phenyl proton in the ortho position relative to the tungsten. The methylene protons constitute two AB spin systems; the lower field AB pattern in the spectrum is attributed to the S-CH2~SiMe3 by comparison of the chemical shifts with those of the corresponding protons of 6 and 8. Subsequently, a single-crystal X-ray crystallographic analysis of 20 confirmed this molecular structure, as shown in Figure 111-10. Two isomers, differing in the arrangement of the oxo and thiolate ligands relative to the unsymmetrical metallacycle, are possible, but only the one where the oxo ligand is trans to the W-CH2 bond, and the thiolato trans to the W-aryl bond, is observed. This chiral complex crystallizes with one molecule of each enantiomer per unit cell (Figure III-10b). 88 SiMe, r Me.S i Cp S-CH,-SI W-CH2-C A-A A. A__AX. CO 8 4 3 * ether 1 0 ° PPm Fig. III-9 80 MHz *H NMR Spectrum of CpW(O)(CH2C(C5H4)Ph2)(SCH2SiMe3) ( 2 0 ) in C6D6. 111-10 Solid State Molecular Structure of CpW(O)(CH2C(C5H4)Ph2)(SCH2SiMe3) (20). a) ORTEP diagram. H atoms have been removed for clarity b) Packing diagram. 91 Selected bond lengths and angles for 20 are collected in Table III-3, along with the corresponding data for some related complexes, where appropriate, for comparison. Thus, the W-S bond in 20 is 13 significantly longer (by 0.130 A) than in CpW(NO)(SR)R ( 6 ) , and the W-S-CH^  angle is 7.3° smaller. The unusually short length of the W-S linkage in 16-electron complex 6 has been previously attributed to its partial double-bond character, resulting from Spn -» Wdn bonding. Such interaction is apparently much less important in the case of 20, even though this is also a formally 16-electron compound. A possible explanation is that the W centre receives additional electron density from the oxo ligand by means of an Oprr -* Wdir interaction. This implies that the W-0 bond has some triple-bond character. Indeed, this bond length is short, 1.706 (3) A, comparable to that found in complex 21 (average 1.707 A) in which a similar W-0 multiple bond is thought to exist. 1 7 o = w - w = o Ri Ri 21 Rx = CH2CMe3 92 Table III-3 Selected Bond Lengths and Angles for CpW(O) (CH2C(C6H"4)Ph2) (SCH"2SiMe3) (20), CpW(NO) (CH2SiMe3) (SCH2SiMe3) (6) and CpW(NO) (CH2C (CgH^ ) Ph), (NCMe) (14) a b Bond (A)- or Angle (deg)- 20 6 1 0 14 W-CP- 2.103 (3)-W-0 1.706 (3) W-S 2.4312 (10) 2.301 (2) S-CH2Si 1.819 (5) 1.851 (7) W-S-CH2 102.90 (15) 110.2 (2) W-C,H. 6 4 2.183 (4) 2.201 (8) W-CH2C 2.222 (3) 2.232 (8) W-CH2-C 117.9 (2) 113.6 (2) O-W-S 92.73 (11) S-W-CH2 70.87 (10) CH.-W-C,H. 2 6 4 70.81 (14) 72.1 (3) C.H.-W-O 6 4 89.71 (14) — Bond Length (A) denoted by A-B - Bond angles (deg) denoted by A-B-C - CP: centroid of the Cp ligand — Estimated standard deviation in parentheses. 93 The metallacycle in complex 20 appears to be somewhat strained. In particular, the W-CH^ -C angle of 117.9 (2)° is significantly wider than 3 expected for an sp -hybridized carbon (109°). The same effect is seen in CpW(NO) (CH2CPh2(C6H4)) (MeCN) (14) but to a lesser degree (W-CR"2-C angle 113.6 (2)°). The arrangement of the bonds about the W atom is shown by the simplified ORTEP diagram in Figure II I - l l , where the Cp ligand has been removed for clarity. The four "piano-stool legs" are arranged in such a way that the bond angles on either side of the oxo ligand are about 20° wider than the other two angles. The reasons for this must be electronic rather than steric, since the oxo ligand is the smallest one present. Again the same effect is seen in 14, to a lesser extent (the difference between the large and the small angles is "v- 15°). Speculation on the mechanism of formation of 20 under the conditions described above would clearly be futile. The origin of the oxygen that constitutes the oxo ligand is not known; adventitious oxygen (trace water or 02) is a possibility, another is the nitrosyl ligand of the starting material itself. Additional experiments, using more rigorously anaerobic and anhydrous conditions, then addition of controlled amounts of oxygen and water, would be necessary to resolve this question. Likewise, the fate of the hydrogen atom that was initially on the phenyl ring before orthometallation took place is not known. The other products of reaction (7) have not been isolated and characterized. Thus i t is not known whether products of simple sulphur insertion, analogous to 6, 7, and 8 obtained from 9 4 Fig. I I I - l l Simplified ORTEP Diagram Shoving the Arrangement of the Four "Piano-Stool Legs" of CpW(O)(CH2C(C6H4)Ph2)(SCH2SiMe3) (20). The Cp ring and a l l H atoms have been removed for cla r i t y . A l l unlabelled atoms are carbons. 95 CpWCNO)!?^  (4) are formed or not. It should be noted that the ratios of the various products of reaction (7) vary according to the conditions employed: i f an excess of sulphur is used, product 20 becomes less abundant and another product (*H NMR (CgD^ ) 6 4.79, s, Cp_) dominates. Whether the preferred site of attack by sulphur is the W-CH2CPh,j or W-CH2SiMe3 bond in 12 cannot be stated definitely from these results. Because 20 is only one product of the reaction, its isolation does not constitute proof that insertion in the W-C^SiMe^ bond is more than marginally favoured, and under one specific set of conditions. Conclusions As discussed in the introduction, the original purpose of the work described in this chapter was to compare the reactivity of the W-CH2SiMe.j and 12 W-CH2CPh3 bonds. The results obtained do not allow any definitive conclusion to be drawn on this matter. It was found that the W-CH2SiMe3 bond is the one that is broken during the thermal decomposition of 12, and is the one into which NO inserts, but reaction of 12 with O2 results in preferential cleavage of the W-CH2CPh3 bond, and the data on the reaction with sulphur are inconclusive on this point. Instead, i t was found that the reactivity of CpW(N0)RR' (12) does not always rigorously parallel that of CpW(N0)R2 (4). Although several reactions (adduct formation with PMe^ , NO insertion, reaction with O2) do proceed analogously for both dialkyl complexes, others (thermal decomposition, reaction with MeCN, reaction with sulphur) follow a completely 96 different course for 12 because of the ability of the CU^CVh^ ligand to orthometallate. This orthometallation is another example of the high reactivity of the metal centre in these 16-electron dialkyls. The many other 2 reactions that they undergo have also been summarized in this thesis; that this formally unsaturated complex is capable of intramolecular C-H activation is perhaps not surprising. One other unusual interaction between such metal centres and their alkyl ligands is found in CpM(NO)(Cl^Ph)^ (M = Mo.W), where 2 18 one of the benzyl ligands is bound in an q fashion to the metal. These complexes as a result show a diminished reactivity, compared to 4 , with reagents such as 0^ and Sg. Clearly, the reactivity of complexes of this family is profoundly affected by the nature of the alkyl ligands. 97 References 1. Legzdins, P.; Rettig, S.J.; Sanchez, L.; Bursten, B.E.; Gatter, M.G. J. Am. Chem. Soc., 1985, 107, 1411. 2. Legzdins, P.; Rettig, S.J.; Sanchez, L., manuscript in preparation. 3. PMe3 was prepared according to a published procedure: Wolfsberger, W.; Schmidbaur, H. Synth. React. Inorg. Met.-Org. Chem.. 1974, 4, 149. 4. For a discussion of solvent properties, see Drago, R.S. Pure Appl. Chem., 1980, 52, 2261. 5. For a discussion of solid state effects in IR spectroscopy, see Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd ed.; Wiley-Interscience: New York, 1978; pp 91-98. 6. Starhoff, N.B.; Lewis, H.C., Jr. Coord. Chem. Rev., 1977, 23, 1. 7. Bruce, M.I. Angew. Chem., Int. Ed. Engl., 1977, 16, 73. 8. Dryden, N.H., Legzdins, P., unpublished observations. 9. Bruno, J.W. ; Smith, G.M. ; Marks, T.J.; Fair, CK. ; Schultz, A.J.; Williams, J.M. J. Am. Chem. Soc., 1986, 108, 40. 10. Crabtree, R.H. Chem. Rev., 1985, 85, 245. 11. Richter-Addo, G. personal communication. 12. Legzdins, P.; Rettig, S.J., Sanchez, L. Organometallics, 1985, 4, 1470. 13. Middleton, A.R.; Wilkinson, G. J. Chem. Soc, Dalton Trans., 1980, 1888. 14. Middleton, A.R.; Wilkinson, G. J. Chem. Soc, Dalton Trans., 1981, 1898. 15. Nelsen, S.F. in Free Radicals; Kochi, J.K. Ed.; Wiley-Interscience: New York, 1973; pp 539-583. 16. Evans, S.V.; Legdins, P.; Rettig, S.J.; Sanchez, L.; Trotter, J. Organometallics, 1987, 9, 7. 17. Feinstein-Jaffe, I.; Gibson, D.; Lippard, S.J.; Schrock, R.R.; Spool, A. J. Am Chem. Soc, 1984, 106, 6305. 18. Legzdins, P.; Phillips, E.C, manuscript in preparation. 98 Spectral Appendix - Selected IR spectra 99 S CpW CCH2SlMa3) 2 CNO-El-Cp3> N u j o l n u l l V A V E N U M B E R 8 C C M - 1 > 100 101 aeoo. o 3200 .0 2000.0 2000.0 1700.0 1400.0 1100.0 BOO. 00 500 .00 zoo. 00 W A V E N U M S E R S C C M - 1 3 103 


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