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Abnormal reactions of N-heterocyclic carbenes with phosphaalkenes Han, Zeyu 2015

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  ABNORMAL REACTIONS OF N-HETEROCYCLIC CARBENES WITH PHOSPHAALKENES by Zeyu Han B.Sc., Nankai University, 2012 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF   THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE  in  The Faculty of Graduate and Postdoctoral Studies  (Chemistry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) July 2015 © Zeyu Han, 2015 ii  Abstract This thesis outlines the results from the project undertaken as a part of my MSc studies: the abnormal reactions of phosphaalkenes with N-heterocyclic carbenes (NHCs) to afford novel 4-phosphino-2-carbenes (IMesP). The focus is on investigating the mechanism of these reactions. Chapter 1 serves as a general introduction of phosphaalkenes, N-heterocyclic carbenes, and abnormal N-heterocyclic carbenes. The possible mechanisms of abnormal reactions of NHCs proposed by other researchers are briefly discussed as well.  Chapter 2 describes the kinetic studies of the abnormal reactions. Specifically, the kinetic studies of the reactions of IMes with MesP=CPh2, MesP=C(4-C6H4F)2 and MesP=C(4-OMeC6H4)2, respectively. The kinetic and thermodynamic data are calculated in order to compare with DFT calculations. During the study, it is noticed the abnormal reaction is catalyzed by base whereas hindered by acid. In Chapter 3, the reactions of MesP=CPh2 with other NHCs are discussed. The NHCs include IMes-d2 (IMes with deuterium at C4 and C5 positions), IMesMe2 (IMes with –CH3 groups at C4 and C5 positions) and IMesMe (IMes with a –CH3 group at C4 position). The deuterium labeling experiments with IMes-d2 are designed to gain further insight into the issues with respect to the proton transfer in the abnormal reactions. The result shows the proton transfers intermolecularly in the process to form IMesP. The experiments related to IMesMe2 and IMesMe are conducted in order iii  to expand the scope of reactions of phosphaalkenes with NHCs. It is revealed that IMesMe2 and IMesMe do not react with phosphaalkenes in the abnormal way. Finally, Chapter 4 describes a few metallic complexes synthesized from IMesP. Treating IMesP with excessive W(CO)5CH3CN only affords a product with tungsten binding at the carbene functionality. More interestingly, some dinuclear complexes are obtained by reacting IMesP with Pd(cod)2Cl2 and (tht)AuCl.            iv  Preface The work presented in this thesis is original, independent work by myself.  Chapter 2 will be submitted as a full paper prepared with Prof. Pierre Kennepohl and Prof. Derek P. Gates.             v  Table of Contents Abstract .......................................................................................................................................... ii Preface ........................................................................................................................................... iv Table of Contents ........................................................................................................................... v List of Tables ............................................................................................................................... viii List of Figures ............................................................................................................................... ix List of Schemes ........................................................................................................................... xiv List of Symbols and Abbreviations .......................................................................................... xvii Acknowledgements ...................................................................................................................... xx 1 Introduction ............................................................................................................................ 1 1.1 Phosphaalkenes ................................................................................................................ 1 1.2 N-heterocyclic carbenes ................................................................................................... 6 1.3 Abnormal N-heterocyclic carbenes ................................................................................. 11 1.4 Examples of abnormal reactions of NHCs and possible mechanisms ........................... 14 1.5 Project goals ................................................................................................................... 22 2 Kinetic studies of the abnormal reaction of NHCs with phosphaalkenes ....................... 24 2.1 Introduction .................................................................................................................... 24 2.2 Results and discussion .................................................................................................... 28  Procedures to conduct kinetic studies......................................................................... 28  Determination of the reaction order and rate constants .............................................. 31  Determination of the activation energies .................................................................... 35  The Erying plots ......................................................................................................... 37 vi   Base facilitates the abnormal reaction ........................................................................ 41  Acid hinders the abnormal reaction ............................................................................ 44 2.3 The reaction of the IMes-tungsten complex with MesP=CPh2 ...................................... 47 2.4 Conclusions .................................................................................................................... 47 2.5 Experimental sections .................................................................................................... 48  Materials and general procedures ............................................................................... 48  General procedure for processing 31P NMR spectra ................................................... 48  Adding error bars in Arrhenius and Erying plots ....................................................... 49  The NMR-scale reaction of IMes with MesP=CPh2 .................................................. 49  The NMR-scale reaction of IMes with MesP=C(4-C6H4F)2 ...................................... 50  The NMR-scale reaction of IMes with MesP=C(4-OMeC6H4)2 ................................ 50  The NMR-scale reaction of IMes with MesP=CPh2 with NaH .................................. 50  The NMR-scale reaction of IMes with MesP=CPh2 with IMesHBF4 ........................ 50  Synthesis of anionic aIMes dicarbene ........................................................................ 51  The NMR-scale reaction of anionic aIMes dicarbene with MesP=CPh2 ................... 51  The synthesis of IMes-W(CO)5 .................................................................................. 51  The reaction of IMes-W(CO)5 with MesP=CPh2 ........................................................ 52 3 The reactions of different NHCs with MesP=CPh2 ........................................................... 53 3.1 The reaction of IMes-d2 with MesP=CPh2 ..................................................................... 53  Purpose of using IMes-d2 ........................................................................................... 53  Preparation of IMes-d2 ............................................................................................... 55  The reaction of IMes-d2 with MesP=CPh2 ................................................................. 61  H/D ratio in the product mixture at C5 position and P-CHPh2 fragment ................... 66  H/D exchange between IMes and IMes-d2 ................................................................. 70  Kinetic studies of the reaction of IMes-d2 with MesP=CPh2 ..................................... 73 3.2 The reaction of the IMesMe2 with MesP=CPh2 ............................................................. 75 vii  3.3 The reaction of the IMesMe with MesP=CPh2 .............................................................. 80 3.4 Conclusions .................................................................................................................... 82 3.5 Experimental sections .................................................................................................... 83  General considerations ............................................................................................... 83  Synthesis of IMes-d2 .................................................................................................. 83  The reaction of IMes-d2 with MesP=CPh2 ................................................................. 84  The reaction of 50 % IMes, 50% IMes-d2 and 100% MesP=CPh2 ............................ 85  The reaction of IMesMe2 with MesP=CPh2 ............................................................... 85  Synthesis of IMesMe-HBF4 ....................................................................................... 85  Synthesis of IMesMe .................................................................................................. 86  The reaction of IMesMe with MesP=CPh2 ................................................................. 87 4 Transition-metal complexes of IMesP ................................................................................ 88 4.1 Introduction .................................................................................................................... 88 4.2 Exploration of the transition-metal complexes of IMesP ............................................... 89 4.3 Conclusion and future work ........................................................................................... 95 4.4 Experimental sections .................................................................................................... 96  General considerations ............................................................................................... 96  Synthesis of 4.1 .......................................................................................................... 96  Synthesis of 4.2 .......................................................................................................... 97  Synthesis of 4.3 .......................................................................................................... 97  Synthesis of 4.4 .......................................................................................................... 98 References .................................................................................................................................. 100 Appendix .................................................................................................................................... 106  viii  List of Tables Table 2.1 Energy of possible intermediates in THF .............................................................. 27 Table 2.2 31P NMR (121 MHz, THF) chemical shifts and T1 of the phosphaalkenes and products. ......................................................................................................................... 28 Table 2.3 Preliminary determination of the reaction order at 343 K. .................................... 31 Table 2.4 Rate constants of the reaction of IMes (2.1) with MesP=CPh2 (2.2) ..................... 33 Table 2.5 Rate constants of reaction of IMes (2.1) with MesP=C(4-C6H4F)2 (2.4) ............... 34 Table 2.6 Rate constants of the reaction of IMes with MesP=C(4-OMeC6H4)2 .................... 35 Table 2.7 Ea, ∆𝐻≠ and ∆𝑆≠ of the abnormal reactions of IMes with phosphaalkenes ........ 39 Table 2.8 Energy comparisons between possible intermediates in THF ............................... 40 Table 2.9 The influence of different bases on the abnormal reaction at 341 K. .................... 41 Table 2.10 The influence of NaH on the rate of the reaction of IMes with MesP=CPh2 at 319 K. .................................................................................................................................... 42 Table 2.11 The influence of IMesHBF4 on the rate of the reaction of IMes with MesP=CPh2 ........................................................................................................................................ 45 Table 3.1 Rate constants of the reactions of IMes with different phosphaalkenes at 319 K. 69 Table 3.2 Determination of rate constants kD at different temperatures. ............................... 74 ix  List of Figures Figure 1.1 HOMO of imine and phospaethylene1 ................................................................... 2 Figure 1.2 First isolable carbene ............................................................................................. 6 Figure 1.3 Electronic structure of a carbene ........................................................................... 7 Figure 1.4 First isolable NHC ................................................................................................. 8 Figure 1.5 Ground-state electronic structure of imidazol-2-ylidenes. The σ-withdrawing and π-donating effects of the nitrogen heteroatoms help to stabilize the singlet carbene structure. 33 ....................................................................................................................... 9 Figure 1.6 First examples of NHC-metal complexes ............................................................ 10 Figure 1.7 1st and 2nd generation of Grubbs catalysts ............................................................. 11 Figure 1.8 aNHC- and NHC- palladium complexes for Suzuki coupling reaction .............. 12 Figure 2.1 31P NMR (121 MHz, THF) spectrum of MesP=CPh2 (2.2) and product 2.3 ........ 25 Figure 2.2 31P NMR (121 MHz, THF) spectrum of MesP=C(4-C6H5F)2 (2.4) and product 2.5 ........................................................................................................................................ 25 Figure 2.3 31P NMR (121 MHz, THF) spectrum of MesP=C(4-OMeC6H4)2 (2.6) and 2.7 .. 25 Figure 2.4 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=CPh2 (341K). ....................................................................................................... 29 Figure 2.5 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=C(4-C6H5F)2 (308K). .............................................................................................................. 30 x  Figure 2.6 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=C(4-OMeC6H4)2 (336K). ....................................................................................................... 30 Figure 2.7 Graph showing 1/[2.2] vs time (s) up to ∼75% conversion for the abnormal reaction at ∼5 K temperature intervals between 318 K and 341 K. ............................................. 32 Figure 2.8 Graph showing 1/[2.4] vs time (s) up to ∼80% conversion for the abnormal reaction between 297 K and 330 K. ............................................................................................. 33 Figure 2.9 Graph showing 1/[2.6] vs time (s) up to ∼50% conversion for the abnormal reaction between 313 K and 341 K. ............................................................................................. 34 Figure 2.10 Arrhenius plot of the reaction IMes with MesP=CPh2. The linear least squares function (y = -7353.6x + 15.665) has an R2 value of 0.98. ............................................ 35 Figure 2.11 Arrhenius plot of the reaction IMes with MesP=C(4-C6H4F)2. The linear least squares function (y = -6998.5x + 15.766) has an R2 value of 0.97. ............................... 36 Figure 2.12 Arrhenius plot of the reaction IMes with MesP=C(4-OMeC6H4)2. The linear least squares function (y = -8104.5x + 15.996) has an R2 value of 0.97. ............................... 36 Figure 2.13 Erying plot of the reaction of IMes with MesP=CPh2 The linear least squares function (y = -7023.4x + 8.864) has an R2 value of 0.99. .............................................. 37 Figure 2.14 Erying plot of the reaction of IMes with MesP=C(4-C6H4F)2 The linear least squares function (y = -6685.6x + 9.019) has an R2 value of 0.98. ................................. 38 Figure 2.15 Erying plot of the reaction of IMes with MesP=C(4-OMeC6H4)2 The linear least squares function (y = -7778x + 9.207) has an R2 value of 0.98. .................................... 38 xi  Figure 2.16 Graph showing 1/[PA] vs time (s) up to ∼80% conversion for the reaction of IMes with MesP=CPh2 at 319 K with different concentrations of NaH. ................................. 42 Figure 2.17 31P NMR (121 MHz, C6D6) spectra of the reaction of anionic aIMes dicarbene with MesP=CPh2. ........................................................................................................... 44 Figure 2.18 Graph showing 1/[PA] vs time (s) up to ∼80% conversion for the reaction of IMes with MesP=CPh2 under the influence of IMesHBF4. ..................................................... 45 Figure 2.19 31P NMR of the reaction of IMes, IMesHBF4 and MesP=CPh2 over time at 319K. ........................................................................................................................................ 46 Figure 2.20 31P NMR (121 MHz, CDCl3) spectrum of the mixture of MesP=CPh2 and IMesHBF4 after two weeks at 341 K. ............................................................................. 46 Figure 3.1 1H NMR (300MHz, DMSO-d6) spectra of IMes (top) and IMes-d2 (bottom) ...... 56 Figure 3.2 2H NMR (61 MHz, C6H6) spectrum of IMes-d2 .................................................. 57 Figure 3.3 2H NMR (61 MHz, C6H6) spectrum of IMes-d2 after removing CD3OD ............ 58 Figure 3.4 1H NMR (300 MHz, DMSO-d6) spectrum of IMes-d2 after removing CD3OD... 59 Figure 3.5 13C NMR (100 MHz, C6D6) spectrum of 90% deuterated IMes-d2 at C4 and C5 positions. ........................................................................................................................ 60 Figure 3.6 13C NMR (100 MHz, C6D6) spectrum of IMes at C4 and C5 positions............... 60 Figure 3.7 31P{1H} NMR (121 MHz, THF) spectrum of products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2. ............................................................................ 62 xii  Figure 3.8 31P{1H} NMR (121 MHz,C6D6) spectrum of the product from the reaction of 90% deuterated IMes-d2 with MesP=CPh2. ............................................................................ 63 Figure 3.9 1H NMR (300 MHz, C6D6) spectrum of the product from the reaction of 90% deuterated IMes-d2 with MesP=CPh2. ............................................................................ 63 Figure 3.10 Possible products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2 ........................................................................................................................................ 64 Figure 3.11 [1H,31P]-HMBC NMR spectrum of the products in C6D6 suggests the presence of the proton at C5 position of IMesP. ................................................................................ 65 Figure 3.12 [1H,31P]-HMBC NMR spectrum of the products in C6D6 suggests the presence of the proton in the P-CHPh2 fragment. .............................................................................. 65 Figure 3.13 Assignments of the products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2 in 31P{1H} NMR (121 MHz, C6D6) spectrum. ........................................... 66 Figure 3.14 Deconvolution of signals of A, B, C and D in 31P NMR (121 MHz, C6D6) spectrum. ........................................................................................................................................ 66 Figure 3.15 Top: 2H NMR (61 MHz, C6H6) of the final products from 90% deuterated IMes-d2 with MesP=CPh2; Bottom: 1H NMR (300 MHz, C6D6) of pure IMesP. ..................... 67 Figure 3.16 Top: 31P NMR (121 MHz, THF) NMR spectrum; Bottom: 2H NMR (61 MHz, THF) spectrum of the product from the reaction of IMes with (Mes-d9)P=CPh2 .......... 69 Figure 3.17 31P {1H} NMR (121 MHz, THF) spectrum of the reaction of 50 mol% IMes, 50 mol% IMes-d2 with 100 mol% MesP=CPh2. ................................................................. 70 xiii  Figure 3.18 Comparison of C4 and C5 atoms in IMes, IMes-d2, mixture of 50% IMes and 50% IMes-d2 in 13C NMR (100 MHz, C6D6) spectra. ............................................................ 71 Figure 3.19 Arrhenius plot of the reaction IMes-d2 with MesP=CPh2. The linear least squares function (y = -8792.5 + 18.36) has an R2 value of 0.98. ................................................ 75 Figure 3.20 IMesMe2 (4,5-dimethyl substituted IMes) ......................................................... 75 Figure 3.21 31P NMR (121 MHz, THF) spectrum of the product from the reaction of IMesMe2 with MesP=CPh2. ........................................................................................................... 76 Figure 3.22 Top: 1H NMR (300 MHz, DMSO-d6) spectrum; bottom: 13C {1H} NMR (75 MHz, DMSO-d6) spectrum of the product from the reaction of IMesMe2 with MesP=CPh2. .. 79 Figure 3.23 1H NMR (300 MHz, C6D6) spectrum of IMesMe. ............................................. 81 Figure 3.24 31P NMR (121 MHz, THF) spectrum of the product from the reaction of IMesMe with MesP=CPh2. ........................................................................................................... 82 Figure 4.1 Examples of IMesP-metal complexes ................................................................. 89 Figure 4.2 Molecular structure of 4.1 (thermal ellipsoids set at 50% probability). All hydrogen atoms are omitted for clarity. .......................................................................................... 90 Figure 4.3 NHCs as ligands in palladium-catalyzed crossing-coupling. .............................. 92 Figure 4.4 Molecular structure of 4.3 (thermal ellipsoids set at 50% probability). All hydrogen atoms are omitted for clarity. .......................................................................................... 94 Figure 4.5 31P NMR (121MHz, THF) of 4.4 ......................................................................... 95  xiv  List of Schemes Scheme 1.1 Examples of synthetic methods for the preparation of phosphaalkenes .............. 4 Scheme 1.2 Examples of phosphaalkenes exhibiting olefin-like reactivities .......................... 5 Scheme 1.3 Cycloaddition reaction of a phosphaalkene with a carbene precursor ................. 6 Scheme 1.4 The reaction of IMes with MesP=CPh2 ............................................................... 6 Scheme 1.5 First reported aNHC-metal complex .................................................................. 11 Scheme 1.6 The first examples of an isolable aNHC ............................................................ 13 Scheme 1.7 Synthesis of the anionic N-heterocyclic dicarbene ............................................ 13 Scheme 1.8 Chlorination of IMes .......................................................................................... 14 Scheme 1.9 Reactions of the frustrated Lewis pair ItBu/B(C6F5)3 ........................................ 15 Scheme 1.10 Reaction of the frustrated Lewis Pair ItBu/B(C6F5)3 with P4 ............................ 15 Scheme 1.11 Preparation of lithium carbene-borane complexes ........................................... 16 Scheme 1.12 Abnormal reaction of NHC with silicon and possible mechanism .................. 17 Scheme 1.13 Different reactivities of NHC and aNHC towards HSiCl3............................... 18 Scheme 1.14 The reaction of NHC•SiCl2 wth aNHC ............................................................ 18 Scheme 1.15 Abnormal reaction of NHC with phosphinidene complex ............................... 19 Scheme 1.16 Synthesis of 4-P-functionalized NHC and possible mechanism ..................... 20 xv  Scheme 1.17 Synthesis of diphosphino-functionalized NHC and possible mechanism........ 21 Scheme 1.18 Abnormal reaction of IMes with MesP=CPh2 ................................................. 22 Scheme 2.1 Reactions of IMes with phosphaalkenes ............................................................ 24 Scheme 2.2 Proposed mechanism I for the reaction of IMes with MesP=CPh2 ................... 26 Scheme 2.3 Proposed mechanism II for the reaction of IMes with MesP=CPh2 .................. 27 Scheme 2.4 Postulated reaction of IMes with MesP=CPh2 in the presence of base ............. 43 Scheme 2.5 Synthesis of anionic aIMes dicarbene and its reaction with MesP=CPh2 ......... 43 Scheme 2.6 No reaction observed between IMes-W(CO)5 and MesP=CPh2. ....................... 47 Scheme 3.1 The abnormal reaction of IMes with MesP=CPh2 ............................................. 53 Scheme 3.2 Proposed reaction of IMes and IMes-d2 with MesP=CPh2 ................................ 54 Scheme 3.3 Deuteration of 1,3-di-tert-butyl-imidazol-2-ylidene (ItBu) ................................ 55 Scheme 3.4 Proposed reaction of IMes-d2 with MesP=CPh2 ................................................ 61 Scheme 3.5 The reaction of IMes with (Mes-d9)P=CPh2 ...................................................... 68 Scheme 3.6 H/D exchange between IMes and IMes-d2 ........................................................ 72 Scheme 3.7 The reaction process of 50 mol% IMes, 50 mol% IMes-d2 with 100 mol% MesP=CPh2. ................................................................................................................... 73 Scheme 3.8 The reactionof IMes-d2 with MesP=CPh2. ......................................................... 74 Scheme 3.9 Cycloaddition reaction of a phosphaalkene with a carbene. .............................. 77 xvi  Scheme 3.10 Postulated reaction of phosphaalkenes with IMesMe2 to form a zwitterion. ... 77 Scheme 3.11 Synthesis of 4-Methyl-1,3-bis-(2,4,6-trimethylphenyl)-imidazolium chloride.80 Scheme 3.12 Synthesis of IMesMe. ...................................................................................... 81 Scheme 4.1 Formation of IMesP from the abnormal reaction of IMes with MesP=CPh2..... 88 Scheme 4.2 Synthesis of 4.1 .................................................................................................. 90 Scheme 4.3 Synthesis of 4.2 .................................................................................................. 91 Scheme 4.4 Synthesis of 4.3 .................................................................................................. 93 Scheme 4.5 Attempted synthesis of bis(IMesP)-Pd compelx 4.4 .......................................... 95         xvii  List of Symbols and Abbreviations Ad adamantyl tBu tert-butyl CDCl3  deuterated chloroform C6D6 deuterated benzene cod cyclooctadiene Δ heat d  doublet DCM  dichloromethane, methylene chloride, CH2Cl2 DMSO dimethyl sulfoxide or (CH3)2SO Ea activation energy Et  Ethyl or CH3CH2 K   Kelvin kcal  kilcalories k     rate constant KHMDS potassium bis(trimethylsilyl)amide °C  degrees Celsius δ delta, chemical shift EI  electron ionization ESI  electrospray ionization Et2O  diethyl Ether C4H10O EtOAc  ethyl acetate C4H8O2 xviii  h  hour HMBC Heteronuclear multiple-bond correlation spectroscopy {1H} proton decoupled (NMR spectroscopy) IMes N,N’-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene J  J coupling constant m/z  mass to charge ratio m-CPBA meta-chloroperoxybenzoic acid MeCN  acetonitrile, C2H3N Me  methyl, CH3 MeOH  methanol CH4O Mes  mesityl, 2, 4, 6-trimethylphenyl mg, g  milligram, gram MHz, Hz  megahertz, hertz mmol  millimole mL  milliliter min  minute MS  mass spectrometry NHC  N-heterocyclic carbene NMR  nuclear magneti cresonance nBuLi  normal butyllithium ORTEP Oak Ridge Thermal Ellipsoid Plot Program  PCy3 tricyclohexylphosphine Ph     phenyl xix  ppm  parts per million R,R’  Side group RT Room temperature, 25 °C s  singlet SPS  solvent purification system t       triplet T1 longitudinal relaxation time or spin-lattice relaxation time THF  tetrahydrofuran, C4H8O tht  tetrahydrothiophene           xx  Acknowledgements First and foremost, I would like to thank my supervisor Prof. Derek Gates for giving me the opportunity to work in his labs and learn from him. I am particularly grateful for his patience and support through many challenges I experiences during my studies. It was also a privilege to work with the great people within the Gates group. I would like to thank Chuantian Zhan, Dr. Eamonn Conrad, Dr. Koaru Adachi, Leixing Chen, Dr. Saeid Sadeh and Shuai Wang for sharing the lab experience with me. A special thanks goes to Andrew Priegert, Ben Rawe, Chris Brown, Dr. Joshua Bates, Khatera Hazin and Spencer Serin for reading and providing insights into how to improve this thesis.  Within the chemistry department I need to thank Prof. Pierre Kennepohl, Prof. Mike Fryzuk and Prof. Alexander Wang for being my exam committee members and providing valuable suggestions related to my thesis. I would also like to thank the UBC NMR staff for training and troubleshooting, UBC mass spectrometry facility for running my samples, and UBC shops and services for their work in keeping the equipment functioning throughout the years.  Outside the world of chemistry, I would like to thank my good friends Amber Shukaliak, Chris Brown, Kevin Liu, Mitch Perry and Hunter Wang for all the enjoyable moments together. Finally I would like to thank my parents for supporting and caring for me all these years.1  1 Introduction 1.1 Phosphaalkenes  Phosphaalkenes are species containing a σ bond and a (3p-2p) π bond between a phosphorus atom and a carbon atom. Comparisons between P=C bonds, N=C bonds and C=C are often made because of their isolobal relationship but they are observed to have different reactivities. Their differences can be rationalized by a few major effects. First of all, it is important to consider the differences in electronegativity: phosphorus, being more electropositive than carbon and nitrogen, bears a positive charge in P=C based system, which is opposite to N=C based system. Furthermore, the P=C π bond is formed through the P3p-C2p orbitals, which poorly overlap. Such a situation is not applicable in N=C based system. Therefore the P=C π bond possess higher reactivity than N=C π bond. The UV photoelectron spectroscopic measurements provide detailed information for the comparison.1 In the model of imine (H2C=NH) and phosphaethylene (H2C=PH), the HOMO of imine corresponds to the lone pair and the π-bond lies much lower in energy. Consequently, imines usually react with metals and electrophiles through its lone pair. On the contrary, the HOMO of phosphaethylene corresponds to the π-bond. The lone pair is 0.40 eV lowering in energy than the π-bond (Figure 1.1). Thus the P=C bond is even more reactive than its lone pair. The high reactivity of P=C π bond can also be reflected from the thermodynamic data. P=C π bond is calculated to be significantly weaker than the C=C π bond (43 kcal/mol vs. 65 kcal/mol).2, 3 As a consequence, 2  phosphaalkenes only exist as isolable species when significant kinetic or thermodynamic stabilization is provided. Usually, kinetic stabilization can be achieved by adding steric bulk at phosphorus or carbon atom to prevent the oligomerization. For example, the phosphaalkene Mes*P=CH2 (Mes* =2,4,6-tris-t-butyl-benzene) is highly resistant towards hydrolysis and oligomerization and can be isolated.4 Thermodynamic stabilization can be achieved by incorporating the P=C bond into a delocalized system, as seen in phosphinines, rendering it more thermodynamically stable.5  Figure 1.1 HOMO of imine and phospaethylene1 In comparison to the bond angle, the C-P-H angle in phosphaethylene (H2C=PH) is calculated to be about 100° whereas the C-N-H angle in imine is about 120°.6 The difference is mainly because of the effect of hybridization. The formation of hybrid orbitals requires two preconditions: (1) a low promotion energy; (2) equal space extension of the mixing orbitals.7 The latter is largely lacking in higher main group elements like phosphorous. Due to the poor overlap between 3s and 3p atomic orbitals, phosphorus is reluctant to give sp and sp2 hybridization.8 Thus in H2C=PH, the 3  valence angle at phosphorus is strongly decreased (about 100°) to accumulate s-character to the nonbonding lone pair. There are a variety of methodologies available for preparing P=C bonds. The first synthesis of a stable acyclic phosphaalkene was reported by Becker in 1976.9 In his synthetic route, the oxophilicity of the silicon atom drives the [1,3] shift to form P=C bond (Eq.(1), Scheme 1.1). Two years later, Bickelhaupt developed preparative procedure for phosphaalkenes through base induced 1,2-elimination of HX from a corresponding precursor (Eq.(2), Scheme 1.1).10 The mesityl group was chosen to provide kinetic stability on the phosphorus side of the P=C bond. An alternative strategy: the “phospha-Peterson” reaction (a variation of the Peterson olefination to form alkenes) is attractive due to its versatility as a route to Mes-P-substituted phosphaalkenes. In general, this reaction requires a ketone or aldehyde to react with either RP(SiR3)Li alone (Eq.(3), Scheme 1.20) or RP(SiMe3)2 and a catalyst (e.g. KOH) (Eq.(4), Scheme 1.1).11-15 In the case of alkyl-P-substituted phosphaalkenes, the base-catalyzed route is less suitable due to the difficulty in generating the alkylsilylphosphide intermediates. It is discovered by our group that Lewis acid-mediated synthesis is more efficient. 16 The Lewis acid (e.g. AlCl3) can catalyze the coupling of silylphosphines and aldehydes or ketones to give α-siloxyalkylphosphines, thus facilitating phosphaalkene formation with byproducts of TMSCl and (Cl2AlOSiMe3)2 (Eq.(5), Scheme 1.1).   4   Scheme 1.1 Examples of synthetic methods for the preparation of phosphaalkenes Phosphaalkenes can undergo various olefin-like reactions. These include 1,2-addition reactions with small molecules such as HX to generate X-P-C-H compounds (Eq.(6), Scheme 1.2);17 Diels-Alder reactions (Eq.(7), Scheme 1.2);18, 19 hydrogenation (Eq.(8), Scheme 1.2)20 or epoxidation (Eq.(9), Scheme 1.2)21 of the P=C bond when the lone pair is protected. 5   Scheme 1.2 Examples of phosphaalkenes exhibiting olefin-like reactivities Regarding the reaction with carbenes, phosphaalkenes are known to react with carbene precursors to afford PC2 heterocycles (Scheme 1.3).22 This reaction can be considered to occur between a phosphaalkene and a fleeting triplet carbene. However, treatment of phosphaalkenes with N-heterocyclic carbenes leads to a completely different result. In 2009, our group investigated the reaction between IMes and MesP=CPh2. To our surprise, the product turned out to be 4-phosphino-2-carbene (IMesP, Scheme 1.4).23 This was an example of abnormal reactions of NHCs. The mechanism of this unanticipated reaction was puzzling, and we therefore decided to investigate the possible mechanistic pathway. 6   Scheme 1.3 Cycloaddition reaction of a phosphaalkene with a carbene precursor  Scheme 1.4 The reaction of IMes with MesP=CPh2 1.2 N-heterocyclic carbenes  The focus of this thesis is on the abnormal reactions of N-heterocylic carbenes with phosphaalkenes. N-heterocyclic carbenes (NHCs) are an exciting class of stable carbenes. By definition, carbenes are neutral compounds containing a divalent carbon atom with a six-electron valence shell. They were hypothesized only as highly reactive intermediates in organic transformations until 1988, when Bertrand and coworkers prepared the first isolable carbene (1.1, Figure 1.2). As shown in Figure 1.2, the carbene is stabilized by adjacent phosphorus and silicon substituents.24   Figure 1.2 First isolable carbene 7  Generally speaking, the lone pair in a carbene exists as a singlet state or a triplet state. The singlet carbene assumes a sp2-hybridized carbon with the non-bonding electrons paired in the same sp2-hybridized orbital, remaining the p orbital unoccupied. The triplet carbene assumes a sp-hybridized carbon and the non-bonding electrons are unpaired in separate p orbitals (Figure 1.3).   Figure 1.3 Electronic structure of a carbene With respect to the bond angle, molecular orbital calculations for :CH2 predicts an H−C−H angle of 103° for the singlet state model and 134° for the triplet state model.25 The H−C−H angle of singlet carbene (sp2 hybridized) slightly deviates from 120° because of the electronic repulsions between the lone pair and the electrons in the two σ-bonding orbitals In 1991, Arduengo et al. reported the isolation and characterization of the first crystalline NHC: 1,3-di(adamantyl)imidazole-2-ylidene (IAd, Figure 1.4).26 The discovery of NHCs is undoubtedly one of the greatest breakthroughs in recent chemistry research. The past 25 years have witnessed a rapid growth of interest in these stable carbenes. Libraries of novel NHCs have been synthesized and investigated.27, 28 Most importantly, as a consequence of their good stability and strong σ-donating properties, NHCs are excellent ligands for transition metals and their complexes have found numerous applications in catalytic chemistry.29, 30  8   Figure 1.4 First isolable NHC Because the bond angles of N-C-N (100-110°) resemble those of acyclic, singlet carbenes,26, 31 NHCs are generally regarded as singlet state carbenes. Besides, the cyclic nature of NHCs helps to favor the singlet state by forcing the carbene carbon into a bent, more sp2-like arrangement. 31 The remarkably high stability of NHCs can be explained from their structures. The electronic stabilization provided by the nitrogen atoms is the most important factor. Calculations show that the nitrogen atoms can stabilize the carbene via their inductive electron-withdrawing ability and donating a lone pair into the empty p-orbital in a singlet state NHC (Figure 1.5). 31,32, 33 Other factors such as the steric effect can contribute to the stability of NHCs as well. NHCs usually have bulky substituents bound to the nitrogen atoms. The bulk can prevent undesired dimerization of carbenes to the corresponding olefin.34  9   Figure 1.5 Ground-state electronic structure of imidazol-2-ylidenes. The σ-withdrawing and π-donating effects of the nitrogen heteroatoms help to stabilize the singlet carbene structure. 33 A major application of NHCs is as ligands for transition metals. The first examples of NHC-metal complexes were reported by Wanzlick and Oflel independently in 1968 by synthesizing imidazol-2-ylidene bearing Hg(II) and Cr(0) species (1.2, 1.3, Figure 1.6).35, 36 However, no catalytic reactivity of these complexes was not observed. In 1995, Herrmann and coworkers first demonstrated that a palladium-NHC complex could catalyze the Heck reaction.37 Ever since then, a huge number of different NHC–metal complexes have been prepared and employed as highly active and robust catalysts. The numerous publications on catalysis mediated by NHC-metal complexes mainly include cross-coupling (catalysed by palladium or other metals),38-41 ruthenium-catalysed olefin metathesis,42, 43 Ir- and Ru-catalysed hydrogenation and hydrogen transfer,44 Au-catalysed activation of π-bonds45 and Rh- and Pt-catalysed hydrosilylation.46 10   Figure 1.6 First examples of NHC-metal complexes The success of NHCs as excellent ligands in catalysts can be attributed to two major factors: one is the strong metal-ligand binding, which increases the stability of catalysts and lowers the catalyst decomposition rate. The other is the steric and electronic influence of NHCs on the metal, which helps to increase catalytic activity. For example, the famous and widely employed Grubbs II catalyst contains an NHC ligand in place of PCy3 as in Grubbs I catalyst (Figure 1.7).47-49 As a consequence, Grubbs II exhibits greater thermal stability and remains catalytically active at much lower catalyst loadings. More importantly, Grubbs II shows significantly higher reactivity than Grubbs I and has dramatically expanded the range of substrates for olefin metathesis. Related mechanistic studies have revealed that the Grubbs II catalyst with an NHC ligand has an affinity for the alkene substrates 104 times greater than its predecessor upon dissociation of PCy3.50 This is very important for improving the catalytic activity because binding the substrate into the ruthenium center is a key step in olefin metathesis. The importance of Grubbs catalysts in olefin metathesis was recognized with the award of the Nobel Prize in 2005. 11   Figure 1.7 1st and 2nd generation of Grubbs catalysts 1.3 Abnormal N-heterocyclic carbenes Thus far, we have introduced the reactions of NHCs through the “normal” way: the carbene center (the C2 position of the ring). In general, the C2 position is the most reactive site. However, some exceptions have been discovered. The first example was reported by Crabtree and coworkers, who found that the NHC could bind Ir at the C4 position (1.4, Scheme 1.5).51 In this case, the carbene center is no longer located between the two nitrogen atoms. In comparison with the normal NHCs, these NHC isomers are usually termed as abnormal NHCs (aNHCs).   Scheme 1.5 First reported aNHC-metal complex 12  Later on, a few other complexes featuring aNHCs were reported.52-55 Besides their unusual mode of binding, these complexes also attracted attention as catalysts. Researches had proven metal coordinated aNHCs complexes as excellent catalysts in the activation of C–H and H–H bonds.56, 57 In some cases they even outperformed the catalytic activity as compared to their normal NHC counterpart. For example, Lebel and coworkers reported that the aNHC-palladium complex (1.5, Figure 1.8) demonstrated catalytic activity towards Suzuki coupling using aryl chlorides at 80 °C whereas the corresponding normal NHC analog (1.6, Figure 1.8) remained inactive under identical conditions.58  Figure 1.8 aNHC- and NHC- palladium complexes for Suzuki coupling reaction Very excitingly, in 2009 Bertrand and coworkers succeeded in the synthesis of a metal-free aNHC that was stable at room temperature (1.7, Scheme 1.6).59 The metal-free aNHC was generated by deprotonating the corresponding imidazolium salt with the C2 hydrogen replaced with a phenyl group. Experimental data suggests that aNHCs are even stronger electron-donor ligands than 13  NHCs.59 The isolation of stable aNHCs not only provides easy access to a variety of corresponding transition-metal complexes, but also potentially allows for their use as organocatalysts.   Scheme 1.6 The first examples of an isolable aNHC Another breakthrough in a related area is attributed to Robinson and coworkers, who prepared the first anionic N-heterocyclic dicarbene in 2010.60 The anionic dicarbene has both normal (C2) and abnormal (C4) carbene centers in the same imidazole ring. Interestingly, the lithium salt of this dicarbene is polymeric in the solid state (1.8, Scheme 1.7).  Scheme 1.7 Synthesis of the anionic N-heterocyclic dicarbene 14  1.4 Examples of abnormal reactions of NHCs and possible mechanisms The goal of this thesis is to explore the mechanism of abnormal reactions of NHCs with phosphaalkenes. Herein the examples of other abnormal reactions of NHCs (especially with p-block elements) and their possible mechanisms will be introduced.  The earliest abnormal reaction of NHCs with a p-block element was discovered in 1997. It was found that the carbene 1,3-dimesitylimidazol-2-ylidene reacted rapidly with 2 equiv. of carbon tetrachloride in tetrahydrofuran at room temperature to produce chloroform and a halogenated carbene 1.9 (Scheme 1.8).61 Remarkably, carbene 1.9 was exceptionally stable and could be even handled in air without decomposition.   Scheme 1.8 Chlorination of IMes  Tamm and coworkers made some breakthrough to enrich the library of abnormal carbene-borane reactions. While working on activating H2 with a frustrated carbene–borane lewis pair, they were surprised to observe the NHC (1,3-di-tert-butylimidazolin-2-ylidene) could be activated at the C4-position in the absence of H2, converting the frustrated normal carbene adduct into a non-frustrated abnormal adduct, which had no reactivity towards H2 (1.10, Scheme 1.9).62  15   Scheme 1.9 Reactions of the frustrated Lewis pair ItBu/B(C6F5)3  Tamm also reported the mixture of NHC and B(C6F5)3 was able to affect the cleavage of one of the six P–P bonds in white phosphorus (P4), thus generating an adduct in which one P atom was bound to C4 of the NHC ring (1.11, Scheme 1.10).63 DFT calculations indicated that the abnormal carbene adduct was thermodynamically favored over its normal congener. A plausible mechanism was postulated to involve the formation of the normal carbene-phosphorous-borane adduct in the first place, then rearrangement to the thermodynamically more stable abnormal adduct. However, the author did not discuss how the “rearrangement” took place.  Scheme 1.10 Reaction of the frustrated Lewis Pair ItBu/B(C6F5)3 with P4 16  It was also revealed by Tamm and coworkers that the anionic dicarbene reacted with B(C6F5)3 to afford abnormal NHC-borane adduct (1.12, Scheme 1.11). This discovery could imply that the abnormal reaction of NHC with borane as described in Scheme 1.9 actually occurred through the anionic dicarbene intermediate.  Scheme 1.11 Preparation of lithium carbene-borane complexes The abnormal reactions of NHCs with silicon also attracts lots of attention. Radius and coworkers once reported that treatment of 2 equiv. of free IiPr and 1 equiv. of Ph2SiCl2 could activate the C4 position of NHC (1.13, Scheme 1.12).64 According to their proposed mechanism, NHC first reacts with silicon in the normal way (1.13a, Scheme 1.12). Then the rearrangement of the NHC adduct to aNHC adduct is triggered by protonation/deprotonation steps (1.13b, Scheme 1.12). However, it is yet unclear how the rearrangement step occurs to afford the abnormal product. Since aNHCs are better donors than NHCs, 1.13b is likely to dissociate one of the chloride substituents, leaving the silicon atom susceptible for further nucleophilic attack of another NHC ligand and ultimately leading to the formation of 1.13. 17   Scheme 1.12 Abnormal reaction of NHC with silicon and possible mechanism Utilizing anionic dicarbenes or aNHCs directly also allows for the synthesis of 4-silicon-functionalized NHCs. Robinson has proven that the anionic dicarbenes react with electrophiles such as TMSCl selectively at C4 position to form aNHC-silicon adduct.60 Roesky and coworkers reported that even though free NHCs could stabilize dichlorosilylene NHC•SiCl2 in the normal way, the reaction of aNHC with 2 equiv. of HSiCl3 gave the aNHC•SiCl2H2 adduct 1.14 under the elimination of SiCl4 (Scheme 1.13).65 Furthermore, aNHC could selectively replace NHC from the solution of NHC•SiCl2 to afford a mixture of aNHC•SiCl2 adduct (1.15, Scheme 1.14).66 These examples indicate that aNHCs or anionic dicarbenes could be essential in the abnormal reactions of NHCs.  18   Scheme 1.13 Different reactivities of NHC and aNHC towards HSiCl3  Scheme 1.14 The reaction of NHC•SiCl2 wth aNHC Another major focus of research on the abnormal behavior of NHCs is their reactions with phosphorous to afford 4-phosphino- or 4,5-diphosphino-functionalized NHCs or imidazoles. Carty and coworkers reported the earliest example of NHCs reacting with phosphinidene complexes at C4 position (1.16, Scheme 1.15).67 They proposed a mechanism in which the first step was the 19  conversion of NHC to aNHC. Then the phosphinidene reacted with aNHC to form the final product 1.16.   Scheme 1.15 Abnormal reaction of NHC with phosphinidene complex In 2010, Bertrand and coworkers proposed a two-step synthesis of a 4-phosphino-substituted NHC 1.17 (Scheme 1.16).68 The first step was a carbene addition to the chlorophosphine to form an NHC-phosphenium intermediate 1.17b. After treatment with potassium hexamethyldisilazide (KHMDS), a 4-phosphino-NHC could be isolated. The postulated mechanism (Scheme 1.16) provides an explanation of how the PPh2 group “rearranges” from C2 to C4 position: the base firstly deprotonates the NHC-phosphenium intermediate (1.17b) with concomitant formation of aNHC (1.17c). 1.17c then reacts with 1.17b to generate 1.17d and reform NHC 1.17a. NHC 1.17a acts as a nucleophile toward 1.17d, leading to the 4-substituted NHC 1.17 and regenerating the starting material 1.17b. This proposal might be applicable to other aforementioned “rearrangement” steps in abnormal reactions of NHCs. 20   Scheme 1.16 Synthesis of 4-P-functionalized NHC and possible mechanism The Mesa group has provided a strategy for the synthesis of diphosphino-functionalized NHCs.69 Treatment of a 2-imidazolium phosphine with 2 equiv of LiN(SiMe3)2 and 1 equiv of ClPPh2 can form a diphosphinoimidazole salt (1.18, Scheme 1.17). A follow-up deprotonation will generate the corresponding NHC (1.19, Scheme 1.17). The authors propose the reaction is likely to proceed through deprotonating C4 or C5 positions by LiN(SiMe3)2 to form an aNHC. Then the PPh2 group “rearranges” from C2 to C4 to form the P-functionalized NHCs in a similar mechanistic pathway as Bertrand proposed in Scheme 1.16.  21   Scheme 1.17 Synthesis of diphosphino-functionalized NHC and possible mechanism The examples discussed above cover most of the recent achievements in the area of abnormal reactions of NHCs with p-block elements. In general, there are two major proposed mechanisms: the first one involves the NHCs initially reacting through C2 position, followed by the conversion of NHC adducts to aNHC adducts. The second one involves the formation of aNHCs or anionic 22  dicarbenes, then directly reacting at the C4 or C5 position. However, more explorations are still required in order to gain further insight into the abnormal behavior of NHCs. 1.5 Project goals As mentioned before, the aim of this thesis is to investigate the mechanism of abnormal behavior of NHCs with phosphaalkenes (Scheme 1.18).  Scheme 1.18 Abnormal reaction of IMes with MesP=CPh2 Previously a PhD student Joshua Bates from our group proposed some mechanisms regarding these reactions and evaluated them by DFT calculations.23 In order to compare with the calculations and further understand the reaction pathway, kinetic studies of the reactions (the determination of reaction order, rate constants) and investigations of the thermodynamic parameters (activation energy (Ea), enthalpy of activation (∆H≠) and entropy of activation (∆S≠)) are needed.  With regard to the issue such as how the proton transfers in the progress to form the final product 4-substituted-phosphino-NHC (IMesP), deuterium labeling experiments will be conducted to monitor the abnormal reaction.   23  In addition, as a part of expanding the scope of the reactions of NHCs with phosphaalkenes, the reactions of IMesMe2 (IMes with –CH3 groups at C4 and C5 positions), IMesMe (IMes with a –CH3 group at C4 position) with MesP=CPh2 will be explored to see whether “normal” NHC products can be generated. Finally, IMesP can be regarded as a bifunctional ligand. Our group has proven it as an effective ligand, which can bind to Au (I), Rh (I) and Ir (I) centers.23, 70 The Bertrand Group also reported a 4-phosphino-substituted NHC ligand similar to IMesP, and they were able to synthesize the homo- and hetero-dinulear complexes containing Cu(I), Au(I), and Pd(II) based on their ligand.71 In this research, further explorations of the metal complexes based on IMesP will be conducted. The ultimate goal is to synthesize the dinuclear complexes and take the advantage of them for catalysis, especially the potential in catalyzing two different reactions (tandem catalysis).        24  2 Kinetic studies of the abnormal reaction of NHCs with phosphaalkenes 2.1 Introduction As mentioned in the previous chapter, the reaction of IMes (2.1) with MesP=CPh2 (2.2) affords a 4-phosphino-substituted NHC (2.3, Scheme 2.1). The scope of this abnormal reaction is not limited to MesP=CPh2. Other phosphaalkenes, such as MesP=C(4-C6H4F)2 (2.4) and MesP=C(4-C6H4OMe)2 (2.6) both react cleanly with IMes to form the 4-phosphino-substituted NHCs (Scheme 2.1, Figure 2.1 – Figure 2.3).   Scheme 2.1 Reactions of IMes with phosphaalkenes 25     Figure 2.1 31P NMR (121 MHz, THF) spectrum of MesP=CPh2 (2.2) and product 2.3   Figure 2.2 31P NMR (121 MHz, THF) spectrum of MesP=C(4-C6H5F)2 (2.4) and product 2.5  Figure 2.3 31P NMR (121 MHz, THF) spectrum of MesP=C(4-OMeC6H4)2 (2.6) and 2.7 2.2 2.3 2.6 2.7 2.4 2.5 26  Previously a PhD student Joshua Bates from our group proposed two mechanisms of the abnormal reactions and DFT calculations were conducted to evaluate the possible pathways.23  Mechanism I is shown in Scheme 2.2. It is in analogy to Bertrand’s proposal about the reaction to selectively substitute C4 position of NHCs with phosphorus (Scheme 1.17).68 This mechanism involves normal nucleophilic addition of IMes to the P=C bond of MesP=CPh2 to afford a zwitterionic intermediate (Ia), then followed by deprotonation by a base to form Ib. Ib continues to react with phosphaalkenes at C4 position to form Ic. In the end, another IMes reacts with Ic to eliminate the phosphaalkene from C2 position and form the abnormal product.  Scheme 2.2 Proposed mechanism I for the reaction of IMes with MesP=CPh2  The mechanism II is similar to Carty’s proposal about the reaction of ItBu with phosphinidene (Scheme 1.15).67 As shown in Scheme 2.3, this mechanism involves the initial generation of an 27  abnormal carbene from a normal carbene (IIa), which then activates the P=C bond of MesP=CPh2 to afford an intermediate IIb. Subsequent proton transfers generate the product IMesP.   Scheme 2.3 Proposed mechanism II for the reaction of IMes with MesP=CPh2 The energies of the possible intermediates were calculated and shown in Table 2.1. By comparing the energy values, mechanism II is overall more energetically favorable than mechanism I.  Table 2.1 Energy of possible intermediates in THF R = Ph Energy (kJ/mol) R = Ph Energy (kJ/mol) Ia 131.1 IIa 51.7 Ib 76.3 IIb 49.0 Ic 244.5 IIc 23.2 In this chapter, the kinetic studies of the abnormal reactions as well as the comparison of the kinetic data with the DFT calculation will be discussed to gain further insight into the fascinating reactions.  28  2.2 Results and discussion  Procedures to conduct kinetic studies  The kinetic studies were conducted by monitoring the 31P NMR spectroscopy. In order to integrate the 31P NMR spectra accurately, the relaxation times (T1) for phosphaalkenes and products IMesP were measured prior to conducting any experiments (Table 2.2).  Table 2.2 31P NMR (121 MHz, THF) chemical shifts and T1 of the phosphaalkenes and products. Compound 31P NMR (ppm) T1 (s) 2.2 234 1.3 2.3 - 37.9 3.8 2.4 234 1.3 2.5 - 36.5 3.8 2.6 217 1.2 2.7 -38.6 2 Kinetic studies have been conducted for the aforementioned three reactions. Herein we will take the reaction of IMes (2.1) with MesP=CPh2 (2.2) as an example to illustrate the experiment procedures. According to their T1, a relaxation delay (d1) of 20 s with a 90° tip angle was set up for all 31P NMR experiments. The parameter d1 should be at least 5 times T1 so that the nuclear spins can be considered completely relaxed. The temperature was calibrated for NMR experiments using standard Bruker samples, which contains 4% MeOH in MeOH-d4 for the 194-283 K range and 80% ethylene glycol in DMSO-d6 for the 300-400 K range.  29  All kinetic experiments were conducted as follows: (i) 1 equvi of IMes and 1 equiv of phosphaalkene were added into an NMR tube in the glovebox; (ii) All the solids were dissolved in 0.3 mL THF added via a syringe; (iii) The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded at 600 s intervals. Representative 31P NMR spectra of reactions are shown in Figure 2.4, Figure 2.5 and Figure 2.6. The signals assigned to the phosphaalkene and final product IMesP were integrated separately in each spectrum. The percent conversion was calculated from the integration numbers of phosphaalkenes and products. The initial concentration of phosphaalkene and the percent conversion can be used to calculate the concentration of product.  Figure 2.4 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=CPh2 (341K). 2.2 2.3 30   Figure 2.5 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=C(4-C6H5F)2 (308K).  Figure 2.6 Selected 31P NMR (121 MHz, THF) spectra of the reaction of IMes and MesP=C(4-OMeC6H4)2 (336K). 2.4 2.5 2.6 2.7 31   Determination of the reaction order and rate constants  The first goal of kinetic studies is to determine the reaction order. One method is to measure the initial rates by varying concentrations of starting materials: taking IMes (2.1) and IMesP=CPh2 (2.2) as an example, according to the rate law: rate = k[2.1]x•[2.2]y, x and y can be calculated by varying the concentrations of 2.1 and 2.2 and measuring corresponding initial rates (Table 2.3). Table 2.3 Preliminary determination of the reaction order at 343 K. Entry [2.1] (mol•L-1) [2.2] (mol•L-1) Initial rate (mol•L-1•s-1) 1 0.079  0.079  1.14 x10-6  2 0.079  0.158  2.31 x10-6  3 0.158  0.079  1.99 x10-6  4 0.421 0.421 30.8 x10-6 By comparison in Table 2.3, when the concentration of either 2.1 or 2.2 was doubled, the initial rate of the reaction doubled. Moreover, Entry 1 and Entry 4 indicated that when the concentrations of 2.1 and 2.2 were 5 times higher respectively, the initial rate got 25 times higher. Thus, it is postulated the reaction to be 1st order for each starting material, the overall reaction order is 2nd order. The rate law of this abnormal reaction can be written as follow: ˗d[𝟐.𝟐]dt= 𝑘[𝟐. 𝟏][𝟐. 𝟐]   If the initial concentrations of the reactants are kept to be equal ([2.1] = [2.2]), the equation can be rewritten as: 32  ˗d[𝟐.𝟐]dt= 𝑘[𝟐. 𝟐]2    After integration, the equation then can be rearranged into this form: 1[𝟐.𝟐]−1[𝟐.𝟐]0 = kt In this equation, [2.2]0 is the initial concentration of the phosphaalkene 2.2 (at t = 0). As can be inferred, if 1/[2.2] is plotted against t, a straight line should be expected and the rate constant k is the slope of the line. Figure 2.5 shows that the plots of 1/[2.2] versus time (s) that are fitted to a linear least squares function to determine rate constants. The rate constants k at different temperatures (318 K, 324 K, 330 K, 335 K, and 341 K) are shown in Table 2.4.  Figure 2.7 Graph showing 1/[2.2] vs time (s) up to ∼75% conversion for the abnormal reaction at ∼5 K temperature intervals between 318 K and 341 K.   33  Table 2.4 Rate constants of the reaction of IMes (2.1) with MesP=CPh2 (2.2) Entry 2.1 (mol•L-1) 2.2 (mol•L-1) temp (K) k  (L•mol-1•s-1) 1 0.421 0.421 318 (6.01±0.30) x 10-4 2 0.421 0.421 324 (9.02±0.44) x 10-4 3 0.421 0.421 330 (13.7±0.14) x 10-4 4 0.421 0.421 335 (19.1±0.86) x 10-4 5 0.421 0.421 341 (28.1±0.83) x 10-4 Using the same method, the kinetic studies of the reaction of IMes with MesP=C(4-C6H4F)2 and MesP=C(4-OMeC6H4)2 were established, respectively. The plots and the rate constants (k) are shown as follows.  Figure 2.8 Graph showing 1/[2.4] vs time (s) up to ∼80% conversion for the abnormal reaction between 297 K and 330 K. 34  Table 2.5 Rate constants of reaction of IMes (2.1) with MesP=C(4-C6H4F)2 (2.4) Entry 2.1 (mol•L-1) 2.4 (mol•L-1) temp (K) k  (L•mol-1•s-1) 1 0.379 0.379 297 (4.07±0.87) x 10-4 2 0.379 0.379 308 (8.41±0.47) x 10-4 3 0.379 0.379 319 (25.1±0.34) x 10-4 4 0.379 0.379 330 (40.2±0.31) x 10-4  Figure 2.9 Graph showing 1/[2.6] vs time (s) up to ∼50% conversion for the abnormal reaction between 313 K and 341 K.    35  Table 2.6 Rate constants of the reaction of IMes with MesP=C(4-OMeC6H4)2 Entry 2.1 (mol•L-1) 2.6 (mol•L-1) temp (K) k  (L•mol-1•s-1) 1 0.421 0.421 313 (0.45±0.04) x 10-4 2 0.421 0.421 324 (1.51±0.01) x 10-4 3 0.421 0.421 336 (2.77±0.06) x 10-4 4 0.421 0.421 341 (4.05±0.04) x 10-4  Determination of the activation energies To determine the activation energies (Ea) of the abnormal reactions, Arrhenius plots are needed. According to the Arrhenius equation: ln(k) = − 𝐸𝑎R1T + ln(A), 1/T is plotted against ln(k) with the x-axis being 1𝑇 and y-axis being ln(k). The activation energy is then calculated from the slope of the Arrhenius plot. Figure 2.10- Figure 2.12 shows the Arrhenius plots for three abnormal reactions.  Figure 2.10 Arrhenius plot of the reaction IMes with MesP=CPh2. The linear least squares function (y = -7353.6x + 15.665) has an R2 value of 0.98.  36   Figure 2.11 Arrhenius plot of the reaction IMes with MesP=C(4-C6H4F)2. The linear least squares function (y = -6998.5x + 15.766) has an R2 value of 0.97.   Figure 2.12 Arrhenius plot of the reaction IMes with MesP=C(4-OMeC6H4)2. The linear least squares function (y = -8104.5x + 15.996) has an R2 value of 0.97.  37   The Erying plots The rate constants and temperatures can be also used to construct the Erying plot. According to the Erying equation: ln𝑘T= −∆𝐻≠R∙1T+ lnkBh+Δ𝑆≠R The Erying plot can be obtained by plotting 1/T against ln(k/T) with the x-axis being 1/T and y-axis being ln(k/T). The enthalpy of activation ∆𝐻≠ and entropy of activation ∆𝑆≠can be easily calculated from the plot using the Erying equation. Figure 2.13-Figure 2.15 show the Erying plots of three abnormal reactions.  Figure 2.13 Erying plot of the reaction of IMes with MesP=CPh2 The linear least squares function (y = -7023.4x + 8.864) has an R2 value of 0.99. 38   Figure 2.14 Erying plot of the reaction of IMes with MesP=C(4-C6H4F)2 The linear least squares function (y = -6685.6x + 9.019) has an R2 value of 0.98.  Figure 2.15 Erying plot of the reaction of IMes with MesP=C(4-OMeC6H4)2 The linear least squares function (y = -7778x + 9.207) has an R2 value of 0.98. 39  The activation energy (Ea), enthalpy of activation (∆𝐻≠) and entropy of activation (∆S≠) of the abnormal reactions are calculated and tabulated in Table 2.7.  Table 2.7 Ea, ∆𝐻≠ and ∆𝑆≠ of the abnormal reactions of IMes with phosphaalkenes Phosphaalkene Ea (kJ/mol) ∆𝐻≠ (kJ/mol) ∆𝑆≠ (J/mol) MesP=CPh2 61.14 ± 1.22  58.39 ±1.21 -123.84 ± 8.86 MesP=C(4-C6H4F)2 58.19 ± 3.13 55.58 ± 3.13 -122.56 ± 9.02 MesP=C(4-OMeC6H4)2 67.38 ± 3.43 64.67 ± 3.43 -120.99 ± 9.21 So far, we have conducted kinetic studies for the reactions of IMes with MesP=CPh2, MesP=C(4-C6H4F)2 and MesP=C(4-OMeC6H4)2, respectively. It is noticed the substituents on phosphaalkenes have a certain impact on the rate of the abnormal reactions (Table 2.4 - Table 2.6). Such a difference in the rates of the reaction is likely due to one step: the nucleophilic addition of carbene to the phosphaalkene. Since the electronegativity of phosphorous (2.19, Pauling scale) is lower than carbon (2.55, Pauling scale), the phosphorous in the P=C bond is partially positive charged. In MesP=C(4-C6H5F)2, the electron withdrawing group (4-C6H5F) renders the phosphorous even more positively charged. This will result in facilitating the nucleophilic attack of the carbene to the P=C bond. In contrast, MesP=C(4-OMeC6H4)2 has an electron-donating group (4-OMeC6H4) as the substituent. Such a group will slow the nucleophilic attack of the carbene to the P=C bond. The Ea values in Table 2.7 are in accordance with the substituent effects: the reaction of IMes with MesP=C(4-OMeC6H4)2 has a highest value (67.38 kJ/mol), whereas the value is lowest for the 40  reaction with MesP=C(4-C6H4F)2 (58.19 kJ/mol). Furthermore, the observed substituent effects on the reactions can be rationalized by DFT calculations (Table 2.8).  Table 2.8 Energy comparisons between possible intermediates in THF Energy (kJ/mol)  R = Ph R= 4-C6H4F Ia 131.1 124.5 Ib 76.3 75.7 IIb 49.0 27.8 IIc 23.2 21.5 Product -47.0 -46.7 In the proposed mechanisms (Scheme 2.2 and Scheme 2.3), the intermediates Ia and IIb result from addition of the carbene to the P=C bond. DFT calculations shows that Ia has the energy of 131.1 kJ/mol with C-Ph substituents, whereas 124.5 kJ/mol with C-C6H4F substituents.23 Similarly, IIb has the energy of 49.0 kJ/mol with C-Ph substituents in comparison of 27.8 kJ/mol with C-C6H4F substituents. This suggests that replacing the C-Ph by C-C6H4F substituents contributes a better stabilizing effect upon the intermediates Ia and IIb. Therefore the reaction is more energetically favorable in the presence of C-C6H4F substituents, which explains why IMes reacts with MesP=C(4-C6H4F)2 in a faster rate.  In addition, the negative values of ∆𝑆≠ mean the entropy of the reactions decreases on forming the transition state, indicating an associative mechanism.72 This could imply that two reactant species (an abnormal carbene and a phosphaalkene) come together to form one species during activation.  41   Base facilitates the abnormal reaction During the exploration, the addition of base was noticed to facilitate the reaction. This effect was observed from a control experiment. In the control experiment, two trials of reactions were conducted. Each of the trial contained the same concentration of IMes (0.316 mol•L-1 in 0.3 mL THF) and MesP=CPh2 (0.316 mol•L-1 in 0.3 mL THF). The only difference was the second trial was added into 5 mol% NaH. 31P NMR spectroscopy was used to monitor their reaction process at 341 K. After 3 hours the trial with NaH went to completion whereas the other did not (Table 2.9). KOH and NaOAc were also found to facilitate the reaction (Table 2.9). However, the reaction did not undergo cleanly in the presence of KOH. It was also observed due to its relatively low basicity, NaOAc could not facilitate the reaction as fast as NaH.  Table 2.9 The influence of different bases on the abnormal reaction at 341 K. * [IMes]=[MesP=CPh2]=0.316 mol•L-1 Base (10 mol%) pKb Trend in basicity Time to fully consume MesP=CPh2 NaH -21  3 hours KOH 0.2 3 hours NaOAc 9.3 6 hours None - 8 hours To further investigate the influence of the base, a series of kinetic experiments with different concentrations of NaH were conducted. The concentrations of IMes and MesP=CPh2 were kept constant (0.316 mol•L-1). The amount of NaH added into the reaction mixture was 0 mol%, 5 mol%, 8 mol% and 10 mol%, respectively. The results are shown in Figure 2.19 and Table 2.10. 42   Figure 2.16 Graph showing 1/[PA] vs time (s) up to ∼80% conversion for the reaction of IMes with MesP=CPh2 at 319 K with different concentrations of NaH. Table 2.10 The influence of NaH on the rate of the reaction of IMes with MesP=CPh2 at 319 K. * [IMes]=[MesP=CPh2]=0.316 mol•L-1 Entry NaH (mol %) k (L•mol-1•s-1)  1 0 6.0 x 10-4 2 5 1.4 x 10-3 3 8 1.8 x 10-3 4 10 2.6 x 10-3 The data demonstrate that the rate of the reaction is getting faster with the amount of NaH increasing. In other words, this reaction is catalyzed by the base. It is very likely the base helps to form the “abnormal carbene”. According to the calculation, the abnormal IMes (aIMes) is 51.7 kJ/mol higher in energy than IMes in THF.23 Such a huge energy gap means the conversion of IMes to aIMes is not energetically favorable. The presence of base such as NaH probably can extract the H+ from the backbone of IMes, thus helping forming “anionic aIMes dicarbene” (Scheme 2.4). The 43  resulting aIMes dicarbene will attack MesP=CPh2 to generate IMesP, in the same way as some anionic N-heterocyclic dicarbenes reacting with electrophiles to afford the abnormal NHC products (Chapter 1, Scheme 1.11).60, 73   Scheme 2.4 Postulated reaction of IMes with MesP=CPh2 in the presence of base Another experiment was designed to gain further evidence for this hypothesis. We were able to synthesize the anionic N-heterocyclic dicarbene by lithiating IMes with nBuLi. This dicarbene was then treacted with MesP=CPh2 in an NMR scale for 6 hours at room temperature. After quenching the reaction mixture with methanol, a product showed a chemical shift of –37.9 ppm in the 31P NMR spectrum, indicating the formation of IMesP (Scheme 2.5, Figure 2.17).  Scheme 2.5 Synthesis of anionic aIMes dicarbene and its reaction with MesP=CPh2 44   Figure 2.17 31P NMR (121 MHz, C6D6) spectra of the reaction of anionic aIMes dicarbene with MesP=CPh2.  Acid hinders the abnormal reaction As discussed above, the reaction appears to be catalyzed by the base. It is speculated that the base can facilitate the formation of anionic aIMes dicarbene as an intermediate. If indeed this hypothesis is correct, the addition of acid will hinder the formation of the dicarbene, thus slowing down the reaction. Kinetic experiments were conducted with imidazolium salts (IMesHBF4) added into the reaction as an acid to further validate the hypothesis.  In the experiment, 10 mol% IMesHBF4 was added into the mixture of 90 mol% IMes and 100 mol% MesP=CPh2 in THF. The progress was monitored by 31P{1H} NMR spectroscopy at 319K. The (1) Before quenching with methanol (2) After quenching with methanol-d4 45  result confirmed our previous hypothesis. In contrast to the reaction without IMesHBF4, the addition of IMesHBF4 was observed to slow the abnormal reaction (Figure 2.18, Table 2.11).   Figure 2.18 Graph showing 1/[PA] vs time (s) up to ∼80% conversion for the reaction of IMes with MesP=CPh2 under the influence of IMesHBF4. Table 2.11 The influence of IMesHBF4 on the rate of the reaction of IMes with MesP=CPh2  * [IMes]=[MesP=CPh2]=0.316 mol•L-1 Entry Acid Temp (K) k (L•mol-1•s-1) 1 10 mol% IMesHBF4 319 1.02 x 10-4 2 No IMesHBF4 319 6.01 x 10-4 It was also noticed that during the formation of IMesP, an unexpected signal showed up (δp = 22.1, Figure 2.19). Interestingly, this signal remained the same intensity over time during the process. However, we lacked the information to identify this unknown compound. The only fact we know 46  is that, if the solution of MesP=CPh2 and IMesHBF4 is heated at 341 K for two weeks, a tiny amount of this compound can be observed (Figure 2.20).   Figure 2.19 31P NMR of the reaction of IMes, IMesHBF4 and MesP=CPh2 over time at 319K.  Figure 2.20 31P NMR (121 MHz, CDCl3) spectrum of the mixture of MesP=CPh2 and IMesHBF4 after two weeks at 341 K.   MesP=CPh2 IMesP 47  2.3 The reaction of the IMes-tungsten complex with MesP=CPh2 The reaction of the IMes-tungsten complex with the phosphaalkene was investigated in order to see if the abnormal reaction could occur without the presence of the carbene functionality. IMes-W(CO)5 can be synthesized in a similar way to the literature.74   Scheme 2.6 No reaction observed between IMes-W(CO)5 and MesP=CPh2. It turned out the IMes-tungsten complex did not react with MesP=CPh2, even heated to 70 °C for one week. This result suggests the essential role of the carbene functionality: the C4- position of the NHC ring cannot be activated once the C2- position is blocked. A further investigation includes deprotonating the C4 position of IMes-W(CO)5 to see whether it reacts with MesP=CPh2 in the abnormal way. 2.4 Conclusions Kinetic investigations of IMes with phosphaalkenes bearing different substituents have been conducted. Rate constants at different temperatures were obtained and used to determine the activation energies (Ea), enthalpy of activation (∆𝐻≠) and entropy of activation (∆𝑆≠) for each of the abnormal reactions. In addition, it was found the reaction was catalyzed by base and hindered by acid. Based on all the kinetic data as well as the DFT calculations, I tend to believe the reaction 48  proceeds through the formation anionic aIMes dicarbene, which is followed by the nucleophilic addition of the carbene at C4 position to the P=C bonds of phosphaalkenes to afford the abnormal product.  2.5 Experimental sections  Materials and general procedures All manipulations of air and/or moisture sensitive compounds were performed under nitrogen atmosphere using Schlenk techniques or in the Innovative Technology glovebox. Tetrahydrofuran (THF) was distilled from Na/benzophenone followed by three freeze/pump/thaw cycles. IMes and phosphaalkenes were prepared according to literature procedure.15, 75 31P NMR (121 MHz) spectra of the starting materials were recorded at room temperature on a Bruker Avance 300 MHz spectrometer. Chemical shifts are reported relative to 85% H3PO4 as an external standard δ = 0 for 31P. Temperature was calibrated for NMR experiments using standard Bruker smaples: 4% MeOH in MeOH-d4 for the 194-283 K range and 80% ethylene glycol in DMSO-d6 for the 300-400 K range.   General procedure for processing 31P NMR spectra The raw NMR data, obtained as described above, were processed using line broadening settings of LB=10 and a base line correction was applied. The sharp signals for the phosphaalkenes (chemical shifts around 233 ppm) and the products (chemical shifts around –38 ppm) were integrated using 49  approximate ranges between 250 and 210 ppm and between -10 and -50 ppm, respectively. The relative integrations, after phasing, were used to determine the percent conversion of the starting materials to the 4-phosphino-substituted NHCs and consequently, the concentration of phosphaalkenes during the acquisition of each spectrum. The data are tabulated in Appendices.  Adding error bars in Arrhenius and Erying plots In this chapter, error bars were reported with 95% confidence. Error bars were calculated based on the standard deviation (SD) of three-trial measurement of the rate constants at each temperature. SD was calculated by the formula: SD = √∑(𝑋−𝑀)2𝑛−1 where X refers to the individual data points, M is the mean for all the n data points. SD is the average difference between the data points and their mean, M. About 95% of the data points are within 2 SD of the mean.  The NMR-scale reaction of IMes with MesP=CPh2  IMes (38 mg, 0.126 mmol) and MesP=CPh2 (40mg, 0.126 mmol) were added into an NMR tube in the glovebox. 0.3 mL THF was added into the NMR tube via a syringe. The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded every 600 s at different temperatures. 50   The NMR-scale reaction of IMes with MesP=C(4-C6H4F)2  IMes (34 mg, 0.11mmol) and MesP=C(4-C6H4F)2 (38 mg, 0.11mmol) were added into an NMR tube in the glovebox. 0.3 mL THF was added into the NMR tube via a syringe. The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded every 600 s at different temperatures.  The NMR-scale reaction of IMes with MesP=C(4-OMeC6H4)2  IMes (38 mg, 0.126 mmol) and MesP=C(4-OMeC6H4)2 (47 mg, 0.126 mmol) were added into an NMR tube in the glovebox. 0.3 mL THF was added into the NMR tube via a syringe. The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded every 600 s at different temperatures.  The NMR-scale reaction of IMes with MesP=CPh2 with NaH  IMes (38 mg, 0.126 mmol), MesP=CPh2 (40mg, 0.126 mmol) and NaH were added into an NMR tube in the glovebox. 0.3 mL THF was added into the NMR tube via a syringe. The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded every 600 s at 319 K.  The NMR-scale reaction of IMes with MesP=CPh2 with IMesHBF4  IMes (38 mg, 0.126 mmol) and MesP=CPh2 (40mg, 0.126 mmol) and IMesHBF4 (5 mg, 0.0126 mmol) were added into an NMR tube in the glovebox. 0.3 mL THF was added into the NMR tube 51  via a syringe. The reactants were mixed well in the NMR tube and 31P NMR spectra were recorded every 600 s at 319 K.  Synthesis of anionic aIMes dicarbene IMes (500 mg, 1.6 mmol) was added to a flask containing 10 mL of hexane at room temperature. After the slurry was stirred about 10 min., 1.6 M nBuLi in hexane (1mL, 1.6 mmol) was added into the flask. The mixture was stirred overnight and then filtered. The off-white residue was rinsed using 10 mL hexane and then vacuumed, leading to the off-white powder. 1H NMR (THF-d8): δ = 2.08 (s, 12H), 2.31 (s, 6H), 6.95 (s, 4H), 6.16 (s, 1H), 7.05 (s, 1H).  The NMR-scale reaction of anionic aIMes dicarbene with MesP=CPh2  MesP=CPh2 (10 mg, 0.03 mmol) was mixed with anionic aIMes dicarbene (10 mg, 0.03 mmol) in C6D6 in an NMR tube at room temperature for 6 hours. Then the reaction was quenched with 0.3 mL methanol. The product showed a chemical shift of δP = -37.9, which was identical to the 31P NMR value of IMesP.    The synthesis of IMes-W(CO)5 To a solution of W(CO)5CH3CN (358 mg, 0.98 mmol) in 5 mL THF was added a solution of IMes (300 mg, 0.98 mmol) in 5 mL THF. The mixture was stirred for 3 hours at 50 °C. Upon cooling, 52  volatiles are removed in vacuo. The product was obtained as a yellow solid, which was recrystallized from DCM/hexane (yield: 70%).  1H NMR (300 MHz, CDCl3): δ 7.07 (s, 2H), 7.04 (s, 4H), 2.37 (s, 6H), 2.09 (s, 12H). 13C {1H} NMR (75 MHz, CDCl3): δ 200.3 (1JCW = 101.64 Hz), 196.9 (1JCW = 101.64 Hz), 191.1 (1JCW = 101.64 Hz), 185.5 (1JCW = 84.7 Hz), 139.8, 137.7, 135.5, 129.5, 123.4, 21.1 and 19.8.  The reaction of IMes-W(CO)5 with MesP=CPh2 To a solution of IMes-W(CO)5 (0.25 g, 0.40 mmol) in THF (8 mL), MesP=CPh2 (0.13 g, 0.40 mmol) was added at ambient temperature. The reaction mixture was stirred for 7 days at 70 °C. No reaction was observed.       53  3 The reactions of different NHCs with MesP=CPh2 3.1 The reaction of IMes-d2 with MesP=CPh2  Purpose of using IMes-d2 In the abnormal reaction of IMes with phosphaalkenes, the P=C bond of phosphaalkenes formally inserts into the C-H bond in the backbone of IMes to afford IMesP (Scheme 3.1). Kinetic studies of this reaction and their comparison with DFT calculations have been discussed in Chapter 2. However, there are still some unresolved issues: how does the proton at C4 position of IMes transfer to P-CHPh2 fragment in order to form IMesP? Is it an intermolecular or intramolecular proton transfer? More explorations are required to understand this fascinating reaction.   Scheme 3.1 The abnormal reaction of IMes with MesP=CPh2 Using IMes-d2 (IMes with deuterium at the C4 and C5 position) can help to probe into the issue regarding whether proton transfer occurs inter- or intra- molecularly (Scheme 3.2). As proposed, the mixture of IMes (1.1) and IMes-d2 (3.1) is treated with MesP=CPh2 (in the ratio of 50%: 50%: 100%). If the proton transfers intramolecularly, IMes and IMes-d2 will react with MesP=CPh2 54  independently to generate two pure products in the ratio of 50%:50%. In contrast, proton/deuterium will scramble if intermolecular proton transfer occurs. As a consequence, the reaction will afford four products with a random ratio.   Scheme 3.2 Proposed reaction of IMes and IMes-d2 with MesP=CPh2 In addition, the kinetic studies of the reaction of IMes-d2 with MesP=CPh2 can be conducted in order to compare with IMes.  55   Preparation of IMes-d2 The method to synthesize IMes-d2 is analogous to the work of Denk.76 It was once reported the protons at C4 and C5 position in 1,3-di-tert-butyl-imidazol-2-ylidene underwent rapid H/D exchange in DMSO-d6, D2O and CD3OD (Scheme 3.3).    Scheme 3.3 Deuteration of 1,3-di-tert-butyl-imidazol-2-ylidene (ItBu) After trying various solvent systems, it was realized that only CD3OD worked for the H/D exchange of IMes. In the meanwhile, a catalytic amount of base (for example, KOH) wass found to be necessary in order to fully deuterate IMes. As has been described in the literature, the ring deuteration of imidazolium salts can be achieved in an excess of D2O with 15 mol% alkali metal hydroxide.77, 78 In our experiment, 100 mg of IMes was dissolved in 3 mL of CD3OD with 10 mol% KOH. After stirring for 3 hours at room temperature, the solvent was removed in vacuo. The product was then obtained as a white solid and recrystallized from pentane. The 1H NMR spectrum of the product showed the signal of the protons at C4 and C5 positions (δ = 7.28) were absent, indicating the successful deuteration (Figure 3.1).  56    Figure 3.1 1H NMR (300MHz, DMSO-d6) spectra of IMes (top) and IMes-d2 (bottom)  57  2H NMR spectroscopy was employed to further assess the successful deuteration of IMes. The spectrum is shown in Figure 3.2. Naturally occurring deuterium signals for the solvent benzene is at 7.14 ppm. Deuterium at the C4 and C5 positions of the N-heterocyclic ring is at 6.41 ppm. Interestingly, deuterium from -CD3 of CD3OD also exists at 3.03 ppm.  Figure 3.2 2H NMR (61 MHz, C6H6) spectrum of IMes-d2  It appears that IMes-d2 is contaminated by a significant amount of CD3OD. A strong interaction between the CD3OD and the carbene makes the removal of CD3OD very difficult. Neither drying the carbenes in vacuo for hours, nor washing them with dry hexanes is efficient enough to remove CD3OD. The presence of CD3OD can further interfere with the reaction of IMes-d2 with MesP=CPh2 to generate another compound (δP = 128). The compound is very likely to be MesP(OMe)-CDPh2.10 58  It is found CD3OD in IMes-d2 can be successfully removed by dissolving carbenes in THF in presence of 4 Å molecular sieves. The solution is stirred for at least 2 hours at room temperature and transferred into a Schlenk flask, filtering off the sieves. The volatiles are then removed in vacuo. The 2H NMR spectrum reveals the removal of CD3OD (Figure 3.3). However, since the molecular sieves are protic, mixing them with IMes-d2 will replace some deuterium with protons. For this reason, the formation of 100% pure IMes-d2 is unsuccessful. According to the integration of the 1H NMR spectrum, IMes-d2 is 90% deuterated at C4 and C5 positions (Figure 3.4).  Figure 3.3 2H NMR (61 MHz, C6H6) spectrum of IMes-d2 after removing CD3OD  Benzene 59   Figure 3.4 1H NMR (300 MHz, DMSO-d6) spectrum of IMes-d2 after removing CD3OD The 13C NMR spectrum gives further information regarding the structure of IMes-d2 I synthesized, particularly about the C4 and C5 positions (CD=CD region). As shown in Figure 3.5, the C4 and C5 atoms of IMes-d2 are equivalent and coupled with D, so their signal is a triplet (δC = 120.21, t, CD=CD, 1JCD = 30 Hz). The existence of IMes-d1 is also observed in the spectrum, the signal of its C4 is a doublet (δC = 120.42, CH=CD, 1JCH = 190 Hz). The second-order coupling between C4 and D in IMes-d1 is too weak to be observed. The signal of C4 and C5 of IMes (δC = 120.5, CH=CH, q, 1JCH = 190 Hz, 2JCH = 14 Hz, Figure 3.6) is barely observed in the 13C NMR spectrum of IMes-d2, indicating the extremely small amount of IMes mixed in IMes-d2.  60   Figure 3.5 13C NMR (100 MHz, C6D6) spectrum of 90% deuterated IMes-d2 at C4 and C5 positions.   Figure 3.6 13C NMR (100 MHz, C6D6) spectrum of IMes at C4 and C5 positions. 61   The reaction of IMes-d2 with MesP=CPh2  The reaction of IMes-d2 with MesP=CPh2 was first conducted to see whether or not it proceeded as the abnormal reaction as shown in Scheme 3.4.   Scheme 3.4 Proposed reaction of IMes-d2 with MesP=CPh2 1 equiv. of IMes-d2 (3.1) and 1 equiv. of MesP=CPh2 (2.1) were stirred in THF for 60 hours at 70 °C. Upon cooling, an aliquot was removed and 31P {1H} NMR spectroscopy was used to monitor the product. At first glance, the chemical shift appeared to be -37.6 ppm, indicating the formation of abnormal NHC products (Figure 3.7). However, upon closer inspection four signals were observed. Considering a small amount of IMes-d1 mixed with IMes-d2 in the starting materials as discussed earlier, some of these “unexpected” signals could have been from the reaction of IMes-d1 with MesP=CPh2.  62   Figure 3.7 31P{1H} NMR (121 MHz, THF) spectrum of products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2.  In order to unequivocally identify the product by NMR techniques, the same reaction was conducted in C6D6. The 31P {1H} NMR spectrum of the products still showed four signals (Figure 3.8). Comparison of the 1H NMR spectrum of this product mixture with that of IMeP revealed the appearance of proton at C5 position (δ = 6.74 ppm, 2JPH = 2.0 Hz, Figure 3.9) and the proton from the P-CHPh2 fragment (δ = 5.33 ppm, 2JPH = 4.4 Hz, Figure 3.9).  63   Figure 3.8 31P{1H} NMR (121 MHz,C6D6) spectrum of the product from the reaction of 90% deuterated IMes-d2 with MesP=CPh2.  Figure 3.9 1H NMR (300 MHz, C6D6) spectrum of the product from the reaction of 90% deuterated IMes-d2 with MesP=CPh2. 64  Figure 3.10 lists some possible products in the product mixture. The appearance of protons at C5 position and the P-CHPh2 fragment in 1H NMR spectroscopy suggests that besides D (the direct product from IMes-d2 and MesP=CPh2), there are A, B, C as well.   Figure 3.10 Possible products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2 In order to assign the aforementioned products (A, B, C and D) in the 31P {1H} NMR spectrum, the [1H,31P]-HMBC NMR spectroscopy (Heteronuclear Multiple Bond Coherence) is employed. To conduct this experiment, 1 equiv of IMes-d2 and 1 equiv of MesP=CPh2 were dissolved in C6D6 in an NMR tube. The selective spectra are shown as Figure 3.11 and Figure 3.12. For the purpose of clarification, the signals in the 31P NMR spectrum are numbered as 1, 2, 3 and 4. Figure 3.11 shows signal 1 and signal 3 correlate with the proton at C5 position of IMesP, suggesting they are either A or C. In the meanwhile, Figure 3.12 shows signal 3 does not correlate with the proton in the P-CHPh2 fragment of IMesP. This means signal 3 can only be C, leaving signal 1 being A. Signal 4 is observed to have no correlation with any protons at C5 or P-CHPh2 fragment. Therefore it should be D. Signal 2 is believed to be B, which only correlates with the proton in the P-CHPh2 fragment (Figure 3.12). The final assignments are shown in Figure 3.13. 65   Figure 3.11 [1H,31P]-HMBC NMR spectrum of the products in C6D6 suggests the presence of the proton at C5 position of IMesP.  Figure 3.12 [1H,31P]-HMBC NMR spectrum of the products in C6D6 suggests the presence of the proton in the P-CHPh2 fragment. 66   Figure 3.13 Assignments of the products from the reaction of 90% deuterated IMes-d2 with MesP=CPh2 in 31P{1H} NMR (121 MHz, C6D6) spectrum.  H/D ratio in the product mixture at C5 position and P-CHPh2 fragment  Figure 3.14 Deconvolution of signals of A, B, C and D in 31P NMR (121 MHz, C6D6) spectrum. 67  As shown in Figure 3.14, after deconvolution the ratio of the four products (A, B, C, D) is integrated to be 1:1.2:1.9:2.2. A further calculation reveals the H/D ratio at C5 position and the P-CHPh2 fragment in the products is 40%: 60%. Considering the H/D ratio is only 10%: 90% at C4 and C5 positions in the starting material (90% deuterated IMes-d2), there are more protons in the product mixture than expected. Monitoring the reaction progress by the 2H NMR spectroscopy reveals some unexpected signals when the reaction goes to completion (Figure 3.15, signals in the box). These signals do not belong to the abnormal NHC products because there are no corresponding signals in the 1H NMR spectrum of IMesP (Figure 3.15, bottom). It is yet not clear what these signals are. But their appearance affects the ratio of H/D in the abnormal NHC products.   Figure 3.15 Top: 2H NMR (61 MHz, C6H6) of the final products from 90% deuterated IMes-d2 with MesP=CPh2; Bottom: 1H NMR (300 MHz, C6D6) of pure IMesP. 68  A further study is conducted to investigate whether CH3 protons from P-Mes in MesP=CPh2 involve in the reaction, thus increasing the H/D ratio in the abnormal NHC products. For this purpose, 1 equiv. of IMes is treated with 1 equiv. of (Mes-d9)P=CPh2. If –CH3 group does not involve in the reaction, only one product should be obtained (Scheme 3.5). Analysis of the reaction by 31P NMR and 2H NMR spectroscopy indicates the formation of only one product (Figure 3.16). In addition, the rate of reaction of IMes with (Mes-d9)P=CPh2 is almost the same as reaction of IMes with MesP=CPh2 (Table 3.1). Therefore it is believed CH3 group from the P-Mes does not interfere with the abnormal reaction. Further investigations of other proton sources are needed as one of the future work.   Scheme 3.5 The reaction of IMes with (Mes-d9)P=CPh2 69    Figure 3.16 Top: 31P NMR (121 MHz, THF) NMR spectrum; Bottom: 2H NMR (61 MHz, THF) spectrum of the product from the reaction of IMes with (Mes-d9)P=CPh2 Table 3.1 Rate constants of the reactions of IMes with different phosphaalkenes at 319 K.   * [IMes]=[PA]=0.42 mol•L-1 Entry Phosphaalkene k (L•mol-1•s-1) 1 (Mes)P=CPh2 6.0 x 10-4  2 (Mes-d9)P=CPh2 6.1 x 10-4 70   H/D exchange between IMes and IMes-d2 In order to understand whether inter- or intra-molecular proton transfer occurs, the reaction of IMes (1.1) and IMes-d2 (3.1) with MesP=CPh2 (in the ratio of 50%: 50%: 100%) in THF was investigated. 31P NMR spectrum indicated four products (A, B, C, D) were obtained (Figure 3.17). Based on previous assignments, the amounts of A and B are predominant, whereas the amounts of C and D are much less. Previously it has been discussed that if the reaction includes intramolecular proton transfer, the amount of A and D should be equal. However, the result contradicts this hypothesis. Thus it is suspected the reaction includes intermolecular proton transfer, which results from an H/D exchange between IMes and IMes-d2.  Figure 3.17 31P {1H} NMR (121 MHz, THF) spectrum of the reaction of 50 mol% IMes, 50 mol% IMes-d2 with 100 mol% MesP=CPh2.  71  The H/D exchange between IMes and IMes-d2 is observed using 13C NMR spectroscopy. As shown in Figure 3.18, (a) displays the C4 and C5 atoms of IMes as a quartet (1JCH = 190 Hz, 2JCH = 14 Hz). Figure 3.18(b) displays the C4 and C5 atoms of IMes-d2 as a triplet (1JCD = 30 Hz) and the C4 atom of IMes-d1 as a doublet (1JCH = 190 Hz). In the experiment, 50% IMes and 50% IMes-d2 are mixed in THF in an NMR tube (Figure 3.18(c)). After 12 hours, it is observed the intensity of IMes-d1 increases (Figure 3.18(d)). This observation indicates that H/D exchange occurs between IMes and IMes-d2 to generate more IMes-d1 over time.    Figure 3.18 Comparison of C4 and C5 atoms in IMes, IMes-d2, mixture of 50% IMes and 50% IMes-d2 in 13C NMR (100 MHz, C6D6) spectra.  (a) (b) (c) (d) 72  The H/D exchange between IMes and IMes-d2 can explain the result in Figure 3.17. As shown in Scheme 3.6, the mixture of IMes and IMes-d2 in solution can afford IMes-d1. So IMes, IMes-d1 and IMes-d2 are actually present in the mixture and they all can react with MesP=CPh2.   Scheme 3.6 H/D exchange between IMes and IMes-d2 Due to the isotope effect, C-D bonds are stronger than C-H bonds.79 As a result MesP=CPh2 preferentially reacts with and IMes or IMes-d1 to afford A and B. The formation of C and D is less energetically favorable due to higher energy required to break C-D bonds. In the end, A and B exist as major products.  73   Scheme 3.7 The reaction process of 50 mol% IMes, 50 mol% IMes-d2 with 100 mol% MesP=CPh2.  Kinetic studies of the reaction of IMes-d2 with MesP=CPh2 Using the same methods as mentioned in Chapter 2, the kinetic studies of the reaction of IMes-d2 with MesP=CPh2 (Scheme 3.8) was conducted. The relaxation time (T1) for 2.1 and 3.2 was measured to be 1.3 s and 3.3 s, respectively. Thus a relaxation delay of 20 s with a 90° tip angle was set up for all 31P NMR experiments. The experiments were performed at 324.2, 330.4, 335.8, and 341.0 K. The concentrations of each product were calculated based on the integrations in 31P NMR spectra. The rate constants (kD) are tabulated in Table 3.2. 74   Scheme 3.8 The reactionof IMes-d2 with MesP=CPh2. Table 3.2 Determination of rate constants kD at different temperatures. Entry 3.1 (mol• L-1) 2.1 (mol• L-1) temp (K) kD  (L•mol-1•s-1) 1 0.316 0.316 324.2 (1.5 ± 0.1) x 10-4 2 0.316 0.316 330.4 (2.8 ± 0.2) x 10-4 3 0.316 0.316 335.8 (4.2 ± 0.2) x 10-4 4 0.316 0.316 341.0 (5.5 ± 0.2) x 10-4 From the Arrhenius plot (Figure 3.19), the activation energy (Ea) was calculated to be 73.10 ± 5.32 kJ/mol. During the experiments, it was noticed the reaction of IMes-d2 with MesP=CPh2 underwent very slow. Even at 341K the reaction needed 24 hours to complete. As a consequence, its activation energy is significantly higher than the reaction with IMes (61.14 kJ/mol). The increasing value of the activation energy is probably caused by the difficulty in breaking the C-D bonds in NHCs to form aNHC.  75   Figure 3.19 Arrhenius plot of the reaction IMes-d2 with MesP=CPh2. The linear least squares function (y = -8792.5 + 18.36) has an R2 value of 0.98.  3.2 The reaction of the IMesMe2 with MesP=CPh2  The diversity of the flanking N-substituents and backbone substituents in NHCs allows for modification of their steric and electronic properties. As a part of further exploring the reactions of NHCs with phosphaalkenes, IMesMe2 is investigated (Figure 3.20).80   Figure 3.20 IMesMe2 (4,5-dimethyl substituted IMes) 76  To examine the reaction, 1 equiv of IMesMe2 and 1 equiv of MesP=CPh2 were dissolved in THF. It turned out this reaction could occur without heating. Analysis of the 31P NMR spectrum of the product in C6D6 revealed the phosphaalkene (δP = 234) was no longer present and had been replaced by a single resonance (δP = 21.2, Figure 3.21). Apparently this was not an abnormal reaction of NHCs.  Figure 3.21 31P NMR (121 MHz, THF) spectrum of the product from the reaction of IMesMe2 with MesP=CPh2. Since the C4 and C5 positions of IMesMe2 are “blocked” by two methyl groups, the generation of an abnormal carbene is not possible. In addition, IMesMe2 is more electron rich in the carbene center than IMes.81 Thus we postulate that IMesMe2 should react with the phosphaalkene at the C2-position. As discussed in Chapter 1, phosphaalkenes are known to react with fleeting electrophilic carbenes to afford PC2 heterocycles (cyclopropanation reaction, Scheme 3.9).22 Likewise, IMesMe2 can react with MesP=CPh2 in this way. 77   Scheme 3.9 Cycloaddition reaction of a phosphaalkene with a carbene. It is also known that phosphaalkynes82 and iminophophines83, 84 react with NHCs to generate zwitterionic species. More recently, Braunschweig and coworkers reported the reaction of NHC (IPrMe2) reacted at C2 position with iminoboranes (RB≡NR) to afford a carbene-borane adduct.85 Similarly, IMesMe2 is possible to react with MesP=CPh2 in this way (Scheme 3.10).   Scheme 3.10 Postulated reaction of phosphaalkenes with IMesMe2 to form a zwitterion.  Mass spectrometry (EI) of the crude product shows a parent mass of 650 g/mol, which is the sum of IMesMe2 (MW = 332 g/mol) and MesP=CPh2 (MW =316 g/mol) plus two protons. This suggests that a carbene-phosphaalkene adduct might be formed. Analysis of product by 1H NMR spectroscopy (Figure 3.22, top) shows that IMesMe2 fragment is present (δ = 7.02, 2.30, 2.18, 1.95). The phosphaalkene fragment is also observed (δ = 7.21-7.28, 1.87, 1.78). In addition, some new signals show up at δ = 8.51, 8.00, 6.78, 6.67, 3.93, 2.46. The 13C {1H} NMR spectroscopy (Figure 3.22, bottom) shows that the carbene functionality no longer 78  exists in the adduct because the corresponding signal (δ = 220) is not present. A signal of doublet (J = 10) shows up at 141.7 ppm. It is assumed to be the signal of C2 atom binding to phosphorous. Further characterizations such as [31P,13C] HSQC NMR spectroscopy as well as X-ray crystallographic analysis of this product are needed to know whether the carbene reacts with the phosphaalkene in the “normal” way (C2 position).  79    Figure 3.22 Top: 1H NMR (300 MHz, DMSO-d6) spectrum; bottom: 13C {1H} NMR (75 MHz, DMSO-d6) spectrum of the product from the reaction of IMesMe2 with MesP=CPh2. 80  3.3 The reaction of the IMesMe with MesP=CPh2 The reaction of a 4-methyl substituted NHC (IMesMe) with the phosphaalkene was also investigated. The aim of this exploration was to see whether an abnormal reaction would occur in the presence of only one proton at the backbone of NHCs.  The isolation of IMesMe has not been reported. The only example is to synthesize the NHC-metal complex in situ by deprotonating the corresponding imidazolium salt.81 Herein we introduce our synthetic strategy to generate IMesMe with good purity and yield. Scheme 3.11 is a known synthetic route for the preparation of the IMesMe precursor.  Scheme 3.11 Synthesis of 4-Methyl-1,3-bis-(2,4,6-trimethylphenyl)-imidazolium chloride. In the literature, potassium tert-butoxide (KtOBu) is used to deprotonate the imidazolium chloride. However, this method always gives a low yield of IMesMe. Moreover, a trace of tBuOH forming from the reaction of KtOBu with the imidazolium salt is extremely hard to get rid of during the purification. This impurity will affect the next step of reacting with the phosphaalkene. To avoid all these problems, we choose to synthesize the imidazolium BF4 salt at first, then deprotonating it with NaH to generate IMesMe (Scheme 3.12). The 1H NMR spectrum of IMesMe is shown in Figure 3.23. 81   Scheme 3.12 Synthesis of IMesMe.  Figure 3.23 1H NMR (300 MHz, C6D6) spectrum of IMesMe. To examine the reaction, 1 equiv of IMesMe and 1 equiv of MesP=CPh2 are dissolved in THF. 31P NMR spectroscopy shows the product has a chemical shift of 21 ppm in spectrum (Figure 3.24). It appears that the IMesMe reacts with MesP=CPh2 in the same way as IMesMe2. The reason that the abnormal reaction does not occur between IMesMe and MesP=CPh2 is possibly due to the 82  instability of abnormal carbene generated from IMesMe. Future work will include further characterizations of the product.   Figure 3.24 31P NMR (121 MHz, THF) spectrum of the product from the reaction of IMesMe with MesP=CPh2. 3.4 Conclusions Based on the studies of the reaction of IMes-d2 with MesP=CPh2, it is discovered the reaction includes intermolecular proton transfer. In combination with the kinetic studies in Chapter 2, the reaction is very likely to proceed in this way: (1) the formation of anionic dicarbene in the first place, which can be facilitated by base; (2) the addition of carbene at C4 position to the P=C bond to afford the abnormal products; (3) during the progress the protons are transferring intermolecularly.  83  In addition, it is discovered that neither IMesMe2 nor IMesMe reacts with MesP=CPh2 to form the abnormal products. Further characterizations are needed to gain insight into the structures of their products. 3.5 Experimental sections  General considerations Air and/or water sensitive manipulations were carried out using Schlenk techniques or in a N2 atmosphere glovebox. Dichloromethane was deoxygenated with nitrogen and dried by passing through a column containing activated alumina. Tetrahydrofuran was distilled from Na/benzophenone. 31P, 1H, 13C NMR spectra were recorded at room temperature on Bruker Avance 300 MHz spectrometers with chemical shifts (δ) in parts per million (ppm). Chemical shifts are referenced and reported relative to 85% H3PO4 as an external standard (δ= 0.0 for 31P) or referenced to TMS and measured relative to the residual solvent peak (C6HD5 or CHCl3: δ= 7.16 or 7.26 for 1H, respectively; C6D6 or CDCl3: δ=128 or 77.16 for 13C, respectively).  Synthesis of IMes-d2 0.5 g (1.6 mmol) of IMes was added into 3 ml of CD3OD with a little amount of KOH. After stirring for 3 hours, the solvent was removed in vacuo. This process was repeated for 3 times to reach a deuterium content of 99%. To get rid of the trace of CD3OD, the carbene was dissolved in THF 84  with 4 Å molecular sieves and stirred for at least 2 hours. After filtering off the molecular sieves, all the volatiles were removed in vacuo. Yield: 0.31 g (70%). 1H NMR (300 MHz, DMSO-d6): δ 7.02(s, 4H), 2.30 (s, 6H), 2.01 (s, 12H). 2H {1H} NMR (61 MHz, C6H6): δ 6.41 (s). 13C {1H} NMR (75 MHz, C6D6): δ 214.3 (s, N2C:), 138.7, 137.5, 135.3, 129.1, 120.4 (t, CD=CD, 1JCD=28.5 Hz), 21.1 and 17.9. ESI-MS in CD3OD: m/z = 308 (M+) calcd. for C21H22D3N2+. Found, 308.  The reaction of IMes-d2 with MesP=CPh2 To a solution of IMes-d2 (0.25 g, 0.82 mmol) in THF (8 mL), MesP=CPh2 (0.26 g, 0.82 mmol) was added at ambient temperature. The reaction mixture was stirred for 30 h at 70 °C. The solvent was then removed in vacuo. 31P {1H} NMR (121 MHz, C6D6):  δ= -38.2.  1H NMR (300 MHz, C6D6):  δ = 7.56-6.39 (m, 16H, aromatic), 2.64 (s, 3H), 2.35 (s, 3H), 2.34 (s, 3H), 2.14 (s, 6H), 1.92 (s, 3H), 1.86 (d, 1JHP = 2.4 Hz, 3H), 1.78 (s, 3H), 1.52 (s, 3H). 2H NMR (61 MHz, C6H6): δ = 6.41, 5.53. 85   The reaction of 50 % IMes, 50% IMes-d2 and 100% MesP=CPh2  To a solution of IMes-d2 (0.12 g, 0.41 mmol), IMes (0.12 g, 0.41 mmol) in THF (8 mL), MesP=CPh2 (0.26 g, 0.82 mmol) was added at ambient temperature. The reaction mixture was stirred for 30 h at 70 °C. The solvent was then removed in vacuo. 31P {1H} NMR (121 MHz, THF):  δ= -37.72, -37.76, -38.13 and -38.17.   The reaction of IMesMe2 with MesP=CPh2 To a solution of IMesMe2 (0.25 g, 0.75 mmol) in THF (8 mL), MesP=CPh2 (0.24 g, 0.75 mmol) was added at ambient temperature. The reaction mixture was stirred for 12h at ambient temperature. The solvent was removed in vacuo to obtain the product.  31P {1H} NMR (121 MHz, C6D6):  δ= 21.1.  1H NMR (300 MHz, C6D6):  δ = 7.56-6.39 (aromatic), 3.75, 2.49, 2.43, 2.30, 2.17, 2.13, 2.02, 1.90, 1.83, 1.79, 1.62, 0.93, 0.90. 13C {1H} NMR (75 MHz, DMSO-d6): δ = 141.7, 141.2, 135.2, 130.3, 129.9, 129.2, 128.8, 128.3, 126.4, 67.5, 25.6, 21.5, 17.2, 8.6.  Synthesis of IMesMe-HBF4 0.8 g (2.26 mmol) of the IMesMe-HCl was dissolved in the minimum amount of water. 0.4 ml (3 mmol) HBF4 (40 wt% in water) was added into the solution. A white precipitate formed 86  instantaneously. The aqueous phase was extracted with three washes of CH2Cl2 (3 × 20 ml). The combined organic phases were dried with MgSO4. CH2Cl2 was removed under vacuum. The product was obtained as white solids. 1H NMR (300 MHz, CDCl3): δ 10.69 (s, 1H), 7.39 (s, 1H), 7.05 (s, 2H), 7.01 (s, 2H), 2.35 (s, 3H), 2.33 (s, 3H), 2.19 (s, 6H), 2.16 (s, 3H), 2.11 (s, 6H).  Synthesis of IMesMe 0.8 g (1.97 mmol) of IMesMe-BF4 was added into15 ml of anhydrous THF. 0.1 g (4.17 mmol) of anhydrous sodium hydride was transferred carefully into the solvent. The reaction mixture was stirred overnight at room temperature. The generated H2 was vented through a bubbler. The resulting sodium salts were filtered using a filter cannula and the liquid phase was transferred into a second Schlenk flask. The solvent was then removed in vacuo. The product was obtained as off-white solid in a yield of 50%.  1H NMR (300 MHz, C6D6): δ 6.84 (s, 2H), 6.81 (s, 2H), 6.29 (s, 1H), 2.24 (s, 6H), 2.17 (s, 3H), 2.15 (s, 3H), 2.11 (s, 6H), 1.65 (s, 3H). 13C {1H} NMR (75 MHz, C6D6): δ 211.3, 140.9, 138.5, 134.5, 134.1, 132.6, 130.8, 130.0, 129.8, 128.4, 121.3, 21.2, 21.1, 17.7, 17.6, 9.3. 87   The reaction of IMesMe with MesP=CPh2 To a solution of IMesMe (0.25 g, 0.78 mmol) in THF (8 mL), MesP=CPh2 (0.25 g, 0.78 mmol) was added at ambient temperature. The reaction mixture was stirred for 12h at ambient temperature. The solvent was removed in vacuo to obtain the product.              31P {1H} NMR (121 MHz, C6D6):  δ= 21.1.         88  4 Transition-metal complexes of IMesP 4.1 Introduction Due to their excellent σ-donor property, NHCs have been widely used in transition metals coordination chemistry. The strong σ-donor ability of NHCs is attributed to the carbon sp2-hybridized lone pair, which is available to donate into a σ-accepting orbital of the metal atom. Being robust to air and moisture, the first NHC-metal complexes were even synthesized before the isolation of NHCs.35, 36 As has been discussed in Chapter 1, nowadays NHC-metal complexes are playing an important role in the area of catalysis chemistry.33, 86 In 2009, our group successfully functionalized the C4-position of NHCs with phosphorous (IMesP) through the reaction of NHCs with phosphaalkenes (Scheme 4.1).23 Considering the phosphine also has a potential to bind to a transition metal, the discovery of IMesP allows for the development of dinuclear complexes.  Scheme 4.1 Formation of IMesP from the abnormal reaction of IMes with MesP=CPh2 Excitingly, the study has shown that the good σ-donating properties of NHCs are retained upon functionalization with the phosphine moiety at the C4 position.70 Previously our group was able to bind Rh(I) or Ir(I) metals to the C2-position of IMesP as well as synthesizing the digold complex 89  in a moderate yield (Figure 4.1).23, 70 This chapter will be focused on further exploration of the metal complexes of IMesP.  Figure 4.1 Examples of IMesP-metal complexes 4.2 Exploration of the transition-metal complexes of IMesP The first attempt was to react tungsten complex with IMesP. This experiment was conducted because tungsten-NHC complexes usually had a good stability and could be easily handled. The reaction of excessive W(CO)5CH3CN with 1 equiv of IMesP was carried out in THF (Scheme 4.2). The resulting product was isolated by removing the solvent in vacuo and recrystallized from DCM. The 31P NMR spectrum (121 MHz, C6D6) showed a chemical shift of -37.5 ppm, which was nearly identical to the 31P NMR value of IMesP, suggesting no metal attached to the phosphorous. This was not surprising when considering the steric bulk around the phosphorous likely hindered coordination to the large W(CO)5 fragment. The molecular structure of this compound confirmed that tungsten only binded to the carbene center (Figure 4.2).  90   Scheme 4.2 Synthesis of 4.1  Figure 4.2 Molecular structure of 4.1 (thermal ellipsoids set at 50% probability). All hydrogen atoms are omitted for clarity.     91  Based on our previous experience, less bulky metal complexes like (tht)AuCl or CuCl can react at the phosphorous site of IMesP to afford linear metal-phosphorous compound.23, 70, 71 Therefore, 1 equiv. of compound 4.1 was treated with 1 equiv. of (tht)AuCl in THF and the solution was stirred for 3 hours. 31P NMR spectroscopy of the product showed a significant shift from -37.9 ppm to 0.1 ppm. The downfield shift of the phosphine resonance indicated its coordination to AuCl. Unfortunately, the reaction always proceeded with the formation of unwanted black precipitates, likely to be the elemental gold. Efforts to grow crystals of 4.2 have been unsuccessful.   Scheme 4.3 Synthesis of 4.2 The next goal is to synthesize IMesP-metal complexes that may have potential catalytic reactivity. NHC-palladium complexes attract our attention because they are widely used in cross coupling.87 Figure 4.3 demonstrates the catalytic process mediated by NHC-palladium complexes. It is believed that electronic and steric properties of NHCs facilitate various steps in this cycle. First of all, the strong σ-donation of NHCs improves the Pd metal’s ability of oxidative addition into carbon-halogen bonds, especially carbon-chlorine bonds that were traditionally considered resistant to oxidative addition.88,89, 90 Secondly, the reductive elimination step is more favorable due to the 92  steric bulk of NHCs.91, 92 Finally, the strong Pd–NHC bond and steric factors help to stabilize the Pd0 active state and reduce the likelihood of decomposition of the catalyst.41   Figure 4.3 NHCs as ligands in palladium-catalyzed crossing-coupling. Because of all these advantages, it is tempting to develop palladium-IMesP complexes and apply them in catalysis. An advantage of IMesP over NHCs is that the former possesses an extra phosphine functionality. Since the linear complex (tht)AuCl can react with IMesP to afford metal-phosphorous compound, the journey of exploring dinuclear complexes of IMesP starts with palladium and gold. More excitingly, during the last two decades Au(I) complexes have been reported to show good catalytic abilities in π-activation of carbon–carbon multiple bonds towards attack of nucleophiles.93-101 Hopefully, the combining Pd(II) and Au(I) complexes in the same ligand will generate a compound with interesting catalytic properties, especially in catalyzing two different reactions! 93  In order to synthesize the dinuclear complex, IMesP was reacted with Pd(cod)Cl2 in THF to generate a palladium-NHC complex as an intermediate. Successive treatment the intermediate with (tht)AuCl gave us the desired dinuclear product 4.3 (Scheme 4.4). 31P NMR spectroscopy (121 MHz, C6D6) of the product showed a chemical shift at -1.0 ppm. X-ray crystallography confirmed the structure to be that of 4.3, with Pd(II) and Au(I) coordinating to the carbene and the phosphorous site, respectively (Figure 4.4).  Scheme 4.4 Synthesis of 4.3 94   Figure 4.4 Molecular structure of 4.3 (thermal ellipsoids set at 50% probability). All hydrogen atoms are omitted for clarity. It was attempted to synthesize bis(IMesP)-palladium complex (4.4) as well by changing the reaction stoichiometry (Scheme 4.5). 1 equiv. of Pd(cod)Cl2 with 2 equiv. of IMesP were mix in THF and stirred for 2 hours at room temperature. 31P NMR spectroscopic data showed two signals at -37.3 and -38.9, respectively (Figure 4.5). Due to the steric interactions between the bulky phosphine and the flanking N-mesityl substituents, it is believed the structure of 4.4 only exists as a trans- geometry. The two resonances can represent diastereomers from RR, SS and RS, RS at phosphorus. Further characterizations are needed to confirm its structure. 95   Scheme 4.5 Attempted synthesis of bis(IMesP)-Pd compelx 4.4  Figure 4.5 31P NMR (121MHz, THF) of 4.4 4.3 Conclusion and future work We are able to synthesize dinuclear complexes from IMesP. As mentioned above, the ultimate goal is to take the advantage of the dinuclear complexes to realize their catalytic properties. The future work will be focused on studying the catalytic activities of 4.3 and 4.4, especially 4.3’s potential in tandem catalysis.  96  4.4 Experimental sections  General considerations Air and/or water sensitive manipulations were carried out using Schlenk techniques or in a N2 atmosphere glovebox. Dichloromethane was deoxygenated with nitrogen and dried by passing through a column containing activated alumina. Tetrahydrofuran was distilled from Na/benzophenone. IMes,75 MesP=CPh2,15 W(CO)5CH3CN,102 (tht)AuCl103 and Pd(cod)Cl2104 were prepared following literature procedures. 31P, 1H, and 13C NMR spectra were recorded at room temperature on Bruker Avance 300 MHz and 400 MHz spectrometers with chemical shifts (δ) in parts per million (ppm). Chemical shifts are referenced and reported relative to 85% H3PO4 as an external standard (δ= 0.0 for 31P) or referenced to TMS and measured relative to the residual solvent peak (C6HD5: δ= 7.16 for 1H; C6D6: δ=128 for 13C).  Synthesis of 4.1 To a solution of W(CO)5CH3CN (200 mg, 0.55 mmol) in THF (5 mL) was added a solution of IMesP (340 mg, 0.55 mmol ) in THF (5 mL).The mixture was stirred for 3 hours at 50 °C. Upon cooling, volatiles were removed in vacuo. The yellow crude product was crystallized from DCM.  Yield: 400 mg, 42%. Crystallographic data of 4.1 are tabulated in the Appendices. 31P {1H} NMR (121 MHz, C6D6): δ = -37.  97  1H NMR (300 MHz, C6D6): δ= 7.67−6.51 (m, 17H, 16 aromatic + 1vinyl), 5.05 (d, JHP= 4 Hz, 1H, CPh2H), 2.52 (s, 3H, CH3), 2.35 (s, 3H, CH3), 2.24 (s, 3H, CH3), 2.16 (s,3H, CH3), 2.11 (s, 3H, CH3), 1.90 (s, 3H, CH3), 1.66 (s, 3H, CH3),1.33 (s, 3H, CH3), 1.22 (s, 3H, CH3). MS (ESI): m/z calcd. for C48H46N2O5PW+: 945.7. Found: 945.2.  Elemental analysis: calcd. for C48H46N2O5PW: C, 60.96; H, 4.90; N, 2.96. Found: C, 60.94; H, 4.85; N, 2.95.  Synthesis of 4.2 To a solution of IMesP-W (100 mg, 0.105 mmol) in THF (5 mL) was added a solution of (tht)AuCl (34 mg, 0.105 mmol)in THF (5 mL). The mixture was stirred for 3 hours at room temperature and the solution turned green from yellow. Volatiles were removed in vacuo.  31P {1H} NMR (121 MHz, C6D6): δ = 0.1.  1H NMR (300 MHz, C6D6): δ= 7.67−6.51 (aromatic), 5.05 (d, JHP= 4 Hz, 1H, CPh2H), 2.52 (s, 3H, CH3), 2.35 (s, 3H, CH3), 2.24 (s, 3H, CH3), 2.16 (s,3H, CH3), 2.11 (s, 3H, CH3), 1.90 (s, 3H, CH3), 1.66 (s, 3H, CH3),1.33 (s, 3H, CH3), 1.22 (s, 3H, CH3).  Synthesis of 4.3 To a solution of Pd(cod)Cl2 (157 mg, 0.55 mmol) in THF (5 mL) was added a solution of IMesP (340 mg, 0.55 mmol ) in THF (5 mL).The mixture was stirred for 6 hours. All the volatiles were 98  removed in vacuo. The product was yellow solid. Successively treating this product with (tht)AuCl (176 mg, 0.55 mmol) in THF (10 mL) for 3 hours afforded an orange solution. 31P NMR spectroscopy showed a significant shift from -38 ppm to -1.0 ppm. Orange solid was obtained after removal of the volatiles. The crude product was crystallized at ambient temperature by vapor diffusion with DCM. Yield: 246 mg, 40%. The structure was confirmed by X-ray crystallographic analysis. Crystallographic data of 4.3 are tabulated in the Appendices. 31P {1H} NMR (121 MHz, C6D6):  δ= -1.0. 1H NMR (300 MHz, C6D6): δ= 7.67−6.49 (m, 17H, 16 aromatic + 1vinyl), 5.17 (d, JHP= 15 Hz, 1H, CPh2H), 3.15 (s, 3H, CH3), 2.68 (s, 3H, CH3), 2.53 (s, 3H, CH3), 2.10 (s,3H, CH3), 2.10 (s, 3H, CH3), 1.87 (s, 3H, CH3), 1.63 (s, 3H, CH3), 1.14 (s, 3H, CH3), 0.92 (s, 3H, CH3). MS (ESI): m/z calcd. for C47H54AuCl3N2PPdS+: 1119.1. Found: 1119.3. Elemental analysis: calcd. for C47H54AuCl3N2PPdS (with dichloromethane in the molecular structure): C, 49.31; H, 4.83; N, 2.40. Found: C, 49.32; H, 4.75; N, 2.46.  Synthesis of 4.4 To a solution of Pd(cod)Cl2 (78 mg, 0.275 mmol) in THF (5 mL) was added a solution of IMesP (340 mg, 0.55 mmol ) in THF (5 mL).The mixture was stirred for 6 hours at room temperature. All the volatiles were then removed in vacuo. Orange solid was obtained after removal of the volatiles. Yield: 156 mg, 40%.  99  31P {1H} NMR (121 MHz, C6D6):  δ= -37.3, -38.8. 1H NMR (300 MHz, C6D6): δ= 7.67−6.51 (m, 32H, aromatic), 6.59 (1H), 5.05 (1H), 2.52 (s, 3H, CH3), 2.35 (s, 3H, CH3), 2.24 (s, 3H, CH3), 2.16 (s,3H, CH3), 2.11 (s, 3H, CH3), 1.90 (s, 3H, CH3), 1.66 (s, 3H, CH3),1.33 (s, 3H, CH3), 1.22 (s, 3H, CH3).          100  References (1) Lacombe, S.; Gonbeau, D.; Cabioch, J. L.; Pellerin, B.; Denis, J. M.; Pfisterguillouzo, G. J. Am. Chem. Soc. 1988, 110, 6964-6967. (2) Schleyer, P. V.; Kost, D. J. Am. Chem. Soc. 1988, 110, 2105-2109. (3) Schmidt, M. W.; Truong, P. N.; Gordon, M. S. J. Am. Chem. Soc. 1987, 109, 5217-5227. (4) Appel, R.; Casser, C.; Immenkeppel, M.; Knoch, F. Angew. Chem. Int. Ed. 1984, 23, 895-896. (5) Baldridge, K. K.; Gordon, M. S. J. Am. Chem. Soc. 1988, 110, 4204-4208. (6) Dillion, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy. Wiley, 1998. (7) Le Floch, P. Coordination Chemistry Reviews 2006, 250, 627-681. (8) Regitz, M.; Scherer, O. Multiple bonds and low coordination in phosphorus chemistry. 1988. (9) Becker, G. Z. Anorg. Allg. Chem. 1976, 423, 242-254. (10) Klebach, T. C.; Lourens, R.; Bickelhaupt, F. J. Am. Chem. Soc. 1978, 100, 4886-4888. (11) Becker, G.; Uhl, W.; Wessely, H. J. Z. Anorg. Allg. Chem. 1981, 479, 41-56. (12) Kawanami, H.; Toyota, K.; Yoshifuji, M. J. Organomet. Chem. 1997, 535, 1-5. (13) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Chem. Commun. 1996, 437-438. (14) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett. 1993, 34, 3413-3416. (15) Yam, M.; Chong, J. H.; Tsang, C. W.; Patrick, B. O.; Lam, A. E.; Gates, D. P. Inorg. Chem. 2006, 45, 5225-5234. (16) Bates, J. I.; Patrick, B. O.; Gates, D. P. New J. Chem. 2010, 34, 1660-1666. (17) Majoral, J. P.; Kraemer, R.; Navech, J.; Mathis, F. Tetrahedron Lett. 1975, 1481-1484. (18) Lefloch, P.; Ricard, L.; Mathey, F. Polyhedron 1990, 9, 991-997. (19) Lefloch, P.; Mathey, F. Tetrahedron Lett. 1989, 30, 817-818. (20) Devaumas, R.; Marinetti, A.; Mathey, F. J. Organomet. Chem. 1991, 413, 411-417. 101  (21) Bauer, S.; Marinetti, A.; Ricard, L.; Mathey, F. Angew. Chem. Int. Ed. 1990, 29, 1166-1167. (22) Mathey, F. Chem. Rev. 1990, 90, 997-1025. (23) Bates, J. I.; Kennepohl, P.; Gates, D. P. Angew. Chem. Int. Ed. 2009, 48, 9844-9847. (24) Igau, A.; Grutzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am. Chem. Soc. 1988, 110, 6463-6466. (25) Harrison, J. F. Accounts Chem. Res. 1974, 7, 378-384. (26) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361-363. (27) Hahn, F. E.; Jahnke, M. C. Angew. Chem. Int. Ed. 2008, 47, 3122-3172. (28) Nelson, D. J.; Nolan, S. P. Chem. Soc. Rev. 2013, 42, 6723-6753. (29) Diez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612-3676. (30) Lee, H. M.; Lee, C. C.; Cheng, P. Y. Curr. Org. Chem. 2007, 11, 1491-1524. (31) Arduengo, A. J.; Dias, H. V. R.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1992, 114, 5530-5534. (32) Heinemann, C.; Muller, T.; Apeloig, Y.; Schwarz, H. J. Am. Chem. Soc. 1996, 118, 2023-2038. (33) Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. Nature 2014, 510, 485-496. (34) Alder, R. W.; Chaker, L.; Paolini, F. P. V. Chem. Commun. 2004, 2172-2173. (35) Wanzlick, H. W.; Schonher.Hj Angew. Chem. Int. Ed. 1968, 7, 141-142. (36) Ofele, K. J. Organomet. Chem. 1968, 12, 42-43. (37) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R. J. Angew. Chem. Int. Ed. 1995, 34, 2371-2374. (38) Valente, C.; Calimsiz, S.; Hoi, K. H.; Mallik, D.; Sayah, M.; Organ, M. G. Angew. Chem. Int. Ed. 2012, 51, 3314-3332. (39) Wurtz, S.; Glorius, F. Accounts Chem. Res. 2008, 41, 1523-1533. (40) Fortman, G. C.; Nolan, S. P. Chem. Soc. Rev. 2011, 40, 5151-5169. 102  (41) Kantchev, E. A. B.; O'Brien, C. J.; Organ, M. G. Angew. Chem. Int. Ed. 2007, 46, 2768-2813. (42) Samojlowicz, C.; Bieniek, M.; Grela, K. Chem. Rev. 2009, 109, 3708-3742. (43) Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746-1787. (44) Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2781-2800. (45) Marion, N.; Nolan, S. P. Chem. Soc. Rev. 2008, 37, 1776-1782. (46) McAdam, C. A.; McLaughlin, M. G.; Johnston, A. J. S.; Chen, J.; Walter, M. W.; Cook, M. J. Org. Biomol. Chem. 2013, 11, 4488-4502. (47) Scholl, M.; Trnka, T. M.; Morgan, J. P.; Grubbs, R. H. Tetrahedron Lett. 1999, 40, 2247-2250. (48) Ackermann, L.; Furstner, A.; Weskamp, T.; Kohl, F. J.; Herrmann, W. A. Tetrahedron Lett. 1999, 40, 4787-4790. (49) Huang, J. K.; Stevens, E. D.; Nolan, S. P.; Petersen, J. L. J. Am. Chem. Soc. 1999, 121, 2674-2678. (50) Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543-6554. (51) Grundemann, S.; Kovacevic, A.; Albrecht, M.; Faller, J. W.; Crabtree, R. H. Chem. Commun. 2001, 2274-2275. (52) Arnold, P. L.; Pearson, S. Coord. Chem. Rev. 2007, 251, 596-609. (53) Schuster, O.; Yang, L. R.; Raubenheimer, H. G.; Albrecht, M. Chem. Rev. 2009, 109, 3445-3478. (54) Sau, S. C.; Santra, S.; Sen, T. K.; Mandal, S. K.; Koley, D. Chem. Commun. 2012, 48, 555-557. (55) Sen, T. K.; Sau, S. C.; Mukherjee, A.; Hota, P. K.; Mandal, S. K.; Maity, B.; Koley, D. Dalton T. 2013, 42, 14253-14260. (56) Prades, A.; Viciano, M.; Sanau, M.; Peris, E. Organometallics 2008, 27, 4254-4259. (57) Heckenroth, M.; Kluser, E.; Neels, A.; Albrecht, M. Angew. Chem. Int. Ed. 2007, 46, 6293-6296. (58) Lebel, H.; Janes, M. K.; Charette, A. B.; Nolan, S. P. J. Am. Chem. Soc. 2004, 126, 5046-5047. 103  (59) Aldeco-Perez, E.; Rosenthal, A. J.; Donnadieu, B.; Parameswaran, P.; Frenking, G.; Bertrand, G. Science 2009, 326, 556-559. (60) Wang, Y.; Xie, Y.; Abraham, M. Y.; Wei, P.; Schaefer, H. F.; Schleyer, P. V.; Robinson, G. H. J. Am. Chem. Soc. 2010, 132, 14370-14372. (61) Arduengo, A. J.; Davidson, F.; Dias, H. V. R.; Goerlich, J. R.; Khasnis, D.; Marshall, W. J.; Prakasha, T. K. J. Am. Chem. Soc. 1997, 119, 12742-12749. (62) Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.; Tamm, M. Angew. Chem. Int. Ed. 2008, 47, 7428-7432. (63) Holschumacher, D.; Bannenberg, T.; Ibrom, K.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Dalton T. 2010, 39, 10590-10592. (64) Schneider, H.; Schmidt, D.; Radius, U. Chem-Eur. J. 2015, 21, 2793-2797. (65) Singh, A. P.; Ghadwal, R. S.; Roesky, H. W.; Holstein, J. J.; Dittrich, B.; Demers, J. P.; Chevelkov, V.; Lange, A. Chem. Commun. 2012, 48, 7574-7576. (66) Singh, A. P.; Samuel, P. P.; Mondal, K. C.; Roesky, H. W.; Sidhu, N. S.; Dittrich, B. Organometallics 2013, 32, 354-357. (67) Graham, T. W.; Udachin, K. A.; Carty, A. J. Chem. Commun. 2006, 2699-2701. (68) Mendoza-Espinosa, D.; Donnadieu, B.; Bertrand, G. J. Am. Chem. Soc. 2010, 132, 7264-7265. (69) Ruiz, J.; Mesa, A. F. Chemistry 2012, 18, 4485-4488. (70) Bates, J. I.; Gates, D. P. Organometallics 2012, 31, 4529-4536. (71) Mendoza-Espinosa, D.; Donnadieu, B.; Bertrand, G. Chem-Asian J. 2011, 6, 1099-1103. (72) Mortimer, M.; Taylor, P. Chemical Kinetics and Mechanism 2002. (73) Kronig, S.; Theuergarten, E.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Angew. Chem. Int. Ed. 2012, 51, 3240-3244. (74) Wu, F.; Dioumaev, V. K.; Szalda, D. J.; Hanson, J.; Bullock, R. M. Organometallics 2007, 26, 5079-5090. (75) Bantreil, X.; Nolan, S. P. Nat. Protoc. 2011, 6, 69-77. (76) Denk, M. K.; Rodezno, J. M. J. Organomet. Chem. 2001, 617, 737-740. 104  (77) Giernoth, R.; Bankmann, D. Eur. J. Org. Chem. 2008, 2008, 2881-2886. (78) Giernoth, R.; Bankmann, D. Tetrahedron Lett. 2006, 47, 4293-4296. (79) Wu, F.; Dioumaev, V. K.; Szalda, D. J.; Hanson, J.; Bullock, R. M. Organometallics 2007, 26, 5079-5090. (80) Clavier, H.; Correa, A.; Cavallo, L.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Slawin, A. M. Z.; Noaln, S. P. Eur. J. Inorg. Chem. 2009, 1767-1773. (81) Hirano, K.; Urban, S.; Wang, C.; Glorius, F. Org. Lett. 2009, 11, 1019-1022. (82) Hahn, F. E.; Le Van, D.; Moyes, M. C.; von Fehren, T.; Frohlich, R.; Wurthwein, E. U. Angew. Chem. Int. Ed. 2001, 40, 3144-3148. (83) Burford, N.; Dyker, C. A.; Phillips, A. D.; Spinney, H. A.; Decken, A.; McDonald, R.; Ragogna, P. J.; Rheingold, A. L. Inorg. Chem. 2004, 43, 7502-7507. (84) Burford, N.; Cameron, T. S.; LeBlanc, D. J.; Phillips, A. D.; Concolino, T. E.; Lam, K. C.; Rheingold, A. L. J. Am. Chem. Soc. 2000, 122, 5413-5414. (85) Braunschweig, H.; Ewing, W. C.; Geetharani, K.; Schafer, M. Angew. Chem. Int. Ed. 2015, 54, 1662-1665. (86) Herrmann, W. A. Angew. Chem. Int. Ed. 2002, 41, 1290-1309. (87) Meijere, A.; Diederich, F. Metal-Catalyzed Cross-Coupling Reactions. Wiley, 2008. (88) Bedford, R. B.; Cazin, C. S. J.; Holder, D. Coord. Chem. Rev. 2004, 248, 2283-2321. (89) Luh, T. Y.; Leung, M. K.; Wong, K. T. Chem. Rev. 2000, 100, 3187-3204. (90) Cardenas, D. J. Angew. Chem. Int. Ed. 2003, 42, 384-387. (91) Culkin, D. A.; Hartwig, J. F. Organometallics 2004, 23, 3398-3416. (92) Mann, G.; Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics 2003, 22, 2775-2789. (93) Corma, A.; Leyva-Perez, A.; Sabater, M. J. Chem. Rev. 2011, 111, 1657-1712. (94) Li, Z. G.; Brouwer, C.; He, C. Chem. Rev. 2008, 108, 3239-3265. (95) Krause, N.; Winter, C. Chem. Rev. 2011, 111, 1994-2009. 105  (96) Nolan, S. P. Accounts Chem. Res. 2011, 44, 91-100. (97) Gaillard, S.; Cazin, C. S. J.; Nolan, S. P. Accounts Chem. Res. 2012, 45, 778-787. (98) Rudolph, M.; Hashmi, A. S. K. Chem. Soc. Rev. 2012, 41, 2448-2462. (99) Wegner, H. A.; Auzias, M. Angew. Chem. Int. Ed. 2011, 50, 8236-8247. (100) Huang, H.; Zhou, Y.; Liu, H. Beilstein J. Org.Chem. 2011, 7, 897-936. (101) Bandini, M. Chem. Soc. Rev. 2011, 40, 1358-1367. (102) Banno, M.; Iwata, K.; Hamaguchi, H. J. Chem. Phys. 2007, 126. (103) Uson, R.; Laguna, A.; Laguna, M.; Briggs, D. A.; Murray, H. H.; Fackler, J. P. Inorg. Syn. 1989, 26, 85-91. (104) Drew, D.; Doyle, J. R. Inorg. Syn. 1990, 28, 346-349.            106  Appendix  Table 1 Kinetic data collected for the formation of 2.3 at 318 K. [PA]0=0.421 mol/L Entry % PA (2.2) % IMesP (2.3) [PA] mol/L Time/s 1 97.4 2.58 0.410 387 2 88.2 11.7 0.371 987 3 79.0 20.9 0.333 1974 4 70.6 29.3 0.297 2961 5 63.8 36.1 0.269 3948 6 57.3 42.6 0.241 4935 7 51.7 48.2 0.218 5922 8 46.0 53.9 0.193 6909 9 41.6 58.3 0.175 7896 10 36.4 63.5 0.153 8883 11 32.8 67.1 0.138 9870 12 29.8 70.1 0.125 10857 13 26.1 73.8 0.110 11844 14 24.7 75.2 0.104 12831 15 21.4 78.5 0.090 13818 16 19.1 80.8 0.080 14805 17 17.7 82.2 0.074 15792 18 15.8 80.5 0.069 16779 19 15.0 84.9 0.063 17766 20 12.4 87.5 0.052 18753 Table 2 Kinetic data collected for the formation of 2.3 at 324 K. [PA]0=0.421 mol/L Entry % PA (2.2) % IMesP (2.3) [PA] mol/L Time/s 1 89.7 9.12 0.382 318 2 81.3 18.8 0.342 818 3 72.0 27.2 0.306 1636 4 64.6 32.3 0.281 2454 5 58.8 40.4 0.249 3272 6 53.2 46.8 0.224 4090 7 47.1 52.3 0.199 4908 107  8 42.7 57.3 0.179 5726 9 38.2 60.0 0.163 6544 10 34.3 65.3 0.145 7362 11 31.2 68.8 0.131 8180 12 28.1 71.9 0.118 8998 13 25.6 74.4 0.107 9816 14 23.4 76.6 0.098 10634 15 21.5 78.5 0.091 11452 16 19.5 87.5 0.077 12270 17 17.7 82.3 0.075 13088 18 16.3 83.7 0.069 13906 Table 3 Kinetic data collected for the formation of 2.3 at 330 K. [PA]0=0.421 mol/L Entry % PA (2.2) % IMesP (2.3) [PA] mol/L Time/s 1 91.3 8.74 0.385 318 2 71.2 28.8 0.300 818 3 55.5 42.6 0.238 1636 4 45.7 50.7 0.200 2454 5 38.1 61.9 0.161 3272 6 32.8 67.2 0.138 4090 7 28.1 71.9 0.118 4908 8 24.1 75.9 0.102 5726 9 22.3 77.7 0.094 6544 10 19.4 80.6 0.082 7362 11 17.5 82.5 0.074 8180 12 16.0 84.0 0.067 8998 13 15.2 84.8 0.064 9816 14 13.7 86.3 0.058 10634 15 13.2 86.8 0.056 11452 16 12.1 87.9 0.051 12270 17 11.5 88.5 0.049 13088 18 11.1 88.9 0.047 13906 Table 4 Kinetic data collected for the formation of 2.3 at 335 K. [PA]0=0.421 mol/L Entry % PA (2.2) % IMesP (2.3) [PA] mol/L Time/s 1 90.4 9.62 0.381 318 108  2 61.7 38.3 0.260 1118 3 44.9 55.1 0.189 2236 4 33.2 66.8 0.140 3354 5 25.3 74.7 0.107 4472 6 20.0 80.0 0.084 5590 7 16.4 83.7 0.069 6708 8 13.6 86.4 0.057 7826 9 11.2 88.8 0.047 8944 10 9.7 90.3 0.041 10062 Table 5 Kinetic data collected for the formation of 2.3 at 341 K. [PA]0=0.421 mol/L Entry % PA (2.2) % IMesP (2.3) [PA] mol/L Time/s 1 92.9 8.05 0.388 318 2 63.5 36.5 0.268 818 3 46.5 53.5 0.196 1636 4 35.0 65.0 0.147 2454 5 26.5 70.8 0.115 3272 6 21.7 78.3 0.092 4090 7 17.9 82.1 0.075 4908 8 15.0 85.0 0.063 5726 9 12.8 87.2 0.054 6544 10 10.9 89.1 0.046 7362 Table 6 Kinetic data collected for the formation of 2.5 at 296 K. [PA]0=0.379 mol/L Entry % PA (2.4) % IMesP (2.5) [PA] mol/L Time/s 1 97.6 2.45 0.370 311 2 94.4 5.6 0.358 1162 3 91.4 8.6 0.346 2013 4 87.8 12.2 0.333 2864 5 84.4 15.6 0.320 3715 6 81.0 19.0 0.307 4566 7 76.9 23.1 0.291 5417 8 72.9 27.1 0.276 6268 9 70.1 29.9 0.266 7119 10 64.5 35.5 0.244 7970 11 64.7 35.3 0.245 8821 109  12 57.7 42.3 0.219 9672 13 53.4 46.6 0.203 10523 14 48.4 51.6 0.183 11374 15 44.4 55.6 0.168 12225 16 40.7 59.3 0.154 13076 17 37.5 62.5 0.142 13927 18 34.5 65.5 0.131 14778 19 31.8 68.2 0.121 15629 20 30.1 69.9 0.114 16480 21 27.7 72.3 0.105 17331 Table 7 Kinetic data collected for the formation of 2.5 at 307 K. [PA]0=0.379 mol/L Entry % PA (2.4) % IMesP (2.5) [PA] mol/L Time/s 1 93.3 6.71 0.354 311 2 85.5 14.5 0.324 1162 3 76.4 20.4 0.299 2013 4 68.9 31.1 0.261 2864 5 59.3 40.7 0.225 3715 6 48.6 45.4 0.196 4566 7 43.1 52.0 0.172 5417 8 38.2 56.6 0.153 6268 9 33.4 61.6 0.133 7119 10 29.9 64.6 0.120 7970 11 26.4 68.2 0.106 8821 12 23.4 71.6 0.093 9672 13 22.0 78.0 0.084 10523 Table 8 Kinetic data collected for the formation of 2.5 at 318 K. [PA]0=0.379 mol/L Entry % PA (2.4) % IMesP (2.5) [PA] mol/L Time/s 1 91.3 8.67 0.346 311 2 69.6 30.4 0.264 1162 3 51.1 48.9 0.194 2013 4 34.7 62.0 0.136 2864 5 26.5 71.0 0.103 3715 6 19.1 80.9 0.072 4566 110  Table 9 Kinetic data collected for the formation of 2.5 at 330 K. [PA]0=0.379 mol/L Entry % PA (2.4) % IMesP (2.5) [PA] mol/L Time/s 1 80.8 19.2 0.306 311 2 47.5 46.3 0.192 1162 3 34.4 59.7 0.138 2013 4 25.4 68.7 0.102 2864 5 17.8 73.9 0.074 3715 6 14.5 85.0 0.055 4566 7 10.8 89.2 0.041 5417 Table 10 Kinetic data collected for the formation of 2.7 at 313 K. [PA]0=0.421 mol/L Entry % PA (2.6) % IMesP (2.7) [PA] mol/L Time/s 1 98.2 1.79 0.413 311 2 96.4 3.61 0.405 1162 3 94.6 5.36 0.397 2013 4 92.7 7.28 0.389 2864 5 91.6 8.45 0.385 3715 6 88.7 11.3 0.373 4566 7 89.0 11.0 0.374 5417 8 87.8 12.2 0.369 6268 9 86.5 13.5 0.363 7119 10 85.1 14.9 0.358 7970 11 84.0 16.0 0.353 8821 12 82.8 17.2 0.348 9672 13 81.9 18.1 0.344 10523 14 80.4 19.6 0.338 11374 15 78.0 22.0 0.328 12225 16 78.7 21.3 0.331 13076 17 77.7 22.3 0.326 13927 18 76.9 23.1 0.323 14778 19 75.9 24.1 0.319 15629 20 75.0 25.0 0.315 16480 21 73.9 26.1 0.310 17331 22 73.1 26.9 0.307 18182 23 72.4 27.6 0.304 19033 24 71.4 28.6 0.300 19884 111  25 70.2 29.8 0.295 20735 26 69.9 30.1 0.293 21586 27 69.0 31.0 0.290 22437 28 68.4 31.6 0.287 23288 29 67.6 32.4 0.284 24139 30 66.8 33.2 0.281 24990 Table 11 Kinetic data collected for the formation of 2.7 at 324 K. [PA]0=0.421 mol/L Entry % PA (2.6) % IMesP (2.7) [PA] mol/L Time/s 1 96.6 3.42 0.406 311 2 93.4 6.61 0.392 1162 3 80.3 9.74 0.375 2013 4 87.4 12.6 0.367 2864 5 85.0 15.0 0.357 3715 6 82.6 17.4 0.347 4566 7 80.0 20.0 0.336 5417 8 77.6 22.4 0.326 6268 9 75.5 24.5 0.317 7119 10 73.7 26.3 0.310 7970 11 71.3 28.7 0.299 8821 12 69.8 30.2 0.293 9672 13 68.2 31.8 0.286 10523 14 66.0 34.0 0.277 11374 15 64.5 35.5 0.271 12225 16 63.2 36.8 0.265 13076 17 61.2 38.8 0.257 13927 18 59.9 40.1 0.252 14778 19 58.2 41.8 0.244 15629 20 57.1 42.9 0.240 16480 21 55.9 44.1 0.235 17331 22 54.6 45.4 0.229 18182 23 53.8 46.2 0.226 19033 24 52.2 47.8 0.219 19884 25 51.4 48.6 0.216 20735 26 50.2 49.8 0.211 21586 27 49.0 51.0 0.206 22437 28 48.1 51.9 0.202 23288 29 46.9 53.1 0.197 24139 112  30 46.0 54.0 0.193 24990 Table 12 Kinetic data collected for the formation of 2.7 at 335 K. [PA]0=0.421 mol/L Entry % PA (2.6) % IMesP (2.7) [PA] mol/L Time/s 1 93.9 6.06 0.395 311 2 83.2 16.8 0.350 1162 3 75.3 24.7 0.316 2013 4 68.6 31.4 0.288 2864 5 63.1 36.9 0.265 3715 6 59.1 40.9 0.248 4566 7 55.6 44.4 0.233 5417 8 52.3 47.8 0.220 6268 9 48.8 49.4 0.209 7119 10 43.9 49.7 0.197 7970 11 45.2 54.8 0.190 8821 12 43.3 56.7 0.182 9672 13 41.5 58.5 0.174 10523 14 40.1 59.9 0.169 11374 15 38.9 61.1 0.163 12225 16 37.6 62.4 0.158 13076 17 36.4 63.6 0.153 13927 18 35.7 64.3 0.150 14778 19 34.3 65.7 0.144 15629 20 33.9 66.1 0.142 16480 Table 13 Kinetic data collected for the formation of 2.7 at 341 K. [PA]0=0.421 mol/L Entry % PA (2.6) % IMesP (2.7) [PA] mol/L Time/s 1 82.0 7.28 0.386 311 2 72.2 16.4 0.342 1162 3 65.2 23.5 0.309 2013 4 59.5 29.5 0.281 2864 5 54.9 34.3 0.259 3715 6 50.4 38.5 0.238 4566 7 46.9 42.1 0.221 5417 8 43.9 45.1 0.207 6268 9 41.1 48.2 0.193 7119 113  10 38.5 50.4 0.182 7970 11 36.2 52.7 0.171 8821 12 34.5 54.7 0.162 9672 13 32.1 57.0 0.151 10523 14 30.5 58.2 0.144 11374 15 29.4 59.8 0.138 12225 16 27.6 61.4 0.130 13076 17 26.2 62.8 0.124 13927 18 25.6 63.7 0.120 14778 19 24.2 64.7 0.114 15629 20 23.1 66.0 0.109 16480 Table 14 Crystallographic data of 4.1 Formula C48H46N2O5PW Formula weight 945.69 Temperature/K 90 (2) Crystal system monoclinic Space group P21/c a/Å 16.3556(12) b/Å 18.6882(13) c/Å 14.1673(10) α/° 90 β/° 107.911(3) γ/° 90 Volume/Å3 4120.5(5) Z 4 ρcalc (mg/mm3) 1.524 Radiation Mo Kα (λ = 0.71073) 2Θ range for data collection 3.406 to 50.83° Data/restraints/parameters 7560/477/524 Goodness-of-fit on F2 1.131 Final R indexes [I>=2σ (I)] R1 = 0.0525, wR2 = 0.0813 Final R indexes [all data] R1 = 0.0736, wR2 = 0.0883    114  Table 15 Crystallographic data of 4.3 Formula C49H57AuCl7N2PPdS Formula weight 1288.51 Temperature/K 90(2) Crystal system monoclinic Space group P21/n a/Å 14.4990(15) b/Å 20.5435(18) c/Å 18.1531(17) α/° 90 β/° 108.275(3) γ/° 90     Volume/Å3         5134.4(9)     Z        4     ρcalc (mg/mm3)         1.667 Crystal size/mm3 0.13 × 0.12 × 0.09 Radiation MoKα (λ = 0.71073) 2Θ range for data collection 3.084 to 61.242° Reflections collected 62831 Independent reflections 15733 [Rint = 0.0525, Rsigma = 0.0502] Data/restraints/parameters 15733/563/623 Goodness-of-fit on F2 1.081 Final R indexes [I>=2σ (I)] R1 = 0.0509, wR2 = 0.1248 Final R indexes [all data] R1 = 0.0745, wR2 = 0.1344   

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