GROUP 10 TRANSITION METAL CHEMISTRY OF BENZANNULATED/REMOTE N-HETEROCYCLIC CARBENE LIGANDS HAN YUAN (B.Sc., SHANDONG UNIVERSITY) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2008 Acknowledgement Acknowledgements I would like to thank: My supervisor Dr. Huynh Han Vinh for his invaluable guidance, inspiration and patience over the whole course of my Ph.D. candidature. It is my good fortune to have worked under him. All that he taught me in the past four years would be of great benefit to my entire life. The technical staff at Nuclear Magnetic Resonance, Mass Spectrometry, X-ray diffraction and Elemental Analysis laboratories in our department for their technical support. Special thanks to Ms Tan and Professor Koh Lip Lin for their great help in measuring crystals as well as solving the structures and Mdm. Han for her kind help in interpreting 2D NMR spectra. Seah Lin, Sin Yee and Wei Lee for their really helpful discussions and friendship. My past and present group members for their kind help and discussions. Special thanks to Chun Hui, Hui Xian and Xiao Tien who became my good friends and made my life in Singapore more enjoyable. My parents for their unconditional love and support, without which I would not have succeeded in doing a Ph.D. study overseas. Other friends in Singapore or China, Xiaofeng, Ming Xing, Kien Voon, Jing Qiu, Sheau Wei, Li Min, and Qin Ran for their constant support and encouragement. NUS for my research scholarship. I Table of contents Table of contents Summary Chart 1. Compounds synthesized in this work V VII List of tables X List of figures XI List of schemes XIV List of abbreviations XVI 1. Introduction 1.1. Definition of carbenes 1.2. Electronic structure, preparation and application of N-heterocyclic carbenes 1.3. Preparation and application of NHC complexes 1.4. Remote N-heterocyclic carbenes and their complexes 2. Palladium(II) and platinum(II) complexes with the 1,3-diisopropylbenzimi- 13 15 dazolin-2-ylidene ligand 2.1. Synthesis, reactivity and catalytic studies of the dimeric Pd(II) complex 15 [PdBr2(iPr2-bimy)]2 2.1.1. Synthesis 15 2.1.2. Reactivity studies 20 2.1.3. Catalytic studies in Suzuki-Miyaura coupling 52 2.2. Synthesis and catalytic studies of mononuclear bis(carbene) Pd(II) complexes 55 2.2.1. Synthesis 55 2.2.2. Catalytic studies in Mizoroki-Heck coupling 59 2.3. Synthesis and reactivity studies of Pt(II) complexes 62 II Table of contents 2.3.1. Synthesis of the monocarbene complex [PtBr2(iPr2-bimy)(DMSO)] 62 and the bis(carbene) complex [PtBr2(iPr2-bimy)2] 2.3.2. Reactivity studies of [PtBr2(iPr2-bimy)(DMSO)] 3. Palladium(II) complexes with the 1,3-dibenzhydrylbenzimidazolin-2- 68 73 ylidene ligand 3.1. Synthesis 73 3.2. Catalytic studies in Suzuki-Miyaura coupling 83 4. Palladium(II) complexes with pyrazole-based remote N-heterocyclic 87 carbene ligands 4.1. Synthesis and catalytic studies of mononuclear Pd(II) complexes with 87 pyrazolin-4-ylidene ligands 4.1.1. Synthesis 87 4.1.2. Catalytic studies in Suzuki-Miyaura coupling 96 4.2. Studies on the influence of 3,5-substituents in pyrazolin-4-ylidenes on 97 complexation 4.2.1. Synthesis of Pd(II) phosphine complexes with different pyrazolin- 98 4-ylidenes 4.2.2. Synthesis of Pd(II) pyridine complexes with different pyrazolin-4- 108 ylidenes 4.3. Synthesis of dinuclear or multinuclear Pd(II) complexes with pyrazolin-4 111 -ylidenes 4.3.1. Synthesis of iodo-bridged dinuclear Pd(II) complexes 111 4.3.2. Synthesis of di(pyrazolin-4-ylidene)-bridged dinuclear or 113 III Table of contents multinuclear Pd(II) complexes 5. Conclusion 123 6. Experimental section 128 Appendix 178 References 193 IV Summary Summary This thesis deals with synthesis, reactivity and catalytic studies of group 10 (mainly palladium) organometallic compounds bearing benzannulated or remote N-heterocyclic carbene ligands. The findings of the research are presented in three chapters. Chapter describes the synthesis and properties of complexes with the 1,3-diisopropylbenzimidazolin-2-ylidene ligand (iPr2-bimy). Reaction of the sterically bulky 1,3-diisopropylbenzimidazolium bromide (A) with Pd(OAc)2 in the presence of NaBr yielded the monocarbene dimeric complex [PdBr2(iPr2-bimy)]2 (1) in high yield. Complex can be readily cleaved by CH3CN, salt A, PPh3, pyridyl or bipyridyl ligands, isocyanides and different NHCs to afford monocarbene complexes with the respective co-ligands. A preliminary catalytic study showed that complex is a highly active precatalyst in aqueous Suzuki-Miyaura coupling reactions. Three Pd(II) bis(carbene) complexes (12-14) with the iPr2-bimy ligand bearing different anionic co-ligands have also been synthesized, and their catalytic activities studied in the Mizoroki-Heck coupling reactions. In addition, the two Pt(II) complexes [PtBr2(iPr2-bimy)(DMSO)] (15) and [PtBr2(iPr2-bimy)2] (16) were obtained when salt A was reacted with PtBr2 in the presence of NaOAc in DMSO. The reactivity of complex 15 with PPh3 and pyridine was studied. 1H NMR and X-ray diffraction analyses revealed interesting intramolecular C-HM anagostic interactions in all complexes with the iPr2-bimy ligand synthesized in this work. Chapter deals with a series of Pd(II) complexes with the 1,3-dibenzhydrylbenzimidazolin-2-ylidene ligand (Bh2-bimy). Reaction of sterically even more demanding 1,3-dibenzhydrylbenzimidazolium bromide (C) with Pd(OAc)2 in V Summary DMSO yielded a monocarbene Pd(II) complex (19) with a N-bound benzimidazole derivative, which resulted from an unusual NHC rearrangement reaction. Reaction of C with Ag2O, on the other hand, cleanly gave the Ag(I) carbene complex [AgBr(Bh2-bimy)] (20), which was used as a carbene-transfer agent to prepare the acetonitrile complex trans-[PdBr2(CH3CN)(Bh2-bimy)] (21). Dissociation of acetonitrile from complex 21 and subsequent dimerization afforded the dinuclear Pd(II) complex [PdBr2(Bh2-bimy)]2 (22) in quantitative yield. Furthermore, the catalytic activity of complex 22 in aqueous Suzuki-Miyaura cross-coupling reactions was studied and compared with that of its less bulky analogue [PdBr2(iPr2-bimy)]2 (1). The synthesis and properties of Pd(II) complexes with pyrazolin-4-ylidene ligands are described in Chapter 4. A few neutral and cationic mononuclear pyrazolin-4-ylidenephosphine complexes (26a/b and 29a/b) were prepared via oxidative addition of 4-iodopyrazolium salts to [Pd2(dba)3]/PPh3 and their catalytic activities are compared in aqueous Suzuki-Miyaura coupling reactions. The substituent effect of pyrazolin-4ylidenes on complexation was studied in a series of Pd(II) complexes with PPh3 (33a-c) or pyridine (34a-c) as co-ligands where the 3,5-substituents of pyrazolin-4-ylidenes were varied from Me, Ph to iPr. In addition, two iodo-bridged dinuclear complexes (35a/b) were also synthesized via oxidative addition of 4-iodopyrazolium salts to [Pd2(dba)3]. The possibility of preparing di(pyrazolin-4-ylidene)-bridged complex was also explored and two such complexes (38-39) were successfully obtained. Most of the new compounds synthesized in this work have been characterized by X-ray diffraction analyses and are depicted in Chart 1. VI Chart Chart 1. Compounds synthesized in this work Ph N N N N Br Ph N N I Br Ph Ph B A C N Br Br N Br N Pd Pd N Br N N Br Pd NCCH3 Br N N trans-4 N N N N PPh3 Pd Br Br Br Pd Br N Br Pd CNR Br N Br Pd Br L L Br Pd Br N N N N N 5a 5d : L L = N N R N C Pd Br Br N N trans- N 5b : L L = N 5c : L L = cis-4 N N Br Pd PPh3 Br N N N Br Pd Br Br N cis- 6a (R = Cy); 6b (R = nBu); 6c (R = Xyl) N N Br Pd Br NH NH VII Chart NH N N N HN Br H H Br Pd N N Pd Br H H Br N N N N N N N C Pd O2CCF3 O2CCF3 cis-10 N N Br Pd NHC Br N N 11a-i (NHC = different N-heterocyclic carbenes) N N X Pd X Pd N N N trans-12 ( X = Br ); trans-13 (X = I) DMSO Pt Br Br N N cis-15 Br Pt Br N N N N trans-16 Ph Br N Pd N Br Ph Ph N cis-14 PPh3 Pt Br Br Ph O2CCF3 N N N cis-17 Ph O2CCF3 Br Pt N Br trans-18 Ph N NR O Ag Br N Ph 19 (R = benzhydryl) Ph 20 Ph Ph Ph Br N Pd NCCH3 N Br Ph Ph 21 N Ph Ph Br Br Pd Pd N Br Br Ph N Ph N Ph Ph Ph 22 VIII Chart N N R R I 25a (R = Ph) ; 25b (R = Me) PPh3 Pd I I N N I R 26a (R = Ph) ; 26b (R = Me) PPh3 Pd O2CCF3 O2CCF3 N N 27a (R = Ph) ; 27b (R = Me) R N N R I R OTf PPh3 Pd I PPh3 N N OTf Ph N N I BF4 R 28a (R = Ph) ; 28b (R = Me) 32a (R = Me); 32b (R = Ph); 32c (R = iPr) 29a (R = Ph) ; 29b (R = Me) Ph N N Ph I Ph I 32a' PPh3 Pd I PPh3 N N BF4 Ph PPh3 Pd PPh3 BF4 I N N Ph trans-33a cis-33b Ph Ph N N Ph Ph N PPh3 Pd I PPh3 N R PPh3 I BF4 Pd Ph3P I N trans-33b BF4 Pd Ph N Ph I Pd N I N N R 34a (R = Me); 34b (R = Ph); 34c (R = iPr) 33c R N N I Pd I I Pd I I N N PPh3 I I BF4 n R 35a (R = Ph); 35b (R = Me) Ph3P N N N N 37a (n = 1); 37b (n = 2); 37c (n = 3) Pd Pd I N N Ph3P N N BF4 N N N N I Pd Ph3P N N N N PPh3 Pd I PPh3 BF4 I Pd Ph3P I Pd PPh3 39 38 IX Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] cis-14 C30H36F6N4O4Pd 737.03 0.200.060.06 223(2) Monoclinic C2/c 21.057(3) 10.773(2) 14.149(2) 90 101.415 90 3146.2(8) 1.556 0.667 1.97-27.49 11028 3611 (Rint = 0.0506) 0.9611, 0.8782 R1 = 0.0571, wR2 = 0.1268 R1 = 0.0625, wR2 = 0.1293 1.257 1.373 / -2.080 cis-152CHCl3 C17H26Br2Cl6N2OPtS 874.07 0.600.460.14 243(2) Monoclinic P21/m 9.547(3) 10.589(3) 14.693(4) 90 104.055(6) 90 1440.9(7) 2.015 8.284 2.20-27.47 9829 3484 (Rint = 0.0531) 0.3901, 0.0827 R1 = 0.0352, wR2 = 0.0926 R1 = 0.0405, wR2 = 0.0947 1.089 2.580 / -1.058 trans-16 C26H36Br2N4Pt 759.50 0.280.240.16 295(2) Orthorhombic Pbca 17.2381(9) 9.5180(5) 17.8717(9) 90 90 90 2932.2(3) 1.720 7.530 2.28-27.49 19674 3372 (Rint = 0.0419) 0.3788, 0.2269 R1 = 0.0269, wR2 = 0.0610 R1 = 0.0538, wR2 = 0.0692 0.992 0.735 / -0.558 cis-17 C31H33Br2N2PPt 819.47 0.400.240.20 223(2) Monoclinic P21/n 10.5275(5) 17.5069(8) 16.5319(7) 90 94.7690(10) 90 3036.3(2) 1.793 7.328 1.70-27.50 21495 6985 (Rint = 0.0391) 0.3219, 0.1576 R1 = 0.0319, wR2 = 0.0753 R1 = 0.0412, wR2 = 0.0783 1.053 1.685 / -1.178 187 Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] trans-18THF C22H31Br2N3OPt 708.41 0.300.200.08 223(2) Orthorhombic Pbca 17.1196(7) 9.7318(4) 29.7136(11) 90 90 90 4950.4(3) 1.901 8.915 1.81-27.50 33569 5690 (Rint = 0.0537) 0.5357, 0.1751 R1 = 0.0305, wR2 = 0.0636 R1 = 0.0444, wR2 = 0.0675 1.022 1.019 / -0.970 192Me2CO C72H62Br2N4O3Pd 1297.48 0.380.200.20 223(2) Triclinic P1 11.581(2) 15.459(4) 18.044(4) 69.890(13) 89.00(2) 82.013(14) 3002.4(12) 1.435 1.692 1.20-27.50 39475 13748 (Rint = 0.0247) 0.7284, 0.5657 R1 = 0.0311, wR2 = 0.0813 R1 = 0.0394, wR2 = 0.0873 1.067 0.662 / -0.299 20 C33H26AgBrN2 638.34 0.240.100.08 223(2) Monoclinic P21/n 17.5789(11) 9.1363(6) 18.2095(12) 90 114.853(2) 90 2653.7(3) 1.598 2.290 1.35-27.48 18198 6065 (Rint = 0.0560) 0.8380, 0.6094 R1 = 0.0574, wR2 = 0.1362 R1 = 0.0889, wR2 = 0.1490 1.020 2.265 / -0.483 21 C35H29Br2N3Pd 757.83 0.540.320.10 223(2) Monoclinic P21/n 16.6225(12) 10.6140(8) 18.0485(14) 90 101.962(2) 90 3115.2(4) 1.616 3.189 1.52-27.50 21635 7164 (Rint = 0.0561) 0.7410, 0.2777 R1 = 0.0454, wR2 = 0.0934 R1 = 0.0769, wR2 = 0.1041 0.973 1.077 / -0.441 188 Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] 222CHCl3 C68H54Br4Cl6N4Pd2 1672.29 0.560.420.16 223(2) Monoclinic P21/c 21.2354(10) 17.7672(8) 18.5717(9) 90 110.1270(10) 90 6579.1(5) 1.688 3.264 1.02-27.50 46299 15108 (Rint = 0.0382) 0.6232, 0.2622 R1 = 0.0415, wR2 = 0.0993 R1 = 0.0637, wR2 = 0.1093 1.029 2.259 / -0.786 26a0.5C6H5CH3 C34.50H35I2N2PPd 868.82 0.140.080.02 295(2) Monoclinic P21/c 9.3123(4) 16.8404(7) 21.6379(9) 90 95.7190(10) 90 3376.4(2) 1.709 2.451 1.54-25.00 19717 5935 (Rint = 0.0657) 0.9526, 0.7254 R1 = 0.0789, wR2 = 0.1464 R1 = 0.1018, wR2 = 0.1548 1.253 1.052 / -0.996 26b0.5CH2Cl2 C26.50H30ClI2N2PPd 803.14 0.360.260.10 295(2) Monoclinic P21/c 9.3019(5) 16.8771(9) 18.9728(9) 90 94.5300(10) 90 2969.2(3) 1.797 2.865 1.62-27.50 20857 6797 (Rint = 0.0357) 0.7626, 0.4252 R1 = 0.0638, wR2 = 0.1509 R1 = 0.0758, wR2 = 0.1573 1.168 1.832 / -0.884 29aCH2Cl2H2O C51H50Cl2F3IN2O4P2PdS 1210.13 0.240.140.04 293(2) Monoclinic P21/c 12.0615(5) 39.2897(18) 11.1728(5) 90 100.8010(10) 90 5200.9(4) 1.545 1.211 1.72-27.50 37279 11951 (Rint = 0.0644) 0.9532, 0.7599 R1 = 0.0607, wR2 = 0.1231 R1 = 0.0962, wR2 = 0.1356 1.038 1.558 / -0.685 189 Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] 29bCH2Cl2 C46H46Cl2F3IN2O3P2PdS 1130.05 0.260.100.06 223(2) Orthorhombic Pnma 10.0914(5) 22.4737(11) 20.9892(11) 90 90 90 4760.2(4) 1.577 1.315 1.81-27.50 32206 5584 (Rint = 0.0761) 0.9253, 0.7262 R1 = 0.0705, wR2 = 0.1551 R1 = 0.1000, wR2 = 0.1674 1.079 1.245 / -0.793 33aMe2CO C51H50BF4IN2PdOP2 1088.98 0.160.140.06 295(2) Monoclinic P21/c 19.396(8) 11.130(5) 24.415(9) 90 109.236(11) 90 4976(3) 1.454 1.110 1.11-25.00 28274 8753 (Rint = 0.1337) 0.9364, 0.8424 R1 = 0.0786, wR2 = 0.1615 R1 = 0.1600, wR2 = 0.1991 0.989 0.894 / -1.001 cis-33bãCH2Cl2 C59H50BF4Cl2IN2PdP2 1239.96 0.300.080.02 223(2) Monoclinic P21/n 18.9177(11) 14.4464(9) 21.7262(12) 90 115.2320(10) 90 5371.1(5) 1.533 1.134 1.20-27.50 37433 12321 (Rint = 0.0630) 0.9777, 0.7272 R1 = 0.0528, wR2 = 0.1248 R1 = 0.0829, wR2 = 0.1408 1.016 2.078 / -0.595 trans-33bã0.5CH3CN C59H49.5BF4IN2.5PdP2 1175.56 0.400.300.14 223(2) Monoclinic P21/c 18.2230(14) 16.6331(14) 17.5608(14) 90 104.543(2) 90 5152.2(7) 1.516 1.078 1.68-25.00 29651 9073 (Rint = 0.0844) 0.9582, 0.4869 R1 = 0.0752, wR2 = 0.1475 R1 = 0.1064, wR2 = 0.1595 1.119 0.895 / -0.854 190 Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] 33c C68H74B2F8I2N4Pd2P2 1649.47 0.120.100.02 223(2) Monoclinic P21/n 10.8110(16) 45.221(7) 15.263(2) 90 96.852(3) 90 7408.4(19) 1.479 1.422 1.42-25.00 42614 13042 (Rint = 0.1841) 0.9721, 0.8479 R1 = 0.1052, wR2 = 0.2488 R1 = 0.2092, wR2 = 0.2907 1.034 1.258 / -0.707 34a C17H19I2N3Pd 625.55 0.260.080.02 223(2) Monoclinic P21/n 11.3735(14) 8.5316(11) 20.507(3) 90 97.151(3) 90 1974.4(4) 2.104 4.069 1.95-27.50 13400 4522 (Rint = 0.0630) 0.9230, 0.4176 R1 = 0.0562, wR2 = 0.1093 R1 = 0.0820, wR2 = 0.1175 1.069 1.059 / -1.060 34b C27H23I2N3Pd 749.68 0.200.160.12 223(2) Monoclinic P21/n 9.5081(5) 13.5672(7) 20.1031(11) 90 93.2980(10) 90 2589.0(2) 1.923 3.121 1.81-27.50 18097 5940 (Rint = 0.0322) 0.7058, 0.5741 R1 = 0.0406, wR2 = 0.0977 R1 = 0.0461, wR2 = 0.1000 1.132 1.154 / -0.512 34cã0.5H2O C21H28I2N3PdO0.5 690.66 0.560.340.20 223(2) Monoclinic P21/n 18.577(2) 9.4289(11) 28.349(3) 90 99.156(2) 90 4902.5(10) 1.871 3.289 1.46-27.47 26478 11178 (Rint = 0.0305) 0.5592, 0.2603 R1 = 0.0455, wR2 = 0.1035 R1 = 0.0595, wR2 = 0.1091 1.075 1.193 / -1.029 191 Appendix Continued . Formula Formula weight Crystal size [mm] Temperature [K] Crystal system Space group a [] b [] c [] [] [] [] V [3] Z Dc [gcm-3] [mm-1] range [] Reflection collected Independent reflections Max., min. transmission Final R indices [I > 2(I)] R indices (all data) Goodness-of-fit on F2 Peak/hole [e-3] 35bã4CH2Cl2 C20H36Cl8I4N4Pd2 1336.53 0.700.140.10 223(2) Triclinic P1 9.306(8) 10.916(8) 10.961(9) 66.564(17) 75.026(16) 80.789(16) 984.9(13) 2.253 4.609 2.04-27.50 6632 4446 (Rint = 0.0239) 0.6557, 0.1407 R1 = 0.0467, wR2 = 0.1265 R1 = 0.0610, wR2 = 0.1362 1.038 1.335 / -0.951 38ã2C6H5CH3 C112H116B4ClF1I3N8P4Pd4 2887.00 0.100.080.04 293(2) Triclinic P1 10.8997(5) 15.5584(7) 18.2820(8) 108.7450(10) 94.0810(10) 100.3340(10) 2860.5(2) 1.676 1.584 1.51-25.00 30914 10065 (Rint = 0.0547) 0.9393, 0.8577 R1 = 0.0818, wR2 = 0.1604 R1 = 0.0955, wR2 = 0.1659 1.281 1.309 / -2.019 39ã2CH2Cl2 C89H88B2Cl4F8I2N4P4Pd2 2119.53 0.220.220.14 223(2) Monoclinic P21/c 18.0676(9) 24.2063(11) 20.8600(10) 90 94.5720(10) 90 9094.1(8) 1.548 1.325 1.41-25.00 53179 16003 (Rint = 0.1323) 0.8363, 0.7593 R1 = 0.0783, wR2 = 0.1641 R1 = 0.1415, wR2 = 0.1892 1.005 0.718 / -0.958 192 References References [1] Reviews: (a) Hahn, F. 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Tan Palladium(II) Complexes of a sterically bulky, benzannulated N-Heterocyclic Carbene with unusual intramolecular C-HãããPd and CcarbeneãããBr Interactions and their Catalytic Activities Organometallics 2006, 25, 3267-3274. 2. Y. Han, H. V. Huynh* Preparation and characterization of the first pyrazolebased remote N-heterocyclic carbene complexes of palladium(II) Chem. Commun. 2007, 1089-1091. 3. Y. Han, H. V. Huynh*, L. L. Koh Pd(II) complexes of a sterically bulky, benzannulated N-heterocyclic carbene and their catalytic activities in the Mizoroki-Heck reaction J. Organomet. Chem. 2007, 692, 3606-3613. 4. Y. Han, H. V. Huynh*, G. K. Tan Synthesis and Characterizations of Pd(II) Complexes Incorporating a N-Heterocyclic Carbene and Aromatic NHeterocycles Organometallics, 2007, 26, 6447-6452. 5. Y. Han, H. V. Huynh*, G. K. Tan Mono- vs Bis(carbene) Complexes: A Detailed Study on Platinum(II)-Benzimidazolin-2-ylidenes Organometallics, 2007, 26, 4612-4617. 6. Y. Han, H. V. Huynh*, G. K. Tan Palladium(II) Pyrazolin-4-ylidenes: Remote N-Heterocyclic Carbene Complexes and Their Catalytic Application in Aqueous Suzuki-Miyaura Coupling Organometallics, 2007, 26, 6581-6585. 7. Y. Han, Y.-T. Hong, H. V. Huynh* Ag(I) and Pd(II) Complexes of a 1,3Dibenzhydryl Substituted Benzannulated N-Heterocylic Carbene: Unexpected Rearrangement, Structures and Catalytic Studies J. Organomet. Chem. 2008, 693, 3159-3165. 8. Y. Han, H. V. Huynh* Mixed Carbene-Isocyanide Pd(II) Complexes: Synthesis, Structures and Reactivity towards Nucleophiles Dalton Trans. 2009, 2201-2209. 9. Y. Han, L. J. Lee, H. V. Huynh* Palladium(II) Pyrazolin-4-ylidenes: Substituent Effects on the Formation and Catalytic Activity of Pyrazole-based Remote NHC Complexes Organometallics 2009, 28, 2778-2786. 10. H. V. Huynh*, Y. Han, J. A. Yang 13C NMR Determination of Ligand Donor Strengths using N-heterocyclic Carbene Complexes of Palladium(II) manuscript in preparation. 11. Y. Han, L. J. Lee, H. V. Huynh* Dinuclear or Tetranuclear Pd(II) Complexes bearing Bidentate Remote N-heterocyclic Carbene Ligands manuscript in preparation. [...]... carbenes (ADCs) have also been reported by Alder shortly after the isolation of the first NHC.5 However, ADCs are not a topic of focus in this thesis and therefore the following discussions will refer to only NHCs 4 Chapter 1 N( iPr)2 P R N N R R N N R R N N(iPr)2 B R N N R N R R N N R N R N N R Me 2N R N S N R P Ar N R N N R R N P R N NMe2 B B N R R N R Figure 1.4 Different types of stable NHCs Amongst... 2,6-dimethylphenyl XVII Chapter 1 Chapter 1 Introduction 1.1 Definition of carbenes Carbenes are neutral compounds featuring a divalent carbon atom with only six valence electrons The geometry at the carbene carbon atom can be either linear or bent, depending on the degree of hybridization The linear geometry is based on an sp-hybridized carbene center with two nonbonding energetically degenerate p orbitals... observed Most carbenes contain an sp2-hybridized carbene center and therefore are bent p py px  px py  linear p bent Figure 1.1 Relationship between the carbene bond angle and the nature of the frontier orbitals As shown in Figure 1.2, four electronic configurations can be conceived at the 1 Chapter 1 sp2-hybridized carbene carbon atom The two nonbonding electrons can occupy the two different orbitals... saturated N- heterocyclic ring Imidazolin-2-ylidene Benzimidazolin-2-ylidene Imidazolidin-2-ylidene R N 1 R N R N N R N R N R 5 2 4 3 Topology unsaturated, aromatic benzannulated, aromatic saturated, nonaromatic  (C2) [ppm] 211-221 223-232 238-245 Angle N1 -C2 -N3 [ °] 101 .2(2) -102 .2(2) 103 .5 (1) -104 .3(1) 104 .7(3) -106 .4(1) Reactivity monomers are favored both monomers and dimers are possible depending on R... carbon is adjacent to two nitrogen atoms, rNHCs contain a carbenoid center which is distant from the nitrogen atoms Computational studies on rNHCs derived from pyridine or quinoline have shown that these new carbenes are even stronger  donors than their well-known normal NHC counterparts.22 Furthermore, preliminary catalytic studies showed that complexes with rNHC ligands are more active in certain C-C... interaction and a linear X-H···M geometry characteristic of hydrogen bonding, the significant downfield shift of the isopropyl C-H protons and the geometric parameters (Vide infra) observed for complex 1 best fit the definition of an anagostic interaction Such an interaction has recently been observed in Rh(I) complexes of NHC ligands. 31 However, the origin of such interactions is still under debate and may... catalyst one of the phosphine ligands in the first generation catalyst is substituted by a NHC ligand (Figure 1.6) Such a modification greatly increases the catalytic efficiency of the complex and also showcases the potential of NHCs replacing well-established phosphine ligands in transition metal catalysis in 11 Chapter 1 general Cl Cl N PCy3 Cl Cl Ru PCy3 Ph 1st generation N Ru Ph PCy3 2nd generation Figure... and catalytic activity of their complexes will be presented in Chapters 2 and 3, respectively 12 Chapter 1 1.4 Remote N- heterocyclic carbenes and their complexes As an extension of the NHC concept discussed above, complexes bearing N- heterocyclic carbene ligands with a remote heteroatom (rNHC) have been reported by Raubenheimer and co-workers recently In contrast to the common NHCs in which a carbenoid... reduction of thiones to free carbenes N S N Na/K N Toluene N Scheme 1.2 Synthesis of the first benzimidazolin-2-ylidene The relatively high stability of NHCs and the rapid development of their preparative methods have enabled NHCs’ applications in organic synthesis and catalysis .10 Several studies have shown that NHCs are powerful nucleophilic organocatalysts due to their high nucleophilicity and ease of. .. applications in the future 1.3 Preparation and application of NHC complexes R N R N N R R N (a) [M] H N R CA [M] [M] (b) (f) R N R N R N N R N R [M] X N R CA N R [ M] BH (e) (c) (d) 1 Ag2O 2 [M] N C [M] R N H N R CA CA = counter anion; B = NH, O, S; X = CH3, H, halogen Scheme 1.3 Major synthetic routes towards NHC complexes Following Arduengo’s discovery, a large number of NHCs have been reported in the . N N Br N N I A B N N Ph Ph Ph Ph Br C Pd Br BrBr Pd Br N N N N 1 N N Pd Br Br NCCH 3 2 N N Pd Br Br Br N N 3 N N Pd PPh 3 Br Br N N Pd PPh 3 Br Br trans-4 cis-4 N N Pd Br Br N 5a L L N N Pd Br N N Pd Br Br Br L L 5b : L L L L 5c : 5d : = = = N N N N N N N N Pd Br Br CNR N N Pd C Br Br trans- cis- N R 7 N N Pd NH NH Br Br 6a. GROUP 10 TRANSITION METAL CHEMISTRY OF BENZANNULATED/ REMOTE N- HETEROCYCLIC CARBENE LIGANDS HAN YUAN (B.Sc., SHANDONG UNIVERSITY) A THESIS SUBMITTED FOR THE DEGREE OF. : = = = N N N N N N N N Pd Br Br CNR N N Pd C Br Br trans- cis- N R 7 N N Pd NH NH Br Br 6a (R = Cy); 6b (R = n Bu); 6c (R = Xyl) Chart 1 VIII N HN NH 8 N N N N Pd Br Br N N Pd Br Br H H H H 9 N N Pd X X N N trans-12 ( X = Br ); trans-13 (X = I) N N N N Pd O 2 CCF 3 O 2 CCF 3 cis-14 N N Pt DMSO Br Br N N N N Pt Br Br cis-15