Abstracts Category : Other

N-Heterocyclic Carbene- and Antimony Pincer-Transition Metal Complexes: Their Synthesis and Catalytic Activity

by Brant Landers

Ph.D. University of Hawaii at Manoa 2015. Commercially available (N-heterocyclic carbene)-Pd ((NHC)-Pd) pre-catalysts were used for the anaerobic oxidation of secondary alcohols employing chloroarenes as the oxidizing agent. The precatalyst (SIPr)Pd(cinnamyl)Cl (SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene) gave the best results showing drastic reductions in the reaction time and catalyst loading when compared to the counterpart bearing the analog unsaturated ligand. The catalytic system is compatible with the use of microwave dielectric heating, utilizing (IMes)Pd(allyl)Cl (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) as the pre-catalyst, where catalyst loading and reaction times can be decreased even further. Secondly, the use of microwave heating for the synthesis of a series of (NHC)Ni(Cp)Cl (Cp = Cyclopentadiene) complexes is presented. This protocol allows for a decrease in reaction time required using conventional heating, while affording comparable or better yields of the complexes bearing NHC ligands. Their application as pre-catalysts in the microwave-assisted anaerobic oxidation of secondary alcohols is also described. In addition, microwave heating is applied for the synthesis of NHC-bearing complexes of CuCl, AgCl, and AuCl. The use of microwave conditions allows for a reduction of the reaction times when compared to conventional heating, while still providing suitable yields of the desired (NHC)-metal-chloride complexes.Lastly, the synthesis of antimony ligands and their iridium(III) complexes is described. Two variations of bis-stibine ligands were prepared from either resorcinol or m-xylene and trichlorostibine. While the resorcinol variation, SbOCOSbtBu = 1,3-bis((ditert-butylstibino)-oxy)benzene, reacted with [Ir(COE)2Cl]2 to form a hydrido chloride complex, the resulting complex was coordinatively saturated with three stibine ligands. The bis-stibine ligand with the carbon backbone, SbCSbtBu = 1,3-bis((ditertbutylstibino)methyl)benzene, did not generated any hydrido chloride Ir(III) complex when reacted with [Ir(COE)2Cl]2; however, unidentified insoluble orange solids formed. The SbCSbtBu ligand coordinated with [Cp*IrCl2]2 to afford the piano stool dimer [(Cp*IrCl2)2--SbCSbtBu]. No activity was observed for the hydrido chloride complex bearing the antimony pincer ligand when tested in the transfer dehydrogenation of cyclooctane employing tert-butyl ethene as the acceptor molecule.