Synthesis And Characterization Of Transition Metal Complexes Of N-heterocyclic Carbenes

The development of environmentally friendly, air-stable, and highly efficient metal catalysts is of practical importance in organic chemistry. N-heterocylic carbenes (NHCs) have become a very important class of ligands in organometallic chemistry and catalysis due to their excellent σ-donor properties, ease of synthesis, and variable steric bulk. Recently, the transition metal complexes of N-heterocyclic carbenes have been widely employed in a number of important organic transformation processes. We focus on the design, synthesis and characterization of novel metal complexes supported by functionalized N-heterocyclic carbene ligands. This dissertation mainly includes three parts:(1) The platinum(Ⅱ) complexes of multidentate N-heterocyclic carbenes,[Pt(L1)2Cl](PF6)(2.1, L1=N-methyl-N（2-pyrimidinyl)imidazolylidene),[Pt(L2)Cl](PF6)(2.2, L2=N-butyl-N-(1,10-phenanthrolin-2-yl)imidazolylidene),[PtL3](PF6)2(2.3, L3=bis(N-picolylimidazolylidenyl)methane),[PtL4](PF6)2(2.4, L4=(bis(N-2-pyrimidylimidazolylidenyl)methane)),[Pt(L5)2](PF6)2(2.5, L5bis(N-pyridylimidazoliumyl)methane),[PtAg2(L5)2](PF6)4(2.6),[PtAg2(L4)2](PF6)4(2.7) have been synthesized and fully characterized by NMR, elemental analysis and X-ray diffraction analysis. A catalytic study shows that complexes2.1-2.5are efficient catalyst precursors for hydrosilylation of alkynes. Complexes2.2and2.4are much more active than complexes2.1,2.3and2.5. Novel heteronuclear platinum/silver complexes2.6and2.7were synthesized, and linked by the Ag-Pt bond, forming a linear structure.(2) A series of mononuclear ruthenium carbene complexes, containing pyrimidine or naphthyridine-functionalized have been synthesized and structurally characterized. All of the complexes contain one ruthenium atom, one NHC ligands, one p-cymene and one chlorine atom forming a classic octagonal coordination sphere.(3) A palladium-catalyzed Heck diarylation of terminal olefins under ligand-free conditions in acetic acid is described. This procedure allows double arylation of terminal olefins affording trisubstituted olefins in good to excellent yields. The methodology is applicable to the coupling of both electron-deficient and electron-rich aryl iodides leading to symmetrical and unsymmetrical β,β-diarylated alkenes.