Design, Synthesis And Characterization Of Functionalized Metal N-Heterocyclic Carbene Complexes And Their Usage In Organic Synthesis

N-heterocyclic carbenes as a class of non-phosphine ligands and alternative to tertiary phosphines are attracting more and more attention, since N-heterocyclic carbene ligands exhibit unique advantages, i.e. their strongerσ-donating characters facilitate oxidative addition of substrates to metals; the strong metal-carbenic bond disfavors ligand dissociation; the presence of sterically encumbering groups bound to the N-atoms favors reductive elimination of the product from metals. Hence the transition metal complexes of N-heterocyclic carbenes have been widely employed in a number of important organic transformation processes.My Ph.D thesis mainly focuses on design, synthesis and characterization of novel metal complexes supported by functionalized N-heterocyclic carbene ligands and the usage of these complexes as excellent catalysts in organic synthesis, which mainly includes four parts:(1) Described the synthesis and structural characterization of a new naphthyridine functionalized (bis)NHC complex of palladium(II) which exhibits a helical structure and has proven a highly efficient catalyst for Heck coupling reactions of aryl bromides with n-butyl acrylate. The TON up to 106 and TOF up to 5 x 105 h"1 can be achieved. This Pd-NHC catalyst has good tolerance towards moisture, however, the influence of air cannot be neglected.(2) A series of novel four-, five-, and six-coordinate Palladium and Nickel complexes containing naphthyridine and pyrimidine functionalized N-heterocyclic carbene ligands were synthesized and structurally characterized and their catalytic behavior in homogeneous coupling reactions were comprehensively studied. This is a unique example that the coordination numbers get higher when the ligands become bulkier, the structural diversity of these Ni(II), Pd(II)-NHC complexes originated from steric pressure of ligands are discussed. Suzuki and Hiyama coupling reactions of a wide range of aryl bromides and chlorides have been comparatively investigated by using tetracoordinate moncarbene, tetracoordinate dicarbene, and pentacoordinate dicarbene palladium complexes as catalysts. The tetracoordinate moncarbene palladium complex showed the highest catalytic activity for both coupling reactions.(3) Developed facile and convenient one-pot sequential and one-flask approaches to prepare unsymmetrically substituted arenes and heteroarenes from commercially available aryl dihalides by using well defined or in-suit generated palladium NHC complexes as catalysts. Heck/Suzuki, Heck/Heck and Heck/Sonogashira sequences double coupling reactions of vrious olefins, substituted arylboronic acids and alkynes proceed smoothly under mild conditions to provide desired products in good to excellent yields. The isolated intermediate poducts bearing additional chlorides after completing two-step coupling reactions could continue reaction with substituted arylboronic acids to prepare unsymmetrical terphenyls.(4) A series of multinuclear, macrocyclic silver and gold complexes including trinuclear silver cluster, one-dimensional Ag-NHC coordination polymer and 18-membered macrocyclic complex supported by pyridine-functionalized benzimidazolylidene ligands were synthesized and structurally characterized. The macrocyclic cations are aligned one above another to form channels filled with hexafluorophosphate anions through Ag…F and H…F interactions and this is the first example of receptor and guest channel complex supported by NHC ligands. Their luminescence behaviour in CH3CN solution was also studied.