Synthesis And Characterization Of Transition Metal Complexes Supported By Pyrazole-Functionalized N-Heterocyclic Carbenes And Their Applications In C-C Coupling Reactions

Direct metal-metal interactions are important because they are often associated with many potentially useful chemical and physical properties of materials such as catalytic behavior,magnetic,optical,or electronic properties.N-heterocyclic carbenes (NHCs)have come to occupy a central position in the armory of organometallic chemists,but transition metal complexes having short metal-metal interaction supported by N-heterocyclic carbene ligans have been few reported.In this dissertation,a serial of poly-nuclear transition metal complexes supported by pyrazole-Functionalized N-heterocyclic carbenes have been synthesized and characterized.As transfer reagents,some tetranuclear and hexanuclear Ag(â… )-NHC clusters were synthesized.They all have the linear N-Ag-C coordination mode which was firstly reported.The hexanuclear Ag(â… )-NHC clusters consist of a Ag₆ ring displaying chair-like cyclohexane conformation which are the highest nuclear Ag(â… )-NHC clusters.Furthermore,a tetranuclear Au(â… )-NHC was synthesized,which represents the first example of multinuclear gold compound supported by functionalized NHC ligand.They are intensely luminescent on solid states.For comparison,some Ag(â… )and Cu(â… )complexes contain short M-M contacts supported or unsupported by bispyrazole-Functionalized polydentate ligands have also been prepared.Furthermore,a trinuclear Ag(â… )-NHC complex supported by a bispyrazole-Functionalized NHC was synthesized,which stacks via intermolecular Ag-Ï€interaction forming infinite one dimensional chain.Finally,four binuclear Ni(â…¡)-NHC or Pd(â…¡)-NHC complexes were prepared by using the reported silver-NHC clusters as carbene-transfer reagents.The hydroxyl bridged binuclear Ni(â…¡)-NHC complex has close approach of two metals and displays concerted catalytic effect in Suzuki and Kumada coupling reactions.