Synthesis, Structural Characterization, And Properties Of Organometallics Complexes Supported By Functionalised N-Heterocyclic Carbene Ligands

Transition metal complexes of phosphine ligands have been widely employed in synthetic organic chemistry and homogeneous catalysis. Phosphines are normally not easily available, air-sensitive and quite expensive. The development of catalyst systems with non-phosphine ligands is of practical interest and thus has been receiving great attention. N-heterocyclic carbenes (NHCs) as strongσ-donating ligands can form stable complexes with various transition metals. Besides, N-heterocyclic carbenes ligands are nontoxic and cheap, which can stable zero-valent metal in the coupling reactions. Therefore, NHCs are excellent alternative of phosphines ligands and are showing broad application in the C-C and C-N coupling reactions in many organic transformations.Firstly we described several imidazolium salts with pyridazine functionality, the precursors of NHC ligands. Treatment of the imidazolium salt with Pd(OAc)₂ or through metal transfer reactions yielded two quite unusual palladacylic complexes. These complexes have been characterized by NMR spectroscopy, elemental analyses and XRD. The two palladacyclic complexes show excellent catalytic activities in Heck-Mizoroki and Suzuki coupling reactions of activated aryl bromides.Then we reported the synthesis of a few imidazolium salts with pyrimidine functionality as precursors of N-heterocyclic carbene ligands, Treatment of the imidazolium salts with Ag₂O gave mono- and disilver complexes of NHCs. The corresonding palladium complexes containing pyrimidine functionalized NHCs were obtained. These complexes have been characterized by NMR spectroscopy, elemental analyses and X-ray diffraction analysis. An unusual pentacoordinated palladium complex was obtained. The palladium complexes of pyrimidine functionalized NHCs exhibit excellent catalytic activities in the Heck coupling reactions of aryl bromides and activated aryl chlorides under mild conditions.Finally we have synthesized some N-heterocyclic carbene ligands with naphthyridine functionality. Treating three of them with Ag₂O we obtained two normal and one abnormal Ag(I) N-heterocyclic carbene complexes N-heterocyclic carbene complexe. These complexes have been characterized by NMR spectroscopy, elemental analyses and X-ray diffraction analysis. The emissive properties in the solid states were also studied.