Abstract
The highly efficient method has been developed for the synthesis of NHC·VOCl3 containing symmetrical or unsymmetrical N-heterocyclic carbene(NHC)ligands by the transmetallation reaction of NHC·AgCl with VOCl3.The total isolated yield of VOCl3[1,3-(2,4,6-Me3C6H2)2(NCH=)2C:](V4')reached 86％by transmetallation reaction,which is much higher than that(48％)by direct coordination method.This methodology has also been used to synthesize the novel vanadium complexes containing unsymmetrical NHC ligands of VOCl3[PhCH2NCH=CHNR)C:](V5',R=2,4,6-Me3C6H2;V6',R=2,4-Me2-6-Ph-C6H2;V7',R=2,6-iPr2-C6H3)with high yield,which could not be obtained by direct coordination method.The catalytic activity and copolymerization ability would be improved by introducing unsymmetrical NHC ligands due to their less steric bulky effect.The vanadium complex V5'containing unsymmetrical NHC ligand exhibits higher catalytic activity(3.7×105 gcopolymer·mol-1 of V·h-1)than that of V4'containing symmetrical NHC ligand.Moreover,the higher propylene incorporation ratio(45.6 mol％)in the copolymers of ethylene with propylene could be obtained by using V5'than that(39.9％)by using V4'.The results would provide a highly efficient strategy for the synthesis of early transition metal complexes containing versitile NHC ligands,affording the catalyst with both high catalytic activity and copolymerization ability for the synthesis of high performance polyolefin elastomers.
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