Catalytic and Stoichiometric Reactions by Half-metallocene Diene Complexes of Niobium and Tantalum

摘要

We have systematically prepared ethylene,benzyne,and alkylidene complexes of niobium and tantalum bearing the fragments of 'MCp(eta~4-l,3-diene)' (M=Nb and Ta),and we found that these complexes have the similar stereochemistry and reactivity to that observed for the corresponding metallocene complexes of Group 4 metals,indicating clearly that the fragments of half-metallocene diene were isoelectronic and isolobal to those of 'MCp_2' (M=Zr and Hf).According to these results,we found three kinds of polymerization of ethylene,norbornene,and methyl methacrylate by using half-metallocene complexes of niobium and tantalum.Mono(diene) complexes 2 and 14 and bis(diene) complexes 16 and 17 upon being activated by MAO catalyzed the living polymerization of ethylene.Di(benzyl) tantalum complexes 18 and 23 served as a unique stereoselective polymerization of norbornene.The half-metallocene tantalum complexes 42 bearing MMA and DAD ligands reacted with one equiv of AlMe_3 at -20degC to give a zwitter inonic hetero-bimetallic enolate species 43,which catalyzed the living polymerization of MMA.