Novel zirconacyclopentadiene complex; 8,8-bis(cyclopentadienyl)-7,9-bis(trimethylstannyl)-8-zirconabicyclo-[4.3.0]nona-1(9),6(7)-diene: Synthesis, X-ray analysis, and catalytic activity for ethylene polymerization

Zirconacyclopentadiene complex 2c containing gem-dimetallated carbon atoms by zirconium and tin was prepared by the oxidative coupling reaction of 'Cp₂Zr' with distannyldiyne compounds. Complex 2c having trimethylstannyl groups was characterized by X-ray diffraction and its structure was compared with zirconacyclopentadiene analogues having tert-butyl groups (2a) or trimethylsilyl groups (3). The five-membered zirconacycle ring of 2c has a planar conformation whereas it is twisted in complexes 2a and 3. The C-Zr-C angle in 2c is smaller than those of the corresponding 2a and 3. The polymerization of ethylene proceeded when these complexes were used in combination with methylaluminoxane and it was found that the catalytic activities of these complexes were remarkably influenced by the substituents on the α-carbon atoms.