Bridged boratabenzene zirconium complexes: Analogues of the ansa-zirconocene polymerization catalysts

Ethylene-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (5a), dimethylsilyl-bridged bis(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (7a), and dimethylmethylene-bridged (cyclopentadienyl)(N,N-diisopropyl-1-aminoboratabenzene-4-yl)zirconium dichloride (6a) have been prepared. X-ray crystal structures of the dimethyl derivatives of 5 and 7 show that the complexes closely resemble the corresponding ansa-zirconocenes. When activated by excess methylaluminoxane, 5a, ga, and 7a are catalysts for the polymerization of olefins.