Scandium and Yttrium Complexes Supported by NNCp Heteroscorpionate Ligands: Synthesis, Structure, and Polymerization of ϵ-Caprolactone

Abstract

Mixtures of two scorpionate/cyclopentadiene regioisomersbpzcpH (1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (1a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (1b)) and bpztcpH (1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadiene (2a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadiene (2b))were prepared by deprotonation of bis(3,5-dimethylpyrazol-1-yl)methane with BunLi followed by reaction with 6,6-diphenylfulvene or 6-tert-butylfulvene and subsequent treatment with saturated aqueous ammonium chloride. Reactions of hybrid scorpionate/cyclopentadiene compounds with [M(CH2SiMe3)3(THF)3] (M = Sc, Y) afford the dialkyl complexes [M(CH2SiMe3)2(bpzcp)] (M = Sc (3), Y (4)) and [M(CH2SiMe3)2(bpztcp)] (M = Sc (5), Y (6)). The cationic alkyl complexes [M(CH2SiMe3)(bpzcp)]+ (M = Sc (7), Y (8)) were also prepared by the reaction of complexes 3 and 4 with [CPh3][B(C6F5)4] in THF. The structures of these compounds were determined by spectroscopic methods, and the X-ray crystal structures of 2 and 3 were also established. The bis(alkyl) complexes 3 and 4 were found to be active initiators for the ring-opening polymerization of ϵ-caprolactone (up to 75% conversion of 200 equiv in 10 min) and yielded polymers with narrow molecular weight distributions