Half-sandwich dibenzyl complexes of scandium: Synthesis, structure, and styrene polymerization activity

Abstract

Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C 5Me 4H)SiMe 2R (R = Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph) 2(THF)] and [Sc(η 5-C 5Me 4SiMe 2Ph)(CH 2Ph) 2(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η 5-C 5Me 4SiMe 2R)(CH 2SiMe 3) 2(THF)]. The four-coordinate complexes display η 1-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph) 2(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η 5-C 5Me 4SiMe 3)(CH 2Ph)(THF) x ][BPh 3(CH 2Ph)]. Benzyl cation formed using [Ph 3C][B(C 6F 5) 4] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.