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

Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C5Me4H)SiMe2R (R = Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η5-C5Me4SiMe3)(CH2Ph)2(THF)] and [Sc(η5-C5Me4SiMe2Ph)(CH2Ph)2(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η5-C5Me4SiMe2R)(CH2SiMe3)2(THF)]. The four-coordinate complexes display η1-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η5-C5Me4SiMe3)(CH2Ph)2(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η5-C5Me4SiMe3)(CH2Ph)(THF)x][BPh3(CH2Ph)]. Benzyl cation formed using [Ph3C][B(C6F5)4] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.