Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System

Abstract

The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy (a), (t-Bu)SCH2Si(CH3)2N(H)Si(CH3)2CH2S(t-Bu) (b), and PhSCH2Si(CH3)2N(H)Si(CH3)2CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl3(THF)3 to afford the corresponding monomeric [CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]CrCl3 (1a) or dimeric {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]CrCl(μ-Cl)}2 (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3)2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl)Al(CH2CH3)2Cl}2 (3a). To deprotonate the N–H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH2Si(CH3)2NSi(CH3)2CH2SCy]Cr(μ-Cl)}2 (4a) and {[(t-Bu)SCH2Si...