688736-35-8Relevant academic research and scientific papers
Ethylene oligomerization promoted by a silylated-SNS chromium system
Albahily, Khalid,Gambarotta, Sandro,Duchateau, Robbert
experimental part, p. 4655 - 4664 (2011/11/07)
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(CH 3)2CH2SCy (a), (t-Bu)SCH2Si(CH 3)2N(H)Si(CH3)2CH2S(t-Bu) (b), and PhSCH2Si(CH3)2N(H)Si(CH 3)2CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl 3(THF)3 to afford the corresponding monomeric [CySCH 2Si(CH3)2N(H)Si(CH3) 2CH2SCy]CrCl3 (1a) or dimeric {[CySCH 2Si(CH3)2NSi(CH3)2CH 2SCy]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 {[CySCH 2Si(CH3)2NSi(CH3)2CH 2SCy]Cr(μ-Cl)}2 (4a) and {[(t-Bu)SCH 2Si(CH3)2NSi(CH3)2CH 2S(t-Bu)]Cr(μ-Cl)}2 (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe 3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)2N(H)Si(CH3) 2CH2SCy]Cr{(μ-Cl)AlCl3}2 (5a) and {[PhSCH2Si(CH3)2N(H)Si(CH3) 2CH2SPh]C{(μ-Cl)AlCl3}2 (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH 2Si(CH3)2N(Al(CH3) 2-μ-Cl)Si(CH3)2CH2SCy]Cr{(μ- Cl)Al(CH3)3} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)2N(CH 3)Si(CH3)2CH2SCy]Cr(μ-Cl)} 2{(Al(CH3)2Cl)2)(μ-Cl)} 2 (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers.
