| Abstract
| - The reaction of the highly selective [CySCH2CH2N(H)CH2CH2SCy]CrCl3 catalyst precursor withalkyl aluminum activators was examined with the aim of isolating reactive intermediates. Reaction withMe3Al afforded a cationic trivalent chromium alkyl species {[CySCH2CH2N(H)CH2CH2SCy]CrMe(μ-Cl)}2{(AlMe3)2(m-Cl}2·(C7H8)2 (1a). Although it was not possible to obtain crystalline samples of sufficient qualityfrom the reaction with MAO (the most preferred activator), the near-to-identical EPR spectra indicated avery close structural similarity with 1a. Ethylene oligomerization tests clearly revealed that 1 and othercationic trivalent dimeric complexes {[CySCH2CH2N(H)CH2CH2SCy] CrCl(μ-Cl)}2{AlCl4}2·(C7H8)1.5 (2),monomeric [(CySCH2CH2N(H)CH2CH2SCy)CrCl2 (THF)][AlCl4] (3), and {[CySCH2CH2N(H)CH2CH2SCy]Cr(η2-AlCl4)}{Al2Cl7} (4) adducts display the same catalyst selectivity as the [CySCH2CH2N(H)CH2CH2SCy]CrCl3 complex and, therefore, are probably all precursors to the same catalytically active species. 2,3, and 4 were obtained upon treatment of [CySCH2CH2N(H)CH2CH2SCy] CrCl3 with different stoichiometricratios of AlCl3.. When i-BAO activator was used, reduction of the metal center occurred readily, affording{([CySCH2CH2N(H)CH2CH2S Cy]Cr)(μ-Cl)]2}{(i-Bu)2AlCl2}2 (5). 5 is also a selective catalyst, thus indicatingthat trivalent species are most probably precursors to a divalent catalytically active complex. Reaction ofCrCl2(THF)2 with the ligand afforded the labile divalent adduct [CySCH2CH2N(H)CH2CH2SCy]CrCl2(THF)(6), also catalytically active and selective. Instead, deprotonation of the ligand with n-BuLi followed byreaction with CrCl2(THF)2 gave the dinuclear complex [(μ-CySCH2CH2NCH2CH2SCy)CrCl]2 (7), which didnot produce oligomers.
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