Deactivation pathways of ethylene polymerization catalysts derived from titanium and zirconium 1,3-bis(furyl)-1,1,3,3-tetramethyldisilazide complexes

Abstract

The stoichiometric reaction between the previously described lithium amide salts, LiN(SiMe₂R)₂ [Li{i}, R = furyl, Li{ii}, R = 2-methylfuryl] and titanium(IV)chloride at low temperature afforded the mono-amide compounds Ti{i}Cl₃ (1a) and Ti{ii}Cl₃ (1b). The analogous zirconium derivatives Zr{i}Cl₃ (3a) and Zr{ii}Cl₃ (3b) were accessed via the reaction of excess trimethylsilylchloride with the mixed tetra-amide species, Zr{i}(NMe₂)₃ (2a) and Zr{ii}(NMe₂)₃ (2b). The bis-amide complexes Ti{ii}₂Cl₂ (4b), Zr{i}₂Cl₂ (5a) and Zr{ii}₂Cl₂ (5b) were synthesized in a straightforward salt metathesis reaction employing two equivalents of Li{i} or Li{ii} with the metal salts, MCl₄(THF)₂. The reactivity of the halide compounds 1 and 3–5 with a variety of alkylating agents was studied, with ligand transfer from the transition-element to the main group metal-alkyl reagent being the predominant reaction pathway. The reaction of 4b with MeLi was, however, partially successful affording the titanium(III) complex, Ti{ii}₂X (X = Cl/Me, 6b′); this compound was subsequently made as the pure chloride 6b from the reaction of two equivalents of Li{ii} with TiCl₃(THF)₃. The targeted dialkyl species, Ti{ii}Me₂ (7b), was successfully isolated from the reaction between the dichloride 4b and dimethylmagnesium. The molecular structures of 1a, 1b, [3a]₂ [3b]₂, 4b, 5b and 6b have been solved using single-crystal X-ray diffraction techniques, indicating varying nuclearity of the complexes and hapticities for the amide ligands in the solid-state. The catalytic activity of selected complexes in the polymerization of ethylene is reported.