Deactivation Pathways of Ethylene Polymerization Catalysts Derived from Titanium and Zirconium 1,3-bis(furyl)-1,1,3,3-tetramethyldisilazide Complexes

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 35 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.