Synthesis and structure of zirconium(IV) alkyl complexes with bi-, tri-, tetra- and penta-dentate amido ligands

The reaction of C6H10(NLiSiMe3)(2)-1,2(Li2L1) with [ZrCl4(thf)(2)] (thf = tetrahydrofuran) afforded the tetraamide [ZrL21] 1. Similarly treatment of (RHNSiMe2)(2)O (H2L2, R = Bu; H2L3, R = cyclohexyl) with LiBun followed by [ZrCl4(thf)(2)] led to [ZrL22] 2 and [ZrL23] 3, respectively, Reaction of Zr(CH2Ph)(4) with H2L3 gave the pale yellow zirconium dibenzyl compound [Zr(CH2Ph)(2)L-3] 4, while the analogous reaction with H2L4 (R = quinolin-8-yl) led to ruby-red [Zr(CH2Ph)(2)L-4] 5, In addition the bis(pyrrole) [(2-C4H3NH)CH=NCH2](2) (H2L5) reacted with Zr(CH2Ph)(4) giving the complex [Zr(CH2Ph)(2)L-5] 6. The crystal structures of 1, 4 and 5 have been determined. Compound 1 has a distorted tetrahedral structure. In 4 and 5 all available donor atoms co-ordinate to zirconium, including the silyl ether moiety, leading to a distorted trigonal bipyramidal structure for 4 and an approximately pentagonal bipyramidal geometry for 5, Although L-3 and L-4 have flexible frameworks, in both 4 and 5 the heteroatom donors and the metal form an essentially coplanar arrangement. The zirconium-amido nitrogen distances proved to be highly variable, depending on the degree of electron deficiency and the co-ordination of the metal centres, and range from an average of 2.056 Angstrom in 1 and 2.096 Angstrom in 4 to 2.169 Angstrom in 5. Complexes 1 and 4 activated with methylaluminoxane gave high molecular weight polyethylene with moderate activity.