Cationic benzyl nickel complexes as homogeneous catalysts for styrene oligomerization. X-ray crystal structure of [Ni( η3-CH 2C 6H 5)(PPh 3) 2]PF 6 · CH 2CI 2

Abstract

New cationic complexes [Ni( η 3-CH 2C 6H 5)(PPh 3) 2]PF 6 (3) and [Ni( η 3-CH 2C 6H 5)((+)-DIOP)]PF 6 (4) were synthesized from the corresponding neutral compounds [Ni( η 3-CH 2C 6H 5)X(PR 3) 2] (X = Cl, Br), by metathetical halide abstraction with TIPF 6. Complex 3 was characterized by X-ray crystallography and shown to have a distorted square-planar geometry with the benzylic group coordinated in a quasi-allylic fashion. Crystals are monoclinic, space group P2 1/ n, a = 11.798(5), b = 19.251(2), c = 18.561(3) Å, β = 93.03°, V = 4208.6 Å 3. Solution NMR studies showed benzyl fluxionality and phosphine lability in compound 3, but not in 4. The latter one is catalytically inactive towards styrene oligomerization, whereas 3 produces styrene oligomers ( M ¯ n ≈ 1000 ) with 67% isotactic content. Although [Ni( η 3-CH 2C 6H 5)CI(PCy 3)] and trans[Ni(Cl)(H)(PCy 3) 2] are inactive, addition of TlPF 6 induced catalytic activity with formation of highly isotactic (90%) styrene oligomers with similar M ¯ n and a different terminal group.