Sterically hindered iminophosphorane complexes of vanadium, iron, cobalt and nickel: a synthetic, structural and catalytic study

Bis(aryliminophosphoranyl)alkanes L-1=(CH2)(n)((R2P)-P-1=NR2)(2) (n=1 or 2, R-1=Ph or Me, R-2=Ph, C6H2Me3-2,4,6 or C6H3Pr2i-2,6) reacted with cobalt a nd nickel dihalides to give chelate complexes of the type MX2(L-1). The rea ction of Li[HC(Ph2P=NR2)(2)] with MX2 afforded the compounds MX{HC(Ph2P=NR2 )(2)} (M=Co, X=Cl; M=Ni, X=Br). The crystal and molecular structures of CoC l2{CH2(Ph2P=NPh)(2)} and NiBr{HC(Ph2P=NC6H3Pr2i)(2)} were determined. While the former has the expected tetrahedral structure, the latter is square pl anar. Ab initio calculations on the latter show that the bonding of the bis (iminophosphoranyl)methanide ligand to nickel involves pi delocalisation ov er the N2P2C framework as well as sigma bonding between nickel and the P2CH carbon atom. Bis(iminophosphoranyl)pyridines C5H3N(R2P=NR')(2)-2,6 (R=Ph o r cyclohexyl, R'=C6H2Me3-2,4,6, C6H3Pr2i-2,6 or SiMe3) reacted with VCl3(th f)(3), FeX2 (X=Cl or Br) or CoCl2 to give the corresponding octahedral (V) or five-co-ordinate (Fe, Co) complexes. The crystal structure of FeBr2{C5H3 N(Ph2P=NSiMe3)(2)-2,6} has been determined; the complex is trigonal bipyram idal. In the presence of methylaluminoxane [MeAlO](n), cobalt complexes of bis(aryliminophosphoranyl)methane are moderately active in ethene polymeris ation, while bis(iminophosphoranyl)pyridine iron complexes show only low ac tivity. The vanadium complexes polymerise ethene under ambient conditions a nd give polymers of very high molecular weight.