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

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Abstract
Bis(aryliminophosphoranyl)alkanes L1 = (CH2)n(R1 2PNR2)2 (n = 1 or 2, R1 = Ph or Me, R2 = Ph, C6H2Me3-2,4,6 or C6H3Pri 2-2,6) reacted with cobalt and nickel dihalides to give chelate complexes of the type MX2(L1). The reaction of Li[HC(Ph2PNR2)2] with MX2 afforded the compounds MX{HC(Ph2PNR2)2} (M = Co, X = Cl; M = Ni, X = Br). The crystal and molecular structures of CoCl2{CH2(Ph2PNPh)2} and NiBr{HC(Ph2P NC6H3Pri 2)2} were determined. While the former has the expected tetrahedral structure, the latter is square planar. Ab initio calculations on the latter show that the bonding of the bis(iminophosphoranyl)methanide ligand to nickel involves π delocalisation over the N2P2C framework as well as σ bonding between nickel and the P2CH carbon atom. Bis(iminophosphoranyl)pyridines C5H3N(R2PNR′)2-2,6 (R = Ph or cyclohexyl, R′ = C6H2Me3-2,4,6, C6H3Pri 2-2,6 or SiMe3) reacted with VCl3(thf)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{C5H3N(Ph2PNSiMe3)2-2,6} has been determined; the complex is trigonal bipyramidal. In the presence of methylaluminoxane [MeAlO]n, cobalt complexes of bis(aryliminophosphoranyl)methane are moderately active in ethene polymerisation, while bis(iminophosphoranyl)pyridine iron complexes show only low activity. The vanadium complexes polymerise ethene under ambient conditions and give polymers of very high molecular weight.
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