Isolation of a new series of eta(2)-olefin complexes of tungsten(IV) containing cyclometallated 2,6-diphenylphenoxide ligation

Addition of ethylene to solutions of the bis(cyclometallated) compounds [W(OC(6)H(3)Ph-C6H4)(2)(L)(2)] (1, L = PMe(2)Ph; 2, L = PMePh(2); OC(6)H(3)Ph-C6H4 = cyclometallated 2,6-diphenylphenoxide) produces the eta(2)-ethylene complexes [W(OC(6)H(3)Ph-C-6 H-4)(2)(L)(eta(2)-C2H4)] (3, L = PMe(2)Ph; 4a, L = PMePh(2)). Addition of alpha-olefins, RCH=CH2 (R = Ph, SiMe(3), CF3) to solutions of 2 produced an equilibrium mixture of 2, free PMePh(2) and the corresponding eta(2)-olefin complexes [W(OC(6)H(3)PhH-C6H4)(2) (PMePh(2))(eta(2)-RCH=CH2)] (4b, R = Ph; 4c, R = SiMe(3); 4d, R = CF3). The solid state structure of the ethylene complex 3 shows a pseudo-octahedral environment about the tungsten metal centre, with mutually trans aryloxide oxygen atoms and mutually cis metallated phenyl rings. The olefin ligand is aligned co-planar with the W-P bond, i.e. perpendicular to the O-W-O axis. The W-C(olefin) distances of 2.275(8) and 2.229(8) Angstrom are longer than the W-C(phenyl) distances of 2.162(7) and 2.127(8) Angstrom. This, combined with an olefin C-C distance of 1.39(1) Angstrom, shows a lack of strong pi-backbonding from the tungsten metal centre. In solution, however, restricted rotation about the tungsten-ethylene bond in 3a is observed in the H-1 NMR spectrum. The bonding of the olefin ligands in these complexes is discussed. Copyright (C) 1996 Elsevier Science Ltd.