Isolation of a new series of η2-olefin complexes of tungsten(IV) containing cyclometallated 2,6-diphenylphenoxide ligation

Article abstract of DOI:10.1016/0277-5387(95)00497-1

Addition of ethylene to solutions of the bis(cyclometallated) compounds [W(OC₆H₃Ph-C₆H₄)₂(L) ₂] (1, L = PMe₂Ph; 2, L = PMePh₂; OC₆H₃Ph - C₆H₄ = cyclometallated 2,6-diphenylphenoxide) produces the η²-ethylene complexes [W(OC₆H₃Ph - C₆ H₄)₂(L) η²-C₂H₄)] (3, L = PMe₂Ph; 4a, L = PMePh₂). Addition of α-olefins, RCH = CH₂ (R = Ph, SiMe₃, CF₃) to solutions of 2 produced an equilibrium mixture of 2, free PMePh₂ and the corresponding η²-olefin complexes [W(OC₆H₃PhH - C₆H₄)₂ (PMePh₂) (η²-RCH=CH₂)] (4b, R = Ph; 4c, R = SiMe₃; 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) A are longer than the W - C(phenyl) distances of 2.162(7) and 2.127(8) A. This, combined with an olefin C - C distance of 1.39(1) A, shows a lack of strong π-backbonding from the tungsten metal centre. In solution, however, restricted rotation about the tungsten - ethylene bond in 3a is observed in the ¹H NMR spectrum. The bonding of the olefin ligands in these complexes is discussed. Copyright