Coordination chemistry of a mixed donor bidentate ligand with nickel. A tetrameric enolate of sodium that binds a phosphine donor

Abstract

The preparation of a mixed donor ligand consisting of an enolate and neutral phosphine is described and its coordination chemistry with nickel reported. The phosphino ketones R2PCH2COPh (R = Cy or Pri) are prepared by the reaction of the corresponding secondary phosphines with bromoacetophenone to form the corresponding phosphonium salts [R2P(H)CH2COPh]+Br− (R = Cy or Pri); subsequent deprotonation leads to the neutral ketones. The enolates are formed by addition of NaN(SiMe3)2 to the neutral ketone. The crystal structure of the sodium enolate having isopropyl substituents at phosphorus displays a tetrameric structure in the solid state and there is an interaction of the phosphorus donor with the sodium anion: Na—P, 2.852(2) Å. The preparation of a series of nickel complexes was achieved by addition of the sodium enolate to the appropriate Ni(II) starting material. The structures of the nickel derivatives are reported. The catalytic behaviour of one of these complexes in the polymerization and oligomerization of ethylene is briefly described. Crystals of {Na[Pri2PC(H)=C(O)Ph]}4, 2b, are tetragonal, a = b = 20.790(2) Å, c = 13.539(7) Å, Z = 4, space group I41/a1; those of [Cy2PC(H)=C(O)Ph](PPh3)NiPh, 3a, are triclinic, a = 10.742(2) Å, b = 19.811(3) Å, c = 10.621(2) Å, α = 101.88(1)°, β = 119.24(1)°, γ = 91.08(1)°, Z = 2, space group [Formula: see text] and those of [Pri2PC(H)=C(O)Ph](PPh3)NiPh, 3b, are triclinic, a = 10.219(1) Å, b = 17.432(3) Å, c = 9.788(1) Å, α = 101.18(1)°, β = 100.19(1)°, γ = 85.32(1)°, Z = 2, space group [Formula: see text] The structures were solved by direct (2b) and Patterson (3a and 3b) methods and were refined by full-matrix least-squares procedures to R = 0.045, 0.044, and 0.032 (Rw = 0.038, 0.041, and 0.030) for 965, 4483, and 5085 reflections with I > 3σ(I) respectively. Keywords: nickel, sodium enolate, homogeneous catalyst, oligomerization.