REACTION OF NICKEL(0) WITH ALPHA-KETO PHOSPHONATES - SYNTHESES, CHARACTERIZATION, AND X-RAY CRYSTAL-STRUCTURE OF (PPH3)2NI(ETA-2-(CO)RC(O)P(O)(OME)2)

Reaction of Ni(l,5-cyclooctadiene)2 with a-keto phosphonates in the presence of PPh3 affords (PPh3)2Ni(7,2-(CO)RC(0)P(0)(OMe)2) (R = phenyl, 1; p-tolyl, 2; p-chlorophenyl, 3; methyl, 4; ethyl, 5), characterized by IR,XH NMR, and31P NMR spectra. The single-crystal X-ray diffraction of 5 [monoclinic, Ρ2ι/η, α = 9.640 (3), b = 18.910 (8), c = 20.821 (8) Â, β = 90.03 (3)°, V = 3796 (2) Â3, Z = 4, Äx = 0.049] has revealed that ethyl keto phosphonates coordinate to the Ni(PPh3)2 moiety in an ??2-CO mode, making the Ni geometry square planar. These complexes undergo exchange reaction of a-keto phosphonate ligand in solution. Judging from the ^-coordination ability of a-keto phosphonates toward Ni(0), a P(0)(OMe)2group has been estimated to be electronegative by as much as a CF3 group. © 1990, American Chemical Society. All rights reserved.