SPECTROSCOPIC AND CHEMICAL STUDIES OF NICKEL(II) HYDRIDES
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The trans influence of X ligands on the spectroscopic properties of the Ni-H bond is reported for the series of square-planar nickel hydrides trans-HNi(X)(PCy3)2(X = Me, Ph, CN, SCN, I, Br, Cl, SPh, S(p-tol), SH, OAc, O2CH, O2CPh, O2CCF3, OPh) prepared by oxidative addition of HX to [Ni(PCy3)2]2N2or derivatives of subsequent products. The infrared-derived parameter v(Ni-H) shows a similar ligand dependence as the proton chemical shift of the hydride ligand, with more covalently bound ligands such as methyl or phenyl producing lower v(Ni-H) and smaller upfield chemical shifts as compared to those ligands that bind to Ni(II) with more electrostatic character such as anionic O-donor ligands. Comparisons with other ligand influenced, spectroscopic scales are made. Carbon dioxide and iodomethane were used as chemical probes of reactivity at the Ni-X or Ni-H bond. The derivatives with stronger Ni-H bonds (S and O donors) show no reactivity at the hydride while the C-bond derivatives exhibit CO2insertion at the hydride. The Ni-H functionality is active toward iodomethane in the C-donor derivatives. A mechanism of hydrogen atom abstraction by methyl radicals is consistent with literature precedents as well as the Ni-H bond strengths determined by spectroscopies. 1989, American Chemical Society. All rights reserved.