Density functional studies of 19-electron organometallic complexes:: Investigation of possible ligand distortions and calculation of the EPR parameters and unpaired electron distributions in CpCr(CO)2No-, CpW(NO)2P(OMe)3, CpMo(CO3)P(OMe)3, and Co(CO)3(2,3-bis(diphenylphosphino)maleic anhydride)

Density functional theory (DFT) was used to calculate the equilibrium geometries and EPR hyperfine coupling constants for the CpCr(CO)(2)NO- and CpW(NO)(2)P(OMe)(3) 19-electron complexes. The calculated EPR hyperfine parameters for both molecules were found to be in good agreement with the experimental values. The EPR study on CpCr(CO)(2)NO- indicated that the nitrosyl ligand bends significantly when the neutral 18-electron parent molecule is reduced. This was confirmed by the DFT calculations, although the degree of bending is not as large as that predicted from the EPR analysis. The calculated geometry for CpW(NO)2P(OMe)3 showed that the nitrosyl ligands are not significantly bent, which is consistent with the crystal structure of the related compound CpW(NO)(2)P(OPh)(3). In both CpCr(CO)(2)NO- and CpW(NO)(2)P(OMe)(3), the unpaired electron is localized to about the same extent on the NO ligands. It is concluded that, although distortion of a Ligand implies significant localization of the unpaired electron on that ligand, an undistorted ligand does not imply that the unpaired electron has no appreciable amplitude on that ligand, DFT was also applied to the 19-electron CpMo(CO)(3)P(OMe)(3) molecule, whose role as a key intermediate in photochemical reactions of Cp2Mo2(CO)(6) with P(OMe)(3) has been inferred from mechanistic studies. It was found that loss of P(OMe)(3) from CpMo(CO)(3)P(OMe)(3) is slightly thermodynamically favorable (Delta E = similar to 1 kcal/mol), This is consistent with the necessity of using an excess of the phosphorus ligand in reactions in which CpMo(CO)(3)PR3 is believed to be the electron-transfer agent. There is no indication of P(OMe)3 ligand distortion in this molecule, just as there is no indication of Cp ring slippage in any of the Cp-containing molecules. Finally, a calculation of the hyperfine coupling constants in the 18 + delta Co(CO)(3)L-2 (L-2 = 2,3-bis(diphenylphosphino)-maleic anhydride) complex was also carried out. The calculated values are in reasonable agreement with experiment.