TEMPERATURE AND SOLVENT DEPENDENCE OF SCALAR COUPLING-CONSTANTS IN SALTS OF TRANS-HFE(CO)3PR3-
Additional Document Info
Salts of [trans-HFe[Fe(CO)3PR3]~ (PR3=T(OMe)3, P(OEt)3, PPh3, and PEt3) are observ d to give variable NMR parameters depending on temperature and solvent, of all the NMR parameters, the changes in phosphorus to hydride coupling constants are most dramatic. For example, [bis(tripnenylphosphine)iminium+] [HFe(CO)3P(OEt)3_] showed a 20-Hz change and sign inversion in Jphin tetrahydrofuran over a temperature range of +50 to -70 C. Both variable-temperature infrared spectroscopy and molecular orbital calculations have been conducted to explore the cause of such extraordinary behavior. The infrared data best fit a mechanism of changing H-Fe-CO angle enforced by a solvent stabilization of an internal dipole moment in the anion. Unlike the above compounds, anionic metal hydrides with phosphorus donor ligands positioned cis to the hydride ligand showed little dependence of temperature and solvent on scalar coupling constants. 1987, American Chemical Society. All rights reserved.