Stereochemical Consequences of Oxygen Atom Transfer and Electron Transfer in Imido/Oxido Molybdenum(IV, V, VI) Complexes with Two Unsymmetric Bidentate Ligands

Two equivalents of the unsymmetrical Schiff base ligand (L-tBu)- (4-tert-butyl phenyl(pyrrolato-2-ylmethylene)amine) and MoCl2(NtBu)O(dme) (dme = 1,2-dimethoxyethane) gave a single stereoisomer of a mixed imido/oxido Mo-VI complex 2(tBu). The stereochemistry of 2(tBu) was elucidated using X-ray diffraction, NMR spectroscopy, and DFT calculations. The complex is active in an oxygen atom transfer (OAT) reaction to trimethyl phosphane. The putative intermediate five-coordinate Mo-IV imido complex coordinates a PMe3 ligand, giving the six-coordinate imido phosphane Mo-IV complex 5(tBu). The stereochemistry of 5(tBu) is different from that of 2(tBu) as shown by NMR spectroscopy, DFT calculations, and X-ray diffraction. Single-electron oxidation of 5(tBu) with ferrocenium hexafluorophosphate gave the stable cationic imido phosphane Mo-V complex [5(tBu)](+) as the PF6- salt. EPR spectra of [5(tBu)] (PF6) confirmed the presence of PMe3 in the coordination sphere. Single-crystal X-ray diffraction analysis of [5(tBu)](PF6) revealed that electron transfer occurred under retention of the stereochemical configuration. The rate of OAT, the outcome of the electron transfer reaction, and the stabilities of the imido complexes presented here differ dramatically from those of analogous oxido complexes.