Synthesis, characterization, and biomimetic chemistry of cis-oxosulfidomolybdenum(VI) complexes stabilized by an intramolecular Mo(O)=S...S interaction.

The reactions of jade-green TpMoIVO(S2PR2) [Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate; R = Et, Pri, Ph] with propylene sulfide produce ochre-red TpMoVIOS{SP(S)R2}. The complexes have been characterized by microanalysis, mass spectrometry, cyclic voltammetry, spectroscopy (IR, NMR, UV-vis, and X-ray absorption), and X-ray crystallography. The distorted-octahedral isopropyl and phenyl derivatives feature a tridentate fac-Tp ligand, a terminal oxo ligand, and a unique five-membered Mo(=S){SP(=S)R2 ring moiety formed by a weak, intramolecular, bonding interaction between the Mo=S1 and (uncoordinated) S3=P moieties. The Mo=S1 [2.227(2) A (R = Pri) and 2.200(2) A (R = Ph)] and S1...S3 distances [2.396(3) A (R = Pri) and 2.383(2) A (R = Ph)] are indicative of a pi-bonded Mo=S1 unit and a weak (bond order ca. 1/3) S1...S3 interaction; the solid-state structures are maintained in solution according to S K-edge X-ray absorption data. The complexes react with excess cyanide to form thiocyanate and TpMoO(S2PR2), under anaerobic conditions, or TpMoO2(S2PR2), under aerobic conditions; the latter models the production of thiocyanate and desulfo molybdenum hydroxylases upon cyanolysis of molybdenum hydroxylases. The complexes react with triphenylphosphine to give TpMoO(S2PR2) and SPPh3, with cobaltocene or hydrosulfide ion to produce [TpMoVOS(S2PR2)]-, and with ferrocenium salts to yield [Tp*MoVO(S3PR2)]+; in the last two reactions, Mo(V) is produced by direct or induced internal redox reactions, respectively. The presence of the Mo(O)=S...S interaction does not radically lengthen the Mo=S bond in the complexes or preclude them from reactions typical of unperturbed oxosulfidomolybdenum(VI) complexes.