Models for the Molybdenum Hydroxylases: Synthesis, Characterization and Reactivity of <i>cis</i>-Oxosulfido-Mo(VI) Complexes

Atom transfer reactions have been employed to convert TpiPrMoO2(OAr) into monomeric cis-oxosulfido-Mo(VI) and dimeric μ-disulfido-Mo(V) species, [TpiPrMoOS(OAr)]n (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; OAr = phenolate or naphtholate derivative; n = 1 and 2, respectively). Dark red, monomeric TpiPrMoOS(OAr) complexes contain distorted octahedral cis-oxosulfido-Mo(VI) centers, with d(MoO) = 1.692(5) Å, d(MoS) = 2.132(2) Å, and ∠(OMoS) = 103.68(16)° for the 2-sec-butylphenolate derivative. Dark red-purple, dimeric [TpiPrMoOS(OAr)]2 complexes undergo SS bond cleavage forming monomeric oxosulfido-Mo(VI) species in solution. In the solid state, the 3,5-di-tert-butylphenolate derivative exhibits a centrosymmetric structure, with distorted octahedral anti oxo-Mo(V) centers bridged by a disulfido-κS,κS‘ ligand. Hydrolysis of the oxosulfido-Mo(VI) complexes results in the formation of [TpiPrMoO]2(μ-S2)(μ-O). In anaerobic solutions, certain oxosulfido-Mo(VI) complexes convert to molybdenyl complexes bearing bidentate 2-mercaptophenolate or related naphtholate ligands formed via intramolecular attack of the sulfido ligand on a coligand CH group. The oxosulfido-Mo(VI) complexes serve as precursors to biologically relevant Mo(V) and heterobimetallic MoO(μ-S)Cu species and undergo a range of biomimetic reactions.