Atom transfer reactions have been employed to convert Tp(/Pr)MoO(2)(OAr) into monomeric cis-oxosulfido-Mo(VI) and dimeric mu-disulfido-Mo(V) species, [Tp(/Pr)MoOS(OAr)](n) (Tp(/Pr) = hydrotris(3-isopropyl-pyrazol-1-yl)borate; OAr = phenolate or naphtholate derivative; n = 1 and 2, respectively). Dark red, monomeric Tp(/PR)MoOS(OAr) complexes contain distorted octahedral cis-oxosulfido-Mo(VI) centers, with d(Mo=O) = 1.692(5) angstrom, d(Mo=S) = 2.132(2) angstrom, and angle(O=Mo=S) = 103.68(16)degrees for the 2-sec-butylphenolate derivative. Dark red-purple, dimeric [Tp(/Pr)MoOS(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-kappa S,kappa S' ligand. Hydrolysis of the oxosulfido-Mo(VI) complexes results in the formation of [Tp(/Pr)MoO](2) (mu-S-2)(mu-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(mu-S)Cu species and undergo a range of biomimetic reactions.