The oxo-Mo(IV) complexes LMoO(S(2)PR(2)-S,S’) [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate; R = Me, Et, Pr-i, Ph] were prepared by reacting MoO(S(2)PR(2))(2) and KL in refluxing toluene. The dioxo-Mo(VI) complexes cis-LMoO(2)(S(2)PR(2)-S) (R = Pr-i, Ph) were prepared by oxidation of the oxo-Mo(IV) complexes or by reaction of LMoO(2)Cl with NaS(2)PR(2). Oxygen atom transfers from Me(2)SO to LMoO(S(2)PR(2)) were first-order with respect to Me(2)SO and complex; the overall second-order rate constants at 40 degrees C range from 9.0(1) x 10(-5) M(-1) . s(-1) for LMoO(S(2)PMe(2)) to 2.08(5) x 10(-4) M(-1) . s(-1) for LMoO(S2PPr2); activation parameters were in the ranges Delta H double dagger = 63(1) to 73(1) kJ . mol(-1), Delta S double dagger = -88(1) to -111(1) J . K-1 . mol(-1), and Delta G double dagger = 100(2) kJ . mol(-1) for LMoO(S-2-PMe(2)) to 98(2) kJ . mol(-1) for LMoO(S2PPr2).