The oxidations of benzyl alcohol, PPh3, and the sulfides (SEt2 and SPh2) (Ph = phenyl and Et = ethyl) by the Os(VI)-hydrazido complex trans-[Os-VI(tpy(Cl)(2)(NN(CH2)(4)O)](2+) (tpy = 2,2 ' :6 ' ,2 " -terpyridine and O(CH2)(4)N- = morpholide) have been investigated in CH3CN solution by UV-visible monitoring and product analysis by gas chromatography-mass spectrometry. For benzyl alcohol and the sulfides, the rate law for the formation of the Os(V)-hydrazido complex, trans- [Os-V(tpy)(Cl)(2)(NN(CH2)(4)O)](+), is first order in both trans-[Os-VI(typ(Cl)(2)(NN(CH2)(4)O)](2+) and reductant, with k(benzyl) (25.0 +/- 0.1 degreesC, CH3CN) = (1.80 +/- 0.07) x 10(-4) M-1 s(-1), k(SEt2) = (1.33 +/- 0.02) x 10(-1) M-1 s(-1), and k(SPh2) = (1.12 +/- 0.05) x 10(-1) M-1 s(-1). Reduction of trans-[Os-VI(tpy)(Cl)(2)(NN(CH2)(4)O)](2+) by PPh3 is rapid and accompanied by isomerization and solvolysis to give the Os(IV)hydrazido product, cis-[Os-IV(tpy)(NCCH3)(2)(NN(CH2)(4)O)](2+), and OPPh3. This reaction presumably occurs by net double Cl-atom transfer to PPh3 to give Cl2PPh3 that subsequently undergoes hydrolysis by trace H2O to give the Final product, OPPh3. In the X-ray crystal structure of the Os(IV)-hydrazido complex, the Os-N-N angle of 130.9(5)degrees and the Os-N bond length of 1.971(7) Angstrom are consistent with an Os-N double bond.