The complex W(CO)3(phen)(EtCN) undergoes oxidative addition with disulfides forming the formally 16-electron complexes W(CO)2(phen)(SR)2(R = Ph, (t)Bu, Me, benzyl). The reactions proceed through intermediates identified spectroscopically as the coordinated disulfide complexes. The rate of oxidative addition of coordinated disulfides is in the order (t)BuSSBu(t) << MeSSMe < PhCH2SSCH2Ph < PhSSPh. The complexes W(CO)2(phen)(SR)2 undergo ligand addition, ligand substitution, and thiol/thiolate exchange reactions. Variable-temperature equilibrium studies yielded thermodynamic parameters for binding of CO to W(CO)2(phen)(SR)2 : R = Ph, DELTAH = -7.2 +/- 0.5 kcal/mol, DELTAS = -29 +/- 3.5 cal/(mol deg); R = (t)Bu, DELTAH = -9.5 +/- 0.5 kcal/mol, DELTAS = -41 +/- 3.5 cal/(mol deg). Reaction with trimethylphosphine yields an equilibrium mixture of the 18-electron adduct W(CO)2(phen)(PMe3)(SPh)2 as well as the 16-electron monocarbonyl complex W(CO)(phen)(PMe3)(SPh)2. Addition of trimethyl phosphite yields only W(CO)(phen)(P(OMe)3)(SPh)2. Pyridine, propionitrile, hydrogen, and THF do not bind to the W(II) complexes. Reaction of W(CO)2(phen)(S(t)Bu)2 with 1 equiv of thiophenol yields W(CO)2(phen)(S(t)Bu)(SPh), which reacts with additional thiophenol to yield W(CO)2(phen)(SPh)2. Reaction with excess hydrogen sulfide yields W(CO)2(phen)(SH)2, which reacts further with thiophenol to yield W(CO)2(phen)(SPh)2. Crystal structures are reported for W(CO)2(phen)(SPh)2 and W(CO)(Phen)(P(OMe)3(SPh)2.