The kinetics of deoxygenation of [MoO 2 (Sap)EtOH] (Sap 2 = N-salicylidene-2-aminophenolate dianion) by thionyl chloride have been studied in acetonitrile and a mixture of tetrahydrofuran and acetonitrile (v/v = 9:1) by spectrophotometry. Under the conditions [MoO 2 (Sap)EtOH] [SOCl 2 ], the reaction of formation of the product MoO(Sap)Cl 2 consists of two consecutive steps. The pseudo-first-order rate constants of the first-step reaction depended on [SOCl 2 ] 1 2 and were significantly affected by the dielectric constant of solvent used, whereas those of the second-step reaction were independent of [SOCl 2 ]. A mechanism is proposed for the deoxygenation, where the reactant reacted initially with MoO 2 (Sap)EtOH is not SOCl 2 , but SOCl + or Cl - ions.