Formation of a Stable Complex, RuCl2(S2CPPh3)(PPh3)2, Containing an Unstable Zwitterion from the Reaction of RuCl2(PPh3)3 with Carbon Disulfide

New insight into the complexity of the reaction of the prominent catalyst RuCl2(PPh3)3 with carbon disulfide has been obtained from a combination of X-ray diffraction and 31P NMR studies. The red-violet compound originally formulated as a cationic π-CS2 complex, [RuCl­(π-CS2)­(PPh3)3]­Cl, has been identified as a neutral molecule, RuCl2(S2CPPh3)­(PPh3)2, which contains the unstable zwitterion S2CPPh3. In the absence of RuCl2(PPh3)3, there is no sign of a reaction between triphenylphosphine and carbon disulfide, although more basic trialkylphosphines form red adducts, S2CPR3. Despite the presence of an unstable ligand, RuCl2(S2CPPh3)­(PPh3)2 is remarkably stable. It survives melting at 173–174 °C intact, is stable to air, and undergoes reversible electrochemical oxidation to form a monocation. When the reaction of RuCl2(PPh3)3 with carbon disulfide is conducted in the presence of methanol, crystals of orange [RuCl­(S2CPPh3)­(CS)­(PPh3)2]­Cl·2MeOH and yellow RuCl2(CS)­(MeOH)­(PPh3)2 also form. 31P NMR studies indicate that the unsymmetrical dinuclear complex (SC)­(Ph3P)2Ru­(μ-Cl)3Ru­(PPh3)2Cl is the initial product of the reaction of RuCl2(PPh3)3 with carbon disulfide. A path connecting the isolated products is presented.