Synthesis, Reactivity, and DFT Studies of S−C−S Zirconium(IV) Complexes

The reactivity of the bis(diphenylthiophosphinoyl) methanediide dianion 1 toward two Zr(IV) complexes was explored. Reaction of 1 with [ZrCp2Cl2] cleanly yields the [Zr(Cp2)(SPPh2CPPh2S)] complex (2), in which the ligand behaves as a pincer ligand with two weak interactions between the ancillary sulfur ligands and the zirconium atom. Complex 2 is unreactive toward aldehydes and ketones. Reaction of 1 with [ZrCl4(THF)2] affords a dimeric structure [Zr(SPPh2CPPh2S)Cl2(THF)]2 (4) in which two [ZrCl2(THF)(SPPh2CPPh2S)] units are bridged by the chloride ligands. Formation of 4 probably results from the dimerization of the [Zr(SPPh2CPPh2S)Cl2(THF)2] complex (3), which was observed in the reaction mixture. The reaction of 4 with pyridine in excess affords [Zr(SPPh2CPPh2S)Cl2(py)2] (5), which is a heptacoordinated complex in which both carbon and sulfur atoms of the SPPh2CPPh2S2- dianion are bound. The molecular structures of 2, 4, and 5 were determined by X-ray crystallography. Complexes 4 and 5 cleanly react with ketones (R1R2CO) and aldehydes (R1HCO) to afford the corresponding geminal 1,1-bis(diphenylthiophosphinoyl) olefins of general formula [(Ph2PS)CC(R1)(R2)] and [(Ph2PS)CC(R1)(H)]. DFT calculations that were carried out on the model complex [Zr(Cp2)(SH2P−C−PH2S)] (2t) indicate that Zr−C bond only features a weak π-interaction between the carbon atom and a vacant orbital at the metal. Rotation of 90° yields complex 2t‘, which exhibits a stronger π-interaction, but this complex lies 30 kcal/mol higher in energy. Calculations on the model complex [Zr(Cl)2(py)2(SH2P−C−PH2S)] (5t) yield the same conclusion regarding the weakness of π-bonding between the ligands and the zirconium fragment.