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 [ZrCp 2 Cl 2 ] cleanly yields the [Zr(Cp 2 )(SPPh 2 CPPh 2 S)] 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 [ZrCl 4 (THF) 2 ] affords a dimeric structure [Zr(SPPh 2 CPPh 2 S)Cl 2 (THF)] 2 ( 4 ) in which two [ZrCl 2 (THF)(SPPh 2 CPPh 2 S)] units are bridged by the chloride ligands. Formation of 4 probably results from the dimerization of the [Zr(SPPh 2 CPPh 2 S)Cl 2 (THF) 2 ] complex ( 3 ), which was observed in the reaction mixture. The reaction of 4 with pyridine in excess affords [Zr(SPPh 2 CPPh 2 S)Cl 2 (py) 2 ] ( 5 ), which is a heptacoordinated complex in which both carbon and sulfur atoms of the SPPh 2 CPPh 2 S 2- 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 (R 1 R 2 C O) and aldehydes (R 1 HC O) to afford the corresponding geminal 1,1-bis(diphenylthiophosphinoyl) olefins of general formula [(Ph 2 P S)C C(R 1 )(R 2 )] and [(Ph 2 P S)C C(R 1 )(H)]. DFT calculations that were carried out on the model complex [Zr(Cp 2 )(SH 2 P−C−PH 2 S)] ( 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 (SH 2 P−C−PH 2 S)] ( 5t ) yield the same conclusion regarding the weakness of π-bonding between the ligands and the zirconium fragment.