Ambient-Temperature Synthesis of 2-Phosphathioethynolate, PCS^-, and the Ligand Properties of ECX^- (E = N, P; X = O, S).

A synthesis of the 2-phosphathioethynolate anion, PCS^-, under ambient conditions is reported. The coordination chemistry of PCO^-, PCS^- and their nitrogen-containing congeners is also explored. Photolysis of a solution of W(CO)₆ in the presence of PCO^- [or a simple ligand displacement reaction using W(CO)₅(MeCN)] affords [W(CO)₅(PCO)]^- (1). The cyanate and thiocyanate analogues, [W(CO)₅(NCO)]^- (2) and [W(CO)₅(NCS)]^- (3), are also synthesised using a similar methodology, allowing for an in-depth study of the bonding properties of this family of related ligands. Our studies reveal that, in the coordination sphere of tungsten(0), the PCO^- anion preferentially binds through the phosphorus atom in a strongly bent fashion, while NCO^- and NCS^- coordinate linearly through the nitrogen atom. Reactions between PCS^- and W(CO)₅(MeCN) similarly afford [W(CO)₅(PCS)]^-; however, due to the ambidentate nature of the anion, a mixture of both the phosphorus- and sulfur-bonded complexes (4a and 4b, respectively) is obtained. It was possible to establish that, as with PCO^-, the PCS^- ion also coordinates to the metal centre in a bent fashion.