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.