Chemistry and ligating properties of the 1,2,4-thiadiphosphole P2SC2But2

New synthetic routes to the 1,2,4- and 1,3,4-thiadiphospholes, P2SC2But2, are presented. Both η1-W(CO)5 and η5-M(CO)3 complexes (M=Mo, W) of the 1,2,4-thiadiphosphole ring are described and the molecular structure of the former determined by a single crystal X-ray study is in good agreement with theoretical calculations. The thermal conversion of the η1-M(CO)5 complex to the η5-M(CO)3 complex is attributable to the entropy change in the reaction. A sequence of [4+2] and [2+2+2] cyclo-addition reactions of the 1,2,4-thiadiphosphole, P2SC2But2, with the phosphaalkyne, PCBut, affords the tetracyclic cage compound P4SC4But4 which has also been structurally characterised.