The chemistry of the 2-phosphaethynolate anion.

Likely the first synthesis of the phosphaethynolate anion, PCO-, was performed already in 1894 when NaPH2 was reacted with CO in an attempt to make Na(CP) under elimination of water. This reaction was repeated only 117 years later when it was discovered that Na(OCP) and H2 are the products of this remarkable transformation. Li(OCP) was synthesized and fully characterized in 1992 but this salt proved to be too unstable to allow a detailed investigation. Remarkably, it needs the heavier analogues of this lithium salt, Na(OCP) and K(OCP), which are remarkably stable and can be even dissolved in water, to fully explore fully the chemistry of this new functional group. Here we review the chemistry of the 2-phosphaethynolate anion, a heavier phosphorus-containing analogue of the cyanate anion, and describe the wide breadth of chemical transformations for which it has been thus far employed. Its use as a ligand, in decarbonylative and deoxygenative processes, and as a building block for novel heterocycles is described. In the mere twenty six years since Becker first reported the isolation of this remarkable anion, it has become a fascinating reagent for the synthesis of a vast library of, often unprecedented, molecules and compounds.