Phosphine Carboxylate—Probing the Edge of Stability of a Carbon Dioxide Adduct with Dihydrogenphosphide

We present a new adduct of carbon dioxide with dihydrogenphosphide, that may be prepared either by direct reaction of NaPH2 with carbon dioxide or by hydrolysis of the phosphaethynolate ion (PCO−). In this hydrolysis transformation, a new mechanism is proposed for the electrophilic reactivity of the phosphaethynolate ion. Protonation to form phosphine carboxylic acid (PH2COOH) and functionalization to form esters is shown to increase the strength of the P–C interaction, allowing for comparisons to be drawn between this species and the analogous carbamic (NH2COOH) and carbonic acids (H2CO3). Functionalization of the oxygen atom is found to stabilize the phosphine carboxylate while also allowing solubility in organic solvents whereas phosphorus functionalization is shown to facilitate decarboxylation. Substituent migration occurs in some cases. Phosphine carboxylate, H2PCO2−, has been prepared for the first time both by the reaction of dihydrogen phosphide with carbon dioxide and by hydrolysis of phosphaethynolate, PCO−. Acidification of the salt yielded phosphine carboxylic acid that has a surprising kinetic stability compared to carbamic and carbonic acids. The mechanism of phosphaethynolate hydrolysis was investigated.