Accessing Phosphonioacetylide Chemistry: Isolable Alkali Metal Precursors for Rod-Shaped Carbon Donor Complexes

Abstract

Rod-shaped neutral carbon ligands such as carbon monoxide and isocyanides play a central role in organometallic chemistry but are relatively weak electron donors compared to N-heterocyclic carbenes. Phosphonioacetylides (R3PCC) have been proposed as promising candidates for stronger electron donation within the class of sp-hybridized carbon ligands. However, their high reactivity has significantly limited their exploration and isolation. In this study, we report the synthesis and characterization of a novel phosphonioacetylide, MeR₂PCC (R = 1,3-di-tert-butylimidazolidin-2-ylidenamino). While it is highly labile at ambient temperature, the compound is stable at −40 °C and can be isolated and stored in the form of alkali metal complexes. The latter undergo efficient transmetallation reactions with a variety of electrophiles, enabling the formation of Lewis base adducts with both main group elements and transition metals, including tungsten(0), nickel(0), and rhodium(I). These results demonstrate that alkali metal phosphonioacetylides serve as versatile precursors for introducing this highly donating and structurally unique ligand into coordination complexes.