Exploiting the Brønsted Acidity of Phosphinecarboxamides for the Synthesis of New Phosphides and Phosphines

Abstract

We demonstrate that the synthesis of new N-functionalized phosphinecarboxamides is possible by reaction of primary and secondary amines with PCO - in the presence of a proton source. These reactions proceed with varying degrees of success, and although primary amines generally afford the corresponding phosphinecarboxamides in good yields, secondary amines react more sluggishly and often give rise to significant decomposition of the 2-phosphaethynolate precursor. Of the new N-derivatized phosphinecarboxamides available, PH 2 C(O)NHCy (Cy=cyclohexyl) can be obtained in sufficiently high yields to allow for the exploration of its Brønsted acidity. Thus, deprotonating PH 2 C(O)NHCy with one equivalent of potassium bis(trimethylsilyl)amide (KHMDS) gave the new phosphide [PHC(O)NHCy] -. In contrast, deprotonation with half of an equivalent gives rise to [P{C(O)NHCy} 2 ] - and PH 3. These phosphides can be employed to give new phosphines by reactions with electrophiles, thus demonstrating their enormous potential as chemical building blocks. Primary expression: The synthesis of four new N-functionalized phosphinecarboxamides, PH 2 C(O)NRR′, and the subsequent reactivity of one of them, PH 2 C(O)NHCy (Cy=cyclohexyl), towards strong bases, affording new phosphides and secondary and tertiary phosphines, is described. These studies demonstrate the enormous synthetic potential of phosphinecarboxamides, which constitute a relatively new family of stable primary phosphines (see scheme).