Structures and properties of carboimidophosphene (HPCNH) and carbodiphosphene (HPCPH). An ab initio study

Abstract

Ab initio calculations are reported for carboimidophosphene (iminomethylenephosphine), carbodiphos-phene (1,3-diphospha-allene) and their conjugate acids. Lsomerization is favoured by inversion about the CN bond and by rotation about CP bonds and is negligibly small (4.2 kcal mol^–1 at DZP//4-31 G) for HPCNH, and large (42 kcal mol^–1) for HPCPH. The electronic structures, harmonic vibrational frequencies, and proton affinities are reported and compared with those of other phospha-cumulenes such as HPCO and H₂CCPH. The protonation occurs preferentially at the P atom in HPCNH (1) and the C atom in HPCPH (4). At the MP4SDQ/6-31 G** level, the proton affinities are predicted to be 210 ± 5 for (1) and 193 ± 5 kcal mol^–1 for (4)(with zero-point energy corrections). The regiospecificity of the dimerization, (2 + 2) cycloadditions, additions to HX reagents, and reacticns with metals are rationalized or predicted.