Structure and properties of phosphaketene (H–PCO): phosphorus versus oxygen protonation?

Abstract

Phosphaketenes carrying bulky substituents to limit dimerization have recently been reported and for comparison the simple model phosphaketene (1) was investigated using ab initio methods. It has an E-bent structure with a CP bond length of 1.728Å; and a CPH bond angle of 90.6°(using the 4-31 G basis set). This is rationalized in terms of stabilizing interactions between the PH and CO fragments so that the C–P bond is essentially a dative single bond enforced by π-back-donation. Both P and O centres carry an overall negative charge; of five possible structures of protonated HPCO considered, phosphorus protonation is unambiguously preferred and the perpendicular structure (11) calculated to be the most stable. Inclusion of polarization functions and correlation energies favours phosphorus protonation further. Also reported are the vibrational frequencies, dissociation energies of the protonated and neutral phosphaketene, and the predicted reactivity in both cycloadditions and additions of HX; comparison is made with reported experimental data where available.