An ab initio study on the stability of isolated phosphaalkene synthons

Using ab initio methods and flexible basis sets, we examined the electronic, geometric, and thermodynamic stabilities of selected phosphaalkene synthons matching the (PCR2)(-) formula (R = H, CH3, C6H5, C6F5, and Mes). All isolated synthons considered were found to be electronically stable and susceptible to neither fragmentation nor isomerization processes. The structures corresponding to the most stable isomers of the studied phosphaalkene synthons contain a P=C double-bond (whose presence was confirmed by natural bond orbital occupancies of sigma(P-C) and pi(P-C) approaching 2 electrons) and two R substituents connected to the carbon atom in either (P=CR2)(- )(for R = H, CH3, C6H5, and Mes) or (P=CF-R-R)(-) (for R = C6F5) manner. Vertical electron detachment energies (spanning the 0.924-3.118 eV range) characterizing the phosphaalkene synthons were predicted and discussed.