From halo-azasilylenes to halo-phosphasilylenes (X-CNSi vs. X-CPSi) at ab initio and DFT levels

The higher the electropositivity of the substituents has been associated with the higher possibility of encountering a triplet ground state silylene [P.P. Gaspar, M. Xiao, D. Ho Pae, D.J. Berger, T. Haile, T. Chen, D. Lei, W.R. Winchester, P. Jiang, J. Organomet. Chem. 646 (2002) 68]. Here, going from the reported halo-azasilylenes X-CNSi [M.Z. Kassaee, S.M. Musavi, H. Hamadi, M. Ghambarian, S.E. Hosseini, J. Mol. Struct. (Theochem) 730 (2005) 33] to the analogues more electropositively substituted halo-phosphasilylenes X-CPSi has reduced the chances of encountering triplet ground state silylenes (X = H, F, Cl and Br). Even though all singlet isomers seem to be more stable than their corresponding triplets, singlet–triplet cross over diagrams may help the future design of new acyclic triplet state silylenes.