Even the normal is abnormal: N-heterocyclic carbene C 2 binding to a phosphaalkene without breaking the P=C π-bond. Majhi, P., K., Chow, K., C., F., Hsieh, T., H., H., Bowes, E., G., Schnakenburg, G., Kennepohl, P., Streubel, R., & Gates, D., P. Chem. Commun., 2015.
Even the normal is abnormal: N-heterocyclic carbene C 2 binding to a phosphaalkene without breaking the P=C π-bond [pdf]Paper  Even the normal is abnormal: N-heterocyclic carbene C 2 binding to a phosphaalkene without breaking the P=C π-bond [link]Website  abstract   bibtex   
The reaction of MesPQCPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the ‘abnormal’ (C4 -substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented ‘normal’ C2 adduct, Me2IMe - P(Mes)QCPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the PQC moiety in 2. DFT calculations indicate that the PQC natural bond order in 2 (1.54) still reflects significant pi-character to the bond (cf. MesPQCPh2: NBO = 1.98). Further computational analysis suggests that p-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct.

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