transfer Phosphasilenes with significant zwitterionic characters undergoes facile hemolytic cleavage of the fragile Si=P bond. This can be utilized for the liberation and transfer of phosphinidene (:PH) to unsaturated organic molecules. Driess et al. demonstrated that a fragile "half"-parent phosphasilene LSi=PH (L = CH[(C=CH2)CMe(NAr)2]; Ar = 2,6-iPr2C6H3) with highly shielded PH moiety is capable of transferring :PH to NHC. Theoretical investigation by DFT (B3LYP/6-31G(d) level) revealed that this phosphasilene bears two highly localized lone pairs on the phosphorus atom due to the LSi=PH ↔ LSi–P+H− resonance. Based on natural bond orbital (NBO) analysis, the σ bond of Si=P involves even contributions from Si and P, while the π bond (HOMO-1) is strongly polarized to the phosphorus atom. This indicates that the π bond between silicon and phosphorus is not predominant, supporting the significance of the zwitterionic resonance structure in the description of Si–P bonding. Small molecule activation The Si=P moiety of phosphasilene has been reported to demonstrate small molecule activation reactivities analogous to those observed in Si=Si, P=C, and other heavier alkene analogues. For example, phosphasilene with silyl substituents has been shown to activate white phosphorus (P4) under relatively mild reaction conditions to form 1,2,3-triphospha-4-silabicyclo[1.1.0]butanes, which is similar to disilenes' reactivity. Analogous to the behavior of phosphaalkenes, phosphasilene can also activate chalcogens such as S8 and Te to form unstable three-membered ring compounds. Using a fragile zwitterionic "half-parent" phosphasilene L'Si=PH (L' = CH[(C=CH2)CMe(NAr)2], Ar = 2,6-iPr2C6H3), Driess and coworkers demonstrated that an unusual N-H activation reactivity can be achieved by the Si=P moiety in ammonia, affording L'Si(NH2)PH2 species. This represent a rare example of catalyst-free 1,2-hydroamination reaction that's been reported in heavier alkene analogues. References Silicon compounds Phosphorus compounds