A Three-Membered Cyclic Phosphasilene.

Small unsaturated phosphacycles are versatile reagents owing to their strain and the added functionality of the double bond and the phosphorus lone pair. Herein we report the synthesis and isolation of the smallest possible cyclic phosphasilene as a stable adduct with an N-heterocyclic carbene (NHC). First reactivity studies show a) that the PSi2 ring is a competent ligand to the Fe(CO)4 fragment via the phosphorus lone pair and b) that the abstraction of the NHC by BPh3 results in the rapid head-to-head or head-to-tail dimerization of the PSi2 unit. The relatively facile NHC cleavage indicates that the P=Si double bond is available for further manipulation.