Bis(methylene)-λ-phosphane anions.

Bis(methylene)-λ-phosphane anions, , anionic phosphorus-centered heteroallene-type molecules, were obtained from the desilylation of a bis(silyl)methyl-substituted phosphaalkene. Their molecular structures, which were determined using spectroscopic techniques and single-crystal X-ray diffraction analysis, suggest that the central di-coordinated P atom is engaged in cumulative C[double bond, length as m-dash]P[double bond, length as m-dash]C π-bonds with the neighboring C atoms. The π-bond character of the C[double bond, length as m-dash]P[double bond, length as m-dash]C moieties was examined on the basis of the experimental results in combination with theoretical calculations; the results obtained suggest that multiple silyl substitutions at the C atom weaken the C[double bond, length as m-dash]P π-bonding character.