Spectroscopic and structural characterization of a phosphavinylidene carbenoid, Mes*-P=C(Cl){Li(DME)(2)}: Stabilization of a carbenanionic center by a cisoid lone pair interaction

Characterization of the phosphavinylidene carbenoid DME-solvate (Z)-Mes*-P= C(CI){ Li(DME)(2)} (Z-2a) or the corresponding THF-solvate (Z-2b) by low-te mperature X-ray diffractometry and multinuclear NMR studies reveals the pre sence of discrete monomeric molecules with donor-solvated metal atoms both in solution and the solid state. The structural parameters of solid 2a and the observed intermolecular exchange of Li+ between different carbanion fra gments in solution suggest a low degree of covalency for the C-Li bond. Thi s is in accord with a theoretical analysis of the bonding which demonstrate s that the electronic structure of the model carbenoids (E/Z)-Me-P=C(Cl){Li (DME)(2)} (5) is very similar to that of the carbanions (E/Z)-[Me-P=C(Cl)]( -) (6). In particular, the low degree of covalency in the C-Li bond in 5 is confirmed by natural population analyses and an analysis of the Laplacian of the electron density. On the basis of these results, the bonding situati on in the phosphavinylidene carbanion system is discussed in terms of an is olobal analogy to N2F2.