CARBENE-PNICTINIDENE ADDUCTS

The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic carbe nes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-yl idene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phos phinidene, and (pentafluorophenyl)arsinidene are reported. These carbe ne-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic carbene with the corresponding pnictinidene cyclic oligom ers. The synthesis and structure of the adduct between 1,3-dimesitylim idazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-di mesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These carbene-pnictinidene adducts possess strongly polarize d pnictinidene-carbene bonds. The C-Pn-C angles are all typically smal l at 97-102 degrees, and there is only a 4% shortening of the nominal Pn=C double bond compared to the Pn-C single bond to the second substi tuent on the pnictogen. The P-31 NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polari zed structures.