Carbene−Pnictinidene Adducts

Abstract

The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These carbene-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These carbene-pnictinidene adducts possess strongly polarized pnictinidene-carbene bonds. The C-Pn-C angles are all typically small 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 substituent on the pnictogen. The (31)P NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polarized structures.

A Tris(trifluoromethyl)antimony Adduct of a Nucleophilic Carbene: Geometric Distortions in Carbene Adducts

“…Just the opposite for is observed 2´Sb(CF 3 ) 3 . Distortions are also observed in the 1,3-dimesitylimidazol-2-ylidene (3) adducts of the pnictinidenes C 6 F 5 As (3´AsC 6 F 5 ) and CF 3 P (3´PCF 3 ) [11], and in the 1,3-dimesitylimidazol-2-ylidene´ger-manium diiodide adduct 3´GeI 2 [12]. There is also a barium±carbene adduct that shows a 14°displacement of the barium from an imidazole 2-fold axis [13].…”

Inversely Polarized Phosphaalkenes as Phosphinidene‐ and Carbene‐Transfer Reagents

“…[15] Similar results were obtained with 1,3-dimesitylimidazol-2-ylidene and the cyclophosphanes (PhP) 5 and (CF 3 P) 4 . [16] For a mechanism that rationalizes the formation of adduct 2 as well as of the heterocycles 4 and 6a, we propose the initial cleavage of one molecule of phosphaalkene 1 by reaction with 2 equiv. of Ph 2 C=C=O.…”

Synthese und Eigenschaften von [Ph2(Carb)P]AlCl4 (Carb = 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-yliden) - ein stabiler Carben-Komplex des dreiwertigen Phosphors [1]

“…Die regioselektive Koordination des Carbens 7 an das Phosphorzentrum in Ph 2 PCl u È berrascht angesichts der glatten Reduktion von PhPCl 2 [18]; tatsa Èchlich ist auch die Addition eines Carbens an das Phosphorzentrum in PhPF 4 [17] angesichts der Reduktion von SF 4 und SO 2 F 2 [9] nicht selbstversta È ndlich. Offensichtlich begu È nstigt die bei steigender Oxidationsstufe des Moleku È lzentrums wachsende Lewis-Acidita È t nicht exklusiv den nucleophilen Angriff hieran, sondern erleichtert in a È hnlichem Maûe u È ber die Ru È ckfu È hrung der partiellen negativen Ladung an X auch den Angriff auf den Substituenten.…”