title: Azavinylidenephosphoranes: a class of cyclic push-pull carbenes.
abstract: The synthesis of a novel family of cyclic push-pull carbenes, namely, azavinylidene phosphoranes, is described. The methodology is based on a formal [3+2] cycloaddition between terminal alkynes and phosphine-imines followed by an oxidation/deprotonation step. Carbenes 6, obtained by simple deprotonation, exhibit typical transient carbene reactivity like the intramolecular CH insertion reaction and a pronounced ambiphilic character exemplified by [2+1] cycloaddition with electron-poor methyl acrylate. Owing to the cyclic structure, carbenes 6 also exhibit an excellent coordination ability toward transition metals. Rh(I) complex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The corresponding Rh(I) -carbonyl complex was also prepared; this indicates that carbenes 6 belong to the strongest σ-donating ligands to date. DFT calculations confirmed the high σ-donation ability of 6 and their classification as push-pull carbenes with a relatively small singlet-triplet energy gap of 23.2-24.3 kcal mol(-1) .
authors.affiliation: Université de Toulouse, UPS, and CNRS, LHFA UMR 5069, 31062 Toulouse Cedex 9 (France), Fax: (+33) 561558204.
authors.forename: Florie
authors.initials: F
authors.lastname: Lavigne
authors.forename: Aimée
authors.initials: A
authors.lastname: El Kazzi
authors.forename: Yannick
authors.initials: Y
authors.lastname: Escudié
authors.forename: Eddy
authors.initials: E
authors.lastname: Maerten
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kato
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saffon-Merceron
authors.forename: Vicenç
authors.initials: V
authors.lastname: Branchadell
authors.forename: Fernando P
authors.initials: FP
authors.lastname: Cossío
authors.forename: Antoine
authors.initials: A
authors.lastname: Baceiredo
keywords: carbene ligands; carbenes; density functional calculations; synthetic methods; ylides