© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 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 CH 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. RhIcomplex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The corresponding RhI–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.
|Journal||Chemistry - A European Journal|
|Publication status||Published - 1 Jan 2014|
- carbene ligands
- density functional calculations
- synthetic methods