Azavinylidenephosphoranes: A Class of Cyclic Push–Pull Carbenes |
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Authors: | Dr. Florie Lavigne Dr. Aimée El Kazzi Yannick Escudié Dr. Eddy Maerten Dr. Tsuyoshi Kato Dr. Nathalie Saffon‐Merceron Prof. Vicenç Branchadell Prof. Fernando P. Cossío Dr. Antoine Baceiredo |
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Affiliation: | 1. Université de Toulouse, UPS, and CNRS, LHFA UMR 5069, 31062 Toulouse Cedex 9 (France), Fax: (+33)?561558204;2. Université de Toulouse, UPS, and CNRS, ICT FR 2599, 31062 Toulouse (France);3. Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona (Spain);4. Departamento de Química Organica I, Universidad del País Vasco–Euskal Herriko Unibertsitatea, Facultad de Química, P.K. 1072, San Sebastian‐Donostia (Spain) |
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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. RhI complex 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. |
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Keywords: | carbene ligands carbenes density functional calculations synthetic methods ylides |
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