CH Bond Activation with Triel Metals: Indium and Gallium Zwitterions through Internal Hydride Abstraction in Rigid Salan Ligands |
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| Authors: | Nicolas Maudoux Dr. Jian Fang Dr. Thierry Roisnel Dr. Vincent Dorcet Prof. Dr. Laurent Maron Prof. Dr. Jean‐François Carpentier Dr. Yann Sarazin |
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| Affiliation: | 1. Organometallics: Materials and Catalysis Department, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS—Université de Rennes 1, Campus de Beaulieu, 35042 Rennes (France);2. Laboratoire de Physique et Chimie de Nano‐objets, UMR 5215 CNRS—Université de Toulouse, 135 avenue de Rangueil, 31077 Toulouse (France);3. Centre de Diffractométrie des Rayons X, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS—Université de Rennes 1, 35042 Rennes (France) |
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| Abstract: | The hydropyrimidine salan (salan=N,N′‐dimethyl‐N,N′‐bis[(2‐hydroxyphenyl)methylene]‐1,2‐diaminoethane) proteo‐ligands with a rigid backbone {ON^(CH2)^NO}H2 react with M(CH2SiMe3)3 (M=Ga, In) to yield the zwitterions {ON^(CH+)^NO}M?(CH2SiMe3)2 (M=Ga, 2 ; In, 3 ) by abstraction of a hydride from the ligand backbone followed by elimination of dihydrogen. By contrast, with Al2Me6, the neutral‐at‐metal bimetallic complex [{ON^(CH2)^NO}AlMe]2 ( [1]2 ) is obtained quantitatively. The formation of indium zwitterions is also observed with sterically more encumbered ligands containing o‐Me substituents on the phenolic rings, or an N (CHPh) N moiety in the heterocyclic core. Overall, the ease of C ?H bond activation follows the order Al?Ga2H NMR spectroscopy show that the formation of the Ga/In zwitterion involves rapid release of SiMe4 followed by evolution of H2, and suggest the formation of a transient metal‐hydride species. DFT calculations indicate that the systems {ON^(CH2)^NO}H2+M(CH2SiMe3)3 (M=Al, Ga, In) all initially lead to the formation of the neutral monophenolate dihydrocarbyl species through a single protonolysis. From here, the thermodynamic product, the model neutral‐at‐metal complex 1 , is formed in the case of aluminum after a second protonolysis. On the other hand, lower activation energy pathways lead to the generation of zwitterionic complexes 2 and 3 in the cases of gallium and indium, and the formation of these zwitterions obeys a strict kinetic control; the computations suggest that, as inferred from the experimental data, the reaction proceeds through an instable metal‐hydride species, which could not be isolated synthetically. |
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| Keywords: | C– H activation density functional calculations gallium hydride abstraction indium zwitterions |
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