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Barium-Catalysed Dehydrocoupling of Hydrosilanes and Borinic Acids: A Mechanistic Insight |
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| Authors: | Erwann Le Coz Ziyun Zhang Dr Thierry Roisnel Prof?Dr Luigi Cavallo Dr Laura Falivene Prof?Dr Jean-François Carpentier Dr Yann Sarazin |
| Institution: | 1. CNRS, ISCR (Institut des Sciences Chimiques de Rennes)–UMR 6226, Univ Rennes, 35000 Rennes, France
These authors contributed equally to the work.;2. Physical Sciences and Engineering Division, Kaust Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 Saudi Arabia These authors contributed equally to the work.;3. CNRS, ISCR (Institut des Sciences Chimiques de Rennes)–UMR 6226, Univ Rennes, 35000 Rennes, France;4. Physical Sciences and Engineering Division, Kaust Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900 Saudi Arabia |
| Abstract: | Two very rare cases of barium boryloxides, the homoleptic Ba(OB{CH(SiMe3)2}2)2?C7H8] and the heteroleptic {LONO4}BaOB{CH(SiMe3)2}2] stabilised by the multidentate aminoetherphenolate {LONO4}?, are presented, and their structural properties are discussed. The electron-deficient Ba(OB{CH(SiMe3)2}2)2?C7H8] shows, in particular, resilient η6-coordination of the toluene molecule. Together with its amido parents Ba{N(SiMe3)2}2?thf2] and Ba{N(SiMe3)2}2]2, this complex catalyses the fast and chemoselective dehydrocoupling of borinic acids R2BOH and hydrosilanes HSiR′3, yielding borasiloxanes R2BOSiR′3 in a controlled fashion. The assessment of substrate scope indicates that, for now, the reaction is limited to bulky borinic acids. Kinetic analysis shows that the rate-limiting step of the catalytic manifold traverses a dinuclear transition state. A detailed mechanistic scenario is proposed on the basis of DFT computations, the results of which are fully consistent with experimental data. It consists of a stepwise process with rate-determining nucleophilic attack of a metal-bound O-atom onto the incoming hydrosilane, involving throughout dinuclear catalytically active species. |
| Keywords: | alkaline earth metals barium borasiloxanes density functional calculations reaction mechanisms |