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Alkaline-Earth-Catalysed Cross-Dehydrocoupling of Amines and Hydrosilanes: Reactivity Trends, Scope and Mechanism

Abstract : Alkaline-earth (Ae=Ca, Sr, Ba) complexes are shown to catalyse the chemoselective cross-dehydrocoupling (CDC) of amines and hydrosilanes. Key trends were delineated in the benchmark couplings of Ph3SiH with pyrrolidine or tBuNH2. Ae\E(SiMe3)2\2⋅(THF)x (E=N, CH; x=2–3) are more efficient than \N^N\Ae\E(SiMe3)2\⋅(THF)n (E=N, CH; n=1–2) complexes (where \N^N\−=\ArN(o-C6H4)C(H)=NAr\− with Ar=2,6-iPr2-C6H3) bearing an iminoanilide ligand, and alkyl precatalysts are better than amido analogues. Turnover frequencies (TOFs) increase in the order Ca30 products) includes diamines and di(hydrosilane)s. Kinetic analysis of the Ba-promoted CDC of pyrrolidine and Ph3SiH shows that 1) the kinetic law is rate=k[Ba]1[amine]0[hydrosilane]1, 2) electron-withdrawing p-substituents on the arylhydrosilane improve the reaction rate and 3) a maximal kinetic isotopic effect (kSiH/kSiD=4.7) is seen for Ph3SiX (X=H, D). DFT calculations identified the prevailing mechanism; instead of an inaccessible σ-bond-breaking metathesis pathway, the CDC appears to follow a stepwise reaction path with N−Si bond-forming nucleophilic attack of the catalytically competent Ba pyrrolide onto the incoming silane, followed by rate limiting hydrogen-atom transfer to barium. The participation of a Ba silyl species is prevented energetically. The reactivity trend Ca
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01274113
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Submitted on : Monday, February 15, 2016 - 2:07:17 PM
Last modification on : Thursday, March 5, 2020 - 2:06:02 PM

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Clément Bellini, Vincent Dorcet, Jean-François Carpentier, Sven Tobisch, Yann Sarazin. Alkaline-Earth-Catalysed Cross-Dehydrocoupling of Amines and Hydrosilanes: Reactivity Trends, Scope and Mechanism. Chemistry - A European Journal, Wiley-VCH Verlag, 2016, 22 (13), pp.4564 - 4583. ⟨10.1002/chem.201504316⟩. ⟨hal-01274113⟩

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