An Intramolecular Silylene Borane Capable of Facile Activation of Small Molecules, Including Metal‐Free Dehydrogenation of Water

• Published in: Angewandte Chemie International Edition 2017-03, Vol.56 (13), p.3699-3702
• Main Authors: Mo, Zhenbo, Szilvási, Tibor, Zhou, Yu‐Peng, Yao, Shenglai, Driess, Matthias
• Format: Article
• Language: English
• Subjects: Benzene; Boranes; Boron; Carbon dioxide; Chemical synthesis; Dehydrogenation; dihydrogen activation; frustrated Lewis pairs; Hydrogenation; Metals; Molecular orbitals; N-heterocyclic silylene; Nitrous oxide; silanone; Silicon
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201700625

The first single‐component N‐heterocyclic silylene borane 1 (LSi‐R‐BMes2; L=PhC(NtBu)2; R=1,12‐xanthendiyl spacer; Mes=2,4,6‐Me3C6H2), acting as a frustrated Lewis pair (FLP) in small‐molecule activation, can be synthesized in 65 % yields. Its HOMO is largely localized at the silicon(II) atom and the LUMO has mainly boron 2p character. In small‐molecule activation 1 allows access to the intramolecular silanone–borane 3 featuring a Si=O→B interaction through reaction with O2, N2O, or CO2, and formation of silanethione borane 4 from reaction with S8. The SiII center in 1 undergoes immediate hydrogenation if exposed to H2 at 1 atm pressure in benzene, affording the silane borane 5‐H2, L(H2)Si‐R‐BMes2. Remarkably, no H2 activation occurs if the single silylene LSiPh and Mes3B intermolecularly separated are exposed to dihydrogen. Unexpectedly, the pre‐organized Si–B separation in 1 enables a metal‐free dehydrogenation of H2O to give the silanone–borane 3 as reactive intermediate. A single for two: The first single‐component N‐heterocyclic silylene borane activates a variety of small molecules, such as O2, N2O, CO2, H2, and H2O. Notably, the activation of H2O by 1 makes it a metal‐free system for dehydrogenation of H2O.