Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623 Berlin (Germany) http://www.organometallics.tu-berlin.de.
Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Beringstrasse 4, 53115 Bonn (Germany) http://www.thch.uni-bonn.de/tc.
Angew Chem Int Ed Engl. 2015 Oct 5;54(41):12158-62. doi: 10.1002/anie.201504941. Epub 2015 Aug 26.
A transition-metal-free transfer hydrogenation of 1,1-disubstituted alkenes with cyclohexa-1,4-dienes as the formal source of dihydrogen is reported. The process is initiated by B(C6 F5 )3 -mediated hydride abstraction from the dihydrogen surrogate, forming a Brønsted acidic Wheland complex and HB(C6 F5 )3 . A sequence of proton and hydride transfers onto the alkene substrate then yields the alkane. Although several carbenium ion intermediates are involved, competing reaction channels, such as dihydrogen release and cationic dimerization of reactants, are largely suppressed by the use of a cyclohexa-1,4-diene with methyl groups at the C1 and C5 as well as at the C3 position, the site of hydride abstraction. The alkene concentration is another crucial factor. The various reaction pathways were computationally analyzed, leading to a mechanistic picture that is in full agreement with the experimental observations.
本文报道了一种无过渡金属参与的 1,1-二取代烯烃与环己-1,4-二烯的转移氢化反应，环己-1,4-二烯作为氢气的形式来源。该过程由 B(C6 F5 )3 介导的从氢气替代物中进行氢化物抽提引发，形成 Brønsted 酸性 Wheland 配合物和 HB(C6 F5 )3 。随后，质子和氢化物依次转移到烯烃底物上，生成烷烃。尽管涉及到几个碳正离子中间体，但通过使用在 C1 和 C5 以及氢化物抽提位置的 C3 位上具有甲基的环己-1,4-二烯，以及反应物的阳离子二聚化等竞争反应途径，很大程度上抑制了副反应的发生。烯烃的浓度也是一个关键因素。通过计算分析了各种反应途径，提出了一个与实验观察完全一致的反应机理。
