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Reversible Dihydrogen Activation by Reduced Aryl Boranes as Main-Group Ambiphiles
Esther von Grotthuss1, Martin Diefenbach1, Michael Bolte1
1Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt (Main), Germany.
Abstract:
A new approach to main-group H2 activation combining concepts of transition-metal and frustrated Lewis pair chemistry is reported. Ambiphilic, metal-like reactivity toward H2 can be conferred to 9,10-dihydro-9,10-diboraanthracene (DBA) acceptors by the injection of two electrons. The resulting [DBA]2- ions cleave the H-H bond with the formation of hydridoborates under moderate conditions (T=50-100 °C; p<1 atm). Depending on the boron-bonded substituents R, the addition is either reversible (R=C≡CtBu) or irreversible (R=H). The reaction rate is strongly influenced by the nature and the coordination behavior of the countercation (Li+ slower than K+ ). Quantum-chemical calculations support the experimental observations and suggest a concerted, homolytic addition of H2 across both boron atoms. As proven by the successful conversion of Me3 SiCl into Me3 SiH, the system Li2 [DBA]/H2 appears generally relevant for the hydrogenation of element-halide bonds.
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