A Ru-η6-arene complex as a C-based Lewis acid in the activation of hydrogen and hydrogenation catalysis.

The PBP ligand (Ph2PC6H4)2BPh was used to prepare ((Ph2PC6H4)2B(Cl)(η(6)-Ph)RuCl (1) and subsequently [((Ph2PC6H4)2B(η(6)-Ph))RuCl][B(C6F5)4] (2). The latter species exhibited Lewis acidity on the η(6)-Ph ring, as reaction with Cy3P gave the donor-acceptor adduct [(Ph2PC6H4)2B(η(5)-C6H5-o-PCy3)RuCl][B(C6F5)4] (3). Steric frustration of this binding was seen with Mes3P, and yet the combination of 2 and Mes3P reacted with H2 to give a 2:1 mixture of 5-o and 5-p, two isomers of [(Ph2PC6H4)2B(η(5)-C6H6)RuCl] (5), along with [Mes3PH][HB(C6F5)3]. Compound 2 behaves as C-based Lewis acid and thus can also be used for catalytic hydrogenation of aldimines at room temperature via a frustrated Lewis pair mechanism.