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)­(η6-Ph)­RuCl (1) and subsequently [((Ph2PC6H4)2B­(η6-Ph))­RuCl]­[B­(C6F5)4] (2). The latter species exhibited Lewis acidity on the η6-Ph ring, as reaction with Cy3P gave the donor–acceptor adduct [(Ph2PC6H4)2B­(η5-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(η5-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.