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 (<b>1</b>) and subsequently [((Ph₂PC₆H₄)₂B­(η⁶-Ph))­RuCl]­[B­(C₆F₅)₄] (<b>2</b>). The latter species exhibited Lewis acidity on the η⁶-Ph ring, as reaction with Cy₃P gave the donor–acceptor adduct [(Ph₂PC₆H₄)₂B­(η⁵-C₆H₅-<i>o</i>-PCy₃)­RuCl]­[B­(C₆F₅)₄] (<b>3</b>). Steric frustration of this binding was seen with Mes₃P, and yet the combination of <b>2</b> and Mes₃P reacted with H₂ to give a 2:1 mixture of <b>5-</b><i><b>o</b></i> and <b>5-</b><i><b>p</b></i>, two isomers of [(Ph₂PC₆H₄)₂B­(η⁵-C₆H₆)­RuCl] (<b>5</b>), along with [Mes₃PH]­[HB­(C₆F₅)₃]. Compound <b>2</b> 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