Synthesis of Pyridines, Quinolines, and Pyrimidines via Acceptorless Dehydrogenative Coupling Catalyzed by a Simple Bidentate P^N Ligand Supported Ru Complex

A ruthenium hydrido chloride complex (1) supported by a simple, heteroleptic bidentate P^N ligand (L1) containing a diarylphosphine and a benzannulated phenanthridine donor arm is reported. In the presence of base, complex 1 catalyzes multicomponent reactions using alcohol precursors to produce structurally diverse molecules including pyridines, quinolines, and pyrimidines via acceptorless dehydrogenative coupling pathways. Notably, L1 does not bear readily (de)­protonated Brønsted acidic or basic groups common to transition metal catalysts capable of these sorts of transformations, suggesting metal–ligand cooperativity does not play a significant role in the catalytic reactivity of 1. A rare example of an η²-aldehyde adduct of ruthenium was isolated and structurally characterized, and its role in acceptorless dehydrogenative coupling reactions is discussed.