Synthesis of Pincer Ruthenium RuCl­(CNN)­(PP) Catalysts from [RuCl­(μ-Cl)­(η⁶‑p‑cymene)]₂

The cationic [RuCl­(η⁶-p-cymene)­(HC­NN^a)]­Cl (1a) (HCNN^a = 1-(6-aryl­pyridin-2-yl)­methanamine) and the neutral RuCl₂­(η⁶-p-cymene)­(HC­NN^b) (1b) (HC­NN^b = 2-amino­methyl­benzo­[h]­quinoline) complexes have been obtained by reaction of the precursor [RuCl­(μ-Cl)­(η⁶-p-cymene)]₂ with the corresponding nitrogen ligand (HCNN^a and HCNN^b) in THF. Complex 1a reacts cleanly with monodentate (P = PPh₃) and bidentate phosphines (PP = dppb, dppf) in ethanol in the presence of NEt₃, affording the pincer catalysts RuCl­(CNN^a)­(PPh₃)₂ (2) and RuCl­(CNN^a)­(PP) (PP = dppb 3, dppf 4). Similarly, the benzo­[h]­quinoline pincer derivative RuCl­(CNN^b)­(dppb) (5) is obtained from 1b and dppb. Complex 3 has also been prepared in a one-pot reaction from [RuCl­(μ-Cl)­(η⁶-p-cymene)]₂, HCNN^a, and dppb in ethanol. Similarly, the chiral complex RuCl­(CNN^a)­((R,S)-Josiphos) was isolated as a single stereoisomer by treatment of [RuCl­(μ-Cl)­(η⁶-p-cymene)]₂ with HCNN^a and (R,S)-Josiphos in 1-butanol. Reaction of 1a and 1b with dppb affords cymene diphosphine species by displacement of the HCCN ligand.