Protonated Aminocyclopentadienyl Ruthenium Hydride Reduction of Benzaldehyde and the Conversion of the Resulting Ruthenium Triflate to a Ruthenium Hydride with H₂ and Base

Reaction of N -phenyl-2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dienimine ( 6 ) with Ru 3 CO 12 formed two isomers of {[2,5-Me 2 -3,4-Ph 2 (η 5 -C 4 CNHPh)]Ru(CO)(μ-CO)} 2 ( 8-trans and 8-cis ). Photolysis of 8 under a H 2 atmosphere led to the formation of the aminocyclopentadienyl ruthenium hydride [2,5-Me 2 -3,4-Ph 2 (η 5 -C 4 CNHPh)]Ru(CO) 2 H ( 9-H ). 9-H reduced benzaldehyde slowly at 75 °C to give benzyl alcohol and 8 . Protonation of 9-H with triflic acid produced {[2,5-Me 2 -3,4-Ph 2 (η 5 -C 4 CNH 2 Ph)]Ru(CO) 2 H}OTf ( 11-H ), which reacted rapidly with benzaldehyde at −80 °C to give benzyl alcohol and [2,5-Me 2 -3,4-Ph 2 (η 5 -C 4 CNHPh)]Ru(CO) 2 OTf ( 9-OTf ). Reaction of 9-OTf with H 2 and base led to the re-formation of 9-H . These reactions provide the transformations required for a catalytic cycle for hydrogenation of aldehydes.