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

Abstract

Reaction of N-phenyl-2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dienimine (6) with Ru3CO12 formed two isomers of {[2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)(μ-CO)}2 (8-trans and 8-cis). Photolysis of 8 under a H2 atmosphere led to the formation of the aminocyclopentadienyl ruthenium hydride [2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)2H (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-Me2-3,4-Ph2(η5-C4CNH2Ph)]Ru(CO)2H}OTf (11-H), which reacted rapidly with benzaldehyde at −80 °C to give benzyl alcohol and [2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)2OTf (9-OTf). Reaction of 9-OTf with H2 and base led to the re-formation of 9-H. These reactions provide the transformations required for a catalytic cycle for hydrogenation of aldehydes