Protonated Aminocyclopentadienyl Ruthenium Hydride Reduction of Benzaldehyde and the Conversion of the Resulting Ruthenium Triflate to a Ruthenium Hydride with H<INF>2</INF> and Base

Reaction of N-phenyl-2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dienimine (<BO>6</BO>) with Ru<INF>3</INF>CO<INF>12</INF> formed two isomers of {[2,5-Me<INF>2</INF>-3,4-Ph<INF>2</INF>(η⁵-C<INF>4</INF>CNHPh)]Ru(CO)(μ-CO)}<INF>2</INF> (<BO>8-trans</BO> and <BO>8-cis</BO>). Photolysis of <BO>8</BO> under a H<INF>2</INF> atmosphere led to the formation of the aminocyclopentadienyl ruthenium hydride [2,5-Me<INF>2</INF>-3,4-Ph<INF>2</INF>(η⁵-C<INF>4</INF>CNHPh)]Ru(CO)<INF>2</INF>H (<BO>9-H</BO>). <BO>9-H</BO> reduced benzaldehyde slowly at 75 °C to give benzyl alcohol and <BO>8</BO>. Protonation of <BO>9-H</BO> with triflic acid produced {[2,5-Me<INF>2</INF>-3,4-Ph<INF>2</INF>(η⁵-C<INF>4</INF>CNH<INF>2</INF>Ph)]Ru(CO)<INF>2</INF>H}OTf (<BO>11-H</BO>), which reacted rapidly with benzaldehyde at −80 °C to give benzyl alcohol and [2,5-Me<INF>2</INF>-3,4-Ph<INF>2</INF>(η⁵-C<INF>4</INF>CNHPh)]Ru(CO)<INF>2</INF>OTf (<BO>9-OTf</BO>). Reaction of <BO>9-OTf</BO> with H<INF>2</INF> and base led to the re-formation of <BO>9-H</BO>. These reactions provide the transformations required for a catalytic cycle for hydrogenation of aldehydes.