A Ruthenium−Dihydrogen Putative Intermediate in Ketone Hydrogenation

The compound fac-[Ru((R)-BINAP)(H)(2-PrOH)3]+ (6) (BINAP = 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl) reacts with (R,R)-dpen (dpen = 1,2-diphenylethylenediamine) under H2 at −60 °C in 2-PrOH-d 8/CD2Cl2 to generate the cationic dihydrogen putative intermediate trans-[Ru((R)-BINAP)(H)(η2-H2)((R,R)-dpen)]+ (2‘) without H−D exchange between the hydrogen ligands and the solvent. A 1H NMR study concludes that the dihydrogen ligand in 2‘ does not protonate 2-PrOH to a catalytically significant extent, and that 2‘ requires an added base or hydride source to be an active catalyst.