Mitsuhiko Fujiwhara

Efficient Access to Chiral Benzhydrols via Asymmetric Transfer Hydrogenation of Unsymmetrical Benzophenones with Bifunctional Oxo-Tethered Ruthenium Catalysts

A concise asymmetric transfer hydrogenation of diaryl ketones, promoted by bifunctional Ru complexes with an etherial linkage between 1,2-diphenylethylenediamine (DPEN) and η(6)-arene ligands, was successfully developed. Because of the effective discrimination of substituents at the ortho position on the aryl group, unsymmetrical benzophenones were smoothly reduced in a 5:2 mixture of formic acid and triethylamine with an unprecedented level of excellent enantioselectivity. For the non-ortho-substituted benzophenones, the oxo-tethered catalyst electronically discerned biased substrates, resulting in attractive performance yielding chiral diarylmethanols with >99% ee.

Atmospheric Hydrogenation of Esters Catalyzed by PNP-Ruthenium Complexes with an N-Heterocyclic Carbene Ligand

New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup.

N-Monomethylation of Aromatic Amines with Methanol via PNHP-Pincer Ru Catalysts

The use of methanol for the selective methylation of aromatic amines with RuHCl(CO)(PNHP) (PNHP = bis(2-diphenylphosphinoethyl)amine) is reported. Various aromatic amines were transformed into their corresponding monomethylated secondary amines in high yields at 150 °C with a very low catalyst loading (0.02-0.1 mol %) in the presence of KO tBu (20-60 mol %). The catalyst precursor, RuHCl(CO)(PNHP), was converted to [RuH(CO)2(PNHP)]+ under the catalytic conditions and also serves as a highly effective catalyst. The robustness of this catalyst contributes to its outstanding catalytic activity, even under reaction conditions, in which CO is liberated from methanol.