title: CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: experimental and computational studies.
abstract: Reaction of [RuCl(CNN)(dppb)] (1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2 P(CH2 )4 PPh2 ) with NaOCH2 CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2 CF3 )(dppb)] (1-OCH2 CF3 ), whose neutron diffraction study reveals a short RuO⋅⋅⋅HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)]⋅(EtOH)n (1-OEt⋅n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] (1-H) and acetaldehyde. Compound 1-OEt⋅n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt⋅n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2 ) of ketones to alcohols (turnover frequency (TOF) up to 6.5×10(4) h(-1) , 40 °C). DFT calculations were performed on the reaction of [RuH(CNN')(dmpb)] (2-H) (HCNN'=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2 P(CH2 )4 PMe2 ) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key "amide" intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2 ; both pathways have low barriers and are alcohol assisted.
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine, Via Cotonificio 108, 33100 Udine (Italy), Fax: (+39) 0432-558803. walter.baratta@uniud.it.
authors.forename: Walter
authors.initials: W
authors.lastname: Baratta
authors.forename: Salvatore
authors.initials: S
authors.lastname: Baldino
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Calhorda
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Costa
authors.forename: Gennaro
authors.initials: G
authors.lastname: Esposito
authors.forename: Eberhardt
authors.initials: E
authors.lastname: Herdtweck
authors.forename: Santo
authors.initials: S
authors.lastname: Magnolia
authors.forename: Carlo
authors.initials: C
authors.lastname: Mealli
authors.forename: Abdelatif
authors.initials: A
authors.lastname: Messaoudi
authors.forename: Sax A
authors.initials: SA
authors.lastname: Mason
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
mesh_terms: D002384:Catalysis; D006865:Hydrogenation; D007659:Ketones / Q000737:chemistry*; D008958:Models, Molecular; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D007659:Ketones; D011725:Pyridines; D012428:Ruthenium
keywords: alkoxides; density functional theory; hydrogen transfer; hydrogenation; ruthenium