Experimental Investigations of a Partial Ru–O Bond during the Metal–Ligand Bifunctional Addition in Noyori-Type Enantioselective Ketone Hydrogenation

Takebayashi, Satoshi; Dabral, Nupur; Miskolzie, Mark; Bergens, Steven H.

doi:10.1021/ja202732q

Cited by 71 publications

(46 citation statements)

References 68 publications

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“…This is the equivalent question, discussed in the literature, as to whether such dihydride complexes react with acetophenone to give directly the alcohol and the amido complex 1 via H + /Htransfer to the ketone in the transition state (path 2 to a polarized TS, then path 3 to 1, and then path 4 to the alkoxide complex 3 of Scheme 2) 1; 2; 4; 5; 7; 30 or to give an alkoxide complex 3 via an initial hydride transfer (path 2 to an ion pair TS that includes a hydrogenbonded alkoxide, then path 5 to 3 in Scheme 2). 19; [31][32][33][34][35][36] Arguments have been made for each pathway depending on the solvent and other conditions. An observation in the current work is that the alkoxide forms quickly from the amido complex and alcohol and is more prevalent at low temperatures.…”

Section: Discussionmentioning

confidence: 99%

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂

et al. 2014

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The hydrido–amido complex OsH(NHCMe2CMe2NH2)(PPh3)2 (1) catalyzes the base-free hydrogenation of ketones in benzene. Kinetic studies using acetophenone revealed that the system has an induction period, after which the rate of the reaction increases. A constant rate was observed when a critical amount of the product alcohol was added, indicating that the reaction is autocatalytic in 1-phenylethanol. Varying the initial conditions showed that the reaction rate is dependent on hydrogen and catalyst concentration and independent of ketone concentration. Above the critical concentrations of 1-phenylethanol, the reaction rate is independent of alcohol concentration. The rate law for pressures up to 5 atm was found to be rate = d[alcohol]/dt = −d[ketone]/dt = k[Os][H2], with k = 30 mol L−1 s−1 at 293 K and the temperature dependence provided energy of activation parameters. Therefore, the heterolytic splitting of dihydrogen is rate determining under these conditions. Only small kinetic isotope effects were measured in contrast with the analogous ruthenium system. Complex 1 reacts with the product alcohol 1-phenylethanol and is partially converted into the dihydride complex trans-OsH2(NH2CMe2CMe2NH2)(PPh3)2 and acetophenone; with excess alcohol, an osmium alkoxide is observed at low temperature. As expected from these results, 1 is a ketone transfer hydrogenation catalyst in isopropanol.

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Section: Discussionmentioning

confidence: 99%

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂

et al. 2014

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“…Bergens et al. later proposed that a partial RuO bond or a strong H‐bond between NH and alkoxide could be present in the transition state based on the observed formation of alkoxide intermediates at low temperatures 12…”

Section: Metal–ligand Cooperation Through Ml Bondsmentioning

confidence: 99%

Metal–Ligand Cooperation

2015

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Metal-ligand cooperation (MLC) has become an important concept in catalysis by transition metal complexes both in synthetic and biological systems. MLC implies that both the metal and the ligand are directly involved in bond activation processes, by contrast to "classical" transition metal catalysis where the ligand (e.g. phosphine) acts as a spectator, while all key transformations occur at the metal center. In this Review, we will discuss examples of MLC in which 1) both the metal and the ligand are chemically modified during bond activation and 2) bond activation results in immediate changes in the 1st coordination sphere involving the cooperating ligand, even if the reactive center at the ligand is not directly bound to the metal (e.g. via tautomerization). The role of MLC in enabling effective catalysis as well as in catalyst deactivation reactions will be discussed.

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“…19 Conversely, Bergens reported that [Ru(H) 2 (binap)(dpen)] reacts with acetophenone leading to [RuH(OR)(binap)(dpen)] at low temperature 20. The formation of the Ru‐amide and 1‐phenylethanol occurs at a subsequent step and an alternative pathway involving a transition state with a partial RuO linkage has been proposed 21. Evidence of the formation of alkoxides [RuH(OR)(PP)(1,2‐diamine)] and alcohol complexes [RuH(HOR)(PP)(1,2‐diamine)] + , which are involved in the heterolytic cleavage of H 2 has been provided by the groups of Morris,18 Noyori,22 and Bergens 23.…”

Section: Introductionmentioning

confidence: 99%

CNN Pincer Ruthenium Catalysts for Hydrogenation and Transfer Hydrogenation of Ketones: Experimental and Computational Studies

Baratta

Baldino

Calhorda

et al. 2014

Chemistry A European J

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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.

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Experimental Investigations of a Partial Ru–O Bond during the Metal–Ligand Bifunctional Addition in Noyori-Type Enantioselective Ketone Hydrogenation

Cited by 71 publications

References 68 publications

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂

Metal–Ligand Cooperation

CNN Pincer Ruthenium Catalysts for Hydrogenation and Transfer Hydrogenation of Ketones: Experimental and Computational Studies

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Experimental Investigations of a Partial Ru–O Bond during the Metal–Ligand Bifunctional Addition in Noyori-Type Enantioselective Ketone Hydrogenation

Cited by 71 publications

References 68 publications

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe2CMe2NH2)(PPh3)2

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe2CMe2NH2)(PPh3)2

Metal–Ligand Cooperation

CNN Pincer Ruthenium Catalysts for Hydrogenation and Transfer Hydrogenation of Ketones: Experimental and Computational Studies

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Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe₂CMe₂NH₂)(PPh₃)₂