71886-64-1Relevant articles and documents
Abiotic reduction of ketones with silanes catalysed by carbonic anhydrase through an enzymatic zinc hydride
Ji, Pengfei,Park, Jeeyoung,Gu, Yang,Clark, Douglas S.,Hartwig, John F.
, p. 312 - 318 (2021/02/26)
Enzymatic reactions through mononuclear metal hydrides are unknown in nature, despite the prevalence of such intermediates in the reactions of synthetic transition-metal catalysts. If metalloenzymes could react through abiotic intermediates like these, then the scope of enzyme-catalysed reactions would expand. Here we show that zinc-containing carbonic anhydrase enzymes catalyse hydride transfers from silanes to ketones with high enantioselectivity. We report mechanistic data providing strong evidence that the process involves a mononuclear zinc hydride. This work shows that abiotic silanes can act as reducing equivalents in an enzyme-catalysed process and that monomeric hydrides of electropositive metals, which are typically unstable in protic environments, can be catalytic intermediates in enzymatic processes. Overall, this work bridges a gap between the types of transformation in molecular catalysis and biocatalysis. [Figure not available: see fulltext.]
Synthetic scope of Ru(OH)x/Al2O3-catalyzed hydrogen-transfer reactions: An application to reduction of allylic alcohols by a sequential process of isomerization/meerwein-ponndorf-verley-iype reduction
Kim, Jung Won,Koike, Takeshi,Kotani, Miyuki,Yamaguchi, Kazuya,Mizuno, Noritaka
supporting information; experimental part, p. 4104 - 4109 (2009/05/07)
Reduction of allylic alcohols can be promoted efficiently by the supported ruthenium catalyst Ru(OH)x/Al2O3. Various allylic alcohols were converted to saturated alcohols in excellent yields by using 2-propanol without any additives. This Ru(OHx/Al 2O3-catalyzed reduction of a dienol proceeds only at the allylic double bond to afford the corresponding enol, and chemoselective isomerization and reduction can be realized under similar conditions. The catalysis is truly heterogeneous and the high catalytic performance can be maintained during at least three recycles of the Ru(OH)x/Al 2O3 catalyst. The transformation of allylic alcohols to saturated alcohols consists of three sequential reactions: oxidation of allylic alcohols to α,β-un-saturated carbonyl compounds; reduction of α,β-unsaturated carbonyl compounds to saturated carbonyl compounds; and reduction of saturated carbonyl compounds to saturated alcohols.
Synthetic scope and mechanistic studies of Ru(OH)x/Al 2O3-catalyzed heterogeneous hydrogen-transfer reactions
Yamaguchi, Kazuya,Koike, Takeshi,Kotani, Miyuki,Matsushita, Mitsunori,Shinachi, Satoshi,Mizuno, Noritaka
, p. 6574 - 6582 (2007/10/03)
Three kinds of hydrogen-transfer reactions, namely racemization of chiral secondary alcohols, reduction of carbonyl compounds to alcohols using 2-propanol as a hydrogen donor, and isomerization of allylic alcohols to saturated ketones, are efficiently promoted by the easily prepared and inexpensive supported ruthenium catalyst Ru(OH)x/Al2O 3. A wide variety of substrates, such as aromatic, aliphatic, and heterocyclic alcohols or carbonyl compounds, can be converted into the desired products, under anaerobic conditions, in moderate to excellent yields and without the need for additives such as bases. A larger scale, solvent-free reaction is also demonstrated: the isomerization of 1-octen-3-ol with a substrate/catalyst ratio of 20000/1 shows a very high turnover frequency (TOF) of 18400 h 1, with a turnover number (TON) that reaches 17200. The catalysis for these reactions is intrinsically heterogeneous in nature, and the Ru(OH)x/Al2O3 recovered after the reactions can be reused without appreciable loss of catalytic performance. The reaction mechanism of the present Ru(OH)x/Al2O 3-catalyzed hydrogentransfer reactions were examined with monodeuterated substrates. After the racemization of (S)-1-deuterio-1-phenylethanol in the presence of acetophenone was complete, the deuterium content at the α-position of the corresponding racemic alcohol was 91%, whereas no deuterium was incorporated into the α-position during the race mization of (S)-1-phenylethanol-OD. These results show that direct carbon-to-carbon hydrogen transfer occurs via a metal monohydride for the racemization of chiral secondary alcohols and reduction of carbonyl compounds to alcohols. For the isomerization, the α-deuterium of 3-deuterio-1-octen-3-ol was selectively relocated at the β-position of the corresponding ketones (99% D at the β-position), suggesting the involvement of a 1,4-addition of ruthenium monohydride species to the α,β-unsaturated ketone intermediate. The ruthenium monohydride species and the α,β-unsaturated ketone would be formed through alcoholate formation/β-elimination. Kinetic studies and kinetic isotope effects show that the Ru - H bond cleavage (hydride transfer) is included in the rate-determining step.
