Origin of Enantioselective Hydrogenation of Ketones by RuH2(diphosphine)(diamine) Catalysts: A Theoretical Study

Microwave-Assisted Synthesis of Zirconium Phosphate Nanoplatelet-Supported Ru-Anadem Nanostructures and Their Catalytic Study for the Hydrogenation of Acetophenone

The catalytic hydrogenation of organic compounds containing carbonyl groups has been extensively studied and widely used in industrial processes. Herein, we report the preparation of a novel nanomaterial, α-zirconium phosphate (α-ZrP) nanoplatelet-supported ruthenium nano-anadem catalyst, which possesses high selectivity in the catalytic hydrogenation of aromatic ketones. The α-ZrP nanoplatelets were prepared using a modified reflux method. Through an ion-exchange and reduction reaction pathway, ruthenium nanoparticles were loaded on ZrP to produce Ru-ZrP with a nano-anadem structure. The successful synthesis of Ru-ZrP composites is supported by a series of characterization techniques (PXRD, SEM, TEM, EDS, XPS, FT-IR, etc.). Compared with pure ZrP nanoplatelets, the catalytic hydrogenation of acetophenone has been dramatically improved when using Ru-ZrP. Full conversion was achieved at room temperature, and the yield of 1-cyclohexylehtanol was up to 95%. The effects of reaction time, reaction temperature, and hydrogen pressure were investigated. The investigation illustrates that there are two proposed reaction pathways in the hydrogenation of acetophenone, which are further supported by computational analyses. Recycling experiments indicate that the Ru-ZrP material could be reused four times without a noticeable activity decrease.

Amine-functionalized metal–organic framework-based Pd nanoparticles: highly efficient multifunctional catalysts for base-free aerobic oxidation of different alcohols

Metal–organic framework-based palladium nanoparticles are found to be highly efficient multifunctional catalysts for the base-free aerobic oxidation of different aliphatic, aromatic and hetero-aromatic alcohols.

The synthesis and reactivity of 16-electron half-sandwich iridium complexes bearing a carboranylthioamide ligand

The 16-electron complex 2 has been synthesized. It can react with different donor ligands and undergoes M–S bond insertion reactions with DMAD. Complex 2 is shown to react with [Cp*Ir] unit to form a M–M-bound binuclear complex. Interestingly, the metal–metal bond could be broken by HCl to produce the selective B(6)–H activation species.

The enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH2(diphosphine)(diamine) complexes: insights from a 3D-QSSR and DFT study

The 3D-QSSR method was carried out to investigate the enantioselectivity of the asymmetric ketone hydrogenation (AKH) catalyzed by RuH₂(diphosphine)(diamine) complexes integrating with DFT method, which could provide a way to design homogeneous transition-metal catalysts.

Phosphine-free chiral iridium catalysts for asymmetric catalytic hydrogenation of simple ketones

Phosphine free iridium catalysts with simple structures show efficient enantioselectivities and activities in the asymmetric hydrogenation of simple ketones by using chiral iridium catalysts to chiral alcohols with up to 96% ee.

The mechanism of enantioselective ketone reduction with Noyori and Noyori–Ikariya bifunctional catalysts

The present article describes the current level of understanding of the mechanism of enantioselective hydrogenation and transfer hydrogenation of aromatic ketones with pioneering prototypes of bifunctional catalysts, the Noyori and Noyori–Ikariya complexes.

Stereoselectivity in Asymmetric Catalysis: The Case of Ruthenium-Catalyzed Ketone Hydrogenation

The ruthenium-catalyzed asymmetric hydrogenation of simple ketones to generate enantiopure alcohols is an important process widely used in the fine chemical, pharmaceutical, fragrance, and flavor industries. Chiral diphosphine-RuCl2-1,2-diamine complexes are effective catalysts for the reaction giving high chemo- and enantioselectivity. However, no diphosphine-RuCl2-1,2-diamine complex has yet been discovered that is universal for all kinds of ketone substrates, and the ligands must be carefully chosen for each substrate. The procedure of finding the best ligands for a specific substrate can be facilitated by using virtual screening as a complement to the traditional experimental screening of catalyst libraries. We have generated a transition state force field (TSFF) for the ruthenium-catalyzed asymmetric hydrogenation of simple ketones using an improved Q2MM method. The developed TSFF can predict the enantioselectivity for 13 catalytic systems taken from the literature, with a mean unsigned error of 2.7 kJ/mol.

Ruthenium(II) Complexes Containing Lutidine-Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of C-N bonds

A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C-N bond assisted either by the pincer ligand or a second coordinated H2 molecule.

Unusual non-bifunctional mechanism for Co-PNP complex catalyzed transfer hydrogenation governed by the electronic configuration of metal center

The unusual non-bifunctional mechanism for Co^II-PNP catalyzed transfer hydrogenation is revealed to be governed by the electronic configuration of the metal center, which is different from traditional bifunctional catalysts.

Unravelling the mechanism of the asymmetric hydrogenation of acetophenone by [RuX2(diphosphine)(1,2-diamine)] catalysts

The mechanism of catalytic hydrogenation of acetophenone by the chiral complex trans-[RuCl2{(S)-binap}{(S,S)-dpen}] and KO-t-C4H9 in propan-2-ol is revised on the basis of DFT computations carried out in dielectric continuum and the most recent experimental observations. The results of these collective studies suggest that neither a six-membered pericyclic transition state nor any multibond concerted transition states are involved. Instead, a hydride moiety is transferred in an outer-sphere manner to afford an ion-pair, and the corresponding transition state is both enantio- and rate-determining. Heterolytic dihydrogen cleavage proceeds neither by a (two-bond) concerted, four-membered transition state, nor by a (three-bond) concerted, six-membered transition state mediated by a solvent molecule. Instead, cleavage of the H-H bond is achieved via deprotonation of the η(2)-H2 ligand within a cationic Ru complex by the chiral conjugate base of (R)-1-phenylethanol. Thus, protonation of the generated (R)-1-phenylethoxide anion originates from the η(2)-H2 ligand of the cationic Ru complex and not from NH protons of a neutral Ru trans-dihydride complex, as initially suggested within the framework of a metal-ligand bifunctional mechanism. Detailed computational analysis reveals that the 16e(-) Ru amido complex [RuH{(S)-binap}{(S,S)-HN(CHPh)2NH2}] and the 18e(-) Ru alkoxo complex trans-[RuH{OCH(CH3)(R)}{(S)-binap}{(S,S)-dpen}] (R = CH3 or C6H5) are not intermediates within the catalytic cycle, but rather are off-loop species. The accelerative effect of KO-t-C4H9 is explained by the reversible formation of the potassium amidato complexes trans-[RuH2{(S)-binap}{(S,S)-N(K)H(CHPh)2NH2}] or trans-[RuH2{(S)-binap}{(S,S)-N(K)H(CHPh)2NH(K)}]. The three-dimensional (3D) cavity observed within these molecules results in a chiral pocket stabilized via several different noncovalent interactions, including neutral and ionic hydrogen bonding, cation-π interactions, and π-π stacking interactions. Cooperatively, these interactions modify the catalyst structure, in turn lowering the relative activation barrier of hydride transfer by ~1-2 kcal mol(-1) and the following H-H bond cleavage by ~10 kcal mol(-1), respectively. A combined computational study and analysis of recent experimental data of the reaction pool results in new mechanistic insight into the catalytic cycle for hydrogenation of acetophenone by Noyori's catalyst, in the presence or absence of KO-t-C4H9.