Asymmetric Transfer Hydrogenation of Ketone Catalyzed by Novel Ru(II)-Chiral Sulfonamide Complex

Two new chiral Ru(II)-sulfonamide complex have been used to catalyze the enantioselective transfer hydrogenation of prochiral ketones and the secondary alcohols are obtained with good to excellent optical yields.     

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation,Transfer Hydrogenation,and Related Processes

The preparation of chiral alcohols and amines by using iridium catalysis is reviewed. The methods presented include the reduction of ketones or imines by using hydrogen (hydrogenations), isopropanol, formic acid, or formate (transfer hydrogenations). Also dynamic and oxidative kinetic resolutions leading to chiral alcohols and amines are included. Selected literature reports from early contributions to December 2012 are discussed.     

Catalytic Mechanisms of Transfer Hydrogenation of Azobenzene with Ammonia Borane by Pincer Bismuth Complex: Crucial Role of C=N Functional Group on the Pincer Ligand

Transfer hydrogenation of azobenzene with ammonia borane mediated by pincer bismuth complex 1 was systematically investigated through density functional theory calculations. An unusual metal-ligand cooperation mechanism was disclosed, in which the saturation/regeneration of the C=N functional group on the pincer ligand plays an essential role. The reaction is initiated by the hydrogenation of the C=N bond (saturation) with ammonia borane to afford 3^CN , which is the rate-determining step with Gibbs energy barrier (ΔG^≠) and Gibbs reaction energy (ΔG) of 25.6 and −7.3 kcal/mol, respectively. 3^CN is then converted to a Bi−H intermediate through a water-bridged pathway, which is followed up with the transfer hydrogenation of azobenzene to produce the final product N,N′-diphenylhydrazine and regenerate the catalyst. Finally, the catalyst could be improved by substituting the phenyl group for the tert-butyl group on the pincer ligand, where the ΔG^≠ value (rate-determining step) decreases to 24.0 kcal/mol.     

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

Reaction of [RuCl(CNN)(dppb)] ( 1‐Cl ) (HCNN=2‐aminomethyl‐6‐(4‐methylphenyl)pyridine; dppb=Ph₂P(CH₂)₄PPh₂) with NaOCH₂CF₃ leads to the amine‐alkoxide [Ru(CNN)(OCH₂CF₃)(dppb)] ( 1‐OCH₂CF₃ ), 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 6.5×10⁴ h^?1, 40 °C). DFT calculations were performed on the reaction of [RuH(CNN′)(dmpb)] ( 2‐H ) (HCNN′=2‐aminomethyl‐6‐(phenyl)pyridine; dmpb=Me₂P(CH₂)₄PMe₂) 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.     

手性羰基铁体系催化酮的不对称氢转移氢化

手性羰基铁络合物很少被用于芳香酮的不对称氢转移氢化.利用不同的羰基铁络合物与手性双胺双膦配体现场络合,形成手性胺膦铁催化体系.考察了它们对多种芳香酮的不对称氢转移催化氢化性能.结果表明,三核的手性胺膦铁簇合物是催化芳香酮不对称氢转移氢化的较好体系.当用三核的铁簇合物[Et₃NH]⁺[HFe₃(CO)₁₁]^-体系催化1,1-二苯基丙酮的氢化时,最高可获得98%的对映选择性.通过现场红外光谱测定,揣测羰基铁簇合物Fe₃(CO)₁₂在催化反应过程中保持三核的簇合物的簇骼不变.     

联二萘酚衍生手性磷酸在亚胺不对称转移氢化反应中的应用研究进展

综述了BINOL衍生手性磷酸在亚胺不对称转移氢化反应中的应用研究进展。根据亚胺不对称转移氢化反应中三类不同的氢供体--Hantzsch酯类氢源、2-取代苯并噻唑啉类氢源及其他氢源,对BINOL衍生手性磷酸催化的亚胺不对称转移氢化反应进行了重点介绍。参考文献５３篇。     

Rhodium-terpyridine Catalyzed Transfer Hydrogenation of Aromatic Nitro Compounds in Water

A rhodium terpyridine complex catalyzed transfer hydrogenation of nitroarenes to anilines with i-PrOH as hydrogen source and water as solvent has been developed. The catalytic system can work at a substrate/catalyst (S/C) ratio of 2000, with a turnover frequency (TOF) up to 3360 h⁻¹, which represents one of the most active catalytic transfer hydrogenation systems for nitroarene reduction. The catalytic system is operationally simple and the protocol could be scaled up to 20 gram scale. The water-soluble catalyst bearing a carboxyl group could be recycled 15 times without significant loss of activity.     

A Concerted Transfer Hydrogenolysis: 1,3,2‐Diazaphospholene‐Catalyzed Hydrogenation of NN Bond with Ammonia–Borane

1,3,2‐diazaphospholenes catalyze metal‐free transfer hydrogenation of a N?N double bond using ammonia–borane under mild reaction conditions, thus allowing access to various hydrazine derivatives. Kinetic and computational studies revealed that the rate‐determining step involves simultaneous breakage of the B? H and N? H bonds of ammonia–borane. The reaction is therefore viewed as a concerted type of hydrogenolysis.     

Pd8簇催化氢化乙炔的反应机理

采用密度泛函理论(DFT)中的B3PW91方法研究了过渡金属Pd₈簇催化氢化乙炔的反应机理. 研究表明: H₂进入Pd₈簇后解离成H原子, 并且只有当H原子吸附在Pd₈簇表面上时, 催化氢化反应才能发生. 过渡金属Pd₈簇催化氢化乙炔的反应机理的研究证实该催化反应从两种反应物出发经过两条不同的反应途径完成催化氢化反应, 两种反应物分别为吸附在Pd₈簇上的乙炔(Pd₈(2H)－CH＝CH)和其同分异构体亚乙烯基吸附物(Pd₈(2H)－C＝CH₂). 两条途径均为多步连续的加氢反应, 不同之处在于从Pd₈(2H)－CH＝CH出发的为单一路径, 解离后的H原子分步依次加成到吸附在Pd₈簇上的乙炔中的C原子上, 直到反应完成生成乙烷. 而从Pd₈(2H)－C＝CH₂出发的路径较为复杂, 分别经过两个不同的过渡态和中间体生成次乙基中间体, 该过程相对应的反应位垒相差约12.552 kJ·mol^-1, 说明这两个过渡态同时存在, 无先后次序. 然后继续加成H原子直到生成乙烷完成反应. 同时, 两条路径分别形成一系列具有应用价值的C₂有机化合物中间体, 其中一些中间体通过分子内质子转移相互转化, 使得原本独立的两条反应路径联系在一起, 成为网状路径.     

Mild and Selective Cobalt‐Catalyzed Chemodivergent Transfer Hydrogenation of Nitriles

Herein, we describe a selective cobalt‐catalyzed chemodivergent transfer hydrogenation of nitriles to synthesize primary, secondary, and tertiary amines. The solvent effect plays a key role for the selectivity control. The general applicability of this procedure was highlighted by the synthesis of more than 70 amine products bearing various functional groups in high chemoselectivity. Moreover, this mild system achieved >2000 TONs (turnover numbers) for the transfer hydrogenation of nitriles.     

A Continuously Regenerable Chiral Ammonia Borane for Asymmetric Transfer Hydrogenations

A novel chiral ammonia borane was designed and developed through the dehydrogenation of ammonia borane with a chiral phosphoric acid, which was highly effective for the asymmetric transfer hydrogenation of imines and β‐enamino esters to afford high levels of reactivities and enantioselectivities. Significantly, this chiral ammonia borane can be continuously regenerated during the transfer hydrogenation with the assistance of water and ammonia borane, which made it possible to obtain satisfactory results using only 0.1 mol % of the chiral phosphoric acid. Notably, the role of chiral phosphoric acid is to produce the chiral ammonia borane.     

Theoretical Study of Hydrogen Production from Ammonia Borane Catalyzed by Metal and Non-Metal Diatom-Doped Cobalt Phosphide

The decomposition of ammonia borane (NH₃BH₃) to produce hydrogen has developed a promising technology to alleviate the energy crisis. In this paper, metal and non-metal diatom-doped CoP as catalyst was applied to study hydrogen evolution from NH₃BH₃ by density functional theory (DFT) calculations. Herein, five catalysts were investigated in detail: pristine CoP, Ni- and N-doped CoP (CoP_Ni-N), Ga- and N-doped CoP (CoP_Ga-N), Ni- and S-doped CoP (CoP_Ni-S), and Zn- and S-doped CoP (CoP_Zn-S). Firstly, the stable adsorption structure and adsorption energy of NH₃BH₃ on each catalytic slab were obtained. Additionally, the charge density differences (CDD) between NH₃BH₃ and the five different catalysts were calculated, which revealed the interaction between the NH₃BH₃ and the catalytic slab. Then, four different reaction pathways were designed for the five catalysts to discuss the catalytic mechanism of hydrogen evolution. By calculating the activation energies of the control steps of the four reaction pathways, the optimal reaction pathways of each catalyst were found. For the five catalysts, the optimal reaction pathways and activation energies are different from each other. Compared with undoped CoP, it can be seen that CoP_Ga-N, CoP_Ni-S, and CoP_Zn-S can better contribute hydrogen evolution from NH₃BH₃. Finally, the band structures and density of states of the five catalysts were obtained, which manifests that CoP_Ga-N, CoP_Ni-S, and CoP_Zn-S have high-achieving catalytic activity and further verifies our conclusions. These results can provide theoretical references for the future study of highly active CoP catalytic materials.     

Spontaneous trans‐Selective Transfer Hydrogenation of Apolar Boron–Boron Double Bonds

The transfer hydrogenation of N‐heterocyclic carbene (NHC)‐supported diborenes with dimethylamine borane proceeds with high selectivity for the trans‐1,2‐dihydrodiboranes. DFT calculations, supported by kinetic studies and deuteration experiments, suggest a stepwise proton‐first‐hydride‐second reaction mechanism via an intermediate μ‐hydrodiboronium dimethylaminoborate ion pair.     

Nickel‐Catalyzed Asymmetric Transfer Hydrogenation of Hydrazones and Other Ketimines

We report the use of nickel catalysts for the catalytic transfer hydrogenation of hydrazones and other ketimines with formic acid. Strongly donating bisphosphines must be used to support the catalysts. As in enzymatic catalysis, attractive weak interactions may be important for stereochemical control by the nickel/binapine catalyst.     

Hydrogenation and Transfer Hydrogenation Promoted by Tethered Ru−S Complexes: From Cooperative Dihydrogen Activation to Hydride Abstraction/Proton Release from Dihydrogen Surrogates

Hydrogenation and transfer hydrogenation of imines with cyclohexa‐1,4‐dienes, as well as with a representative Hantzsch ester dihydrogen surrogate, are reported. Both processes are catalyzed by tethered Ru?S complexes but differ in the activation mode of the dihydrogen source: cooperative activation of the H?H bond at the Ru?S bond leads to the corresponding Ru?H complex and protonation of the sulfur atom, whereas the same cationic Ru?S catalyst abstracts a hydride from a donor‐substituted cyclohexa‐1,4‐diene to form the neutral Ru?H complex and a low‐energy Wheland intermediate. A sequence of proton and hydride transfers on the imine substrate then yields an amine. The reaction pathways are analyzed computationally, and the established mechanistic pictures are in agreement with the experimental observations.     

Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.     

Chemoselective Hydrazine‐mediated Transfer Hydrogenation of Nitroarenes by Co3O4 Nanoparticles Immobilized on an Al/Si‐mixed Oxide Support

Cobalt oxide nanoparticles (size 2 to 3.5 nm) were successfully impregnated on an alumina–silica (mixed oxide) support through an experimentally viable and easily reproducible protocol. The prepared material was well characterized by XRD, HR‐TEM, BET surface area, EDX and XPS analyses. Porous alumina–silica having a high surface area served as a protective heterogeneous support on which the well‐dispersed Co₃O₄ nanoparticles served as an active catalytic species for the hydrazine‐mediated transfer hydrogenation of nitroarenes. About 2 mol % of the active catalyst in ethanol at 60 °C was adequate for a successful conversion. Moreover, transfer hydrogenation of nitroarenes by the catalyst was found to take place chemoselectively in the presence of other labile functional groups such as halide, alkene, nitrile, carbonyl, and ester. This inexpensive catalyst was also able to catalyze the reaction on a gram scale reaction and found to be robust and recyclable up to eight runs.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

Hydroaminomethylation Beyond Carbonylation: Allene–Imine Reductive Coupling by Ruthenium‐Catalyzed Transfer Hydrogenation

Ruthenium(II)‐catalyzed hydrogen transfer from 2‐propanol mediates reductive coupling of 1,1‐disubstituted allenes with formaldimines with complete branch‐regioselectivity, thus representing a new method for hydroaminomethylation beyond classical hydroformylation/reductive amination.