110-89-4

Photocatalytic reaction at 298 K by platinum-loaded titanium(IV) oxide (TiO2-Pt) particles suspended in deaerated aqueous solutions of 2-propanol or (S)-lysine (Lys) was investigated. The TiO2 catalysts with various amounts of Pt loadings were prepared by impregnation from aqueous chloroplatinic acid solution onto a commercial TiO2 (Degussa P-25) followed by hydrogen reduction at 753 K. The physical properties of deposited Pt, e.g., particle size, surface area, and electronic state, were studied respectively by transmission electron microscopy, volumetric gas adsorption measurement, and X-ray photoelectron spectroscopy as well as infrared spectroscopy of adsorbed carbon monoxide. The increase in Pt amount mainly resulted in an increase of the number of Pt deposits, not of their size. The catalysts were suspended in the aqueous solutions and photoirradiated at a wavelength >300 nm under an argon (Ar) atmosphere. The overall rate of photocatalytic reactions for both 2-propanol and Lys, corresponding to the rate of consumption of these substrates, was negligible without Pt loading, increased drastically with the loading up to ca. 0.3%, and was almost constant or a little decreased by the further loadings. However, the rate of formation of pipecolinic acid (PCA) from Lys was improved gradually with a increase of Pt loading up to ca. 2 wt %. These dependences were discussed as a function of Pt surface area, which is employed as a measure that includes the properties of both number and size of Pt deposits. For the photocatalytic dehydrogenation of 2-propanol, the rate dependence could be interpreted semiquantitatively with the model that only the TiO2 particles loaded with at least one Pt deposit can photocatalyze, but the reaction rate is independent of the number of Pt deposits. Therefore, the overall rate is proportional to the number of Pt-loaded TiO2 particles. On the other hand, for the interpretation of the rate of PCA and H2 productions, the number of Pt deposits on each TiO2 particle had to be taken into account. The efficient production of PCA at higher Pt loadings was attributed to the reduction of a Schiff base intermediate produced via oxidation of Lys with positive holes and subsequent intramolecular condensation at the Pt deposit that is close to the site for the oxidation. Otherwise, photoexcited electrons are consumed for H2 production and the intermediate remains unreduced or undergoes further oxidation. It was suggested that the intermediate produced at the TiO2 surface sites within a distance of several nanometers from the Pt deposit undergoes efficient reduction to PCA. Thus, the importance of the distribution of Pt deposits for the preparation of highly active and selective TiO2-Pt photocatalyst has been clearly demonstrated.

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Rate (k1) and equilibrium constants (K1) for piperidine and morpholine addition to benzylidene Meldrum's acid (BMA) and substituted BMA's (Z=4-NO2, 3-Cl, 4-CN, 4-OMe, 4-NMe2, 4-NEt2) were determined in water and in 50percent, 70percent, and 90percent aqueous Me2SO.The equilibrium for addition is highly favorable, with K1 values (piperidine) as high as 7.8*107M-1, which is the highest value measured in a series of olefins of the type PhCH=CXY.The rates are also quite high (k1 up to 2.1*106M-1s-1), indicating a relatively high intrinsic rate constant (k0=k1 for K1=1) which ranks BMA second among seven PhCH=CXY-type olefins with respect to kinetic reactivity.This ranking is "reasonable" based on a correlation between k0 for nucleophilic addition to PhCH=CXY and k0 for deprotonation of carbon acids of the type CH2XY.βnucn (d log k1/ d log K1, variation of amine) is very amall, particularly in aqueous solution.This result appears to be part of a trend toward lower βnucn values with increasing thermodynamic stability of the adducts of PhCH=CXY. αnucn (d log k1/ d log K1, variation of Z) is significantly larger than βnucn, implying a substantial imbalance in these reactions.However, after correction of αnucn for the effect of the developing positive charge on the amine nitrogen the remaining "true" imbalance is quite small.The small imbalance as well as the high k0 value are consistent with the Meldrum's acid anion deriving most of its exceptional stability from its bislactone structure rather than from resonance.Strong ?-donor substituents (4-NMe2, 4-NEt2) have a strong stabilizing effect on the olefin, leading to a large reduction in K1.Contrary to expectations based on the principle of nonperfect synchronization (PNS), this resonance effect does not lead to a strong reduction of the intrinsic rate constant, probably because the polarization in the olefin (Me2N+=C6H4+CHC(COO)2-C(CH3)2) helps in partially offsetting the PNS effect caused by delayed development of resonance on the carbanionic side of the adduct

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A ruthenium(II) diamine complex can catalyze the intramolecular cyclization of amino alcohols H2N(CH2)nOH via two pathways: (i) one yields the cyclic secondary amine by a redox-neutral hydrogen-borrowing route with loss of water; and (ii) the second gives the corresponding cyclic amide by a net oxidation involving loss of H2. The reaction is most efficient in cases where the product has a six-membered ring. The amide and amine pathways are closely related: DFT calculations show that both amine and amide formations start with the oxidation of the amino alcohol, 5-amino-1-pentanol, to the corresponding amino aldehyde, accompanied by reduction of the catalyst. The intramolecular condensation of the amino aldehyde takes place either in the coordination sphere of the metal (path I) or after dissociation from the metal (path II). Path I yields the Ru-bound zwitterionic form of the hemiaminal protonated at nitrogen, which eliminates H2, forming the amide product. In path II, the free hemiaminal dehydrates, giving an imine, which yields the amine product by hydrogenation with the reduced form of the catalyst generated in the initial amino alcohol oxidation. For amide to be formed, the hemiaminal must remain metal-bound in the key intermediate and the elimination of H2 must occur from the same intermediate to provide a vacant site for β-elimination. The elimination of H2 is affected by an intramolecular H-bond in the key intermediate. For amine to be formed, the hemiaminal must be liberated for dehydration to imine and the H2 must be retained on the metal for reduction of the imine intermediate.

The reactions named in the title, which form N-(2,4-dinitro-1-naphthyl) derivatives of these heterocyclic amines, occur in two distinct stages.In stage I, the spectrum of a ?-adduct intermediate develops at a rate which is measurable in a stopped flow apparatus; in stage II, it decays at a slower and easily measurable rate.The kinetics of both stage I and stage II have been studied.Pyrrolidine and piperidine are similar in their stage I behavior, but reactivity in stage II is about 11000 times greater in the pyrrolidine system.This huge difference between systems apparently so similar is judged to arise from steric interactions forced by differences in conformation between the amino moieties in the intermediate ? adducts as they release the nucleofuge.It calls into question the rate-limiting proton transfer interpretation of base catalysis in analogous aminodephenoxylation reactions in protic solvents.

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A novel amine-assisted route for low temperature homogeneous hydrogenation of CO to methanol is described. The reaction proceeds through the formation of formamide intermediates. The first amine carbonylation part is catalyzed by K3PO4. Subsequently, the formamides are hydrogenated in situ to methanol in the presence of a commercially available ruthenium pincer complex as a catalyst. Under optimized reaction conditions, CO (up to 10 bar) was directly converted to methanol in high yield and selectivity in the presence of H2 (70 bar) and diethylenetriamine. A maximum TON of 539 was achieved using the catalyst Ru-Macho-BH. The high yield, selectivity, and TONs obtained for methanol production at low reaction temperature (145 °C) could make this process an attractive alternative over the traditional high temperature heterogeneous catalysis.

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Herein, we report an enzymatic cascade involving an oxidase, an imine reductase and a hydrogenase for the H2-driven synthesis of N-heterocycles. Variants of putrescine oxidase from Rhodococcus erythropolis with improved activity were identified. Substituted pyrrolidines and piperidines were obtained with up to 97% product formation in a one-pot reaction directly from the corresponding diamine substrates. The formation of up to 93% ee gave insights into the specificity and selectivity of the putrescine oxidase.

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Protonated pyridine (PyH+) has been reported to act as a peculiar and promising catalyst for the direct electroreduction of CO2 to methanol and/or formate. Because of recent strong incentives to turn CO2 into valuable products, this claim triggered great interest, prompting many experiments and DFT simulations. However, when performing the electrolysis in near-neutral pH electrolyte, the local pH around the platinum electrode can easily increase, leading to Py and HCO3? being the predominant species next to the Pt electrode instead of PyH+ and CO2. Using a carefully designed electrolysis setup which overcomes the local pH shift issue, we demonstrate that protonated pyridine undergoes a complete hydrogenation into piperidine upon mild reductive conditions (near 0 V vs. RHE). The reduction of the PyH+ ring occurs with and without the presence of CO2 in the electrolyte, and no sign of CO2 electroreduction products was observed, strongly questioning that PyH+ acts as a catalyst for CO2 electroreduction.

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The gas-phase elimination kinetics of the above-mentioned compounds were determined in a static reaction system over the temperature range of 369-450.3°C and pressure range of 29-103.5 Torr, The reactions are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3-(piperidin-1-yl) propionate, log κ1(s-1) = (12.79 ± 0.16) - (199.7±2.0) kJ mol-1 (2.303 RT)-1; ethyl 1-methylpiperidine-3-carboxylate, log κ1(s-1) = (13.07 ± 0.12)-(212.8 ± 1.6) kJmol-1 (2,303 RT) -1; ethyl piperidine-3-carboxylate, log κ1(s -1) = (13.12 ± 0.13) - (210.4 ± 1.7) kJ mol -1 (2.303 RT)-1 and 3-piperidine carboxylic acid, log κ1(s-1) = (14.24 ± 0.17) - (234.4 ± 2.2) kJ mol-1 (2.303 RT)-1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six-membered cyclic transition state type of mechanism. The intermediate β-amino acids decarboxylate as the α-amino acids but in terms of a semipolar six-membered cyclic transition state mechanism.

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Vapor phase dehydration of 5-amino-1-pentanol to produce piperidine was investigated over various oxide catalysts such as ZrO2, TiO2, Al2O3 and SiO2. Among the tested catalysts, SiO2 selectively produced piperidine at 300 °C. A high 5-amino-1-pentanol conversion of 99.9% with a piperidine selectivity of 94.8% was achieved over weak acidic SiO2. In an experiment using isotope such as deuterated water, surface hydroxy groups of SiO2 are concluded to be the active centers.

1-Azaphenothiazine catalyses the intramolecular cyclization of N-(bromoalkyl)phthalimides in the presence of anhydrous K2CO 3 to form spiro cyclic quaternary ammonium salts, namely azoniaspiro compounds, under microwave irradiation. A novel and ecofriendly method was developed for the synthesis of azoniaspiro compounds, and the role of azaphenothiazine as a catalyst in such reactions has been established for the first time. In the future, this protocol can be extended to the synthesis of various substituted N-heterocycles by hydrolyzing the resulting azoniaspiro compounds.

Piperidine and morpholine add to substituted benzylidenemalononitriles (Z-C6H4CH=C(CN)2) to form a zwitterionic adduct, Z-C6H4CH(R2NH+)C(CN)2-(T+/-), which is in rapid acid-base equilibrium with the anionic adduct, Z-C6H4CH(R2N)C(CN)2-(T-).Rate constans for amine addition (k1) were determined by direct rate measurements while equilibrium constans for addition (K1) as well as pKa+/- values of the zwitterions were obtained spectrophotometrically.The bulk of the measurements was carried out in 50percent Me2SO-50percent water with piperidine, while a smaller number of experiments were performed with morpholine, and with both amines in water and in 70percent Me2SO-30percent water.The reactions show the typical bahavior of a carbanion-forming process in which the carbanion derives a good part of its stabilization from polar effects while resonance effects play a more modest role.This behavior includes a high intrinsic rate constant (k0 = k when K = 1), a small transition-state imbalance, and a relatively small solvent effect on the intrinsic rate constant.The observation of an imbalance suggests that the deprotonation of malononitrile derivatives by carboxylate ions should also have an imbalanced transition state.The fact that none has been observed is attributed to a solvation effect of the carboxylic acid, which enhances the Broensted βB value, as recently suggested by Murray and Jencks.The 4-Me2N substituent leads to strong resonance stabilization of the olefin as indicated by a low K1 value.Contrary to expectation of a lowered intrinsic constant, this resonance stabilization has little effect on k0.This suggests theoperation of a compensating factor which increases k0 and which can be understood as an attenuation of the reduction in k0 caused by late development of resonance at the carbanionic center of the adduct.

Rate and equilibrium measurements are reported for the reactions of 1,3,5-trinitrobenzene with pyrrolidine and with piperidine in dimethyl sulphoxide (DMSO) and in a DMSO-water mixture.These reactions lead to the formation of anionic ?-adducts via zwitterionic intermediates and it is shown that proton transfer is rate-limiting or partially rate-limiting.In DMSO the rate of proton transfer is an order of magnitude faster for the reaction with pyrrolidine than for the reaction with piperidine.However, the addition of water reduces this difference.Implications for the mechanism of base catalysis in nucleophilic aromatic substitution reactions are discussed.

The storage of renewable energy is the major hurdle during the transition of fossil resources to renewables. A possible solution is to convert renewable electricity to chemical energy carriers such as hydrogen for storage. Herein, a highly efficient formate-piperidine-adduct (FPA) based hydrogen storage system was developed. This system has shown rapid reaction kinetics of both hydrogenation of piperidine-captured CO2 and dehydrogenation of the FPA over a carbon-supported palladium nano-catalyst under mild operating conditions. Moreover, the FPA solution based hydrogen storage system is advantageous owing to the generation of high-purity hydrogen, which is free of carbon monoxide and ammonia. In situ ATR-FTIR characterization was performed in order to provide insight into the reaction mechanisms involved. By integrating this breakthrough hydrogen storage system with renewable hydrogen and polymer electrolyte membrane fuel cells (PEMFC), in-demand cost-effective rechargeable hydrogen batteries could be realized for renewable energy storage.

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An unusual fragmentation reaction that affords a carbamoyl anion discovered during the course of the synthesis of rigidified PCP analogues is reported.

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The hydrolysis reactions of N-(2,4-dinitrophenyl)piperidine (7) and N-(2,4-dinitrophenyl)morpholine (8) were studied.Both reactions lead quantitatively to the formation of 2,4-dinitrophenol.They are second order toward the HO- concentration and are strongly catalyzed by the amine leaving group.The catalysis is interpreted in terms of the formation of 1,3-? complexes with the amine or the HO-, which then react with another hydroxide ion to give the final product.The reactivity of the 1,3-? complexes toward HO- is higher than that of the substrates themselves.

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Herein, we report the synthesis of specific silica-supported Co/Co3O4 core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.

The adsorption and reaction of a variety of organonitrogen compounds on a Ni(100) surface have been examined with temperature-programmed reaction, Auger electron spectroscopy, and infrared spectroscopy. Monomethylamine adsorbs via the nitrogen lone pair of electrons and then undergoes C-N bond scission yielding adsorbed carbon, dihydrogen, and ammonia. Aniline pi -bonds to the surface and polymerizes to form a thermally stable poly(aniline) surface film. Pyridine undergoes a temperature-induced orientational transformation. At low temperatures pyridine adsorbs with its ring parallel to the surface. At higher temperatures it appears to form an alpha -pyridyl species with an activation barrier of 85 kJ/mol. Methyl groups on 2,6-lutidine sterically hinder this reaction.

Cyclization of diols with ammonia in an H2 atmosphere over an industrial CuO-ZnO-Al2O3 catalyst for the synthesis of methanol (SNM-1) gives nitrogen-containing five-, six-, or seven-membered heterocyclic compounds.The yields of cyclic amines in the 180-230 deg C temperature range are 46 to 97 percent. - Keywords: diols, ammonia, cyclization, heterocyclic amines, copper-containing catalyst

The heat of hydrogenation of 1-azacyclopentene was determined via a measurement of the heat of hydrogenation of its trimer, and of the dissociation energy of the trimer. The observed ΔHhydrog was -15.9 ± 0.3 kcal/mol and is considerably smaller than that for cyclopentene (-26.9 ± 0.1 kcal/mol). The data were combined with the results of theoretical calculations (MP3/6-311++G**//RHF/6-31G*) to give information on the heats of formation, heats of hydrogenation, and strain energies of a number of cyclic and acyclic imines. The "resonance energy" of pyridine was estimated based on these data.

A novel concept of base proliferation for improving the photosensitivity of base-sensitive materials is described by presenting the autocatalytic transformation of 9-fluorenylmethyl carbamates to aliphatic amines. A 9-fluorenylmethyl carbamate, as a base amplifier, was subjected to a base-catalysed fragmentation reaction to liberate the corresponding amine, which can then act as a catalyst for decomposing parent molecules, leading to autocatalytic decomposition. Consequently, the amine is generated from an equimolar amount of the carbamate using a catalytic amount of the same amine. 1-(9-Fluorenylmethoxycarbonyl)piperidine and 1-(9-fluorenylmethoxycarbonyl) cyclohexylamine were suitable as base amplifiers because of their thermal stability under neutral conditions and high base-catalytic reactivity. On the basis of the results, 1,3-bis[1-(9-fluorenylmethoxycarbonyl)-4-piperidyl] propane and 1,6-bis[(9-fluorenylmethoxy)carbonylamino]hexane were designed as base amplifiers which liberate aliphatic diamines to crosslink poly(glycidyl methacrylate) photochemically in the presence of a photobase generator. Addition of the base amplifiers resulted in a marked improvement of the photosensitivity characteristics of the polymer by a factor of 16 and 50, respectively.

The development of heterogeneous, chemoselective, and tandem catalytic systems using abundant metals is vital for the sustainable synthesis of fine and commodity chemicals. We report a robust and recyclable single-site cobalt-hydride catalyst based on a porous aluminum metal–organic framework (DUT-5 MOF) for chemoselective hydrogenation of arenes. The DUT-5 node-supported cobalt(II) hydride (DUT-5-CoH) is a versatile solid catalyst for chemoselective hydrogenation of a range of nonpolar and polar arenes, including heteroarenes such as pyridines, quinolines, isoquinolines, indoles, and furans to afford cycloalkanes and saturated heterocycles in excellent yields. DUT-5-CoH exhibited excellent functional group tolerance and could be reusable at least five times without decreased activity. The same MOF-Co catalyst was also efficient for tandem hydrogenation–hydrodeoxygenation of aryl carbonyl compounds, including biomass-derived platform molecules such as furfural and hydroxymethylfurfural to cycloalkanes. In the case of hydrogenation of cumene, our spectroscopic, kinetic, and density functional theory (DFT) studies suggest the insertion of a trisubstituted alkene intermediate into the Co–H bond occurring in the turnover limiting step. Our work highlights the potential of MOF-supported single-site base–metal catalysts for sustainable and environment-friendly industrial production of chemicals and biofuels.

Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect.

Palladium catalysts supported on acidic fluorinated magnesium hydroxide Pd/MgF2-x(OH)x were prepared through precipitation or impregnation methods. Applications to the hydrogenation of various aldimines and ketimines resulted in good catalytic activities at mild temperatures using one atmosphere of hydrogen. Quinolines, pyridines and other N-heterocycles were successfully hydrogenated at higher temperature and hydrogen pressure using low palladium loadings and without the use of any acid additive. Such reactivity trend confirmed the positive effect of the Br?nsted and Lewis acid sites from the fluorinated magnesium hydroxide support resulting in the effective pre-activation of N-heterocycle substrates and therefore in the good catalytic activity of the palladium nanoparticles during the hydrogenations. As demonstrated in the hydrogenation of imines, the catalyst was recycled up to 10 times without either loss of activity or palladium leaching. This journal is

PROBLEM TO BE SOLVED: To provide an industrially simple production method of a cyclic compound. SOLUTION: A production method of a cyclic compound includes a step to obtain a reduced form (B) by reducing an unsaturated bond in a ring structure of an aromatic compound (A) by means of catalytic hydrogenation of the aromatic compound (A) or its salt using palladium carbon as a catalyst under a normal pressure, in which the aromatic compound (A) has one or more ring structures selected from a group consisting of a five membered-ring, a six membered-ring, and a condensed ring of the five membered-ring or the six membered-ring with another six membered-ring, a hetero atom can be included in the ring structure, and the aromatic compound (A) can have one or two side chains bonded to the ring structure and does not have any carbon-carbon triple bond in the side chain. SELECTED DRAWING: None COPYRIGHT: (C)2021,JPOandINPIT

The reduction of polar bonds, in particular carbonyl groups, is of fundamental importance in organic chemistry and biology. Herein, we report a manganese pincer complex as a versatile catalyst for the transfer hydrogenation of amides, carbamates, urea derivatives, and even polyurethanes leading to the corresponding alcohols, amines, and methanol as products. Since these compound classes can be prepared using CO2as a C1 building block the reported reaction represents an approach to the indirect reduction of CO2. Notably, these are the first examples on the reduction of carbamates and urea derivatives as well as on the C-N bond cleavage in amides by transfer hydrogenation. The general applicability of this methodology is highlighted by the successful reduction of 12 urea derivatives, 26 carbamates and 11 amides. The corresponding amines, alcohols and methanol were obtained in good to excellent yields up to 97%. Furthermore, polyurethanes were successfully converted which represents a viable strategy towards a circular economy. Based on control experiments and the observed intermediates a feasible mechanism is proposed.

Using bromopyridines and methoxyphenyl boronic acid as starting materials, consecutive Suzuki-Miyaura cross-coupling and hydrogenation reactions were undertaken using a heterogeneous Pd/C catalyst in one-pot manner under mild conditions (balloon-pressure at room temperature for hydrogenation) with excellent yield. To counter Pd leaching as well as catalyst poisoning, addition of an appropriate amount of H2O was crucial to achieving successful AcOH-promoted hydrogenation, which ensured a selective reduction of the pyridine rings to the corresponding piperidines.

Developing more efficient routes to achieve C-N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials. Over the past decade, improvements in catalyst design have moved synthesis away from expensive metals to newer inexpensive C-N cross-coupling approaches via direct amine alkylation. For the first time, we report the use of an amide-based nickel pincer catalyst (1) for direct alkylation of amines via activation of sp3 C-H bonds. The reaction was accomplished using a 0.2 mol% catalyst and no additional activating agents other than the base. Upon optimization, it was determined that the ideal reaction conditions involved solvent dimethyl sulfoxide at 110 °C for 3 h. The catalyst demonstrated excellent reactivity in the formation of various imines, intramolecularly cyclized amines, and substituted amines with a turnover number (TON) as high as 183. Depending on the base used for the reaction and the starting amines, the catalyst demonstrated high selectivity towards the product formation. The exploration into the mechanism and kinetics of the reaction pathway suggested the C-H activation as the rate-limiting step, with the reaction second-order overall, holding first-order behavior towards the catalyst and toluene substrate.

The kinetics of quinuclidine displacement of BH3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale (NFB), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R′3-nRnX (X = P, N; R′ = aryl, alkyl) has allowed the formulation of related substituent parameters (nfPB, nfAB), providing a means of calculating NFB values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nfPB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.

A method of reducing an aromatic ring under relatively mild condition using sub-nano particles of a transition metal supported on super paramagnetic iron oxide nanoparticles (SPIONs). The catalyst is efficient for catalyzing the reduction of both carbocyclic and heterocyclic compound. In compound comprising both carbocyclic and heterocyclic aromatic rings, the catalyst displays high regioselectivity for the heterocyclic ring.

The development of cost-effective, noble metal-free catalytic systems for the hydrogenation of unsaturated aliphatic, aromatic, and heterocyclic compounds is fundamental for future valorization of general feedstock. With this aim, we report here the preparation of highly dispersed bimetallic Ni/Co nanoparticles (NPs), by a one-pot deposition-precipitation of Ni and Co phases onto mesoporous SBA-15 silica. By adjusting the chemical composition in the starting mixture, three supported catalysts with different Ni to Co weight ratios were obtained, which were further subjected to treatments under reducing conditions at high temperatures. Characterization of the resulting solids evidenced a homogenous distribution of Ni and Co elements forming the NPs, the best results being obtained for Ni/Co-2 : 2 samples, for which 50 wt.percent Ni–50 wt.percent Co NPs are found located on the surface of the residual phyllosilicate. Ni/Co-2 : 2, presenting the best performances for the hydrogenation of 2-methyl-quinoline, was further evaluated in the catalytic hydrogenation of selected imines, oximes and N-heteroarenes. Due to the high dispersion of bimetallic Ni?Co NPs, excellent properties (activity and selectivity) in the conversion of the selected substrates are reported.

A compound represented by the structure of formula (I): The compound is useful as a ligand for ruthenium to form an organometallic complex. The complex may be immobilized on an oxidic support to form an active, heterogeneous catalyst for the hydrogenolysis of amides to form amines and optionally alcohols.

The reductive amination of carboxylic acids is a very green, efficient and sustainable method for the production of (bio-based) amines. However, with current technology, this reaction requires two to three reaction steps. Here, we report the first (heterogeneous) catalytic system for the one-pot reductive amination of carboxylic acids to amines, with solely H2 and NH3 as the reactants. This reaction can be performed with relatively cheap ruthenium-tungsten bimetallic catalysts in the green and benign solvent cyclopentyl methyl ether (CPME). Selectivities of up to 99% for the primary amine could be achieved at high conversions. Additionally, the catalyst is recyclable and tolerant for common impurities such as water and cations (e.g. sodium carboxylate).

Hydrogenation of over a dozen aromatic compounds, including both heteroarenes and arenes, over palladium on carbon (Pd/C, 1–100 molpercent) with H2-balloon pressure at room temperature is reported. Analyses using pyridine as a model substrate revealed that acetic acid was the best solvent, as using only 1 molpercent Pd/C provided piperidine quantitatively. Substrate scope analysis and density functional theory calculations indicated that reaction rates are highly dependent on frontier molecular orbital characteristics and the steric bulkiness of substituents. Moreover, the established method was used for the concise synthesis of the anti-Alzheimer drug donepezil (Aricept?).

Fluorinated piperidines are desirable motifs for pharmaceutical and agrochemical research. Nevertheless, general synthetic access remains out of reach. Herein, we describe a simple and robust cis-selective hydrogenation of abundant and cheap fluoropyridines to yield a broad scope of (multi)fluorinated piperidines. This protocol enables the chemoselective reduction of fluoropyridines while tolerating other (hetero)aromatic systems using a commercially available heterogenous catalyst. Fluorinated derivatives of important drug compounds are prepared, and a straightforward strategy for the synthesis of enantioenriched fluorinated piperidines is disclosed.

The N-doped carbon layer coated SBA-15 support has been accomplished via a pyrolysis process. The ultra-low loading Ru nanoparticles (ca. 0.1 wt.%) was incorporated into the support by impregnation and the sequential reduction. The images of HAADF-STEM revealed that the Ru particles with sub-1-nm size (0.2-0.7 nm) were uniformly dispersed on the support. The ultrafine Ru particles displayed the excellent activity for the hydrogenation of olefins, arenes, phenol derivatives and heteroarenes in aqueous phase. The aliphatic or alicyclic compounds were produced selectively without the hydrogenolysis of C–O and C–N bonds. The high turnover frequency (TOF) values can reach up to 10,000 h?1. Notably, the activity of these catalysts improved dramatically with decreasing the sizes of Ru particles. Meanwhile, the N-doped carbon layer coating endowed the high stability of the Ru catalysts and prevented the leaching of the Ru species owning to the strong interaction between doped-N atoms and the ultrafine Ru particles. Overall, this work provides a highly attractive strategy to construct the supported sub-1-nm Ru particles utilized for the aqueous hydrogenation.

A rhodium-catalyzed method for the hydrogenation of N-heteroarenes is described. A diverse array of unsubstituted N-heteroarenes including pyridine, pyrrole, and pyrazine, traditionally challenging substrates for hydrogenation, were successfully hydrogenated using the organometallic precatalysts, [(η5-C5Me5)Rh(N-C)H] (N-C = 2-phenylpyridinyl (ppy) or benzo[h]quinolinyl (bq)). In addition, the hydrogenation of polyaromatic N-heteroarenes exhibited uncommon chemoselectivity. Studies into catalyst activation revealed that photochemical or thermal activation of [(η5-C5Me5)Rh(bq)H] induced C(sp2)-H reductive elimination and generated the bimetallic complex, [(η5-C5Me5)Rh(μ2,η2-bq)Rh(η5-C5Me5)H]. In the presence of H2, both of the [(η5-C5Me5)Rh(N-C)H] precursors and [(η5-C5Me5)Rh(μ2,η2-bq)Rh(η5-C5Me5)H] converted to a pentametallic rhodium hydride cluster, [(η5-C5Me5)4Rh5H7], the structure of which was established by NMR spectroscopy, X-ray diffraction, and neutron diffraction. Kinetic studies on pyridine hydrogenation were conducted with each of the isolated rhodium complexes to identify catalytically relevant species. The data are most consistent with hydrogenation catalysis prompted by an unobserved multimetallic cluster with formation of [(η5-C5Me5)4Rh5H7] serving as a deactivation pathway.

We report here a novel Ti3-BPDC metal-organic framework (MOF) constructed from biphenyl-4,4′-dicarboxylate (BPDC) linkers and Ti3(OH)2 secondary building units (SBUs) with permanent porosity and large 1D channels. Ti-OH groups from neighboring SBUs point toward each other with an O-O distance of 2 ?, and upon deprotonation, act as the first bidentate SBU-based ligands to support CoII-hydride species for effective cascade reduction of N-heteroarenes (such as pyridines and quinolines) via sequential dearomative hydroboration and hydrogenation, affording piperidine and 1,2,3,4-tetrahydroquinoline derivatives with excellent activity (turnover number ～ 1980) and chemoselectivity.

The first B(C6F5)3-catalyzed deoxygenative reduction of amides into the corresponding amines with readily accessible and stable ammonia borane (AB) as a reducing agent under mild reaction conditions is reported. This metal-free protocol provides facile access to a wide range of structurally diverse amine products in good to excellent yields, and various functional groups including those that are reduction-sensitive were well tolerated. This new method is also applicable to chiral amide substrates without erosion of the enantiomeric purity. The role of BF3 ? OEt2 co-catalyst in this reaction is to activate the amide carbonyl group via the in situ formation of an amide-boron adduct. (Figure presented.).

A ruthenium(II)-catalyzed deoxygenative transfer hydrogenation of amides to amines using HCO2H/NEt3 as the reducing agent is reported for the first time. The catalyst system consisting of [Ru(2-methylallyl)2(COD)], 1,1,1-tris(diphenylphosphinomethyl) ethane (triphos) and Bis(trifluoromethane sulfonimide) (HNTf2) performed well for deoxygenative reduction of various secondary and tertiary amides into the corresponding amines in high yields with excellent selectivities, and exhibits high tolerance toward functional groups including those that are reduction-sensitive. The choice of hydrogen source and acid co-catalyst is critical for catalysis. Mechanistic studies suggest that the reductive amination of the in situ generated alcohol and amine via borrowing hydrogen is the dominant pathway. (Figure presented.).

A compound by the name 1,1,1-tris(di(3,5-dimethoxyphenyl)phosphino-methyl)ethane. The compound can be represented by the structure of formula (I): The compound is useful as a ligand for ruthenium to form an organometallic complex. The complex is an active catalyst for the hydrogenolysis of amides to form amines and optionally alcohols.

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A formal deoxygenative hydrogenation of amides to amines with RuCl2(NHC)(PNHP) (NHC = 1,3-dimethylimizadol-2-ylidene, PNHP = bis(2-diphenylphosphinoethyl)amine) is described. Various secondary amides, especially NH-lactams, are reduced with H2 (3.0-5.0 MPa) to amines at a temperature range of 120-150 °C with 1.0-2.0 mol % of PNHP-Ru catalysts in the presence of Cs2CO3. This process consists of (1) deaminative hydrogenation of secondary amides to generate primary amines and alcohols, (2) dehydrogenative coupling of the transient amines with alcohols to generate imines, and (3) hydrogenation of imines to give the formally deoxygenated secondary amine products.

The axial coordination properties of six zinc tetraarylporphyrins with seven different nitrogenous bases were examined in CH2Cl2 for derivatives containing four β,β′-fused butano or benzo groups and the equilibrium constants (logK) determined using spectral titration methods. The examined compounds are represented as butano(YPh)4PorZn and benzo(YPh)4PorZn, where Por is the porphyrin dianion and Y is a CH3, H or Cl substituent on the para-position of each meso-phenyl ring of the macrocycle. The initial four-coordinate butano-And benzoporphyrins will axially bind one nitrogenous base to form five-coordinate derivatives in CH2Cl2 and this leads to a 4-22 nm red-shift of the Soret and Q bands. The logK values range from 1.98 to 4.69 for butano(YPh)4PorZn and from 3.42 to 5.36 for benzo(YPh)4PorZn, with the exact value depending upon the meso and β-substituents of the porphyrin and the conjugate acid dissociation constants (pKa) of the nitrogenous base.

The first transition-metal-free catalytic protocol for controlled reduction of amide functions using cheap and bench-stable hydrosilanes as reducing agents has been established. By altering the hydrosilane and solvent, the new method enables the selective cleavage of unactivated C-O bonds in amides and allows the C-N bonds to selectively break via the deacylated cleavage. Overall, this novel process may offer a versatile alternative to current methodologies employing stoichiometric metal systems for the controlled reduction of carboxamides.

The first transition-metal-free catalytic protocol for controlled reduction of amide functions using cheap and bench-stable hydrosilanes as reducing agents has been established. By altering the hydrosilane and solvent, the new method enables the selective cleavage of unactivated C-O bonds in amides and allows the C-N bonds to selectively break via the deacylated cleavage. Overall, this novel process may offer a versatile alternative to current methodologies employing stoichiometric metal systems for the controlled reduction of carboxamides.

Synthesis of a Cp Ru complex bearing an NH 2 -functionalized N -heterocyclic carbene (C-N H) was achieved by treatment of CpRuBr(isoprene) with an equimolar amount of a silver complex, which was generated from Ag 2 O and 1-(2-aminoethyl)-3-methylimidazolium bromide, in CH 3 CN at room temperature. The new CpRuBr(C-N H) complex showed a higher catalytic performance than the related CpRuCl(P-N H) and CpRuCl(N-N H) complexes. In the reaction of N -arylcarboxamides, the amine products were obtained in satisfactory yields under mild temperature conditions.

PROBLEM TO BE SOLVED: To provide a method for efficiently producing cyclic amines. SOLUTION: The present invention provides a method for producing cyclic amines represented by formula (2), including subjecting alkanolamines to cyclodehydration in the presence of a solid catalyst containing at least one selected from titanium oxide, silicon oxide, and zirconium oxide (R3-R10 independently represent H, C1-4 alkyl, a hydroxy group, hydroxymethyl or C1-4 alkoxy; X is C or N; Y is alkyl, a hydroxy group, C1-4 hydroxyalkyl or C1-4 aminoalkyl). SELECTED DRAWING: None COPYRIGHT: (C)2018,JPOandINPIT

Titania (TiO2) is widely used in the chemical industry as an efficacious catalyst support, benefiting from its unique strong metal-support interaction. Many proposals have been made to rationalize this effect at the macroscopic level, yet the underlying molecular mechanism is not understood due to the presence of multiple catalytic species on the TiO2 surface. This challenge can be addressed with metal-organic frameworks (MOFs) featuring well-defined metal oxo/hydroxo clusters for supporting single-site catalysts. Herein we report that the Ti8(μ2-O)8(μ2-OH)4 node of the Ti-BDC MOF (MIL-125) provides a single-site model of the classical TiO2 support to enable CoII-hydride-catalyzed arene hydrogenation. The catalytic activity of the supported CoII-hydride is strongly dependent on the reduction of the Ti-oxo cluster, definitively proving the pivotal role of TiIII in the performance of the supported catalyst. This work thus provides a molecularly precise model of Ti-oxo clusters for understating the strong metal-support interaction of TiO2-supported heterogeneous catalysts.

Hydrogenation of arenes is an important reaction not only for hydrogen storage and transport but also for the synthesis of functional molecules such as pharmaceuticals and biologically active compounds. Here, we describe the development of heterogeneous Rh-Pt bimetallic nanoparticle catalysts for the hydrogenation of arenes with inexpensive polysilane as support. The catalysts could be used in both batch and continuous-flow systems with high performance under mild conditions and showed wide substrate generality. In the continuous-flow system, the product could be obtained by simply passing the substrate and 1 atm H2 through a column packed with the catalyst. Remarkably, much higher catalytic performance was observed in the flow system than in the batch system, and extremely strong durability under continuous-flow conditions was demonstrated (>50 days continuous run; turnover number >3.4 × 105). Furthermore, details of the reaction mechanisms and the origin of different kinetics in batch and flow were studied, and the obtained knowledge was applied to develop completely selective arene hydrogenation of compounds containing two aromatic rings toward the synthesis of an active pharmaceutical ingredient.

Ordered mesoporous N-doped carbon (OMNC) encapsulating Co nanoparticles (NPs) have been prepared under direct polymerization between [Co(NH2CH2CH2NH2)2]Cl2 and carbon tetrachloride through a hard template method. The catalysts (Co@OMNC) are pyrolyzed at various temperatures and characterized by elemental analysis, Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the quinoline transfer hydrogenation with formic acid (FA) as the hydrogen source under a base-free condition, the encapsulated Co NPs are physically isolated from the acidic reaction solution, which prevents them from poisoning or leaching. The rich mesopores and N dopants afford enhanced adsorption of quinoline. Co@OMNC-700 (pyrolyzed at 700 °C) gives the best activity (98.8% conversion) as well as >99% 1,2,3,4-tetrahydroquinoline (THQ) selectivity at 140 °C for 4 h, exhibiting significantly improved performance compared to using H2 as the hydrogenation source. Moreover, Co@OMNC-700 is stable for recycling and exhibits high efficiency in FA dehydrogenation. Co@OMNC-700 is also a high-performance catalyst in the transfer hydrogenation of various unsaturated hydrocarbons. On the contrary, without the protection of OMNC, the exposed Co NPs in a control catalyst, Co/OMNC-700, lead to obvious Co leaching and low efficiency for the transfer hydrogenation of quinoline with FA.

The hydrogenation of nitrogen-containing heterocyclic precursors in aqueous medium at low temperature without imposing molecular hydrogen pressure is quite challenging. Herein, we report the synthesis and performance of a novel catalyst capable of facile hydrogenation (employing tetrahydroxydiboron (THDB) as the reductant) of N-heteroarenes in water at 80 °C with good recyclability. Rhodium particles in the sub-nano range (3O4), using aqueous ammonia as a reducing agent at 50 °C. HRTEM and elemental mapping images reveal a homogeneous distribution of 3O4 nanoparticles having an average size within a narrow range of 7-9 nm. The superparamagnetic nature of the composite was confirmed by VSM analysis. The Rh@Fe3O4 catalyst was found to be highly efficient in the heterogeneous hydrogenation of nitrogen-containing heterocyclic compounds with quantitative conversion. It showed selectivity towards the hydrogenation of 1,2,3,4-tetrahydroquinoline (py-THQ) in water using THDB with a high TOF of 1632 h-1. These results are compared with the conversion and selectivity data obtained from reduction with molecular hydrogen gas pressure. The catalytic activity is extended to the successful hydrogenation of simple aromatics like benzene, toluene etc. Isotopic labelling studies were performed to determine the source of hydrogen in quinoline hydrogenation in the presence of THDB. It was found that it could be used for 16 consecutive cycles with gaseous hydrogen, without any undesired by-products; it also retained its original crystallinity.

Rhodium nanoparticles immobilized on reduced graphene oxide were obtained from the microwave-induced thermal decomposition of Rh6(CO)16 in the ionic liquid [bmim][BF4] (bmim = 1-butyl-3-methylimidazolium cation) in the absence of additional stabilizing agents. The resulting rhodium nanoparticles are 99%, without interfering with other reducible groups, and with high conversions. Related catalysts prepared using conventional thermal heating were prepared for comparison purposes and were found to be considerably less active.

Novel heterogeneous catalysts were prepared by impregnation of titania with a solution of cobalt acetate/melamine and subsequent pyrolysis. The resulting materials show an unusual nitrogen-modified titanium structure through partial implementation of nitrogen into the support. The optimal catalyst displayed good activity and selectivity for challenging pyridine hydrogenation under acid free conditions in water as solvent.

Deoxygenative hydrogenation of amides to amines homogeneously catalyzed by a complex of an Earth-abundant metal is presented. This manganese-catalyzed reaction features high efficiency and selectivity. A plausible reaction mechanism, involving metal-ligand cooperation of the manganese pincer complex, is proposed based on NMR studies and relevant stoichiometric reactions.

A straightforward synthetic route has been adopted to synthesize highly nonplanar electron deficient perchlorometallo-porphyrins. Herein, we report the synthesis and characterization of MTPP(NO2)Cl7 where M = CoII, NiII, CuII and ZnII. Further, we examined their optical and electrochemical redox properties and the results are compared with MTPPCl8. MTPP(NO2)Cl7 exhibited red-shifted (～10-15 nm) absorption spectra relative to MTPPCl8 due to the strong electron withdrawing nature of the nitro group. Mixed β-substitution alters the electrochemical redox properties to such an extent that an appreciable increase in the anodic shift in reduction potential (200-300 mV) is observed for MTPP(NO2)Cl7 relative to MTPPCl8 whereas only a minimal shift (15-50 mV) in the oxidation potential is observed. Nonplanarity of the macrocyclic core was investigated by single crystal X-ray analysis and DFT calculations. A higher ΔCβ (0.706 ?) for 1d as compared to 2d (0.642 ?) undoubtedly signifies nonplanarity induced by the nitro group. To substantiate the effect of mixed substitution, we performed axial ligation studies of Zn(ii) complexes with nitrogenous bases and basic anions and found higher log:β2 values as well as a linear relation between log:β2 and pKa as compared to perbromoporphyrins. Highly electron deficient β-substituted Co(ii) porphyrins (1a and 2a) were utilized as novel sensors for selective rapid visual detection of CN- ions.

A ruthenium complex with a tetradentate bipyridine ligand was proved to be a highly efficient catalyst for the conversions of CO2. Turnover numbers up to 300 000, 9800, and 2100 were achieved for the hydrogenations of CO2 to formamides, formamides to methanol and amines, and the direct hydrogenation of CO2 to methanol, respectively.

Amide acetals and iminium esters were hydrogenated into amines under very mild reaction conditions over common hydrogenation catalysts. This finding provides a new strategy for the selective reduction of amides. The synthetic utility of this approach was demonstrated by the selective reduction of amides bearing ester and nitrile groups.

The use of γ-Al2O3 as a heterogeneous catalyst in scCO2 has been successfully applied to the amination of alcohols for the synthesis of N-alkylated heterocycles. The optimal reaction conditions (temperature and substrate flow rate) were determined using an automated self-optimising reactor, resulting in moderate to high yields of the target products. Carrying out the reaction in scCO2 was shown to be beneficial, as higher yields were obtained in the presence of CO2 than in its absence. A surprising discovery is that, in addition to cyclic amines, cyclic ureas and urethanes could be synthesised by incorporation of CO2 from the supercritical solvent into the product.

We describe a tandem process to generate active Ru nanoparticles (≈7 nm) immobilised in situ on carbon from an organometallic precursor and formic acid to afford the hydrogenation of a wide range of arenes and heteroarenes in yields up to 72 % with high conversions and selectivities for the desired products. The hydrogenation of several substrates analogous to lignin-derived fragments to the corresponding alicyclic products was also achieved. Our experimental investigations evidenced that the observed enhanced activity for arene hydrogenation was driven by the unique structural advantages of the organometallic precursor to activate formic acid, in which the presence of a nitrogen ligand is crucial to achieve a high catalytic activity. TEM analysis revealed the formation of Ru0 nanoparticles, and Hg0 poisoning experiments support the heterogeneous nature of the active catalyst.

The chemoselective hydrogenation of heteroarenes is one of the most important synthetic reactions for the production of key intermediates in agrochemicals, pharmaceuticals and various fine chemicals. The development of new heterogeneous catalysts for the environmentally benign synthesis of heterocycle hydrogenated products is a fundamental objective for chemists. Here, we report that 12CaO·7Al2O3 with a unique sub-nanocage structure loaded with Ru nanoparticles exhibits higher activity, chemoselectivity and sustainability for the hydrogenation of heteroarenes in a solvent-free system than traditional oxide-supported metal catalysts. Conversion of >99% and a selectivity close to 99% were achieved for the hydrogenation of quinoline under mild conditions. This catalyst was also successfully applied to the hydrogenation of a variety of N- and O-heteroarenes with high yields. The superior catalytic performance can be attributed to a cooperative effect between the hydrogen-storage ability and large amount of strong basic sites on the surface of the support, which promotes heterolytic H2 cleavage and prevents poisoning of the metal surface caused by the adsorption of heteroarenes.

N-Heterocyclic compounds have been tested in the selective hydrogenation catalysed by small 1-3 nm sized Ru nanoparticles (NPs) embedded in various imidazolium based ionic liquids (ILs). Particularly a diol-functionalised IL shows the best performance in the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline (1THQ) with up to 99% selectivity.

New Rh-NPs stabilised by N-Heterocyclic Carbenes (NHC) were synthesized by decomposition of [Rh(η3-C3H5)3] under H2 atmosphere and fully characterized. Surface studies by FT-IR and NMR spectroscopy employing isotopically labelled ligands were also performed. The Rh0.2 NPs are active catalysts in the reduction of various aromatic substrates. In the reduction of phenol, high selectivities to cyclohexanone or cyclohexanol were obtained depending on the reaction conditions. However, this catalytic system exhibited much lower activity in the hydrogenation of substituted phenols. Pyridine was easily hydrogenated under mild conditions and interestingly, the hydrogenation of 4-methyl and 4-trifluoromethylpyridine resulted slower than that of 2-methylpyridine. The hydrogenation of 1-(pyridin-2-yl)propan-2-one provided the β-enaminone 13a in high yield as a consequence of the partial reduction of the pyridine ring followed by isomerization. Quinoline could be either partially hydrogenated to 1,2,3,4-tetrahydroquinoline or fully reduced to decahydroquinoline by adjusting the reaction conditions.

Tuning the catalytic performance of metal nanoparticles (NPs) is very important in nanocatalysis. Herein, we report that amine-rich mesoporous silica hollow nanospheres (HS-NH2) synthesized by one-pot condensation could efficiently stabilize ultra-small Pd NPs and also increase the surface electron density of Pd NPs due to the coordinating and electron-donating effects of the amine group. Pd NPs supported on HS-NH2 afford TOF as high as 5052 h-1 in quinoline hydrogenation reaction and are much more active than Pd/C with a TOF of 960 h-1 as well as most reported solid catalysts. The intrinsic activity of Pd NPs increases as the particle size of Pd decreases, revealing that quinoline hydrogenation is a structure-sensitive reaction. The results of TEM, XPS, CO adsorption and CO stripping voltammetry indicate that the high activity of Pd NPs supported on HS-NH2 is mainly attributed to their ultra-small particle size and high surface electron density. Our primary results demonstrate that the organo-modified silica nanospheres are promising solid supports for modifying the electronic properties of metal NPs supported and consequently tailoring their catalytic functions.

Readily accessible cationic IrIII metallacycles catalyze efficiently the chemoselective hydrosilylation of tertiary and secondary amides to amines. The catalyst described herein operates at low loadings using inexpensive 1,1,3,3-tetramethyldisiloxane and allows fast reactions with high yields, selectivities, and turnover numbers. A transient iminium intermediate has been observed for the first time by using mass spectrometry, and the activation of the catalyst and the silane reagent have been studied by using DFT calculations. These fundamental insights support the present and future improvements of IrIII metallacycles through proper ligand modifications and enable further broad applications of catalysts based on metallacycles.