Supported platinum catalysts have been studied for the reductive amination of levulinic acid (LA) by H2 to N-alkyl-5-methyl-2-pyrrolidones under solvent-free conditions. The activity depends on the type of metal (Pt, Re, Pd, Rh, Ru, Cu, Ni), support material, and coloaded oxides of transition metals (V, Cr, Mo, W, Re). In 24 kinds of catalyst tested, Pt and MoO X (molybdenum oxide) coloaded TiO2 (Pt-MoO X /TiO2) shows the highest activity. Pt-MoO X /TiO2 is effective for reductive amination of LA with wide varieties of amines under mild conditions (3 bar of H2, 100 °C, solvent-free) to give high isolated yield of pyrrolidinones and shows higher turnover number (TON) than previously reported catalysts for reductive amination of LA with an aliphatic amine. The catalyst can be separated from the reaction mixture by filtration, and the recovered catalyst can be reused. This is the first general and reusable heterogeneous catalytic system for the reductive amination of LA. On the basis of mechanistic studies, high activity of Pt-MoO X /TiO2 can be attributed to acid–base interaction between the acid sites of Pt-MoO X /TiO2 and carboxyl groups in LA and an intermediate.

A versatile, selective, and recyclable heterogeneous catalytic method for the methylation of C–H bonds in alcohols, ketones, and indoles with methanol under oxidant-free conditions using a Pt-loaded carbon (Pt/C) catalyst in the presence of NaOH is reported. This catalytic system is effective for various methylation reactions: (1) the β-methylation of primary alcohols, including aryl, aliphatic, and heterocyclic alcohols, (2) the α-methylation of ketones, and (3) the selective C3-methylation of indoles. The reactions are driven by a borrowing-hydrogen mechanism. The reaction begins with the dehydrogenation of the alcohol(s) to afford aldehydes, which subsequently undergo a condensation reaction with the nucleophile (aldehyde, ketone, or indole), followed by hydrogenation of the condensation product by Pt–H species to yield the desired product. In all of the methylation reactions explored in this study, the Pt/C catalyst exhibits a significantly higher turnover number than other previously reported homogeneous catalytic systems. Moreover, it is demonstrated that the high catalytic activity of Pt can be rationalized in terms of the adsorption energy of hydrogen on the metal surface, as revealed by density functional theory calculations on different metal surfaces.

Herein, we report a heterogeneous TiO -supported Re catalyst (Re/TiO ) that promotes various selective hydrogenation reactions, which includes the hydrogenation of esters to alcohols, the hydrogenation of amides to amines, and the N-methylation of amines, by using H and CO . Initially, Re/TiO was evaluated in the context of the selective hydrogenation of 3-phenylpropionic acid methyl ester to afford 3-phenylpropanol (pH2 =5 MPa, T=180 °C), which revealed a superior performance over other catalysts that we tested in this study. In contrast to other typical heterogeneous catalysts, hydrogenation reactions with Re/TiO did not produce dearomatized byproducts. DFT studies suggested that the high selectivity for the formation of alcohols in favor of the hydrogenation of aromatic rings is ascribed to the higher affinity of Re towards the COOCH group than to the benzene ring. Moreover, Re/TiO showed a wide substrate scope for the hydrogenation reaction (19 examples). Subsequently, this Re/TiO catalyst was applied to the hydrogenation of amides, the N-methylation of amines, and the N-alkylation of amines with carboxylic acids or esters.

TiO2-supported Re, Re/TiO2, was found to promote selective hydrogenation of carboxylic acids having aromatic and aliphatic moieties to the corresponding alcohols. Re/TiO2 showed superior results compared to other transition-metal-loaded TiO2 and supported Re catalysts for selective hydrogenation of 3-phenylpropionic acid. 3phenylpropanol was produced in 97% yield under mild conditions (5 MPa H-2 at 140 degrees C). Contrary to typical heterogeneous catalysts, Re/TiO2 does not lead to the formation of dearomatized byproducts. The catalyst is recyclable and shows a wide substrate scope in the synthesis of alcohols (22 examples; up to 97% isolated yield)

Supported platinum catalysts are studied for the reductive amination of ketones under ammonia and hydrogen. For a model reaction with 2-adamantanone, Pt-loaded MoO x /TiO 2 (Pt-MoO x /TiO 2 ) shows the highest yield of primary amine. The catalyst is effective for the selective transformation of various aliphatic and aromatic ketones to the corresponding primary amines, which demonstrates the first example of the selective synthesis of primary amines by this reaction. The yield of the amine increases with increase in the negative shift of the C=O stretching band in the infrared spectra of adsorbed acetone on the catalysts, suggesting that Lewis acid sites on the support material play an important role in this catalytic system. Primary amines are important intermediates in the bulk and fine chemical industries.[1] The reductive amination of carbonyl compounds [2][3][4][5][6] and borrowing-hydrogen type amination of alcohols [7][8][9][10] can be practical synthetic methods of amines. However, amination of carbonyl compounds by NH 3 generally produces secondary amines, [11][12][13][14][15] because primary amines are more reactive than NH 3 , resulting in the conversion of the primary amines to secondary amines. As for the synthesis of primary amines from aldehydes, a few catalysts such as heterogeneous Ru catalysts [16,17] and a homogeneous Rh catalyst [18] are available. The selective synthesis of primary amines by reductive amination of ketones is more challenging. Reductive amination of a ketone with NH 3 and H 2 by Cu- [11] and zeolite [12] based heterogeneous catalysts resulted in selective formation of a secondary amine as a major product together with a primary amine as a minor product. Recently reported homogeneous methods for the selective synthesis of primary amines from ketones with NH 3 did not use H 2 but used less atom-efficient reductants such as HCO 2 NH 4 , [19] the Hantzsch ester, [20] silane, [21] and NaBH 4 . [22] To our knowledge, there are no reports on the selective synthesis of primary amines by the reductive amination of ketones with NH 3 and H 2 . During a course of our efforts on the reductive CÀN bond formation reactions by heterogeneous Pt catalysts, [23,24] we found that Pt and MoO x coloaded TiO 2 (Pt-MoO x /TiO 2 ) was effective for this catalytic reaction. We report herein the first example of the selective synthesis of primary amines by the reductive amination of ketones under 4 bar NH 3 and 2 bar H 2 . We also show the relationship between Lewis acidic nature of the support oxides and the catalytic efficiency.First, we screened Pt catalysts supported on various support materials (MoO x /TiO 2 , Nb 2 O 5 , q-Al 2 O 3 , ZrO 2 , TiO 2 , MgO, SiO 2 , ZSM-5, C, and CeO 2 ) for a model reaction of 2-adamantanone (1 a) in o-xylene under 4 bar NH 3 and 2 bar H 2 . Table 1 summarizes the yields of the corresponding primary amine (2 a), alcohol (3 a), and secondary amine (4 a) with 0.5 mol % of Pt catalysts. The catalytic tests were performed under the same conditions (0.5 mol % Pt with respe...

We have prepared a push-pull porphyrin with an electron-donating triarylamino group at the β,β'-edge through a fused imidazole group and an electron-withdrawing carboxyquinoxalino anchoring group at the opposite β,β'-edge (ZnPQI) and evaluated the effects of the push-pull structure of ZnPQI on optical, electrochemical, and photovoltaic properties. ZnPQI showed red-shifted Soret and Q bands relative to a reference porphyrin with only an electron-withdrawing group (ZnPQ), thus demonstrating the improved light-harvesting property of ZnPQI. The optical HOMO-LUMO gap was consistent with that estimated by DFT calculations. The ZnPQI-sensitized solar cell exhibited a relatively high power conversion efficiency (η) of 6.8 %, which is larger than that of the ZnPQ-sensitized solar cell (η=6.3 %) under optimized conditions. The short-circuit current and fill factor of the ZnPQI-sensitized solar cell are larger than those of the ZnPQ-sensitized solar cell, whereas the open circuit potential of the ZnPQI-sensitized cell is smaller than that of the ZnPQ-sensitized cell, leading to an overall improved cell performance of ZnPQI. Such fundamental information provides a new tool for the rational molecular design of highly efficient dye-sensitized solar cells based on push-pull porphyrins.

HBEA supported Pt metal nanoclusters effectively catalyze direct dehydrogenative synthesis of quinazolinones from o-aminobenzamide and alcohols under promoter-free conditions.

For the hydrogenation of a tertiary amide (N-acetylpiperidine), Lewis acidic support materials (Nb 2 O 5 and MoOx/TiO 2 ) increase the catalytic activity of Pt metal nanoparticles by a factor of > 100. In situ infrared (IR) study shows that coordination of the C=O group of amide to surface Lewis acid sites weakens the C= O bond, and the activated amide undergoes hydrogen transfer from H species on Pt sites. Among 19 types of heterogeneous catalysts tested, Pt/Nb 2 O 5 shows the highest catalytic activity. Pt/Nb 2 O 5 is generally effective for the selective hydrogenation of various tertiary amides and e-caprolactam to the corresponding amines under additive-free and solventless conditions and shows an order of higher turnover number (TON) than previously reported catalysts. Pt-MoOx/TiO 2 is the secondary most effective and is reusable 10 times after the reaction.The hydrogenation of carboxylic acids and their derivatives is a key transformation in the pharmaceutical and fine chemical industries and biomass conversion. [1, 2] The reaction is more difficult than the hydrogenation of carbonyl compounds because of the lower electrophilicity of the C=O group in carboxylic acid derivatives. Among the derivatives of carboxylic acid, carboxamides have relatively low electrophilicity of the C=O bond, [2a] and thus catalytic hydrogenation of amides by molecular hydrogen has been a challenging reaction. [1, 2] The synthesis of amines by reduction of the corresponding amides has been carried out by an unsustainable method using excess amount of a dangerous reductant such as LiAlH 4 . [1] Reduction of amides without the hydride reagents is a key research area in pharmaceutical industry. [3] Homogeneous catalysts for hydrogenation of amides by H 2 have been reported, [4][5][6][7][8][9][10][11][12][13] but most of them require acidic or basic additives in the reaction mixture as well as an expensive organic ligand. More importantly, most of the homogeneous systems lead to cleavage of CÀN bonds of amides to give alcohols and amines. [5][6][7][8][9][10][11][12][13] Klankermayer, Cole-Hamilton and co-workers [4] recently developed the first homogenous catalytic system, a Ru-Triphos complex with an acidic additive, CH 3 SO 3 H or HN(SO 2 CF 3 ) 2 , for the hydrogenation of amides to amines with preservation of the CÀN bonds. Early heterogeneous catalysts, such as Cu/Cr oxides, selectivity catalyzed hydrodeoxygenation of amides to amines under harsh conditions (20 À 30 MPa H 2 , ca 250 8C). [1] Ru/Re, Rh/Re and Ru/Mo nanoparticles reported by Fuchikami [14] and Whyman [15] and Rh-MoOx/SiO 2 + CeO 2 [16] are effective catalysts for this reaction under milder conditions, but these catalysts suffer from problems such as need of high H 2 pressure (7-10 MPa) and limited substrate scope. The TiO 2 -supported Pt/Re catalyst [17] was reported to catalyze the hydrogenation of some amides under low H 2 pressure (2 MPa) both in batch and in continuous flow reactors, but the system suffers from limited substrate scope and deactivation in t...