28107-09-7Relevant articles and documents
Self-assembly of a Mixed Valence Copper Triangular Prism and Transformation to Cage Triggered by an External Stimulus
Dai, Rui-Rong,Lai, Ya-Liang,Li, Dan,Wang, Xue-Zhi,Zhou, Xian-Chao,Zhou, Xiao-Ping
, p. 17374 - 17378 (2020)
A triangular prismatic metal-organic cage based on mixed valence copper ions has been designed and synthesized by using metallocycle panels and pillar ligands. The triangular prism will be quickly transformed to a 10-nuclear cage upon an external chemical stimulus, which features a bicapped square antiprism structure. This prismatic cage can act as a catalyst for oxidation of aromatic alcohols to their corresponding aromatic aldehydes with high yields at room temperature under O2 atmosphere.
Characterization of secondary phosphine oxide ligands on the surface of iridium nanoparticles
Cano, Israel,Martínez-Prieto, Luis M.,Fazzini, Pier F.,Coppel, Yannick,Chaudret, Bruno,Van Leeuwen, Piet W.N.M.
, p. 21655 - 21662 (2017)
The synthesis of iridium nanoparticles (IrNPs) ligated by various secondary phosphine oxides (SPOs) is described. This highly reproducible and simple method via H2 reduction produces well dispersed, small nanoparticles (NPs), which were characterized by the state-of-the-art techniques, such as TEM, HRTEM, WAXS and ATR FT-IR spectroscopy. In particular, multinuclear solid state MAS-NMR spectroscopy with and without cross polarization (CP) enabled us to investigate the different binding modes adopted by the ligand at the nanoparticle surface, suggesting the presence of three possible types of coordination: as a purely anionic ligand Ir-P(O)R2, as a neutral acid R2P-O-H and as a monoanionic bidentate H-bonded dimer R2P-O-H?O=PR2. Specifically, the higher basicity of the dicyclohexyl system leads to the formation of IrNPs in which the bidentate binding mode is most abundant. Such cyclohexyl groups are bent towards the edges, as is suggested by the study of 13CO coordination on the NP surface. This study also showed that the number of surface sites on faces available for bridging CO molecules is higher than the number of sites for terminal CO species on edges and apices, which is unexpected taking into account the small size of the nanoparticles. In addition, the IrNPs present a high chemoselectivity in the hydrogenation of cinnamaldehyde to the unsaturated alcohol.
Facile Synthesis of Small Gold Nanoparticles Stabilized by Carbon Nanospheres for Selective Hydrogenation of 4-Nitrobenzaldehyde
Liu, Minghui,Wang, Jiasheng,Liu, Yingcen,Lu, Rongwen,Zhang, Shufen
, p. 997 - 1001 (2019)
We report the facile synthesis of small gold nanoparticles stabilized by carbon nanospheres (Au@C) for highly active and selective hydrogenation of 4-nitrobenzaldehyde. The formation of such a Au@C unique structure can be attributed to the high distribution of Au(III) species in the melamine-formaldehyde resin nanospheres, which were formed via the coordination of Au(III) with the abundant imino groups of melamine-formaldehyde pre-polymer. After the subsequent condensation and confined in situ reduction, small gold nanoparticles, and carbon nanospheres were formed simultaneously. Under the reaction conditions of 80 °C and 1.6 MPa, 99.3% conversion and >99% selectivity were achieved for the hydrogenation of 4-nitrobenzaldehyde to 4-aminobenzaldehyde.
One-Pot Synthesis of Au11(PPh2Py)7Br3 for the Highly Chemoselective Hydrogenation of Nitrobenzaldehyde
Liu, Chao,Abroshan, Hadi,Yan, Chunyang,Li, Gao,Haruta, Masatake
, p. 92 - 99 (2016)
In this study, the gold clusters Au11(PPh3)7Cl3 and Au11(PPh2Py)7Br3 (PPh2Py = diphenyl-2-pyridylphosphine) are synthesized via a one-pot procedure based on the wet chemical reduction method. The Au11(PPh3)7Cl3 cluster is found to be active in the chemoselective hydrogenation of 4-nitrobenzaldehyde in the presence of hydrogen (H2) and a base (e.g., pyridine). Interestingly, the cluster with the functional ligand PPh2Py shows similar activity without losing catalytic efficiency in the absence of the base. The structure of the gold clusters and reaction pathway of the catalytic hydrogenation are investigated at the atomic/molecular level via UV-vis spectroscopy, electrospray ionization (ESI) mass spectrometry, and density functional theory (DFT) calculations. It is found that one ligand (PPh3 or PPh2Py) removal is the first step to expose the core of the gold clusters to reactants, providing an active site for the catalytic reaction. Then, the H-H bond of the H2 molecule becomes activated with the aid of either free amine (base) or ligand PPh2Py which is attached to the gold clusters. This work demonstrates the promise of the functional ligand PPh2Py in the catalytic hydrogenation to reduce the amount of materials (free base: e.g., pyridine) that ultimately enter the waste stream, thereby providing a more environmentally friendly reaction medium.
Size dependence of atomically precise gold nanoclusters in chemoselective hydrogenation and active site structure
Li, Gao,Jiang, De-En,Kumar, Santosh,Chen, Yuxiang,Jin, Rongchao
, p. 2463 - 2469 (2014)
We investigate the catalytic properties of water-soluble Au n(SG)m nanocluster catalysts (H-SG = glutathione) of different sizes, including Au15(SG)13, Au 18(SG)14, Au25(SG)18, Au 38(SG)24, and captopril-capped Au25(Capt) 18 nanoclusters. These Aun(SR)m nanoclusters (SR represents thiolate generally) are used as homogeneous catalysts (i.e., without supports) in the chemoselective hydrogenation of 4-nitrobenzaldehyde (4-NO2PhCHO) to 4-nitrobenzyl alcohol (4-NO2PhCH 2OH) with ～100% selectivity in water using H2 gas (20 bar) as the hydrogen source. These nanocluster catalysts, except Au 18(SG)14, remain intact after the catalytic reaction, evidenced by UV-vis spectra, which are characteristic of nanoclusters of each size and thus serve as spectroscopic "fingerprints". We observe a drastic size dependence and steric effect of protecting ligands on the gold nanocluster catalysts in the hydrogenation reaction. Density functional theory (DFT) modeling of the 4-nitrobenzaldehyde adsorption shows that both the -CHO and -NO2 groups closely interact with the S-Au-S staples on the gold nanocluster surface. The adsorptions of the 4-nitrobenzaldehyde molecule on the four different sized Aun(SR)m nanoclusters are moderately strong and similar in strength. The DFT results suggest that the catalytic activity of the Aun(SR)m nanoclusters is primarily determined by the surface area of the Au nanocluster, consistent with the observed trend of the conversion of 4-nitrobenzaldehyde versus the cluster size. Overall, this work offers molecular insight into the hydrogenation of 4-nitrobenzaldehyde and the catalytically active site structure on gold nanocluster catalysts.
Singlet oxygen-engaged selective photo-oxidation over pt nanocrystals/porphyrinic MOF: The roles of photothermal effect and pt electronic state
Chen, Yu-Zhen,Wang, Zhiyong U.,Wang, Hengwei,Lu, Junling,Yu, Shu-Hong,Jiang, Hai-Long
, p. 2035 - 2044 (2017)
The selectivity control toward aldehyde in the aromatic alcohol oxidation remains a grand challenge using molecular oxygen under mild conditions. In this work, we designed and synthesized Pt/PCN-224(M) composites by integration of Pt nanocrystals and porphyrinic metal-organic frameworks (MOFs), PCN-224(M). The composites exhibit excellent catalytic performance in the photo-oxidation of aromatic alcohols by 1 atm O2 at ambient temperature, based on a synergetic photothermal effect and singlet oxygen production. Additionally, in opposition to the function of the Schottky junction, injection of hot electrons from plasmonic Pt into PCN-224(M) would lower the electron density of the Pt surface, which thus is tailorable for the optimized catalytic performance via the competition between the Schottky junction and the plasmonic effect by altering the light intensity. To the best of our knowledge, this is not only an unprecedented report on singlet oxygen-engaged selective oxidation of aromatic alcohols to aldehydes but also the first report on photothermal effect of MOFs.
Sophisticated construction of au Islands on Pt-Ni: An ideal trimetallic nanoframe catalyst
Wu, Yuen,Wang, Dingsheng,Zhou, Gang,Yu, Rong,Chen, Chen,Li, Yadong
, p. 11594 - 11597 (2014)
We have developed a priority-related chemical etching method to transfer the starting Pt-Ni polyhedron to a nanoframe. Utilizing the lower electronegativity of Ni in comparison to Au atoms, in conjunction with the galvanic replacement of catalytically active Au to Ni tops, a unique Au island on a Pt-Ni trimetallic nanoframe is achieved. The design strategy is based on the structural priority mechanism of multimetallic nanocrystals during the synthesis and thus can be generalized to other analogous metal-bimetallic nanocrystal combinations (such as Pd and Cu islands on Pt-Ni nanoframes), which is expected to pave the way for the future development of efficient catalysts.
Size Specific Activity of Polymer Stabilized Gold Nanoparticles for Transfer Hydrogenation Catalysis
Chavda, Nikeshsinh,Trivedi, Abhishek,Thakarda, Jaydev,Agrawal, Yadvendra K.,Maity, Prasenjit
, p. 1331 - 1339 (2016)
Abstract: [Poly (N-Vinyl Pyrrollidone)] (PVP) (K30, average Mol. Wt., 40?kDa) stabilized gold nanoparticles with four different size (mean diameter) of 1.4?±?0.2, 3.8?±?0.4, 5.5?±?0.8 and 7.8?±?1?nm were synthesized using solution based chemical reduction method and used as catalysts for transfer hydrogenation reaction. Transfer hydrogenation of several organic functional groups (>C=O, –CH=O, –NO2, –CH=CH2, –C≡C–H, –C≡N) were studied using potassium formate (HCOOK) as hydrogen source in water. The major focus of this work was on catalytic activity, product selectivity and recycling ability of Au:PVP nanoparticles as a transfer hydrogenation catalyst. The size specific catalytic activity showed that up to 3.8?nm sized gold nanoparticles are highly active catalyst and afterwards its activity diminishes sharply with increasing particle size. Mechanistic insight showed that formate ions are activated on gold surface and produced bound hydride species, which is the active intermediate for this catalytic transformation. Graphical Abstract: [Figure not available: see fulltext.]
Oxidation of Benzyl Alcohols by Polymer Supported V(IV) Complex Using O2
Renuka,Gayathri
, p. 1266 - 1276 (2019)
Polymer supported and unsupported oxovanadium(IV) complexes with 2,6-bis(benzimidazolyl)pyridine were synthesized and characterized by elemental analyses, molar conductance, magnetic moment measurements, electronic, IR, ESR spectral studies, LC–MS and thermogravimetric analysis. Based on the results, an octahedral geometry was intended around V(IV) complexes. Polymer-anchored V(IV) complex catalyzed the oxidation of benzyl alcohols in acetonitrile with O2 as an oxidant. Several parameters were differed to optimize the reaction conditions. Under the optimized reaction conditions, benzyl alcohol oxidation confirmed 96% conversion with 100% selectivity towards benzaldehyde. The developed catalyst revealed excellent benzyl alcohol oxidation at moderate temperature in presence of oxygen making the reaction simpler and environmentally benign. The polymer anchored V(IV) complex showed excellent recyclability as compared to its unsupported analogue. Graphical Abstract: [Figure not available: see fulltext.].
Probing the role of surface energetics of electrons and their accumulation in photoreduction processes on TiO2
Molinari, Alessandra,Maldotti, Andrea,Amadelli, Rossano
, p. 7759 - 7765 (2014)
We address the role of the energetics of photogenerated electrons in the reduction of 4-nitrobenzaldehyde on TiO2. This model molecule bears two functional groups featuring different reducibilities. Electrochemistry shows that reduction to 4-aminobenzyl alcohol occurs in entirely distinct potential ranges. Partial reduction of the -NO2 group, affording 4-aminobenzaldehyde, takes place through surface states at potentials positive of the flatband potential (Efb). Dark currents caused by reduction of the aldehyde group are observed only at potentials more negative than E fb, and the process requires an electron accumulation regime. Photocatalysis with TiO2 suspensions agrees with the electrochemical data. In particular, reduction of the nitro group is a relatively fast process (k=0.059 s-1), whereas that of the aldehyde group is slower (k=0.001 s-1) and requires electron photoaccumulation. Control of the photogenerated charge is a prospective means for achieving chemoselective reductions. Electron energetics: Parallel investigations on TiO2 electrodes and illuminated suspensions show that partial reduction of O 2NC6H4CHO to H2NC6H 4CHO is mediated by intra-bandgap states (see figure). When this process is complete, a second reduction affording H2NC 6H4CH2OH occurs under an electron accumulation regime.
