Identifying the Azobenzene/Aniline reaction intermediate on TiO2-(110) : a DFT Study

Density functional theory (DFT) calculations, both with and without dispersion corrections, have been performed to investigate the nature of the common surface reaction intermediate that has been shown to exist on TiO2(110) as a result of exposure to either azobenzene (C6H5N═NC6H5) or aniline (C6H5NH2). Our results confirm the results of a previous DFT study that dissociation of azobenzene into two adsorbed phenyl imide (C6H5N) fragments, as was originally proposed, is not energetically favorable. We also find that deprotonation of aniline to produce this surface species is even more strongly energetically disfavored. A range of alternative surface species has been considered, and while dissociation of azobenzene to form surface C6H4NH species is energetically favored, the same surface species cannot form from adsorbed aniline. On the contrary, adsorbed aniline is much the most stable surface species. Comparisons with experimental determinations of the local adsorption site, the Ti–N bond length, the molecular orientation, and the associated C 1s and N 1s photoelectron core level shifts are all consistent with the DFT results for adsorbed aniline and are inconsistent with other adsorbed species considered. Possible mechanisms for the hydrogenation of azobenzene required to produce this surface species are discussed

Gold catalysts for the synthesis of aromatic azocompounds from nitroaromatics in one step

[EN] One-step selective hydrogenation of nitroaromatics to obtain symmetric azocompounds with high yields has been performed with a gold supported on cerium oxide catalysts. Au/TiO2 and Au/CeO2 catalysts direct the reaction by two different pathways and with different selectivities. In situ FTIR studies reveal that the surface concentration of the intermediate nitrosobenzene is decisive in directing the reaction trough the different reaction pathways. In this way, while on Au/TiO2 a fast hydrogenation of the nitrosobenzene intermediate leads to a low surface concentration of the nitrosocompound, on Au/CeO2 nitrosobenzene is more stabilized on the catalyst surface leading to a lower hydrogenation and a higher coupling rate, resulting in high selectivities to azobenzene. On Au/CeO2, the relative weak adsorption of the azo with respect to the azoxycompound on the catalyst surface avoids the consecutive hydrogenation of azocompounds to the corresponding anilines until all the azoxy has been consumed. Asymmetric azobenzenes have also been obtained with very high yields on TiO2, through the Mills reaction.The authors wish to acknowledge the financial support from the Spanish Ministries of Education and Science and Economy and Competitiveness under the project Consolider-Ingenio 2010 (CSD2009-00050 "Development of more efficient catalysts for the design of sustainable chemical processes and clean energy production") and the Severo Ochoa program (SEV-2012-0267), respectively. D.C. thanks the Spanish MEC for postgraduate scholarship, project MAT2006-14274-C02-01.Cómbita Merchán, DF.; Concepción Heydorn, P.; Corma Canós, A. (2014). Gold catalysts for the synthesis of aromatic azocompounds from nitroaromatics in one step. Journal of Catalysis. 311:339-349. https://doi.org/10.1016/j.jcat.2013.12.014S33934931

Catalytic stereoselective addition to alkynes. Borylation or silylation promoted by magnesia-supported iron oxide and cis-diboronation or silaboration by supported platinum nanoparticles

Iron oxide nanoparticles supported on magnesia (FeO/MgO) have been prepared by NaBH4 reduction of Fe(SO4) on MgO and spontaneous reoxidation upon storage. XPS of FeO/MgO indicates the presence of Fe(0) (16%) and Fe(II) (84%) on this solid. TEM images show that catalytically active FeO/MgO is constituted by iron oxide nanoparticles of about 25 nm dispersed on fibrous MgO. FeO/MgO in the presence of catalytic amounts of triphenylphosphine promotes highly regio- and stereoselective monoborylation of aromatic, aliphatic, terminal and internal alkynes. Chemical analysis of the liquid after the reaction and control experiments using Fe(II) salts in the absence or presence of PPh3 supports that catalysis is heterogeneous. The possibility that trace amounts of copper impurities present in the iron precursor influence the catalytic activity of FeO/MgO was studied using a commercially available high-purity Fe(SO4) as precursor (99.999% Fe purity) showing again good (but lower) activity. In addition, a control experiment using as catalyst MgO containing 30 times higher amounts of Cu than that present in low purity Fe did not lead to complete alkyne conversion, although product formation was observed in a large extent. Alkynes react with complete chemoselectivity versus alkenes. In contrast to FeO/MgO, Pt supported on MgO or active carbon efficiently promotes the stereoselective diboronation and silaboration of alkynes in the absence of triphenylphosphine at lower temperature to render the cis configured diboronated and silaborated alkene.Financial support by the Spanish Ministry of the Economy and Competitiveness (Severo Ochoa and CTQ2012-32315) and the Generalidad Valenciana (Prometeo 2012-014) is gratefully acknowledged. This work was also funded by the Deanship of Scientific Research (DSR), King Abdulaziz University under grant No. 75-130-35-HiCi. The authors, therefore, acknowledge technical and financial support of KAU.Khan, A.; Asiri, AM.; Kosa, SA.; García Gómez, H.; Grirrane, A. (2015). Catalytic stereoselective addition to alkynes. Borylation or silylation promoted by magnesia-supported iron oxide and cis-diboronation or silaboration by supported platinum nanoparticles. Journal of Catalysis. 329:401-412. https://doi.org/10.1016/j.jcat.2015.05.006S40141232

Synthesis and structural characterization of dizincocenes Zn2( 5-C5Me5)2 and Zn2( 5-C5Me4Et)2

The synthesis and structural characterization of the dimetallocenes Zn-2(eta(5)-C5Me5)(2) and Zn-2(eta(5)-C5Me4Et)(2) are reviewed together with unsuccessful attempts to obtain analogous complexes containing other cyclopentadienyl ligands. The possibility of preparing related dimetallocenes structures for the late-transition elements is also examined and an overview of known metal-metal bonded molecular compounds of the group 12 elements is given.Grirrane ., A.; Resa, I.; Rodriguez, A.; Carmona, E. (2008). Synthesis and structural characterization of dizincocenes Zn2( 5-C5Me5)2 and Zn2( 5-C5Me4Et)2. Coordination Chemistry Reviews. 252(15-17):1532-1539. doi:10.1016/j.ccr.2008.01.014S1532153925215-1

Multinuclear silver(i) XPhos complexes with cyclooctatetraene: Photochemical C-C bond cleavage of acetonitrile and cyanide bridged Ag cluster formation

Cationic mono-, di-, tri- and tetra-nuclear silver complexes with Buchwald-type phosphane (XPhos) and cyclooctatetraene (COT) have been synthesized and characterized. Formation of [(XPhos-Ag)(COT)][SbF] (n = 1 and 2) complexes was confirmed by single-crystal X-ray crystallography and multinuclear NMR spectroscopy. Variable-temperature NMR spectroscopy in CDCl solution shows the fluxionality of the COT ring in the mono-Ag(i) XPhos complex. Fluxionality of COT was also confirmed in the case of the di-Ag(i) XPhos complex by solid-state and solution P NMR spectroscopy. The C-C bond cleavage of coordinated acetonitrile [XPhos-Ag(i)-NCCH] resulting in cyanide bridged Ag cluster formation [(XPhos-Ag)(μ-CN)(μ-Ag)] (n = 1, 2, 3 and 4) upon light excitation of [(XPhos-Ag)(COT)] was confirmed by HRESI-MS, UV-Absorption and HR-TEM.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2015-69153-C2-1-R) and Generalidad Valenciana (Prometeo 2013-014) is gratefully acknowledged

Nanosized copper stabilized on ternary P, N, S-doped graphene from chitosan shellfish waste: preparation and catalysis of single and double A3-type amine coupling

Heteroatom-doping carbons are conventionally accessed through multistep procedures, often necessitating tedious postgrafting and the use of harsh conditions, while providing less-defined heterogeneous catalysts. We herein disclose a time-saving approach based on straightforward modification of chitosan, an abundant marine waste, followed by its graphitization to access texturally tunable, ternary-doped nitrogen, phosphorus, and sulfur-containing porous carbon material. The presence of functional groups in the edges ensures total exfoliation and dispersion of the sheets, whereas the presence of different coordinating sites inside accounts for efficient stabilization of the embedded metal nanoclusters. Preliminarily, good catalytic activity was noticed for the synthesis of propargylamines and dipropargylamines. The following approach combining active metals and discarded biowaste constitutes a highly versatile entry to heterogeneous carbon-based catalysts.UEMF is acknowledged for financial support. AA thanks UEMF and UPV for an Erasmus+ 2019-1-ES01-KA107-062073 Scholarship