Electrospray Ionization Based Methods for the Generation of Polynuclear Oxo- and Hydroxo Group 6 Anions in the Gas-Phase

Electrospray ionization (ESI) of the Lindqvist (n-Bu4N)2[M6O19] (M = Mo, W) polioxometalates provides a straightforward entry for the generation of an assortment of oxo- and hydroxo anions in the gas-phase. In particular, the series of oxo dianions of general formula [(MO3)nO]2- (n = 2-6; M = Mo, W), monoanions, namely [(MO3)nO]- (n = 1, 2) and [(MO3)n]- (n = 1, 2), and the hydroxo [(MO3)n(OH)]- (n = 1-6) species can be readily generated in the gas-phase upon varying the solvent composition as well as the ionisation conditions (typically the Uc cone voltage). Complementary tandem mass experiments (collision induced dissociation and ion-molecule reactions) are also used aimed to investigate the consecutive dissociation of these species and their intrinsic gas-phase reactivity towards methanol. Special emphasis is paid to some of the key factors of these group 6 anions related to the gas-phase activation of methanol, such as molecular composition, open vs closed shell electronic nature and cluster siz

Nanolayered Co-Mo-S Catalysts for the Chemoselective Hydrogenation of Nitroarenes

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/acscatal.7b00170[EN] Nanolayered molybdenum disulfide cobalt-promoted materials (Co-Mo-S) have been established as chemoselective catalysts for thehydrogenation of nitroarenes under relatively mild conditions. Co-Mo-S catalysts have been prepared by a one-pot hydrothermal synthesis that allows the formation of unsupported catalysts with a large number of active sites per unit volume. Via application of these catalysts, the hydrogenation of the nitro functionality has been performed selectively in the presence of double and triple bonds, aldehydes, ketones, and carboxylic acid derivative groups, thus affording the corresponding anilines in good to excellent yields. Interestingly, the partial hydrogenation of some dinitroarenes has also been successfully accomplished. In addition, its catalytic performance has been evaluated for the preparation of the bioactive compound paracetamol through a one-pot direct hydrogenative amidation reaction.The financial support of the European Union (FP7-NMP-2013-EU-Japan-604319-NOVACAM) is gratefully acknowledged. I.S. thanks Spanish MINECO for a "Formacion Postdoctoral" fellowship. The authors also thank the Microscopy Service of Universitat Politecnica de Valencia for kind help with TEM and STEM measurements.Sorribes-Terrés, I.; Liu, L.; Corma Canós, A. (2017). Nanolayered Co-Mo-S Catalysts for the Chemoselective Hydrogenation of Nitroarenes. ACS Catalysis. 7(4):2698-2708. https://doi.org/10.1021/acscatal.7b00170S269827087

From well-defined clusters to functional materials: molecular Engineering of amorphous molybdenum sulfides for hydrogen evolution Electrocatalysis

Developing precious-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is crucial to establishing H2 produced from renewable energy sources as an alternative energy carrier to fossil fuels. Amorphous molybdenum sulfide-based materials are promising candidates that provide highly active HER electrocatalysts by introducing active sites at both the edge positions and the typically inactive basal planes. Herein, we report an innovative bottom-up synthesis of amorphous molybdenum sulfides using molecular complexes with Mo3S4 and Mo3S7 cluster cores as building entities. The ability to control the precursor of choice has made it viable to enhance the HER activity of these materials. Furthermore, the tunability of the atomic composition of the molecular cluster precursors allows the modification of the derived materials with atomic-scale precision, enabling us to track the synthesis mechanism and, in combination with Density Functional Theory (DFT) calculations, to decipher the nature of the HER active sites

Efficient and Selective N‐Methylation of Nitroarenes under Mild Reaction Conditions

Herein, we report a straightforward protocol for the preparation of N,N‐dimethylated amines from readily available nitro starting materials using formic acid as a renewable C1 source and silanes as reducing agents. This tandem process is efficiently accomplished in the presence of a cubane‐type Mo3PtS4 catalyst. For the preparation of the novel [Mo3Pt(PPh3)S4Cl3(dmen)3]+ (3+) (dmen: N,N′‐dimethylethylenediamine) compound we have followed a [3+1] building block strategy starting from the trinuclear [Mo3S4Cl3(dmen)3]+ (1+) and Pt(PPh3)4 (2) complexes. The heterobimetallic 3+ cation preserves the main structural features of its 1+ cluster precursor. Interestingly, this catalytic protocol operates at room temperature with high chemoselectivity when the 3+ catalyst co‐exists with its trinuclear 1+ precursor. N‐heterocyclic arenes, double bonds, ketones, cyanides and ester functional groups are well retained after N‐methylation of the corresponding functionalized nitroarenes. In addition, benzylic‐type as well as aliphatic nitro compounds can also be methylated following this protocol

[Cr(dmbipy)(ox)2]−: a new bis-oxalato building block for metal assembling. Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2]·5H2O (X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O

The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4 [Cr(dmbipy)(ox)2 ]$5H2O (1), AsPh4 [Cr(dmbipy)(ox)2 ]$5H2O (2), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n$17/2nH2O (3) and {Ag(H2O)[Cr(dmbipy)(ox)2]}n$3nH2O (4) (PPh4 + ¼ tetraphenylphosphonium cation; AsPh4 + ¼ tetraphenylarsonium cation; dmbipy ¼ 4,4 0 -dimethyl- 2,2 0 -bipyridine; ox 2 ¼ oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2] anions, XPh4 + cations [X ¼ P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr–O and Cr–N bond distances varying in the ranges 1.950(2)–1.9782(12) and 2.047(3)–2.0567(14) A˚ , respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)– 83.11(5) , and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5) (2)]. The [Cr(dmbipy)(ox)2] unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2] unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1–4 in the temperature range 1.9– 300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by p–p stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2] unit (AA ¼ bidentate nitrogen donor) as a building bl

On the catalytic transfer hydrogenation of nitroarenes by a cubane-type Mo3S4 cluster hydride: disentangling the nature of the reaction mechanism

Cubane-type Mo3S4 cluster hydrides decorated with phosphine ligands are active catalysts for the transfer hydrogenation of nitroarenes to aniline derivatives in the presence of formic acid (HCOOH) and triethylamine (Et3N). The process is highly selective and most of the cluster species involved in the catalytic cycle have been identified through reaction monitoring. Formation of a dihydrogen cluster intermediate has also been postulated based on previous kinetic and theoretical studies. However, the different steps involved in the transfer hydrogenation from the cluster to the nitroarene to finally produce aniline remain unclear. Herein, we report an in-depth computational investigation into this mechanism. Et3N reduces the activation barrier associated with the formation of Mo–HHOOCH dihydrogen species. The global catalytic process is highly exergonic and occurs in three consecutive steps with nitrosobenzene and N-phenylhydroxylamine as reaction intermediates. Our computational findings explain how hydrogen is transferred from these Mo–HHOOCH dihydrogen adducts to nitrobenzene with the concomitant formation of nitrosobenzene and the formate substituted cluster. Then, a b-hydride elimination reaction accompanied by CO2 release regenerates the cluster hydride. Two additional steps are needed for hydrogen transfer from the dihydrogen cluster to nitrosobenzene and N-phenylhydroxylamine to finally produce aniline. Our results show that the three metal centres in the Mo3S4 unit act independently, so the cluster can exist in up to ten different forms that are capable of opening a wide range of reaction paths. This behaviour reveals the outstanding catalytic possibilities of this kind of cluster complexes, which work as highly efficient catalytic machines

Palladium doping of In2O3 towards a general and selective catalytic hydrogenation of amides to amines and alcohols

Herein, the first general heterogeneous catalytic protocol for the hydrogenation of primary, secondary and tertiary amides to their corresponding amines and alcohols is described. Advantageously, this catalytic protocol works under additive-free conditions and is compatible with the presence of aromatic rings, which are fully retained in the final products. This hydrogenative C–N bond cleavage methodology is catalyzed by a Pd-doped In2O3 catalyst prepared by a microwave hydrothermal-assisted method followed by calcination. This catalyst displays highly dispersed Pd2+ ionic species in the oxide matrix of In2O3 that have appeared to be essential for its high catalytic performance

Unraveling a Biomass-Derived Multiphase Catalyst for the Dehydrogenative Coupling of Silanes with Alcohols under Aerobic Conditions

Herein, a novel silver and chromium nanostructured N-doped carbonaceous material has been synthesized by a biomass-annealing approach using readily available chitosan as a raw material. The resulting catalyst AgCr@CN-800 has been applied for the dehydrogenative coupling reaction of various silanes with different alcohols to obtain the corresponding silyl ethers under aerobic and mild conditions. Besides excellent activity and selectivity, the as-prepared catalyst exhibits good stability and reusability. Characterization by XRD, XPS, ICP-MS, HRTEM, in combination with careful examination of the structure with Cs-corrected HAADF-STEM revealed that catalyst AgCr@CN-800 comprises Ag and CrN aggregated particles, as well as highly dispersed Ag-Nx and Cr-Nx sites embedded in N-doped graphitic structures. A comparative catalytic study using structure-related catalysts in combination with acid-leaching treatments has shown that the most active species are the Ag particles, and that their activity is boosted by the presence of Cr-derived species. By in-situ Raman spectroscopy experiments, it has been found that the dehydrogenative coupling of silanes with alcohols in the presence of catalyst AgCr@CN-800 takes place through an oxygen-assisted mechanism

Base-Free Catalytic Hydrogen Production from Formic Acid Mediated by a Cubane-Type Mo3S4 Cluster Hydride

Formic acid (FA) dehydrogenation is an attractive process in the implementation of a hydrogen economy. To make this process greener and less costly, the interest nowadays is moving toward non-noble metal catalysts and additive-free protocols. Efficient protocols using earth abundant first row transition metals, mostly iron, have been developed, but other metals, such as molybdenum, remain practically unexplored. Herein, we present the transformation of FA to form H2 and CO2 through a cluster catalysis mechanism mediated by a cuboidal [Mo3S4H3(dmpe)3]+ hydride cluster in the absence of base or any other additive. Our catalyst has proved to be more active and selective than the other molybdenum compounds reported to date for this purpose. Kinetic studies, reaction monitoring, and isolation of the [Mo3S4(OCHO)3(dmpe)3]+ formate reaction intermediate, in combination with DFT calculations, have allowed us to formulate an unambiguous mechanism of FA dehydrogenation. Kinetic studies indicate that the reaction at temperatures up to 60 °C ends at the triformate complex and occurs in a single kinetic step, which can be interpreted in terms of statistical kinetics at the three metal centers. The process starts with the formation of a dihydrogen-bonded species with Mo–H···HOOCH bonds, detected by NMR techniques, followed by hydrogen release and formate coordination. Whereas this process is favored at temperatures up to 60 °C, the subsequent β-hydride elimination that allows for the CO2 release and closes the catalytic cycle is only completed at higher temperatures. The cycle also operates starting from the [Mo3S4(OCHO)3(dmpe)3]+ formate intermediate, again with preservation of the cluster integrity, which adds our proposal to the list of the infrequent cluster catalysis reaction mechanisms.Funding for open access charge: CRUE-Universitat Jaume

Selective Dehydrogenation of Formic Acid Catalyzed by Air-Stable Cuboidal PN Molybdenum Sulfide Clusters

Formic acid is considered as a promising hydrogen storage material in the context of a green hydrogen economy. In this work, we present a series of aminophosphino and imidazolylamino Mo3S4 cuboidal clusters which are active and selective for formic acid dehydrogenation (FAD). Best results are obtained with the new [Mo3S4Cl3(ediprp)3](BPh4) (4(BPh4)) (ediprp=(2-(diisopropylphosphino)ethylamine)) cluster, which is prepared through a simple ligand exchange process from the Mo3S4Cl4(PPh3)3(H2O)2 precursor. Under the conditions investigated, complex 4+ showed significantly improved performance (TOF=4048 h−1 and 3743 h−1 at 120 °C in propylene carbonate using N,N-dimethyloctylamine as base after 10 min and 15 min, respectively) compared to the other reported molybdenum compounds. Mechanistic investigations based on stoichiometric and catalytic experiments show that cluster 4+ reacts with formic acid in the presence of a base to form formate substituted species [Mo3S4Cl3-x(OCOH)x(ediprp)3]+ (x=1–3) from which the catalytic cycle starts. Subsequently, formate decarboxylation of the partially substituted [Mo3S4Cl3-x(OCOH)x(ediprp)3]+ (x=1, 2, 3) catalyst through a β-hydride transfer to the metal generates the trinuclear Mo3S4 cluster hydride. Dehydrogenation takes place through protonation by HCOOH to form Mo−H⋅⋅⋅HCOOH dihydrogen adducts, with regeneration of the Mo3S4 formate cluster. This proposal has been validated by DFT calculations.Funding for open access charge: CRUE-Universitat Jaume