Enhanced Fatty Acid Photodecarboxylation over Bimetallic Au-Pd Core-Shell Nanoparticles Deposited on TiO2.

Photodecarboxylation of biomass-derived fatty acids to alkanes offers significant potential to obtain hydrocarbons and economic benefits due to the mild conditions and high activity. Herein, the photodecarboxylation of hexanoic acid into alkanes using TiO2-supported monometallic Au or Pd and bimetallic Au-Pd catalysts is reported. It was found that bimetallic Au-Pd catalysts, featuring a core-shell structure evidenced by EDX-mapping and element line profile, show better photocatalytic performance, achieving 94.7% conversion of hexanoic acid and nearly 100% selectivity to pentane under UV-vis irradiation in the absence of H2 than the monometallic Au analogue. This remarkable enhancement in activity compared to its TiO2 supported monometallic Au or Pd analogues can be attributed to the synergistic effect between Au and Pd within the nanostructured Au(core)-Pd(shell) alloy for achieving more efficient charge-separation efficiency upon visible light excitation. This photocatalyst exhibits a wide scope converting multiple fatty acids into hydrocarbons. Moreover, it can even photocatalyze the conversion of raw bio-oils into alkanes directly. No obvious activity loss was observed during the reusability tests, demonstrating the good stability of the present catalyst. Density functional theory (DFT) calculations indicate that oxidation of carboxylates on TiO2 leads to alkyl radicals that become bound to metal nanoparticles. The superior catalytic performance of Au(core)-Pd(shell)/TiO2 is derived from the weaker adsorption for H on the alloy and the lower hydrogen evolution reaction overpotential. Our research can result in an efficient bio-oil upgrading, resulting in the synthesis of biofuels from biomass under mild conditions.

Gold Nanoparticles Supported on Ceria Nanoparticles Modulate Leukocyte-Endothelium Cell Interactions and Inflammation in Type 2 Diabetes.

Gold-ceria nanoparticles (Au/CeO2) are known to have antioxidant properties. However, whether these nanoparticles can provide benefits in type 2 diabetes mellitus (T2D) remains unknown. This work aimed to study the effects of Au/CeO2 nanoparticles at different rates of gold purity (10, 4.4, 1.79 and 0.82) on leukocyte-endothelium interactions and inflammation in T2D patients. Anthropometric and metabolic parameters, leukocyte-endothelium interactions, ROS production and NF-κB expression were assessed in 57 T2D patients and 51 healthy subjects. T2D patients displayed higher Body Mass Index (BMI) and characteristic alterations in carbohydrate and lipid metabolism. ROS production was increased in leukocytes of T2D patients and decreased by Au/CeO2 at 0.82% gold. Interestingly, Au/CeO2 0.82% modulated leukocyte-endothelium interactions (the first step in the atherosclerotic process) by increasing leukocyte rolling velocity and decreasing rolling flux and adhesion in T2D. A static adhesion assay also revealed diminished leukocyte-endothelium interactions by Au/CeO2 0.82% treatment. NF-κB (p65) levels increased in T2D patients and were reduced by Au/CeO2 treatment. Cell proliferation, viability, and apoptosis assays demonstrated no toxicity produced by Au/CeO2 nanoparticles. These results demonstrate that Au/CeO2 nanoparticles at 0.82% exert antioxidant and anti-inflammatory actions in the leukocyte-endothelium interaction of T2D patients, suggesting a protective role against the appearance of atherosclerosis and cardiovascular diseases when this condition exists.

Synthesis, Structure, Reactivity and Catalytic Implications of a Cationic, Acetylide-Bridged Trigold-JohnPhos Species.

The cationic complex [(JohnPhos-Au)3 (acetylide)][SbF6 ] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide-trigold(I)-JohnPhos system; the trinuclear-acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented µ,η1 ,η2 ,η1 coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)2 ] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [AuI L1][SbF6 ] complexes in CH2 Cl2 at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [CuI L1][PF6 ] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.

Double A3 -Coupling of Primary Amines Catalysed by Gold Complexes.

A novel family of dipropargylamines has been synthesised in one pot through a double catalytic A3 -coupling of five components. Cationic [AuI -L][SbF6 ] complexes (L=JohnPhos) are extremely active catalysts for the double A3 -coupling of primary amines (aliphatic or aromatic), formaldehyde and trimethylsilylacetylene. Several reactions of LAu-amine complexes with organic reagents were studied and followed by NMR and HRMS (ESI) analyses, providing information about the reaction mechanism. Specifically, the role of the π-gold(I) acetylide complexes as active catalyst species was firmly confirmed. Most of the intermediates of this five-component coupling were identified by GC-MS spectrometry, lending support to the mechanistic proposal. In some cases, cationic amine-gold(I)-L complexes corresponding to the activated reagent or intermediate were isolated and characterised by single-crystal X-ray diffraction analysis, their spectroscopic properties were recorded, and their catalytic activity evaluated. Protic solvents influence the course of the reaction by effecting the double deprotection of dipropargylamines, providing a convenient route to dipropargylamines with double-deprotected silyl moieties. When NaOH is present in the reaction media, formation of cationic acetylide-dipropargylamine gold(I) and neutral hydroxide LAuOH complexes, respectively, as high and less active intermediate catalyst forms occur.

Preparation of Tremorine and Gemini Surfactant Precursors with Cationic Ethynyl-Bridged Digold Catalysts.

Tremorine and precursors of gemini surfactants were synthesised in a one-pot, three-step, double-catalytic A3 coupling reaction and characterised by structural and spectroscopic methods. The cationic [AuI (L1)]SbF6 complex is a more active catalyst compared to neutral L2- and L3-AuI bis(trifluoromethanesulfonyl)imidate complexes (L1, L2=Buchwald-type biaryl phosphane; L3=triphenylphosphine) in promoting the double A3 coupling of ethynyltrimethylsilane, secondary amines (cyclic, aliphatic, or aromatic) and formaldehyde. The solvent influences the catalytic performance by desilylation of silyl acetylene or deactivation of the catalyst by a halide anion. Acetylide-bridged cationic digold(I) L1 and L2 complexes were isolated and characterised by means of single-crystal X-ray structure analysis and their spectroscopic properties. Iodine in the acetylene reagent deactivates the AuI catalyst by formation of the less active iodido-bridged cationic digold(I) L1 complex, which was fully characterised by single-crystal X-ray crystal structure analysis and spectroscopy. The nature of the phosphine ligand of the gold complexes used as catalyst affects the stability and activity of the formed cationic ethynyl-bridged AuI2 -L intermediates, isolation of which lends support to the proposed double A3 coupling mechanism.

Catalytic Activity of Cationic and Neutral Silver(I)-XPhos Complexes with Nitrogen Ligands or Tolylsulfonate for Mannich and Aza-Diels-Alder Coupling Reactions.

Cationic and neutral silver(I)-L complexes (L=Buchwald-type biaryl phosphanes) with nitrogen co-ligands or organosulfonate counter ions have been synthesised and characterised through their structural and spectroscopic properties. At room temperature, both cationic and neutral silver(I)-L complexes are extremely active catalysts in the promotion of the single and double A(3) coupling of terminal (di)alkynes, pyrrolidine and formaldehyde. In addition, the aza-Diels-Alder two- and three-component coupling reactions of Danishefsky's diene with an imine or amine and aldehyde are efficiently catalysed by these cationic or neutral silver(I)-L complexes. The solvent influences the catalytic performance due to limited complex solubility or solvent decomposition and reactivity. The isolation of new silver(I)-L complexes with reagents as ligands lends support to mechanistic proposals for such catalytic processes. The activity, stability and metal-distal arene interaction of these silver(I)-L catalysts have been compared with those of analogous cationic gold(I) and copper(I) complexes.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I. The Mo-Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo-Mo, Mo-X, and Mo-L bonds present in these molecules.

Cationic copper(I) complexes as highly efficient catalysts for single and double A(3) -coupling Mannich reactions of terminal alkynes: mechanistic insights and comparative studies with analogous gold(I) complexes.

Cationic CuL complexes (L=Buchwald-type phosphane) with N co-ligands have been characterised by structural and spectroscopic properties. These copper(I) complexes are extremely active catalysts, far more active than analogous gold(I) complexes, to promote the single and double A(3) coupling of terminal alkynes, pyrrolidine and formaldehyde. The activity data show the possible ways in which the solvent can influence the catalytic performance by limiting complex solubility, by solvent decomposition or instability of the copper(I) redox state. Isolation of copper(I) complexes that are likely to be the key catalytic species has allowed light to be shed on the reaction mechanism.

Deactivation of cationic Cu(I) and Au(I) catalysts for A(3) coupling by CH(2)C(l2) : mechanistic implications of the formation of neutral Cu(I) and Au(I) chlorides.

Care should be exercised when using CH2 Cl2 as a solvent for reactions in which amines are a reagent, since undesirable deactivation of cationic copper(I) and gold(I) catalysts to form the corresponding inactive neutral chloride complexes [LMCl] (M=Cu or Au) can occur as a result of the generation of hydrogen chloride in the medium. Cu(I) and Au(I) deactivation has been proved for the Mannich three-component coupling reaction. A series of Cu(I) and Au(I) complexes with potential mechanistic implications were isolated and characterized by X-ray crystallography.

Isolation and X-ray characterization of palladium-N complexes in the guanylation of aromatic amines. Mechanistic implications.

In the context of palladium-catalyzed guanylation of anilines herein, we have been able to characterize and isolate bis(anilino) and bis(guanidino)Pd(II) complexes using reaction conditions under which stoichiometric amounts of palladium salts are used. Characterization of these palladium complexes strongly supports a mechanistic proposal for the catalytic guanylation of anilines using PdCl2(NCCH3)2 as catalyst that involves the intermediacy of these Pd(II) complexes.

Air-stable, dinuclear and tetranuclear σ,π-acetylide gold(I) complexes and their catalytic implications.

Two for one gold: Factors governing the formation of isolable digold(I) σ,π-acetylide complexes are given (see scheme), indicating the general tendency of phosphine-Au(I) precatalysts to form this type of complexes, which are involved as reaction intermediates in gold(I)-catalyzed reactions. Mechanistic insights into the intermolecular hydroamination of aniline and terminal alkynes catalyzed by gold(I) have shown the role of a fluxional, cationic σ,π-digold alkynide complex as one of the intermediates in the formation of imines.

Orthogonal C-N plus C-C tandem reaction of iodoanilines leading to styrylguanidines catalyzed by supported palladium nanoparticles.

Two birds, one nanoparticle: A highly efficient and selective tandem reaction comprising C-N and C-C cross-coupling of iodoanilines to form styrylguanidines by using a recyclable, heterogeneous, supported palladium nanoparticle catalyst is reported (see scheme). A mechanistic proposal based on coordination of palladium nanoparticles to the basic N atoms of aniline and guanidine is supported by isolation of palladium complexes with aniline or guanidine.

Thiodiacetate-manganese chemistry with N ligands: unique control of the supramolecular arrangement over the metal coordination mode.

Compounds based on the Mn-tda unit (tda=S(CH(2)COO)(2)(-2) ) and N co-ligands have been analyzed in terms of structural, spectroscopic, magnetic properties and DFT calculations. The precursors [Mn(tda)(H(2)O)](n) (1) and [Mn(tda)(H(2)O)(3)]·H(2)O (2) have been characterized by powder and X-ray diffraction, respectively. Their derivatives with bipyridyl-type ligands have formulas [Mn(tda)(bipy)](n) (3), [{Mn(N-N)}(2)(µ-H(2)O)(µ-tda)(2)](n) (N-N=4,4'-Me(2)bipy (4), 5,5'-Me(2)bipy, (5)) and [Mn(tda){(MeO)(2)bipy}·2H(2)O](n) (6). Depending on the presence/position of substituents at bipy, the supramolecular arrangement can affect the metal coordination type. While all the complexes consist of 1D coordination polymers, only 3 has a copper-acetate core with local trigonal prismatic metal coordination. The presence of substituents in 4-6, together with water co-ligands, reduces the supramolecular interactions and typical octahedral Mn(II) ions are observed. The unicity of 3 is also supported by magnetic studies and by DFT calculations, which confirm that the unusual Mn coordination is a consequence of extended noncovalent interactions (π-π stacking) between bipy ligands. Moreover, 3 is an example of broken paradigm for supramolecular chemistry. In fact, the desired stereochemical properties are achieved by using rigid metal building blocks, whereas in 3 the accumulation of weak noncovalent interactions controls the metal geometry. Other N co-ligands have also been reacted with 1 to give the compounds [Mn(tda)(phen)](2)·6H(2)O (7) (phen=1,10-phenanthroline), [Mn(tda)(terpy)](n) (8) (terpy=2,2':6,2''-terpyridine), [Mn(tda)(pyterpy)](n) (9) (pyterpy=4'-(4-pyridyl)-2,2':6,2''-terpyridine), [Mn(tda)(tpt)(H(2)O)]·2H(2)O (10) and [Mn(tda)(tpt)(H(2)O)](2)·2H(2)O (11) (tpt=2,4,6-tris(2-pyridyl)-1,3,5-triazine). Their identified mono-, bi- or polynuclear structures clearly indicate that hydrogen bonding is variously competitive with π-π stacking.

Stereoselective single (copper) or double (platinum) boronation of alkynes catalyzed by magnesia-supported copper oxide or platinum nanoparticles.

Copper(II) oxide nanoparticles supported on magnesia have been prepared from Cu(II) supported on magnesia by hydrogen reduction at 400 °C followed by storage under ambient conditions. X-ray photoelectron spectroscopy of the material clearly shows that immediately after the reduction copper(0)-metal nanoparticles are present on the magnesia support, but they undergo fast oxidation to copper oxide upon contact with the ambient for a short time. TEM images show that the catalytically active CuO/MgO material is formed of well-dispersed copper oxide nanoparticles supported on fibrous MgO. CuO/MgO exhibits a remarkable catalytic activity for the monoborylation of aromatic, aliphatic, terminal, and internal alkynes, the products being formed with high regio- (borylation at the less substituted carbon) and stereoselectivity (trans-configured). CuO/MgO exhibits complete chemoselectivity towards the monoborylation of alkynes in the presence of alkenes. Other metal nanoparticles such as gold or palladium are inactive towards borylation, but undergo undesirable oligomerization or partial hydrogenation of the C≡C triple bond. In contrast, platinum, either supported on magnesia or on nanoparticulate ceria, efficiently promotes the stereoselective diborylation of alkynes to yield a cis-configured diboronate alkene. By using platinum as the catalyst we have developed a tandem diborylation/hydrogenation reaction that gives vic-diboronated alkanes from alkynes in one pot.

Preparation of symmetric and asymmetric aromatic azo compounds from aromatic amines or nitro compounds using supported gold catalysts.

This protocol describes the aerobic oxidation of aromatic anilines to aromatic azo compounds using gold (Au) nanoparticles supported on TiO(2) as a catalyst. Yields above 98% are achieved under a few bars of oxygen pressure. It should be noted that the use of stoichiometric amounts of environmentally unfriendly reagents, e.g., transition metals and nitrites, commonly used in current syntheses of azo compounds, is avoided using this approach. The protocol is illustrated with the synthesis of parent azobenzene from aniline, and this reaction takes 22 h. Au on TiO(2) can also be used as a hydrogenation catalyst, making it possible to prepare azo compounds directly from nitroaromatics through a two-step (hydrogenation followed by aerobic oxidation), one-pot, one-catalyst reaction. In addition, the catalytic process is efficient for the synthesis of symmetric and a range of asymmetric aromatic azo compounds from the mixtures of two anilines substituted with electron-donor and electron-acceptor substituents.

Structural analysis of zincocenes with substituted cyclopentadienyl rings.

New zincocenes [ZnCp'(2)] (2-5) with substituted cyclopentadienyl ligands C(5)Me(4)H, C(5)Me(4)tBu, C(5)Me(4)SiMe(2)tBu and C(5)Me(4)SiMe(3), respectively, have been prepared by the reaction of ZnCl(2) with the appropriate Cp'-transfer reagent. For a comparative structural study, the known [Zn(C(5)H(4)SiMe(3))(2)] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C(5)Me(5))(C(5)Me(4)SiMe(3))] (6) and [Zn(C(5)Me(5))(C(5)H(4)SiMe(3))] (7), the last two obtained by conproportionation of [Zn(C(5)Me(5))(2)] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by (13)C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp' ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, eta(5)/eta(1)(sigma) structures, in which the monohapto C(5)Me(4)SiMe(3) ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn--C bond of comparable strength to the Zn--Me bond in ZnMe(2). Zincocene 5 has dynamic behaviour in solution, but a rigid eta(5)/eta(1)(sigma) structure in the solid state, as revealed by (13)C CPMAS NMR studies, whereas for 6 the different nature of the Cp' ligands and of the ring substituents of the eta(1)-Cp' group (Me and SiMe(3)) have permitted observation for the first time of the rigid eta(5)/eta(1) solution structure. Iminoacyl compounds of composition [Zn(eta(5)-C(5)Me(4)R)(eta(1)-C(NXyl)C(5)Me(4)R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6-dimethylphenylisocyanide) have also been obtained and characterised.

Gold-catalyzed synthesis of aromatic azo compounds from anilines and nitroaromatics.

The selective formation of aromatic azo compounds at preparative or industrial levels requires stoichiometric amounts of environmentally unfriendly transition metals or nitrites. Here, we show that gold nanoparticles supported on titanium dioxide (TiO2) and nanoparticulated cerium dioxide (CeO2) catalyze the aerobic oxidation of aromatic anilines to aromatic azo compounds with yields above 98% under mild reaction conditions. Gold on TiO2 can also act as a reductive catalyst to access the compound directly from nitroaromatics through a two-step, one-pot reaction. The catalytic process shows promise for efficient synthesis of symmetric aromatic azo compounds, and even a range of asymmetric aromatic azo compounds.

Solid-state structures and solution studies of novel cyclopentadienyl mercury compounds.

New mercury cyclopentadienyl complexes Hg(eta1-Cp')Cl have been prepared by the reaction of HgCl2 and the appropriate KCp' salts or by the transmetalation of HgCl2 with ZnCp'2 (Cp'=C5Me4H, 1; C5Me4But, 2; C5Me4SiMe3, 3; C5H4SiMe3, 4). By contrast, only the SiMe3-substituted bis(cyclopentadienyl) derivatives, Hg(C5Me4SiMe3)2 (5) and Hg(C5H4SiMe3)2 (6), can be isolated by the above synthetic procedures and the appropriate ratio of reagents or from HgCp'Cl and KCp'. Solution NMR studies reveal nonfluxional behavior of the SiMe3-substituted complexes 3, 5, and 6. X-ray studies of the solid-state structures show that the six compounds contain eta1-Cp' ligands, with linear or almost linear C-Hg-Cl or C-Hg-C coordination environments. The two HgCp'2 compounds, 5 and 6, have the expected insular structures, but the HgCp'Cl derivatives show supramolecular associations by means of weak secondary Hg...Cl interactions. Thus, the HgCp'Cl compounds 1, 3, and 4 form three different polymeric chain structures with typically two Hg...Cl interactions of 3.04-3.46 A per mercury. By contrast, 2 forms a tetramer, [Hg(C5Me4SiMe3)Cl]4, with a cubelike arrangement of four Hg and four Cl atoms. Density functional theory has been used to investigate the electronic structure of the compounds.

Zinc-zinc bonded zincocene structures. Synthesis and characterization of Zn2(eta5-C5Me5)2 and Zn2(eta5-C5Me4Et)2.

While, in general, decamethylzincocene, Zn(C5Me5)2, and other zincocenes, Zn(C5Me4R)2 (R = H, But, SiMe3), react with dialkyl and diaryl derivatives, ZnR'2, to give the half-sandwich compounds (eta5-C5Me4R)ZnR', under certain conditions the reactions of Zn(C5Me5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(eta5-C5Me5)2 (1) in low yields, most likely as a result of the coupling of two (eta5-C5Me5)Zn* radicals. An improved, large scale (ca. 2 g) synthesis of 1 has been achieved by reduction of equimolar mixtures of Zn(C5Me5)2 and ZnCl2 with KH in tetrahydrofuran. The analogous reduction of Zn(C5Me4R)2 (R = H, SiMe3, But) yields only decomposition products, but the isotopically labeled dimetallocene 68Zn2(eta5-C5Me5)2 and the related compound Zn2(eta5-C5Me4Et)2 (2) have been obtained by this procedure. Compound 2 has lower thermal stability than 1, but it has been unequivocally characterized by low-temperature X-ray diffraction studies. As for 1 a combination of structural characterization techniques has provided unambiguous evidence for its formulation as the Zn-Zn bonded dimer Zn2(eta5-C5Me4Et)2, with a short Zn-Zn bond of 2.295(3) A indicative of a strong Zn-Zn bonding interaction. The electronic structure and the bonding properties of 1 and those of related dizincocenes Zn2(eta5-Cp')2 have been studied by DFT methods (B3LYP level), with computed bond distances and angles for dizincocene 1 very similar to the experimental values. The Zn-Zn bond is strong (ca. 62 kcal.mol-1 for 1) and resides in the HOMO-4, that has a contribution of Zn orbitals close to 60%, consisting mostly of the Zn 4s orbitals (more than 96%).