1,721,200 research outputs found
Synthesis, characterization and molecular structures of the new [Bi@Rh12(CO)27]3–, [(Bi@Rh12(CO)26)2Bi]5–, [Bi@Rh14(CO)27Bi2]3– and [Bi@Rh17(CO)33Bi2]4– carbonyl clusters
No full textNew nickel-phosphorus homoleptic carbonyl clusters: synthesis, characterization, and catalytic properties
No full textHighly Active Catalysts Based on the Rh4(CO)12 Cluster Supported on Ce0.5Zr0.5 and Zr Oxides for Low-Temperature Methane Steam Reforming
No full textSyngas and Hydrogen productions from methane are industrially carried out at high temperatures (900 ◦C). Nevertheless, low-temperature steam reforming can be an alternative for small-scale plants. In these conditions, the process can also be coupled with systems that increase the overall efficiency such as hydrogen purification with membranes, microreactors or enhanced reforming with CO2 capture. However, at low temperature, in order to get conversion values close to the equilibrium ones, very active catalysts are needed. For this purpose, the Rh4(CO)12 cluster was synthetized and deposited over Ce0.5Zr0.5O2 and ZrO2 supports, prepared by microemulsion, and tested in low-temperature steam methane reforming reactions under different conditions. The catalysts were active at 750 ◦C at low Rh loadings (0.05%) and outperformed an analogous Rh-impregnated catalyst. At higher Rh concentrations (0.6%), the Rh cluster deposited on Ce0.5Zr0.5 oxide reached conversions close to the equilibrium values and good stability over long reaction time, demonstrating that active phases derived from Rh carbonyl clusters can be used to catalyze steam reforming reactions. Conversely, the same catalyst suffered from a fast deactivation at 500 ◦C, likely related to the oxidation of the Rh phase due to the oxygen-mobility properties of Ce. Indeed, at 500 ◦C the Rh-based ZrO2-supported catalyst was able to provide stable results with higher conversions. The effects of different pretreatments were also investigated: at 500 ◦C, the catalysts subjected to thermal treatment, both under N2 and H2, proved to be more active than those without the H2 treatment. In general, this work highlights the possibility of using Rh carbonyl-cluster-derived supported catalysts in methane reforming reactions and, at low temperature, it showed deactivation phenomena related to the presence of reducible supports
The redox chemistry of [Ni9C(CO)17]2– and [Ni10(C2)(CO)16]2–: Synthesis, electrochemistry and structure of [Ni12C(CO)18]4– and [Ni22(C2)4(CO)28(Et2S)]2–
No full textThis paper reports a detailed study of the oxidation and reduction reactions of simple nickel mono-carbide and mono-acetlyde carbonyl clusters. The reduction of [Ni9C(CO)17]2– with Na/naphtalene affords the new [Ni12C(CO)18]4– mono-carbide cluster. Under the same experimental conditions, [Ni10(C2)(CO)16]2– reacts with Na/naphtalene yielding a mixture of the previously reported [Ni11(C2)(CO)15]4– and [Ni12(C2)(CO)16]4– mono-acetylide tetra-anions. The oxidation reactions of both [Ni9C(CO)17]2– and [Ni10(C2)(CO)16]2–, carried out with miscellaneous reagents, e.g., [C7H7][BF4], [Cp2Fe][PF6], AgNO3, are more complicated and less selective, leading to mixtures of products, among which the previously reported [Ni8C(CO)16]2–, [Ni16(C2)2(CO)23]4–, [Ni38C6(CO)42]6– and [Ni32C6(CO)36]6– species have been identified. Interestingly, oxidation of [Ni10(C2)(CO)16]2– with Pd(Et2S)2Cl2 affords the new tetra-acetylide [Ni22(C2)4(CO)28(Et2S)]2–, even if in low yields. The new species [Ni12C(CO)18]4– and [Ni22(C2)4(CO)28(Et2S)]2– have been structurally characterized by means of single crystal X-ray diffraction. Electrochemical and spectroelectrochemical studies have been performed on [Ni12C(CO)18]4–. This compound can be electrochemically oxidized and reduced reversibly affording [Ni12C(CO)18]3– and [Ni12C(CO)18]5–, respectively. The same species can be obtained by chemical methods but, due to their limited stability during work-up, it has not been possible to isolate them
Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2- (n = 2-4)
No full textThe reactions of [Pt3n(CO)6n]2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph2PCH2CH2PPh2 (dppe) result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppe)]2-, [Pt9(CO)16(dppe)]2-, and [Pt12(CO)20(dppe)2]2-. Their formation is accompanied by slight amounts of neutral species such as Pt4(CO)4(dppe)2, Pt6(CO)6(dppe)3, and Pt(dppe)2. A similar behavior was observed with the chiral ligand R-Ph2PCH(Me)CH2PPh2 (R-dppp), and two isomers of [Pt9(CO)16(R-dppp)]2- were identified. All the new species were spectroscopically characterized by means of IR and 31P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh3, as well as more rigid bidentate ligands, that is, CH2C(PPh2)2 (P^P), CH2(PPh2)2 (dppm), and o-C6H4(PPh2)2 (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt3 units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt9(CO)16(dppe)]2-, [Pt9(CO)16(R-dppp)]2-, [Pt12(CO)22(PPh3)2]2-, and [Pt9(CO)16(PPh3)2]2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt6(CO)10(dppe)]2- and [Pt6(CO)10(PPh3)2]2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt12(CO)20(dppe)2]2-
Molecular hydride carbonyl clusters and nanoclusters
Full text linkThis minireview outlines the actual status of the chemistry of hydride metal carbonyl clusters (MCCs) by means of pertinent examples, without being comprehensive. After a brief introduction to the topic, the major synthetic routes for the introduction of hydride ligands in MCCs are described, with particular focus on the different typologies of reagents that can be employed. The structures of hydride MCCs and the different coordination modes of hydride ligands are, then presented, based on single-crystal X-ray and neutron diffraction data available. Some general considerations on 1H NMR studies of hydride MCCs are described, including fluxionality and the problems of detecting hydrides in larger MCCs. Moreover, electrochemical studies of hydride MCCs are summarized, focusing on electrochemistry as an indirect tool for determining the hydride nature of large MCCs, and tuning the redox potentials of MCCs by protonation/deprotonation reactions. Applications of hydride MCCs in catalysis and electrocatalysis are only briefly described at the end of this minireview, since this topic has been recently reviewed
Synthesis, molecular structures and solution NMR studies of N-heterocyclic carbene-amine silver complexes
No full textSurface decorated metal carbonyl clusters: bridging organometallic molecular clusters and atomically precise ligated nanoclusters
Full text linkIn this Frontier Article, the work carried out within our research group in Bologna in the field of surface decorated metal carbonyl clusters will be outlined and put in a more general context. After a short Introduction, clusters composed of a metal carbonyl core decorated on the surface by metal-ligand fragments will be analyzed. Both metal-ligand fragments behaving as Lewis acids and Lewis bases will be considered. Then, the focus will be moved to clusters composed of a naked metal core decorated and stabilized on the surface by metal-carbonyl fragments. The structure and bonding (where theoretical studies are available) of such surface decorated metal carbonyl clusters will be presented, and compared to atomically precise ligated nanoclusters
Synthesis of New Central and Planar Chiral Enantiomerically pure 5-Ferrocenyl-Oxazolines and a 5-Ferrocenyl-thiazoline
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