Benedetto Corain

Heteropolymetallic complexes of 1,1′-Bis(diphenylphosphino)ferrocene (dppf). III. Comparative physicochemical properties of (dppf)MCl2 (M = Co, Ni, Pd, Pt, Zn, Cd, Hg)

Abstract 1,1′-Bis(diphenylphosphino)ferrocene (dppf) metal dichlorides (metal = Co, Ni, Pd, Pt, Zn, Cd, and Hg) are examined as a class of related complexes. Their electronic, infrared, mass, 31P NMR, and Mossbauer spectra as well as the HeI and HeII photoelectron spectra of dppf are presented and discussed. Cyclovoltammetric tests in dichloroethane indicate that the ferrocene moiety undergoes a strong stabilization towards oxidation, and the ferricinium derivatives are well characterized in the case of Pd(II) and Pt(II). Differential scanning calorimetric tests reveal that all the complexes are thermally very stable, particularly the Zn(II) and Cd(II) derivatives, which melt without previous decomposition in the temperature range 300–305 °C. Cyclovoltammetric and field desorption mass spectral tests reveal that the [(dppf)MCl2]+ species are stable only when M = Pd, Pt.

Catalysis and polymer networks: the role of morphology and molecular accessibility

Catalysis and polymer networks — the role of morphology and molecular accessibility B. Corain a, M. Zecca a, K. Jeřabek b,∗ a Universita’ di Padova, Dipartimento di Chimica Inorganica, Metallorganica e Analitica and Centro di Studio sulla Stabilita’ e Reattivita’ dei Composti di Coordinazione, C.N.R., via Marzolo 1, 35131 Padova, Italy b Institute of Chemical Processes Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Praha 6 Suchdol, Czech Republic

Generating palladium nanoclusters inside functional cross-linked polymer frameworks

The use of functional resins as designable supports for palladium nanoclusters is reviewed. Data are related to the generation of Pd nanoparticles under various conditions and inside gel-type or macroporous frameworks. The combination of different physico-chemical techniques (ISEC, ESR and PGSE NMR) is illustrated as a powerful tool for evaluating nanomorphology and molecular accessibility, mainly of gel-type resins. A few examples of catalytic applications are presented and discussed and prospects for wider utilizations are evaluated.

Heteropolymetallic complexes of 1,1′-bis(diphenylphosphino)ferrocene (dppf): VII. Redox behaviour of dppf

Abstract The electrochemical oxidation of 1,1′-bis(diphenylphosphino)ferrocene (dppf) at a platinum electrode in 1,2-dichloroethane has been studied by cyclic voltammetry, controlled potential electrolysis, and 31P NMR spectroscopy. The compound undergoes a ferrocene-based reversible oxidation, which is followed by a fast chemical reaction, involving the phosphorus substituent on the cyclopentadienyl rings, to give dppfO, dppfO2, dppfH+ and dppfH22+. Kinetic data suggest that the reaction involes a reversible intramolecular electron transfer between the ferrocene core and the electron-rich substituents to give a phosphinium radical ion, which undergoes a second order rate-determining dimerization or a reaction with the parent compound to give a ferrocenylphosphine dimer cation radical, the ultimate fate of which is the formation of protonated and oxygenated dppf derivatives by nucleophilic attack by water present in the reaction medium. Evidence for the formation of the transient monomeric phosphinium radical was obtained by trapping it with 1,1′-diphenylethylene to give phosphorus-bonded monoalkene adducts of dppf.

The speciation of aluminum in aqueous solutions of aluminum carboxylates. Part I. X-ray molecular structure of Al[OC(O)CH(OH)CH3]3

Abstract The crystal structure of tris(2-hydroxypropanoate-(L))aluminum(III) was determined by X-ray crystallography and refined to R=0.044. The molecular structure is uncomplicated and contains monomeric [Al(lact)3]entities, in which the metal atom is surrounded by a distorted octahedral {O6} coordination sphere where the oxygen atoms of the carboxylate and of the hydroxyl group are the donating sites. The major source of the geometrical distortion is in the OAlO angles of the metallo-organic ring (c83°. The AlO distances range from 1.86 to 1.91 A. All hydroxyl hydrogen atoms are involved in very tight intermolecular hydrogen bonds (c. 2.50 A) which involve the carbonyl groups of adjacent Al(lact)3 unities. The solid state IR spectrum of Al(lact)3 is interpreted in terms of monohapto ‘end on’ coordination of the carboxylate donating site to AlIII.

Metal-catalysed carbon—carbon bond formation in the reaction of β-dicarbonyls with nitriles

Abstract A new synthetic procedure to carbon—carbon bond formation between CH acidic compounds and nucleophiles, like Michael acceptors and nitriles, is based on the use of metal(II) centres as catalysts in a homogeneous phase. The contributions to the inorganic, organic and mechanistic aspects of the reaction of β-dicarbonyls with nitriles are reviewed. Metal catalysis appears, for the investigated systems, largely superior to the traditional approach, which employs organic bases as catalysts, and the perspectives of an extension of this metal-catalysed procedure are illustrated.

Dalton communications. Synthesis and structure of the first phosphine oxide complex of copper(I): evidence for a marked ‘borderline’ character of the metal centre

The remarkable stability of [Cu(dppf)(odppf)]BF4[dppf = 1,1′-bis(diphenylphosphino)ferrocene, odppf = 1,1′-bis(oxodiphenylphosphoranyl)ferrocene], characterized in the solid state by X-ray analysis and in solution by 31P NMR spectroscopy, reveals a marked borderline character of copper(I).

Synthesis and catalytic activity of metal nanoclusters inside functional resins: an endeavour lasting 15 years

Cross-linked functional polymers (functional resins) are versatile, designable and useful supports for metal nanoclusters that are able to provide reasonably thermally and mechanically stable multi-functional metal catalysts characterized by good activity and selectivity. The paper reviews authors’ contributions to the field from the early 1990s to the present.

Hydrogenation of benzene to cyclohexene over polymer-supported ruthenium catalysts

Abstract Partial liquid-phase hydrogenation of benzene to cyclohexene over ruthenium catalysts supported on charcoal and anionic cross-linked polymers is described. The influence of the polarity of polymeric supports, nature of the solvent and the presence of zinc additives on the performance of the catalyst in a glass-lined reactor at 100–110°C and a pressure of 1.5 MPa have been studied. It has been found that at 42–47% conversion of benzene, the selectivity to cyclohexene, observed in water with Ru catalysts supported on a strongly hydrophilic microporous resin, is higher than that displayed by Ru supported on charcoal. The effect of water on the performance of the catalyst is probably a result of formation of a suitable environment around Ru particles and of a good accessibility of metal particles dispersed within the hydrophilic polymer support.

Redox properties of the nickel(II),(I),(0)-triphenylphosphine system in acetonitrile

The cathodic behaviour of electrochemically generated nickel(II) has been investigated in acetonitrile in the presence of triphenylphosphine at a platinum electrode. An appropriate combination of voltammetric, spectrophotometric and NMR findings has allowed us to establish that Ni(II) is present in solution as [Ni(PPh3)2 (CH3CN)42+.]. For the reduction of this species an EECE mechanism is proposed which is consistent with the data. It undergoes an irreversible two-electron reduction giging the Ni(0) complex [Ni(PPh3)4] which reacts quickly with the depolarizer. In this last homogeneous redox reaction the not previously reported Ni(I) complex [Ni(PPh3)4+] is obtained. The degree of reversibility of the redox processes involved has been discussed taking into account the structure, the coordination number and the nature of the ligands in both the redox partners.