Giancarlo Favero

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.

Oxidative addition of alkanenitriles to nickel(0) complexes via π-intermediates

Abstract The alkanenitriles R(C 6 H 5 )CHCN (R = H, CH 3 ) coordinate rapidly and quantitatively through the CN group to the complexes [Ni(PCy 3 ) 2 ] or [{Ni(PCy 3 ) 2 } 2 N 2 ]. Both the end-on [Ni(PCy 3 ) 2 (σ-R′CN)] and the edge-on [Ni(PCy 34 )(π-R′CN)] adducts are formed,and are present in an equilibrium the position of which is governed by the amount of added PCy 3 . The π-complexes react to give the cyano-organometal complexes [Ni(PCy 3 ) n (R′)(CN)] through an oxidative addition involving splitting of the CCN bond. The complexes obtained are unstable and slowly decompose under the reaction conditions to give the coupling R′-R′ (R = H) or the β-elimination R′(-H) (R = CH 3 ) products. The kinetics of the reaction and the stereochemical result suggest a template mechanism in agreement with the findings above.

Reactivity of simple alcohols on Fe2O3powders

The interaction between α-Fe2O3 powders and methanol, ethanol, propan-1-ol and butan-1-ol has been studied by means of FTIR and XPS. Mass spectrometry has been used to characterise the volatile products. Methanol is chemisorbed mainly dissociatively whereas molecular chemisorption is prevalent in higher alcohols. When methanol is chemisorbed, heating induces the formation of formate (at temperatures >400 K) while hydrocarbons are the main products (at temperatures >500 K) of the other alcohols. Considerations are made concerning surface acidic sites in connection with the thermal treatment of the sample and with alcohol chemisorption.

Mechanism of reductive elimination of benzonitrile in cyanophenyl complexes of nickel(II) : II. Reactions of [cyano(phenyl)bis(tricyclohexylphosphine)nickel(II)]☆

Abstract The thermal decomposition of the complex Ni(CN)(C 6 H 5 )(PCy 3 ) 2 (Cy = cyclohexyl) in decalin has been examined. The complex reacts with P(OC 2 H 5 ) 3 to give C 6 H 5 CN in quantitative yield. The mechanism of this reaction has been investigated and compared with that of the similar reaction shown by Ni(CN)(C 6 H 5 )(PEt 3 ) 2 . The results indicate that the easiest path for the reaction involves a bimolecular attack of P(OC 2 H 5 ) 3 at the metal atom before reductive elimination of C 6 H 5 CN.

The distribution of aluminium in the earth: from cosmogenesis to Sial evolution

Abstract In this review the present distribution of aluminium in the Earth crust is discussed historically, starting from the origin of this element in cosmic nucleosynthesis processes and following its fate during the formation of the Solar System, the origin of the Earth, the segregation of siderophile-chalcophile from lithophile elements, the extraction of crustal material from the primitive fertile mantle and the subsequent redistribution of aluminium in sedimentary rocks and in the hydrosphere, which both are a peculiar feature of our planet, intimately connected with the presence of life.

Reductive elimination of benzonitrile from cyanophenyl complexes of nickel(II) : III. Reactions of [cyano(phenyl)bis(triethylphosphine)nickel(II)] with triethylphosphite. General reaction mechanism

Abstract The kinetics of the elimination of C 6 H 5 CN in the reaction of Ni(CN)(C 6 H 5 )-[P(C 2 H 5 ) 3 ] 2 with P(OC 2 H 5 ) 3 have been studied in toluene at 15°C. The results and the rate law show that the elimination mainly takes place by intramolecular decomposition of the 4-coordinate Ni(CN)(C 6 H 5 )[P(OC 2 H 5 ) 3 ] 2 formed in initial substitution steps. A minor contribution to the formation of C 6 H 5 CN comes from the 5-coordinate species Ni(CN)(C 6 H 5 )[P(C 2 H 5 ) 3 ][P(OC 2 H 5 ) 3 ] 2 . The intimate mechanism of these reactions, involving splitting or formation of C—CN bonds in cyanophenyl complexes, is discussed in terms of the peculiar bonding properties of the CN group.

The elimination of benzonitrile in the reaction of [cyano-(phenyl)bis(triethylphosphine)nickel(II)] with 1,2-bis-(diethylphosphino)ethane

Abstract Mechanistic studies on the reaction in benzene of the complex Ni(CN)-(C 6 H 5 )[P(C 2 H 5 ) 3 ] 2 with the diphosphine (C 2 H 5 ) 2 P(CH 2 ) 2 P(C 2 H 2 ) 2 (DEE), leading to reductive elimination of C 6 H 5 CN, are reported. The results indicate that ready substitution of P(C 2 H 5 ) 3 by DEE in the substrate complex precedes the rate-determining elimination step. The rate-law indicates that this process involves a 5-coordinate intermediate of the type Ni(CN)(C 6 H 5 )(P) 3 (P = coordinated ligand phsophorus atoms).

Coordination chemistry of CO and NH3 on CuCl(111) : an experimental and theoretical study of the CO and NH3 bonding to a d10 ion

Abstract A detailed investigation of the electronic structure of CO chemisorbed on CuCl has been carried out by coupling diffuse reflectance infrared (IR) spectroscopy to the local-density-functional molecular-cluster approach. IR measurements indicate a red-shift of the CO stretching mode on passing from the free molecule to the chemisorbed one, proving a slight weakening of the CO bond upon chemisorption. Theoretical results, obtained for CO on CuCl(111) by using the Cu22Cl24CO model cluster, reproduce such a slight bond weakening giving for the CO stretching a red-shift of 38 cm−1 with respect to the free molecule. The bonding of CO to CuCl(111) implies a donation from the CO 5σ HOMO into the empty levels of the coordinatively unsaturated Cu surface ions assisted by a significant backdonation from the fully occupied 3d orbitals of the Lewis acid site into the CO 2π ∗ LUMO. The interaction of NH3 to CuCl(111) has been also investigated by employing the Cu22Cl24NH3 model cluster. The bonding interaction is here limited to a donation from the NH3 3a1 HOMO into the empty levels of the unsaturated Cu sites. Any backbonding from the 3d orbitals of the Lewis acid site is prevented by the high energy of the NH3 2e LUMO. At variance to NH3 on ZnO(0001), the low value of the Lewis acid site effective charge makes negligible the electrostatic interaction with the permanent dipole moment of NH3.

Reactivity of the macrocyclic complex [Ni(C22H22N4)] toward cyanogen

Abstract The macrocyclic complex (2,3:9,10-dibenzo- 5,7,1 2,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca- 2,4,6,9,11,13-hexaenato(2−)- k4N)nickel(II), [Ni(Bzo2Me4[14]hexaenatoN4)] reacts with cyanogen under mild conditions to give addition-insertion to the methine CH group. The two resulting complexes are characterized by one or two cyanoimino methyl C(NH)CN substituents, from which HCN can be easily released to give the corresponding cyano derivatives. The mono cyano complex [Ni(Bzo2(CN)Me4 [14]hexaenatoN4)] crystallizes in the monoclinic system (space group P21/n) and has a saddle-shaped structure, in which the benzene and β-diiminato groups are tilted in opposite directions, with respect to the plane defined by the four nitrogen and the nickel atoms (CN bond distance 1.141(14) A).

An experimental and theoretical study of the interaction of CH3OH and CH3SH with ZnO

The adsorption of CH3SH on ZnO surfaces has been studied by means of X-ray photoelectron and IR spectroscopies. The CH3SH uptake was measured as a function of exposure and temperature. The adsorption is mainly dissociative, even though there is evidence for adsorbed molecular species at room temperature on the ZnO(0001) polar surface. As a whole, experimental results are in agreement with the usual model of dissociative adsorption of Bronsted acids on oxides. Decomposition of adsorbed thiolate species to sulfide occurs to a significant extent above 523 K. The interaction of CH3SH/CH3S– with the Lewis-acid site available on the ZnO(0001) surface has also been theoretically studied by coupling the molecular cluster approach to density functional theory. Calculations relative to the adsorption of CH3OH/CH3O– have also been carried out for comparison. The bonding between the CH3O–/CH3S– species and the Lewis-acid site is confirmed to play a leading role in determining the actual relative acidity scale on ZnO. As far as the molecular structure of the adsorbed species is concerned, the C—S bond is perpendicular to the surface, while the O atom of the CH3O– fragment is not on top of the Lewis-acid site and a non-negligible bonding interaction between the methyl group and the surface is found. These data agree very well with IR measurements which show, for the C—H stretching frequencies, significantly different red shifts for the adsorbed species with respect to the free molecules. Comparison with results recently published by us concerning the adsorption of H2O, HCN and H2S on ZnO(0001) indicate that, according to titration displacement reactions, the theoretical scale of the relative acidity is HCN > H2S > CH3SH > H2O > CH3OH.