Hard Lewis Bases Research Articles

Chemisorption bond energies of Lewis acids and bases on oxygen modified Mo(100) surfaces

The acid-base properties of three molybdenum (100) surfaces chemically modified by 1.5, 1.2, and 1.0 monolayers (ML) of atomic oxygen were investigated by thermal desorption spectroscopy using a series of molecular Lewis bases. The molecules used in this study were of three types, hard Lewis bases, ammonia and dimethylether, soft Lewis bases, phosphine, ethene and propene, and two π acids, carbon monoxide and 3,3,3-trifluoropropene. The trends in desorption energies are consistent with the expectation that the molecules would adsorb at localized, acidic surface sites. The desorption energies are correlated with proton affinities, and the 1.5 ML oxygen modified surface was found to most resemble a gas phase proton.

The reaction of alkoxides with dicobalt octacarbonyl: Trapping of the Co(I) intermediate in the disproportionation (?base reaction?) with a hardLewis base

The reaction of alkoxides with dicobalt octacarbonyl: Trapping of the Co(I) intermediate in the disproportionation (?base reaction?) with a hardLewis base

Properties of aluminum trichloride solutions in liquid SO 2: Formation of the SOCl + cation

The addition of AlCl 3 to liquid SO 2 yields anhydrous solutions in which the stability of cationic species such as the 9,10-diphenylanthracene dication is shown to be considerably increased. Aluminum trichloride solutions are also conductive and are oxidizing agents. The strong solubility of AlCl 3 appears to be anomalous when compared to that of other compounds made of a hard Lewis acid and a hard Lewis base and is probably due to a reaction with the solvent. The reaction: ▪ giving rise to the oxidizing and electrophilic SOCl + cation accounts for the properties of AlCl 3 solutions, particularly their sulfinating power towards benzene.

Interaction of dicobaltoctacarbonyl with some organic solvents

Co 2CO 8 is known to have different chemical behaviour when it is dissolved in common organic solvents, according to their properties. Hydrocarbon solvents do not react with the solute: anyway, an equilibrium is established between at least three isomeric forms of Co 2(CO) 8, one with bridging COs (the only form present in solid state), the others with all COs terminal [1 ]. Solution in solvents which are hard Lewis bases, B, gives rise to a disproportionation reaction [2], whose general stoichiometry is: 3 Co 2(CO) 8 + 12 B → 2 [CoB ++ 6] [Co(CO) − 4] 2 + 8CO The kinetic behaviour is very complicated and suggests the presence of several competing mechanisms, involving CO dissociation, base coordination and electron transfer [3]. The reaction rates are sensitive more to the steric characteristic of the base than to its basicity or to its dielectrinc constant. When Co 2(CO) 8 is dissolved in CS 2 at room temperature, it reacts slowly with the solvent to yield a great variety of C, S or C xS ycontaining cobalt carbonyl derivatives [4]. The most part of them shows structures in which a particular stable pyramidal unit Co 3E (E = C or S) is present. The pyramids are linked by metal-metal bond or by groups (or atoms) formed from CS 2 or by the CS 2 itself, coordinated in different ways to the cobalt atoms. The C atom, even when it is part of the heavy-atom framework as isolated atom, comes from the CS 2, as demonstrated by the IR spectroscopic analysis of the vibration of the carbide C atom of C0 6C(CO) 12S 2 [5]. The reaction mechanism is certainly very complex but it could be rationalised, at least at initial stages, according to the experimental evidence, in terms of formation of a monometallic intermediate (CO) 3− ▪, which can react further with the excess of C0 2(CO) 8; giving rise in particular to more stable C0 3E structure. Among them, SC0 3(CO) 9 seems to play an important role in the formation paths of the reaction products, for it has been identified as the main product at the beginning of the reaction. The different ways of coordination and fragmentation of CS 2, as shown by the structures of the reaction products, point out that this reaction is a good example of the activation of a not very reactive molecule, like CS 2, by cobalt carbonyls.