23268-96-4Relevant academic research and scientific papers
Electron Donor-Acceptor Complexes. 1. Linear Free Energy Correletion of the Charge-Transfer Transition Energy with the Kinetics of Halogenolysis of Alkylmetals
Fukuzumi, S.,Kochl, J.K.
, p. 2246 - 2254 (2007/10/02)
Mulliken charge-transfer theory is used to relate the properties of transient donor-acceptor complexes between alkylmetals and halogens with the kinetics of the accompanying cleavage reaction (halogenolysis).The formulation derives from the charge-transfer transition energy hνCT which is proportional to the second-order rate constant for halogenolysis of a variety of tetraalkyltin compounds in hexane or carbon tetrachloride solutions.The description of the activation process for halogenolysis as an electron transfer in the CT complex, e.g., --> , leads to a linear free energy relationship in which the activation free energy is equal to the driving force for ion pair formation.The latter is equated to the charge-transfer transition energy plus a contribution from the solvation energy, by employing a comparative procedure for the evaluation of alkylmetals.An independent measure of the solvation energy obtained from the gas-phase ionization potentials of alkylmetals and their free energy changes in solution supports the electron-transfer formulation of the activation process.The charge-transfer mechanism is generalized for the halogenolysis of alkylmetals.
Mechanisms of the rupture of the carbon-tin bond by halogens I. Electrophilic substitution at a saturated carbon atom
Boue, S,Gielen, M,Nasielski, J
, p. 443 - 460 (2007/10/18)
The reaction between halogens and tetraalkyltins is strongly influeced by the dielectric constant, the polarisability and the nucleophilicity of the solvent. These three aspects of solvent action are relatd to the ability of tin to make use of its empty 5d orbitals: the Sn polarisation, enhanced by the pentaco-ordination of the metal, governs the reactivity of the alkyl groups attached to it, appropriate attention being given to the incursion of steric effects. In polar media, the solvent itself acts as the nucleophilic catalyst and the reaction is best described by the following scheme {A figure is presented}. In less active solvents, the halogen molecule plays the role of nucleophile in a predetermining step the most likely mechanism may be written as follows: {A figure is presented}.
Mechanisms of the rupture of the carbon-tin bond by halogens II. Free-radical substitution in solution
Boue, S,Gielen, M,Nasielski, J
, p. 461 - 479 (2008/10/08)
The experiments describes in this paper show that the light-induced bromodemetallation of tetraalkyltins in chlorobenzene is a free radical substitution on tin, followed by a propagation step: {A figure is presented}. The stabilisation of R? by hyperconjugation seems to be an important factor for the reaction, but there is evidence for the influence of the other three substituents of tin and of the nature of the attacking radical on the reaction mechanism. The relation between the strucutre and the reactivity of tetraalkyltins suggests that the carbon-tin bond is only slightly loosened in the transition state; this agrees with the great reactivity of the Br atom.
Mechanisms of the rupture of the carbon-tin bond by halogens I. Electrophilic substitution at a saturated carbon atom
Boue, S,Gielen, M,Nasielski, J
, p. 481 - 494 (2008/10/08)
In chlorobenzene, some tetraalkyltins are able to alter the reactivity of bromine towards their homologues and this is no more true in solvents of high nucleophilicity. This perturbating power, which is linked to the nature of the substituents bound to the metal, is best explained by the formation of a complex R4Sn(-)-X(+)2 which acts as a modified halogen towards another alkyltin molecule. This mixing-effect changes sometimes considerably the kinetics and the mechanism of the reactions and suggests that the accessibility of empty 5d orbitals of the metal plays an important part in the reactivity of tetraalkyltins, as well in SE2 as in radical substitutions.
