Electron transfer reactions of Bromo Norbornenes with Ph2P- and Me3Sn- anions. A computational Study

PEISINO, L. E.; CRESPO ANDRADA K. F.; PIERINI, A.B.

Florianopolis - Brasil

Conferencia; 10th Latin American Conference on Physical Organic Chemistry; 2009

As known, the ET to these compounds can involve a concerted-dissociative pathway by which the C-Br bond breaks as the electron is being transferred (inter-DET), or a stepwise mechanism, with radical anions (RAs) as intermediates (inter-ET);2 their dissociation being ascribed to an intramolecular ET from the p systems to the s C-Br bond (intra-DET) (Scheme 1). Based on the potential energy surfaces and thermochemistry evaluated, the most plausible ET mechanism followed by the series of compounds is proposed. The regio- and thermo-chemistry of the coupling reaction of Me3Sn- and Ph2P- anions with the radicals formed in the dissociation was also modeled. The reaction with Me3Sn- is faster than with Ph2P- anions and the preferred stereochemistry depends, in the absence of steric factors, on the stability of the radical as determined by NBO studies. The calculations were carried out with the Gaussian 03 package. Geometry optimizations were performed using the hybrid density functional B3LYP with a LACVP pseudopotential basis set for tin and the 6-31+G* basis set for the remaining atoms. The solvent effect was included through the Polarizable Continuum Model (PCM) by Tomasi et al.. To conclude, the mechanism of the inter-ET reaction by specific donors, the stereochemistry and the relative reactivity order of compounds 1-5 with the Ph2P- and Me3Sn- anions in the SRN1 cycle were theoretically determined. All these results are on agreement with our previews experimental observations. 1-Rossi, R.A.; Peñéñory, A.B.; Pierini, A.B.; Chem. Rev. 2003, 103, 71. 2-Pierini, A.B.; Vera, D.M.; J. Org. Chem. 2003, 68, 9191-9199.