The modelling of nucleophilic and electrophilic additions to organometallic complexes using molecular graphics techniques

Abstract

A new formalism has been developed in order to evaluate intermolecular interaction energies for inorganic and organometallic complexes in the framework of the extended Hückel method. In order to provide the shortest possible response time on an interactive computer graphics facility, this model should require the minimum amount of computer time, which explains why approximate procedures are used to evaluate electrostatic, charge transfer and exchange repulsion components. When applying this model to typical examples of electrophilic addition reactions to organometallic complexes, it is found that it is essential to take account of charge transfer interactions, the electrostatic component alone being not sufficient, even qualitatively, for a proper description of the reaction mechanism. The results, presented as color-coded dot molecular surfaces, show a very good agreement with experiment as to the site of attack, namely (i) on metal for the electrophilic attack on Fe(cp)2, Fe(CO)5 and X(cp)(CO)2, X = Co, Rh; (ii) on the cp ligand for the nucleophilic attack on Co(cp)2+ and Rh(cp)2+; (iii) on bz for the nucleophilic attack on Fe(cp)(bz)+. Finally, modellizations of the nucleophilic attack on a coordinated olefin and of the relation between structure and acidic properties of zeolites are presented and discussed.

The modeling of nucleophilic and electrophilic additions and substitutions using extended Hückel‐based reaction potentials

“…6 by calculating directly the matrix elements (pIl/r(v) in the basis of the EH atomic orbitals, or (ii) a very convenient procedure can be found by expanding the charge distribution into multicentered multipoles, i.e., where k-(A) is the order of the highest multipole on atom A, RA is the distance between atom A and reactant R , (vA, +A) is the direction pointing from atom A to reactant R , Yk,(vA, 4A) are real spherical harmonics normalized to 4~/ ( 2 k + l), and…”

“…In the case of S-R dis-tances characteristic of electron donor-acceptor interactions, the first three terms undoubtedly predominate [ 6 ] , whereas the exchange component is indispensable for describing short-range repulsion. At the present stage of our development, the S-R interaction energy E,, is therefore expressed as where E,,, Ep,, E,, and E, stand for electrostatic, polarization, charge transfer, and exchange-repulsion components, respectively, and T specifies the position of the reactant.…”

“…Further comparisons with accurate evaluations of the IIE components performed using the Morokuma analysis [ 131 have indeed shown that the MEP term predominates most often in such interactions. However, we have recently found [6] that this approach was questionable for describing the reactivity of organometallic complexes because of the important charge transfer (cT), and in some cases polarization (POL), effects between interacting partners arising through the d orbitals of the metal atom of the complex. This led us to develop a modelization of electrophilic and nucleophilic addition reactions to organometallic complexes using extended Huckel (EH)-based [ 141 reaction potentials.…”

Structure-activity relationship between the 3D distribution of the electrophilicity of sugar derivatives and their cytotoxic and antiviral properties

“…Calculated from extended H/ickel (EH) wave functions, using a formalism we have recently developed [4,5], this energy has the advantage of being a local property which can play the role of a reactivity index. The interaction energy Eint(r) between the substrate and the incoming reactant located in r is expressed as the sum of several components Eint(r) = E~s(r) + Eot(r) + E~x(r) (1) with Ees, Ect, Ee× being electrostatic, charge-transfer, and exchange-repulsion components, respectively.…”

Recent developments in molecular graphics: visualization of chemical structures and properties

“…The detailed expressions we have developed for E~s, Ect, and E~x have been reported elsewhere (Weber et al 1988a, Weber et al 1989. It suffices here to mention that the electrostatic component corresponds to the classic Coulomb energy arising from the interaction of molecular, i.e., electronic and nuclear, charge distributions, whereas the charge transfer component accounts for the energy decreasing due to the delocalization of the electrons of one partner onto the other one as a result of their middle-range interaction.…”