Charge-decomposition analysis

In accord with the Dewar-Chatt-Duncanson model, we find that the dominant interaction is donation from the C C n bond into the rhodium LUMO. This interaction is enhanced when the double bond lies in the rhodium-diphosphine plane and with electron donating substituents which raise the energy of 7ito more closey match the LUMO Charge Decomposition Analysis (CDA) [81] shows that the amount of donation is... 

Although, as stated above, olefin epoxidation is commonly referred to as an electrophilic oxidation, recent theoretical calculations suggest that the electronic character of the oxygen transfer step needs to be considered to fully understand the mechanism [451]. The electronic character, that is, whether the oxidant acts as an electrophile or a nucleophile is studied by charge decomposition analysis (CDA) [452,453]. This analysis is a quantitative interpretation of the Dewar-Chatt-Dimcanson model and evaluates the relative importance of the orbital interactions between the olefin (donor) and the oxidant (acceptor) and vice versa [451]. For example, dimethyldioxirane (DMD) is described as a chameleon oxidant because in the oxidations of acrolein and acrylonitrile, it acts as a nucleophile [454]. In most cases though, epoxidation with peroxides occurs predominantly by electron donation from the 7t orbital of the olefin into the a orbital of the 0-0 bond in the transition state [455,456] (Fig. 1.10), so the oxidation is justifiably called an electrophilic process. 

S. Dapprich, G. Frenking, Investigation of donor-acceptor interactions A charge decomposition analysis using fragment molecular orbitals, /. Phys. Chem. 99 (1995) 9352. 

A charge decomposition analysis of positively and negatively charged carbonyl complexes is presented by R.K. Szilagy and G. Frenking, Organometallics, 16 (1997) 4807. 

Another experimental probe of BD versus a donation is Mossbauer spectroscopy of a series of iron complexes.54 Plots of isomer shift versus quadrupole splitting for [FeH(PPXL)]+ for L such as H2, N2, CO, MeCN, and Cl show that the H2 complexes fell way off the straight line defined by the a donors, more so than even CO. It was concluded that it bonding in H2 complexes is very significant, more so than in N2 or CO complexes. Theoretical analyses concur that H2 is a much better -acceptor ligand than early calculations showed. More quantitative measures of BD are provided by charge decomposition analysis (CDA) and extended transition state (ETS) analysis.41,55-60... 

Table 4.4. Charge Decomposition Analysis of M(CO)s(L) and trans-M(CO)4(H2)2 Complexes (Electron Units)...

Benzene-ALXs and ethene-AlXs (X = H, F, Cl) interactions were investigated using Frenking s charge decomposition analysis, NPA and the V p contour... 

Atomic charges and orbital populations has been computed by means of Natural Bond Orbital analysis [29]. In order to estimate quantitatively the importance of ligand —> metal a-donation and metal —> ligand 7r-back-donation to interaction energies, we used the Charge Decomposition Analysis (CDA) [30] method of Frenking and coworkers [30] as implemented in the AOMIX program [31, 32]. 

Table 2.6 Charge decomposition analysis of MCgo and MC2H4 donation (a), back-donation (tt)...

The M-Ceo bonds are analyzed in terms of Charge Decomposition Analysis giving quantitative estimates of electron donation, back donation and repulsive polarization. The 7T back-donation has the dominant contribution to the metal-fullerene bond for the second and third row metal-fullerene bond for the second and third row metal MC60/C2H4 complexes. We found and interpreted the correlation between BDE and amount of tt back-donation and a donation. 

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