PHILICITY OF CARBENES. A NEW VIEW

The electronic properties of carbenes including thermodynamic parameters such as new electronic philicity indices Ie, Ph, and for comparizon chemical hardnesses η, proton affinities (РA) calculated by DFT method (B3LYP5/6-31G*/RHF for definition of electronic indices and B3LYP5/3-21G/RHF, B3LYP5/3-21G/UHF for definition of chemical hard¬nesses) have been discussed in the paper. With their help, the estimation of philicities, electron-donating and electron-withdrawing abilities of a wide range of carbenes of both nucleophilic and electrophilic type was carried out. It was established that the philicities of carbenes according to electronic indices Іе, Ph depend on the carbenic structure (the backbone of the molecule and steric effects of substituents) and also on the reagent structure, particularly its steric effect. For typical nucleophilic carbenes, the Ph is in the range of 1–3,0, for neutral carbenes 1–1,5, IeH 8,5–22,2 eV, for neutral carbenes IeH 8,5–10,5, for typical electrophilic – in the intervals of PhH –0,3–0,5, IeH –3,4–3,4 eV. The intermediate values (Ph 0,5–1,0, IeH 3,4–8,5 eV) are characteristic for typical ambiphilic carbenes. In the evaluation of electron-donating and electron-withdrawing properties, the values of ED and EA should be taken into account (maximal EDH values were found for neutral carbene 20 (13,8 eV) and for superbasic anionic carbenes (for 22 18,4 eV)). The highest electron acceptability EAH was found for cationic carbene 29 (11,8 eV). In the reactions with carbon ions, the values of the IeH, PhH indices decrease significantly, and the electron acceptability increases. Increasing the steric effects leads to «inversion» of philicities for nucleophilic carbenes (Ph up to 0,1), and the properties of electrophilic carbenes become even more pronounced (Ph up to –2,7). The found dependences of the electronic properties of carbenes allow regulating the structure of carbenes to achieve certain characteristics, which together with stability factors can be used in the design of structures for synthesis and practical application.