Публикации

Activation of the CÍÄC bond in acetylenic hydrocarbons, catalyzed by iodide complexes of platinum(IV), and the subsequent CÄC coupling reaction make it possible to synthesize 1,4-diiodo-substituted dienes with high stereo- and regioselectivity. The reaction involves intermediate formation of bis-σ-vinyl platinum(IV) complexes which can be isolated in the pure state. Under similar conditions palladium(II) complexes catalyze iodine addition to acetylene.

Addition of benzeneselenol to terminal alkynes HC:CR, catalyzed by Pd(0) complexes, leads to formation of mixtures of mono- and bis(phenylseleno)alkenes, depending on the nature of the R substituent. Electron-donor groups (R = Bu, CH₂OH, CH₂NMe₂) give rise to addition according to the Markovnikov rule, whereas from alkynes with electron-acceptor groups (R = Ph, COOMe) mixtures of products are formed as a result of side reactions. A probable reaction mechanism includes oxidative addition of benzeneselenol to the metal, alkyne insertion into the Pd-Se bond, and reductive elimination.

A detailed density functional study was performed for the vinyl−vinyl reductive elimination reaction from bis-σ-vinyl complexes [M(CH CH₂)₂X_n]. It was shown that the activity of these complexes decreases in the following order: Pd^IV, Pd^II > Pt^IV, Pt^II, Rh^III > Ir^III, Ru^II, Os^II. The effects of different ligands X were studied for both platinum and palladium complexes, which showed that activation barriers for C−C bond formation reaction decrease in the following order: X = Cl > Br, NH₃ > I > PH₃. Steric effects induced either by the ligands X or by substituents on the vinyl group were also examined. In addition, the major factors responsible for stereoselectivity control on the final product formation stage and possible involvement of asymmetric coupling pathways are reported. In all cases ΔE, ΔH, ΔG, and ΔG_aq energy surfaces were calculated and analyzed. The solvent effect calculation shows that in a polar medium halogen complexes may undergo a reductive elimination reaction almost as easily as compounds with phosphine ligands.