Ab Initio Study of the Mechanisms of Intermolecular and Intramolecular [4 + 2] Cycloaddition Reactions of Conjugated Enynes

Ananikov V.P., J.Phys.Org.Chem., 2001, 14, 109-121.
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The mechanisms of intermolecular and intramolecular enyne [4 + 2] cycloaddition reactions were investigated in detail using high-level ab initio methods. The structures of all transition states and intermediates were located using the MP2 method, potential energy surfaces were calculated at the MP2, MP3, MP4(SDQ), MP4(SDTQ), CCSD and CCSD(T) theory levels and the solvent effect was studied within PCM model.

Stable Pt(IV) Vinylic Complexes with Unusual Regioselectivity Formed in the Reaction of Methylpropiolate Triple Bond Activation

Ananikov V.P., Mitchenko S.A., Beletskaya I.P., J.Organomet.Chem., 2001, 636, 175-181.
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An unusual fact of HC-C-COOMe triple bond activation by Pt(IV) iodide leading to the formation of new bis-σ-vinyl complexes [Pt(CH-CI-COOMe)(CIH-C-COOMe)(Sol) 3−nIn]2−n (where n=2, 3) with different regioselectivity in vinyl ligands is reported. The isolated complex can be involved in C–C coupling reaction resulting in a head-to-tail connection of vinyl groups in a substituted diene unit.

Catalytic Triple Bond Activation and Vinyl Plus Vinyl Reductive Coupling by Pt(IV) Complexes. A Density Functional Study

Ananikov V.P., Musaev D.G., Morokuma K., Organometallics, 2001, 20, 1652-1667.
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A density functional theoretical study has been performed for the mechanisms of platinum(IV)-catalyzed alkyne-to-conjugated diene conversion reaction, which involves two subsequent triple bond activation steps followed by vinyl−vinyl coupling. Calculations have shown that acetylene triple bond activation by PtI 62- in water or methanol solution may proceed through either external nucleophile addition or intramolecular insertion, with the former mechanism occurring with a lower barrier and leading to thermodynamically favored product. The rate-determining step of the entire catalytic cycle is found to be the formation of a platinum(IV) cis-divinyl derivative. Although vinyl−vinyl coupling reaction may take place from both six-coordinated octahedral and five-coordinated square-pyramidal platinum(IV) divinyl complexes, the five-coordinated derivative was found to react with a significantly lower barrier. The results obtained here are in good agreement with available experimental data and reveal important details of the catalytic reaction mechanism. The present investigation also has shown that no reliable conclusions may be drawn for the system studied without taking solvent effects into account.