Formation and thermodynamic stability of novel methyl–vinyl derivatives of PtIV as possible intermediates for Csp3–Csp2 cross-coupling

• The reaction of PtI42− with CH3I and alkynes yields methyl–vinyl PtIV derivatives.
• Reaction involves CH3I oxidative addition followed by iodoplatination of CC bond.
• The reaction is highly exothermic, and this provides favorable thermodynamics.
• The new organoplatinum derivatives contain organic ligands in the cis-positions.

Methyl–vinyl derivatives of PtIV were obtained in a sequence of the reactions of methyl iodide oxidative addition to PtII iodo complexes followed by iodoplatination of C–C triple bond of R1CCR2 (R1 = Ph, R2 = C(O)OC2H5; R1 = R2 = C(O)OCH3) in acetone solution under excess of I−. In the reaction of the ethyl phenylpropiolate equilibrium formation of PtIV methyl–vinyl derivative occurs. The reaction is highly exothermic, ΔH = –(81 ± 7) kJ/mol, and this provides a favorable thermodynamics even though a significant decrease in entropy, ΔS = −(249 ± 23) J/(K mol). In the reaction of dimethyl acetylenedicarboxylate the chelate metallocycle is quantitatively formed. The quantitative yield of the organometallic product is explained by more favorable thermodynamics of the reaction: chelation of the metal center by the oxygen atom of the carboxymethyl group in the σ-vinyl ligand forming metallocycle provides an additional stabilization of the product. In the formed organoplatinum compounds vinyl and methyl ligands are located in the mutual cis-positions, which is essential for further accomplishment of Csp3–Csp2 coupling reaction.

The sequence of the reactions of methyl iodide oxidative addition to PtII iodo complexes followed by iodoplatination of C–C triple bond of alkynes yields methyl–vinyl derivatives of PtIV with mutual cis-arrangement of the organic ligands, which is essential for further accomplishment of Csp3–Csp2 coupling reaction.Figure optionsDownload as PowerPoint slide