Combined Kinetico‐Mechanistic and Theoretical Elucidation of the Oxidative Addition of Iodomethane to Cycloplatinated(II) Complexes: Controlling the Rate of trans/cis Isomerization

Abstract

The oxidative addition of iodomethane to cycloplatinated(II) complexes containing allyldiphenylphosphane (PPh2allyl) ligands, namely, [Pt(C^N)Me(PPh2allyl)] [1–4; C^N = deprotonated 2‐phenylpyridyne (ppy), 1; 2,2′‐bipyridine (bpy), 2; 2,2′‐bipyridine N‐oxide (O‐bpy), 3; and 7,8‐benzoquinoline (bzq), 4], occurs readily with trans stereochemistry to give the trans‐PtIV isomers 1a–4a, which then transform slowly to the cis‐PtIV isomers 1b–4b. All of the complexes were characterized by NMR spectroscopy, and the structures of 1b, 3a, and 3b were determined by single‐crystal X‐ray diffraction. Kinetic studies through UV/Vis spectroscopy suggested that the oxidative addition reaction proceeded through an SN2 reaction. The rate of the oxidative addition reaction was measured at different temperatures, and large negative ΔS≠ values consistent with the proposed mechanism were found for each reaction. This reaction was also monitored by NMR spectroscopy to determine a correct value for the rate of the trans/cis isomerization. The theoretical aspects of the mechanism for the oxidative addition reaction were also studied by density functional theory (DFT) calculations to support the claimed experimental results.