DFT Computation of Mechanism for the Free Radical Chain Reaction Oxidation of Bis(Acetylacetonato‐ <i>O</i> , <i>O</i> ′)Platinum(II) by Diiodine to Form <i>trans</i> ‐Pt ^IV (acac) ₂ I ₂

In seminal work on the oxidation of Pt II (acac) 2 to trans ‐Pt IV (acac) 2 I 2 (acac = [acetylacetonato‐ O , O ′] − ) by diiodine, Hopgood and coworkers proposed that coordination of diiodine to platinum(II) occurs forming a complex Pt II (acac) 2 ( η 1 ‐I 2 ) with a linear “Pt‐I–I” motif and that this complex reacts with I • via a free‐radical chain reaction following photochemical initiation of I • from uncoordinated diiodine (Hopgood et al. 1973). We report a computational study of this fundamental mechanistic proposal, finding support for the kinetic evidence. The iodine doublet interacts initially with the π ‐system of an acac group via the central γ ‐carbon atom, [(I···acac)Pt(acac)( η 1 ‐I 2 )] • , followed by migration to the platinum center leading to formation of an intermediate trans ‐[IPt(acac) 2 I···I] • in which the “Pt‐I···I” group is bent (104.2°), and the peripheral iodine atom is weakly interacting (I···I 3.395 Å). Subsequent migration of I • to the other acac ligand leads to formation of a C γ ···I interaction in trans ‐[Pt(acac)(acac···I)I 2 ] • and finally departure to continue propagation releasing the end‐product trans ‐Pt IV (acac) 2 I 2 . The reverse reaction occurs by photochemical initiation of I • allowing access to trans ‐[Pt(acac)(acac···I)I 2 ] • . Both the oxidation and the reverse reaction compute as low energy processes, Δ G † ca . 7 and ca . 10 kcal mol −1 , respectively, consistent with rapid reactions observed experimentally.