Secondary kinetic deuterium isotope effect in oxidative addition reaction of cycloplatinated(II) complexes with MeI

Oxidative addition reaction of CH3I or CD3I with the cycloplatinated(II) complexes [PtMe(C boolean AND N) L], 1a-1e, in which C boolean AND N = 2-phenylpyridinate (ppy) or benzo[h] quinolinate (bhq), and L = PPh3, PMePh2 or P(OPh)(3), in CH2Cl2 solvent gave the organoplatinum(IV) products [PtMe2I(C boolean AND N) L]. NMR spectroscopy (H-1 and P-31), and X-ray crystallography (supported by DFT calculations) clearly indicated that in each case the thermodynamic isomer products 2a-2e, with I ligand trans to C of C boolean AND N rather than the related kinetic isomer in which I ligand is trans to Me, is obtained. Kinetics of the reactions were studied by using UV-vis spectroscopy and the reactions are suggested to occur by a common S(N)2 mechanism, on the basis of their clean second-order kinetics, failure of radical traps to inhibit the reactions, and the observation of large negative values of Delta S double dagger. Rates of the reactions are significantly dependent on nature of the phosphine ligand L with the trend being PMePh2 > PPh3 > P(OPh)(3). The kinetic isotope effect (KIE) values, k(H)/k(D), were obtained in the present study and are found to be close to the normal value of 1 in the corresponding reactions, showing that nature of the ancillary ligands containing phosphorous donor atoms and the cycloplatinated ligands, C boolean AND N, are not effective on the values of k(H)/k(D). For example, KIE values, in reactions involving the ppy complexes [PtMe(ppy) L], 1a-1c, at 20 degrees C are 1.06 (L = PPh3, 1a), 0.97 (L = P(OPh)(3), 1c) and 0.92 (L = PMePh2, 1b). Note that nature of the C boolean AND N ligands are found to be almost non-effective on both rates of the reactions and the related KIE values. (C) 2015 Elsevier B. V. All rights reserved.