Reactivity comparison of five-and six-membered cyclometalated platinum(ii) complexes in oxidative addition reactions
2015
Raoof, Fatemeh | Boostanizadeh, Maryam | Esmaeilbeig, Ahmad R. | Nabavizadeh, S Masoud | Aghakhanpour, Reza Babadi | Ghiassi, Kamran B. | Olmstead, Marilyn M. | Balch, Alan L.
The compound [PtMe(bzpy)(DMSO)] (1; bzpy = 2-benzylpyridinate) was synthesized by reaction of cis-[PtMe₂(DMSO)₂] with 1 equiv. of bzpyH under reflux conditions in toluene through C–H activation of the carbon–hydrogen bond in 2-benzylpyridine. Then, the complex [PtMe(bzpy)(PPh₃)], 2, was prepared by addition of PPh₃ to complex 1. Complex 2 undergoes oxidative addition with methyl iodide to give [PtMe₂I(bzpy)(PPh₃)], 3. NMR spectroscopy (¹H and ³¹P) and X-ray crystallography (supported by DFT calculations) clearly showed that the thermodynamic isomer product 3, with iodide trans to C of bzpy rather than the related kinetic isomer, 3, in which iodide is trans to methyl, is obtained. Mechanistic studies using UV-vis spectroscopy and DFT calculations indicate that the reaction occurs via a SN2 mechanism. The kinetic study of the oxidative addition of methyl iodide to the non-planar, six-membered cyclometalated complex with that of the five-membered cyclometalated [PtMe(ppy)(PPh₃)], in which ppy = 2-phenylpyridinate, shows that the ring size of the chelating unit has a significant impact on the rate of the reaction.
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