(688e) A Detailed Theoretical Study of the Mechanism and Energetics of Methane to Methanol Conversion by Cis-Platin and Catalytica

The conversion of methane to methyl bisulfate by dichloro(?-2-{2,2?-bipyrimidyl})platinum(II) [Pt(Bpym)Cl2] (also known as Catalytica) and cis-platin has been studied using hybrid DFT in conjunction with the conductor like polarizable continuum solvent model (CPCM). We have investigated the activation barriers along the three major phases of the catalytic process, namely (a) C-H activation, (b) Pt(II) to Pt(IV) oxidation, (c) and functionalization and have elucidated the full potential energy profiles for plausible catalytic pathways. For Catalytica oxidation of Pt(II) to Pt(IV) is the highest barrier step for all the catalytic active forms considered. Moreover oxidation of Pt(II) to Pt(IV) is significantly easier for cis-platin compared to Catalytica, which explains the faster catalytic transformation by cis-platin than Catalytica. Our calculations suggest that the oxidation barrier is significantly affected by the ligand environment on the Pt center of the catalyst. We predict that monoprotonation of the bipyrimidine ring in Catalytica does not significantly affect the oxidation process if catalysis proceeds through electrophilic C-H activation trans to the protonated pyrimidine ring, but the barrier is significantly increased with respect to the non-protonated form if electrophilic C-H activation proceeds cis to the protonated pyrimidine ring. We also determine a full potential energy profile for catalytic conversion by cis-platin proceeding through oxidative C-H addition, subsequent deprotonation, followed by oxidation of Pt(II) to Pt(IV) and then functionalization.