Comparison between oxidative addition and σ-bond metathesis as possible mechanisms for the Catalytica methane activation process by platinum(II) complexes:: A density functional theory study

The Catalytica process converts methane to methyl bisulfate in good yield at relatively low temperature in fuming sulfuric acid and may help make methane a useful bulk chemical precursor. We have computationally examined the methane C-H activation step of the process. We find that the most likely catalyst for this step is either (bipyrimidine)Pt(OSO3H)(+) or (bipyrimidine)PtCl+. In the former case C-H activation takes place by a-bond metathesis, whereas the latter involves C-H activation by an oxidative addition mechanism. It appears that the need to run the reaction at 180-220 degreesC stems from the fact that methane has to displace either one Cl- ligand or one HSO4- oxygen. Protonation of bipyrimidine by sulfuric acid appears unfavorable, although the resulting highly charged catalysts exhibit lower activation barriers.