Comparison between oxidative addition and sigma-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 a t relatively low temperature in fuming sulfuric acid and may help make meth ane a useful bulk chemical precursor. We have computationally examined the methane C-H activation step of the process. We find that the most likely ca talyst 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 mechani sm. 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 HSO 4- oxygen. Protonation of bipyrimidine by sulfuric acid appears unfavorable , although the resulting highly charged catalysts exhibit lower activation barriers.