Thomas M. Gilbert¹ and Tom Ziegler, Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4. (¹On sabbatical from Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115 USA)

The Catalytica process converts methane to methyl bisulfate in good yield at relatively low temperature, and may help make methane a useful bulk chemical rather than a fuel mining waste product. We have computationally examined the methane C-H activation step of the process. We find that the most likely catalyst for this step is (bipyrimidineH₂)Pt(OSO₃H)³⁺, formed when the sulfuric acid solvent protonates the peripheral nitrogens of the bipyrimidine ligand and replaces the chloride ligands of the additive (bipyrimidine)PtCl₂. That this catalyst prefers a chelated bisulfate ligand to a monodentate one explains why the reaction temperature must be high: one Pt-O bond must break to provide access to the reactive site on the metal. In general, we find most steps of the metathesis (C-H bond breaking parallel to the Pt square plane) and oxidative addition (C-H bond breaking perpendicular to the plane) pathways to C-H activation to be energetically competitive. However, a metathesis step by which a methane hydrogen transfers to a peripheral oxygen of the bisulfate ligand (rather than the Pt-bound oxygen) appears barrierless, and is highly exothermic. Thus this pathway is far more energetically favorable than any other.