Richard
A. Walton
Lecture in Inorganic Chemistry
November 4, 2004
4:30 p.m. WTHR 104
Towards an Alkane Hydroxylation Catalyst Using Dioxygen as the Oxidant
Professor John E. Bercaw,
Centennial Professor of Chemistry
Department of Chemistry,
California Institute of Technology
Conversions of readily available, but normally very chemically inert alkanes to more valuable compounds could allow more efficient use of these feedstocks. For example, development of a catalyst for the selective conversion of methane and dioxygen to methanol would allow conversion of abundant natural gas to a liquid fuel. Organometallic chemists have devised reagents that activate the carbon-hydrogen bonds of alkanes, including methane, but most of these are not well suited to incorporation into a catalytic cycle for alkane oxidation. The "Shilov System", stoichiometric oxidation of alkanes to alcohols by aqueous platinum(IV), exhibits unusual selectivity and better compatibility with oxidants and protic reagents. Using a variety of kinetics, isotopic labeling and stereochemical studies, we have defined some of the essential features of the mechanism for the Shilov reaction. Our mechanistic understanding has led to the development of well characterized platinum(II) complexes that react cleanly with the C-H bonds of hydrocarbons. A series of bis(aryl)diimine-ligated methyl cations of Pt(II) ([(ArN=CR–CR=NAr)PtMe(L)]+[BF4]- (Ar = aryl; R = H, CH3; L = water, trifluoroethanol)) are found to react smoothly with alkanes and arenes at approximately room temperature in trifluoroethanol solvent to yield methane and the corresponding alkyl- or aryl-Pt(II) cations. These studies have provided insights into the unusual (and useful) selectivity exhibited by the Shilov System. Reactions of platinum alkyls with Cu(II) and O2 have been developed that indicate that a truly catalytic variant based on O2 may be possible.
| Previous Lecturers | |
|---|---|
| 2003 | Tobin Marks, Northwestern University |
| 2002 | Stephen Lippard, Massachusetts Inistitute of Technology |
| 2000 | F. Albert Cotton, Texas A&M University |
