On the mechanism of Dirhodium(II) Caprolactamate oxidations: Metal-centered electron transfer processes in the catalytic formation of iminum ions

ORGN 5

Jason M. Nichols, jnicholz@umd.edu, Arthur J. Catino, acatino@umd.edu, James M. Myslinski, jmysl@umd.edu, and Michael P. Doyle, mdoyle3@umd.edu. Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742
Dirhodium caprolactamate [Rh2(cap)4] is an effective catalyst for oxidative functionalization including the oxidative Mannich reaction. Experiments with various radical indicators as well as kinetic isotope effects suggest that C-H bond activation occurs via hydrogen-atom abstraction with tert-butyloxy radical to generate a carbon-centered radical. Radical production through a step-wise electron transfer/proton transfer process proceeding through the intermediacy of an aminium radical cation is considered unlikely based on the kinetic isotope effects of substituted N,N-dimethyl anilines. The ability of Rh2(cap)4 to catalytically generate an iminium ion is a function of its narrow redox couple and the facility of electron transfer between dirhodium and the carbon-centered radical. A mechanistic model featuring higher-valent dirhodium species is proposed to explain this phenomenon.

 

Metal-Mediated Reactions and Syntheses
8:00 AM-12:00 PM, Sunday, 10 September 2006 Moscone Center -- Room 134, Oral

Division of Organic Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006