Tert-butylperoxyl radicals are electron-transfer agents in the oxidation of tertiary amines to iminium ions with dirhodium(II) caprolactamate

ORGN 118

Caitlyn L. Edgley, cattedge@umd.edu1, Jason M. Nichols, jnicholz@umd.edu1, James M. Myslinski, jmysl@ mail.utexas.edu2, and Michael P. Doyle1. (1) Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, (2) Deparment of Chemistry and Biochemistry, University of Texas, Austin, Austin, TX 78712
Tetrakis-(µ-caprolactamato)-dirhodium(II) [Rh2(cap)4] in conjunction with aqueous tert-butyl hydroperoxide (TBHP) is an excellent catalyst for the oxidative Mannich reaction. Isotope effects indicate that electron transfer plays a role in the oxidative formation of iminium ions from N,N-dialkylanilines. Selectivity experiments indicate that tert-butylperoxyl radical is generated by the catalytic decomposition of TBHP by Rh2(cap)4. Kinetic order determinations show a first order rate-dependence of amine at high TBHP concentrations and a complex order of Rh2(cap)4. Linear free energy relationships (LFER) were determined against the oxidation potentials (E0) of both the dirhodium complex and dialkylaniline. A large negative LFER was found for the dialkylaniline and no LFER was found for the dirhodium catalyst. These results indicate a cationic transition state consistent with an electron-transfer that does not include the dirhodium complex as the oxidizing agent. This implicates the tert-butylperoxyl radical in an unusual role as the electron transfer agent in the oxidative formation of iminium ions.

 

Physical Organic Chemistry, Combinatorial and Process Chemistry, New Reactions and Methodology, Peptides, Proteins and Amino Acids
8:00 PM-10:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Hall A, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Sci-Mix

Division of Organic Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008