Rate constants for reactions of triethylborane-water and -methanol complexes as hydrogen atom donors to alkyl radicals

ORGN 767

Jing Jin, jjin2@uic.edu and Martin Newcomb, men@uic.edu. Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Room 4500, Chicago, IL 60607
Trialkylborane-water complex was reported as a hydrogen atom transfer trapping agent for radicals that serves as an alternative for traditional tin hydride reagents by Spiegel et al . (J. Am. Chem. Soc . 2005, 127, 12513). In our study, rate constants for reactions of several triethylborane complexes with secondary alkyl radicals were determined using radical clock methods. Complexes of Et3B with water, deuterium oxide, methanol, THF, and pyridine were studied. Hydrogen atoms from the hydroxy group of water or alcohol and from the alpha-position of the alkylborane were donated. The H-atom transfer reactions of these complexes are relatively slow. The rate constant for reaction of Et3B-OH2 with a secondary alkyl radical at room temperature is ca. 2 × 10 4 M -1 s -1 at room temperature, about 2 orders of magnitude smaller than that for reaction of Bu3SnH.
 

Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High Energy Species
8:00 AM-12:00 PM, Thursday, March 29, 2007 McCormick Place Lakeside -- Room E451A/B, Level 4, Oral

Division of Organic Chemistry

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007