Monday, June 18, 2007 Golden Eagle Eyrie (Boise Centre on the Grove) 145
On the mechanism of Grignard formation and reaction in promoted hydrocarbon media
R. W . Holman, Jessie Byers, Jesse Zamora, Jennifer Teixeira, and Marilu Perez. Idaho State University, Pocatello, ID
Grignard reagent formation involves polar intermediates that are stabilized by solvation in ethereal solvents. Hydrocarbons, a more “green” alternative to ethers, are incapable of such stabilization and unsuitable as pure solvents. We have recently reported that catalytic butyldiglime in cyclohexane facilitates Grignard formation and reaction, producing identical products in comparable yields. Catalytic amounts of 2-methyl-THF or THF will initiate Grignard formation, generating a high polarity gradient media involving heterogeneous chemistry with multiple solid phases and two liquid phases (determined by 13C NMR to be a polar phase containing Grignard reagent, additive, and hydrocarbon and a non-polar phase containing pure hydrocarbon). Glyme, t-butyl-methyl ether, TMEDA and other similar species do not promote this chemistry. Potential explanations include dielectric, hard-soft acid base, steric, hapticity/chelation, and relative solubility issues. The mechanism for promoted hydrocarbon Grignard chemistry differs markedly from its classic analogue and is the focal point of our on going NMR investigation.