The kinetics of the racemization of aromatic 1,3-disubstituted allenes catalyzed by gold phosphine complexes has been investigated. The rate of gold-catalyzed allene racemization displayed first-order dependence on allene, and catalyst concentration and kinetic analysis of gold-catalyzed allene racemization as a function of allene and phosphine electron-donor ability established the accumulation of electron density on the phosphine atom and the depletion of electron density on the terminal allenyl carbon atoms in the rate-limiting transition state for racemization. These and other observations were in accord with a mechanism for allene racemization involving rapid and reversible inter- and intramolecular allene exchange followed by turnover-limiting, unimolecular conversion of a chiral gold η2-allene complex to an achiral η1-allylic cation intermediate through a bent and twisted η1-allene transition state. With respect to proper ligand selection, these studies reveal that both electron-poor phosphine ligands and polar solvents facilitate racemization.
CITATION STYLE
Harris, R. J., Nakafuku, K., & Widenhoefer, R. A. (2014). Kinetics and mechanism of the racemization of aryl allenes catalyzed by cationic gold(i) phosphine complexes. Chemistry - A European Journal, 20(38), 12245–12254. https://doi.org/10.1002/chem.201402729
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