Elishua Litle

Elishua Litle

Brandeis / Chemistry
Hosted by Wade's Lab
 
Correlating Ligand Exchange Kinetics and Lewis Acidity with the
Catalytic Activity of Gold Complexes

Elishua Litle, Benjamin Reiner, Casey Wade

Abstract: Cationic gold(I) complexes are versatile catalysts for a myriad of synthetically relevant reactions
including C–C, C–O, and C–N bond formation with activated and un-activated -bonds. Recently chemists have used the Gutmann–Beckett method in order to quantify the Lewis acidity of cationic gold complexes in hopes of correlating acceptor numbers (AN) with catalytic activity. Previous research in the Wade lab has indicated that the catalytic activity of gold Lewis acids might correlate more strongly with substrate exchange rates rather than AN. By using a Mukaiyama aldol as a model reaction, I have determined the catalytic activity of different gold(I) catalysts using time-resolved 1H NMR spectroscopy. Substrate exchange rates have been modeled by line shape analysis of variable temperature 31P NMR spectra obtained for solutions of cationic gold complexes in the presence of two equivalents of triethyl phosphine oxide. Tolman Electronic Parameters (TEP) were tabulated from literature values. Acceptor numbers have been calculated by measuring the difference in 31P NMR chemical shift between a Et3PO internal standard and gold-coordinated Et3PO species. Preliminary results suggest that TEP, AN, or ligand exchange kinetics alone are not sufficient to predict the reactivity of a wide range of cationic gold(I) complexes.
 
Support: SMURF (Summer MRSEC Undergrad Research Fellowship)