Lithium Diisopropylamide: Nonequilibrium Kinetics and Lessons Learned about Rate Limitation

The kinetics of lithium diisopropylamide (LDA) in tetrahydrofuran under nonequilibrium conditions are reviewed. These conditions correspond to a class of substrates in which the rates of LDA aggregation and solvation events are comparable to the rates at which various fleeting intermediates react with substrate. Substrates displaying these reactivities, by coincidence, happen to be those that react at tractable rates on laboratory time scales at -78 °C. In this strange region of nonlimiting behavior, rate-limiting steps are often poorly defined, sometimes involve deaggregation, and at other times include reaction with substrate. Changes in conditions routinely cause shifts in the rate-limiting steps, and autocatalysis is prevalent and can be acute. The studies are described in three distinct portions: (1) methods and strategies used to deconvolute complex reaction pathways, (2) the resulting conclusions about organolithium reaction mechanisms, and (3) perspectives on the concept of rate limitation reinforced by studies of LDA in tetrahydrofuran at -78 °C under nonequilibrium conditions.