Finding the Proton in a Key Intermediate of anti-Markovnikov Alkyne Hydration by a Bifunctional Catalyst

摘要

Many of Nature's metalloenzyme active sites feature a metal ion or ions and a variety of acidic or basic groups, which act in concert, allowing enzymes to achieve turnover frequencies rarely rivaled by synthetic catalysts. A major contributor to enzymatic rate accelerations is secondary structure, with a network of hydrogen bond or proton donors and acceptors that lower the energy of intermediates or transition states. We are interested in the increased activity and selectivity of small-molecule bifunctional catalysts and their secondary structure. Catalysts for anti-Markovnikov hydration of terminal alkynes to give aldehydes or for alkene isomerization are made 1000-10 000 times faster using bifunctional phosphine ligands. However, the same features that increase the efficiency of bifunctional catalysts also complicate studies of their mechanism. We are developing methods to study these complex systems.