Transition metal catalysis under high pressure: A useful liaison?!

High Pressure (1-10 kbar in fluid media) has become a powerful method for accelerating reactions having a negative activation volume ({Delta}V{double_dagger} < 0). This is generally the case for addition reactions, probably best known is the activation of cycloadditions by high pressure. Transition metal catalyses typically consist of various single reaction steps, which could each be favored or disfavored by high pressure, making predictions of the overall activation volume in such reactions difficult. The authors have studied the influence of high pressure (up to 10 kbar) in palladium catalyzed arylations and acylations of alkenes as well as in allylic substitutions. The authors will present evidence, that high pressure can considerably accelerate such reactions as well as favorably change chemo-, regio-, diastereo- and enantioselectivity under careful chosen reaction conditions. For example, the ratio of metal to ligand becomes crucial at high pressures both for the rate as well as for various aspects of selectivity in the palladium-catalyzed arylation of 2,3-dihydrofuran.