Overcoming Pd Catalyst Deactivation in the C-H Coupling of Tryptophan Residues in Water Using Air as the Oxidant.

The Pd-catalyzed C-H activation of natural tryptophan residues has emerged as a promising approach for their direct synthetic modification. While using water as the solvent and harnessing air as the oxidant is enticing, these conditions induce catalyst deactivation by promoting the formation of inactive Pd(0) clusters. In this work, we have studied optimized Pd-based catalytic systems via nonsteady state kinetic analysis and in situ X-ray absorption spectroscopy (XAS) to overcome catalyst deactivation, which enables the effective use of lower Pd loadings.