Structure-performance relations in homogeneous Pd catalysis by in situ EXAFS spectroscopy.

X-ray absorption fine structure (XAFS) spectroscopy is used to unravel the structure of homogeneous catalysts in their catalytically active phase (solution), for which other characterization techniques failed in providing detailed structural information. Application of in situ EXAFS shows that the conformation of the allylic fragment of (P-P)Pd(1,1-dimethylallyl) catalytic intermediate complexes in solution (i.e., reaction medium) differs from that in the solid state, dependent on the bidentate ligand. The change in orientation directly explains differences in regioselectivity in the allylic alkylation reaction, displayed by the distinct complexes.