Resolving Heterogeneity Problems and Impurity Artifacts in Operationally Homogeneous Transition Metal Catalysts

Work done in the field of resolving heterogeneity problems and impurity artifacts in operationally homogeneous transition metal catalysts are discussed. Unintended heterotopy with loss of all the ligands initially present in the precatalyst are found to nullify the effect of sophisticated ligand design such as in the multifunctional ligands. Narayanan et al. have shown that nanoparticle shape and size can strongly affect activity. Finke and co-workers have now modified their conclusions for the Maitlis catalyst and find in operando X-ray absorption fine structure (XAFS), kinetic, and kinetic poisoning evidence for the predominant species and active catalyst being subnanometer Rh 4 clusters. Conlon and co-workers studied the Suzuki-Miyaura reaction catalyzed by Pd/C by estimating the solution levels of Pd by hot filtration followed by high-performance liquid chromatography (HPLC) analysis for the organics and inductively coupled plasma-mass spectrometry (ICP-MS) analysis for the palladium.