Heterogeneity in Heck Reactions with Heterogeneous Precatalysts

The Heck reaction is the most attractive C-C coupling way, which constitutes a universal approach of producing various classes of organic compounds for the development of new processes used in industry. A deeper understanding of the nature of true catalytic species starting with heterogeneous precatalysts will motivate potential breakthroughs in the rational design of future generations of homogeneous C-C coupling catalysts in nature. Heterogeneous catalyst systems are expected to achieve a high turnover number or good catalyst recycling with a minimal level of residual metal in the products via homogeneous catalysis. This review is focused on the investigation of heterogeneity towards Heck reactions with heterogeneous precatalysts, concisely summarizing the worldwide research published up to date with our appropriate discussion. The review includes the literature of heterogeneity studies involving various types of solid material-supported metal particles and various heterogenized metal complexes used as precatalysts. Either the cases where leached metal species from heterogeneous precatalysts were claimed to be true catalysts, or the cases where heterogenized metal species were asserted to contribute to catalysis are presented here. Meanwhile, some important experimentations and methods for assessing catalyst heterogeneity, which are linked with the design of effective homogeneous C-C coupling catalysts using heterogeneous precatalysts are briefly introduced to catalysis readers.