Palladium-free Wacker-inspired oxidation: challenges and opportunities in catalysis.

Palladium-catalysed Wacker-type oxidation of olefins to ketones or aldehydes is one of the most prominent homogeneous reactions globally, even performed at a multi-tonne scale. From a fundamental and an applied point of view, it is extremely appealing to replace palladium catalysts by other metal-based catalysts to increase the efficiency, selectivity and sustainability, particularly considering the reactivity of well-defined first-row transition metal complexes as catalysts. In this case, the ligand(s) coordinating to the metal(s) play a major role in controlling selectivity and activity, thanks to unique mechanistic considerations. This mechanistically-driven feature article emphasizes the advantages and disadvantages of currently existing approaches. Besides the main efforts devoted to homogeneous catalysis, heterogenous systems and biocatalysis have also been studied as they offer complementary strategies. Overall, this review presents an up-to-date analysis of key contributions while highlighting existing gaps for future developments in this important and exciting field.