Strategies for sustainable palladium catalysis

Abstract

• Overview of the current state of the art for sustainable palladium catalysis. • Critical survey of the recovery of palladium catalysts from secondary waste sources. • Summary of the design and scope of palladium catalysts employed at low-loadings. • Discussion of the design and scope of reusable, homogeneous palladium catalysts. • Comparison of the various approaches to sustainable palladium catalysis. Palladium is established both as an indispensable metal in modern synthetic chemistry and as a key component in catalytic converters and electronic equipment. The unrelenting demand for this metal increases both the financial and environmental cost, through mining, of this metal, rendering consumption unsustainable in its current form. This review provides a critical survey of the main approaches being pursued to address this issue, including low-loading catalysis, recyclable catalysts and the use of palladium recovered from secondary sources. The literature discussed herein reveals that catalysts that operate at low loadings are an attractive, sustainable option for many transformations, even when compared to catalyst systems that can be reused multiple times. Both low-loading and reusable catalysts depend on a finite natural supply of palladium, making the development of catalysts based on metal recovered from end-of-life materials (urban mining) a promising field of research. The way in which low-loading is achieved in different catalyst designs influences the choice of reaction temperature and solvent, which has additional environmental implications. Such factors are discussed for a wide range of systems alongside reaction and substrate scope, supported by extensive supplementary information . The survey aims to provide an insight into the relative merits of the approaches being explored and how the field of palladium-based catalysis might progress towards more sustainable use of this critical metal.