LAUSR

This article examines a selection of case studies that highlight key strategies that have enabled the structural authentication of important species that shed light on fundamental on-cycle intermediates in palladium- and nickel-catalysed C-C, C-N, and C-O cross-coupling reactions. Particular emphasis is placed on studies in which the structures of rather intractable intermediates have been confirmed unambiguously by X-ray crystallography, while also contextualising the mechanistic insights that these reports have contributed.