Metal-support interactions regulate substrate binding in Fe/Co/Se cluster catalysts

Here, we investigate the stereo-electronic requirements of a family of Fe/Co6Se8 molecular clusters to achieve a Goldilocks regime of substrate affinity for the catalytic coupling of tosyl azide and tert-butyl isocyanide. The reactivity of a catalytically competent iron-nitrenoid intermediate, observed in situ, is explored towards nitrene transfer and hydrogen atom abstraction. The dual role of isocyanide, which on one hand prevents catalyst degradation, but, in large amounts, slows down reactivity is exposed. The impact of distal changes (number of neighboring active sites and identity of supporting ligands) on substrate affinity, electronic properties, and catalytic activity is investigated. Overall, the study reveals that the dynamic, push-pull interactions between the substrate (tBuNC), active site (Fe), and support (Co6Se8) create a regime where increased substrate activation occurs concomitantly with expedited dissociation.