Heterogeneous catalytic processes are central to our chemical products and energy economies, and yet their reactive interfaces are often poorly understood. Single-atom catalysts provide a well-defined platform in which a controlled density of substrate-accessible active sites is correlated with a redox active support, and yet their synthesis and characterization often lack true atomic precision. Seeking to access a new generation of tunable, well-defined catalytic manifolds, can we replicate and probe the catalytic interface in an atomically defined inorganic construct? To address this challenge, we developed rational synthetic methods to access a new class of atomically precise propeller-shaped clusters, M3Co6Se8L6 (L = Ph2PNTol; M = 3d metal), featuring three catalytically active “edge” metal sites tethered at the surface of an inorganic Co6Se8 “support”. Detailed electrochemical, crystallographic, spectroscopic and substrate binding studies enabled careful probing of the edge-support interaction, revealing a dynamic coordinative and electronic interplay between substrate (i.e. organic azide), active site (M), and support (Co6Se8). Reactivity studies confirmed that Fe3Co6Se8L6 is an exceptional catalyst for carbodiimide formation from TsN3 and CNtBu, yet the identity of a presumptive iron-bound nitrenoid intermediate remains unconfirmed. Herein, we detail the isolation and characterization of key catalytic intermediates in this transformation, including a series of mono-, bis- and tris-M(NR) complexes, and discuss how group transfer at one edge site influences the others. Further, we describe the unique physicochemical processes that are at play within the nanopropeller framework, and how these processes enable the formation of metal-ligand multiple bonds at the edge sites.

Probing the metal-support interface within an atomically precise inorganic nanocluster

ACS Spring Meeting 2021

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