Metal–Support Interactions in Molecular Single-Site Cluster Catalysts

This
study provides atomistic insights into the interface between
a single-site catalyst and a transition metal chalcogenide support
and reveals that peak catalytic activity occurs when edge/support
redox cooperativity is maximized. A molecular platform MCo6Se8(PEt3)4(L)2 (1-M, M = Cr, Mn, Fe, Co, Cu, and Zn) was designed in which
the active site (M)/support (Co6Se8) interactions
are interrogated by systematically probing the electronic and structural
changes that occur as the identity of the metal varies. All 3d transition
metal 1-M clusters display remarkable catalytic activity
for coupling tosyl azide and tert-butyl isocyanide,
with Mn and Co derivatives showing the fastest turnover in the series.
Structural, electronic, and magnetic characterization of the clusters
was performed using single crystal X-ray diffraction, 1H and 31P nuclear magnetic resonance spectroscopy, electronic
absorption spectroscopy, cyclic voltammetry, and computational methods.
Distinct metal/support redox regimes can be accessed in 1-M based on the energy of the edge metal’s frontier orbitals
with respect to those of the cluster support. As the degree of electronic
interaction between the edge and the support increases, a cooperative
regime is reached wherein the support can deliver electrons to the
catalytic site, increasing the reactivity of key metal-nitrenoid intermediates.