Oxidation of ethane to ethanol in a Fe₂(dobdc) metal-organic framework.^[1]

The active sites of metal-organic framework catalysts are not only well-defined and tunable, but also site-isolated. As such, catalytic intermediates that are prone to deactivation by dimerization, such as terminal metal-oxo or metal-dioxygen species, should be much more stable within a rigid framework support. As a result, the metal-organic framework Fe₂(dobdc) and its mixed Fe/Mg analogues can activate the strong C–H bonds in ethane using N₂O as the terminal oxidant, producing ethanol with high selectivity.

A promising approach to developing highly tunable metal-organic framework catalysts is to synthesize frameworks with open chelating sites. In analogy to how molecular catalysts are tailored by choice of ligand and metal source, we envisioned that a metal-organic framework with chelating linkers could be used as a platform to synthesize catalysts for a variety of reactions through judicious choice of chelating linker and metal source used in post-synthetic metalation.

Reaction of [(PY5Me₂)Mo(CF₃SO₃)]¹⁺ with water to form [(PY5Me₂)MoO]²⁺ and H₂ (left) and with sulfur to form [(PY5Me₂)MoS₂]²⁺ Right: The side-on bound S₂ moiety resembles the edge sites in MoS₂, an important catalyst in hydrodesulfurization and H₂ generation.^[2][3]

We have also explored catalysis in molecular systems, focusing on transition metal complexes supported by the ligand PY5Me₂. This series of molecules has achieved H₂ evolution from water, and more recently, CO₂ reduction. The complex [(PY5Me₂)Mo(CF₃SO₃)]⁺ reacts with water to form [(PY5Me₂)MoO]²⁺ with the concomitant evolution of H₂. More recently, we have demonstrated that the divalent cobalt complex, [(PY5Me₂)Co(H₂O)]²⁺, generates H₂ at high turnover frequencies and 100% Faradaic efficiency. Future endeavours include investigating other PY5Me2 complexes, especially those containing first row transition metals; synthesizing new PY5Me₂ derivatives and pentadentate ligand scaffolds to tailor the electronic properties of these complexes; and developing systems that demonstrate interesting reactivity in regard to substrates such as H₂O, H₂, O₂, N₂, CO₂, and CH₄.