Toward “metalloMOFzymes”: Metal–Organic Frameworks with Single-Site Metal Catalysts for Small-Molecule Transformations

Metal–organic frameworks (MOFs)
are being increasingly studied
as scaffolds and supports for catalysis. The solid-state structures
of MOFs, combined with their high porosity, suggest that MOFs may
possess advantages shared by both heterogeneous and homogeneous catalysts,
with few of the shortcomings of either. Herein, efforts to create
single-site catalytic metal centers appended to the organic ligand
struts of MOFs will be discussed. Reactions important for advanced
energy applications, such as H2 production and CO2 reduction, will be highlighted. Examining how these active sites
can be introduced, their performance, and their existing limitations
should provide direction for design of the next generation of MOF-based
catalysts for energy-relevant, small-molecule transformations. Finally,
the introduction of second-sphere interactions (e.g., hydrogen bonding
via squaramide groups) as a possible route to enhancing the activity
of these metal centers is reported.