Metal-organic frameworks have recently attracted attention as heterogeneous catalysts due to their high content of metal centres and large surface area and pore volume, along with their impressive topological richness. Therefore, many studies describing the use of MOFs as heterogeneous Lewis acid catalysts have been published. In this regard, these efforts have been directed towards probing the catalytic activity. Further information is required in terms of kinetic parameters and comparison of performance with their homogeneous counterparts, or other conventional heterogeneous catalysts. Here we have attempted to put MOFs into perspective with respect to their homogeneous counterparts and more conventional heterogeneous catalysts to show their advantages and limitations. We have exemplified a number of reactions reported in the literature wherein MOFs have been used as catalysts, and we have carried them out using homogeneous counterparts, i.e. benzoates and acetates, and other well defined conventional solid catalysts. The activities and selectivities of the catalysts are compared and then put into perspective on the basis of kinetic parameters, such as turnover numbers and turnover frequencies.Additionally, we illustrate using selected examples what the potential advantages of MOF catalysts could be, and how they may outperform the potential of other solid catalysts.

Room to swing a cat: A chiral disulfonimide has been designed as a powerful new motif for asymmetric catalysis. As a first illustration, a highly efficient and enantioselective Mukaiyama aldol reaction has been developed (see scheme). The actual catalyst is proposed to be an N-silyl imide which is generated in situ

A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor. The results are compared with their zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies using isotopically labeled isopropanol provide evidence that the transfer hydrogenation occurs through a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. The generality of the procedure has been demonstrated by accomplishing the transformation with aldehydes, ketones, and α,β-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Brønsted-acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to γ-valerolactone in good yield of 75 %.

Counteranion control enables the enantioselective, organo Lewis acid catalyzed Hosomi-Sakurai reaction of (hetero)aromatic aldehydes and allylsilanes using an easily handled disulfonimide precatalyst (see scheme). The key to the success of this system is to turn the usually undesired silylium ion catalysis into the desired catalytic regime and pair the cation with an enantiopure disulfonimide anion, thereby applying the concept of asymmetric counteranion-directed catalysis.