Computational screening of MOF-supported transition metal catalysts for activity and selectivity in ethylene dimerization

Deposition of small metal-oxide clusters on the Zr-based nodes of a metal-organic framework has been demonstrated to provide access to a variety of single-site catalysts. Well-defined catalytic active sites are amenable to detailed computational studies of potential catalytic pathways, and they invite screening a wide range of metals to assess their expected activity. Here we report the application of density functional theory to a variety of transition metals (in particular Ti^IV, V^II, V^IV, Cr^II, Cr^III, Mn^II, Mn^IV, Fe^II, Fe^III, Ni^II, Co^II, Co^III, Cu^II, Cu^III, Pd^II, Mo^II, and W^II) supported on NU-1000 inorganometallic nodes to evaluate their activity for ethylene dimerization. We found that the rate-determining step varies between different catalysts, which illustrates the importance of considering more than a single step when comparing catalytic cycles across a variety of metals. Our calculations are consistent with the known good activity of supported Ni^II for ethylene dimerization, and they predict that Cr^II and Pd^II are also potentially useful catalysts for this process. We also screen modifications to the organic linker of Ni^II-NU-1000 by considering the addition of Me, iPr, tBu, CF₃ and NH₂ groups to study the influence of sterically demanding and, the case of CF₃ and NH₂, respectively, electron-donating and -withdrawing, substituents on the activity for ethylene dimerization; we predict no improvements in activity or selectivity (for 1-butene) with such substitutions.