Beyond the Active Site: Tuning the Activity and Selectivity of a Metal–Organic Framework-Supported Ni Catalyst for Ethylene Dimerization

To modify its steric and electronic properties as a support for heterogeneous catalysts, electron-withdrawing and electron-donating ligands, hexafluoroacetylacetonate (Facac–) and acetylacetonate (Acac–), were introduced to the metal–organic framework (MOF), NU-1000, via a process akin to atomic layer deposition (ALD). In the absence of Facac– or Acac–, NU-1000-supported, AIM-installed Ni(II) sites yield a mixture of C4, C6, C8, and polymeric products in ethylene oligomerization. (AIM = ALD-like deposition in MOFs). In contrast, both Ni-Facac-AIM-NU-1000 and Ni-Acac-AIM-NU-1000 exhibit quantitative catalytic selectivity for C4 species. Experimental findings are supported by density functional theory calculations, which show increases in the activation barrier for the C–C coupling step, due mainly to rearrangement of the siting of Facac– or Acac– to partially ligate added nickel. The results illustrate the important role of structure-tuning support modifiers in controlling the activity of MOF-sited heterogeneous catalysts and in engendering catalytic selectivity. The results also illustrate the ease with which crystallographically well-defined modifications of the catalyst support can be introduced when the node-coordinating molecular modifier is delivered via the vapor phase.