Metal–Organic Framework Supported Single Site Chromium(III) Catalyst for Ethylene Oligomerization at Low Pressure and Temperature

A chemically and thermally stable, mesoporous, crystalline metal–organic framework, NU-1000, serves as a structurally well-defined support for catalytic reactions. Depositing chromium­(III), a metal widely used in homogeneous ethylene oligomerization catalysts, onto the Zr₆ node of NU-1000 allows for the atomically precise determination of the structure of the Cr³⁺ catalyst through single-crystal X-ray diffraction studies. Chromium modification of NU-1000 was accomplished via solvothermal deposition in MOFs (SIM); termed Cr-SIM-NU-1000, the elaborated material features individual Cr atoms directed in single-site fashion into the mesopore of NU-1000. It was found that NU-1000 serves to stabilize the catalyst against both the typical chemical deactivation of homogeneous systems and leaching from heterogeneous systems. Cr-SIM-NU-1000 exhibits superior catalytic activity, as compared to Cr₂O₃, for ethylene oligomerization, with 20% conversion at a turnover frequency of about 60 h^–1 and products ranging from C₈–C₂₈. Given that this catalysis occurs at low temperature (ambient) and low pressure (1 bar C₂H₄), along with minimal quantity of cocatalyst, the high activity shown by Cr-SIM-NU-1000 enables significant reduction in materials usage and waste. Postcatalytic characterization reveals Cr-SIM-NU-1000 remains intact with no leaching under the reaction conditions.