Relation Between Coordination and Lewis-Acid Property of MOF-Derived Mononuclear Zn(II) Catalyst Toward Epoxide Hydroxylation

Lewis-acid properties of the coordinatively unsaturated metal ions are highly relevant to the coordination environment; however, it remains a challenge to establish the coordination structure-activity relationship, especially in heterogeneous catalysis. Here, a typical metal-organic framework, ZIF-8, is selected as the precursor to prepare Lewis-acid based Zn-N/P-C mononuclear catalysts, with well-designed external structures but difference in the local coordination. The obtained mononuclear Zn(II) catalysts can not only inherit the advantages of MOF in coordination, but also simulate the homogeneous environment during the catalysis owing to the monodispersed metal sites in ZIF-8. Eventually, relation between coordination and Lewis-acid property toward epoxide hydroxylation has been illustrated. Results show the substituted coordination atom of P and the decrease of coordination number strongly enhance the Lewis-acidity of Zn2+, causing the TOF values changes from 8.7 to 80.1 h(-1) based on Zn content. The work affords an understanding and inspiration of coordination environment matters toward Lewis-acid catalysis in organic transformations.

Automated summary

The study prepared Lewis-acid based Zn-N/P-C mononuclear catalysts using ZIF-8 as precursor to illustrate the relationship between coordination structure and Lewis-acid properties in catalytic reactions. The results showed that by modulating the coordination atom and number, the Lewis acidity of Zn2+ can be greatly enhanced, leading to improved catalytic activity.