Cycloalkanes oxidation with O2 in high-efficiency and high-selectivity catalyzed by 3D MOFs with limiting domain and Zn(AcO)2 through synergistic mode

Abstract

To achieve efficient and selective cycloalkane oxidation, binary catalytic systems had been constructed on the basis of 3D MOFs [Zr6O4(μ3-OH)4(Metalloporphyrin)2(μ1-OH)4(μ1-H2O)4] and Zn(AcO)2. MOFs were prepared to construct limiting domains to suppress diffusiveness of free radicals under disorder state, and Zn(AcO)2 had been employed as synergistic catalysis sites. Catalytic system constructed by PCN-222-d(Co) and Zn(AcO)2 exhibited excellent catalytic performance. In contrast to T(4-COOCH3)PPCo as homogeneous catalyst, an enhancement from 3.83% to 5.51% was obtained from conversion, meanwhile selectivity was increased from 79.9% to 94.4% in cyclohexane oxidation. Primary source of the excellent performance were inhibition of diffusiveness of free radicals under disorder state, and enhancement on C-H bonds oxidation with oxidation intermediate R-OOH catalyzed by Zn(II). Synergistic catalysis process and catalytic mechanism were investigated via controlled experiments, radical trapping, and EPR analyses. This study provides a useful reference for oxidative functionalization of cycloalkanes with O2, and a significant contribution for other chemical conversions involving in free radicals.