The exquisite selectivity and excellent activity of oxidative transformation performed by metalloenzymes have been sources of inspiration for chemists trying to emulate their catalytic functions. Synthesis of model compounds to mimic the active site of metalloenzyme has been an active area of research in the past decade. However, these model compounds in homogeneous solution are still somewhat sensitive to the environments, and they show lower activity and selectivity than the corresponding enzymes. The necessary function of the protein backbone is usually not considered in a homogeneous solution of biomimetic metal complex. It is known that the protein backbone plays important roles in site-isolation, nanoconfinement, and substrate duct to facilitate a specific catalytic action. Therefore, further integration of a scaffold with a model metal complex catalytic system would be most desirable to better mimic the structure and reactivity of metalloenzyme. For achieving an integration of an appropriate ligation with metal complex, site-isolation and confinement can be acquired by (a) appropriate design of the periphery of ligands allowing for effective homogeneous catalysis to be tethered to a scaffold to achieve site-isolation and (b) introduction of neighboring functionality on the support to simulate the local environment of active center of the metalloenzyme. 1 New materials that can provide the advantages of both heterogeneous and homogeneous oxidation catalysis are thus much desired. In recent years, several supermolecular constructs have been developed for encapsulating biomimetic metal complex to mimic the catalytic functions of metalloenzymes, including metalomicelle, 2 supramolecule, 3 and zeolite, 4 but most of them are not dealing with systematic designs, often only capturing one particular aspect in mimicking nature. Mesoporous silica materials possess some unique properties that are suitable for encapsulating small biomimetic metal complexes with great utility, such as large surface area, controllable geometric parameters with

We report the synthesis and characterization of two hydroxo-bridged dinuclear cupric complexes, HPC [((phen) 2 Cu-OH-Cu(phen) 2 ) 3+ , phen ) 1,10-phenanthroline] and HBC [((bpy) 2 Cu-OH-Cu(bpy) 2 ) 3+ , bpy ) 2,2′-bipyridine], encapsulated in porous materials for the oxidation of 3,5-di-tert-butylcatechol (DTBC) to the corresponding quinone, 3,5-di-tert-butylquinone (DTBQ), to mimic catechol oxidases (COs). The separations of the two Cu(II) centers are 2.9, 3.51, and 3.65 Å for CO, HPC, and HBC, respectively. The stability of dinuclear cupric complexes, turnover number (TON), and selectivity of DTBQ were examined in NaY zeolite (pore size 0.74 nm) and the solid mesoporous silicas (MPSs) MCM-41 (2.4 nm), MCM-48 (2.5 nm), and MAS-9 (9.0 nm). The studies showed that the MCM-41 and MCM-48 provided a better stability against the irreversible dissociation of dinuclear cupric complexes for their matching size, while NaY has too small and MAS-9 has too large pore size to stabilize these dinuclear copper complexes. The EPR studies showed that HBC immobilized in MPS solids yielded more mononuclear cupric complexes than HPC samples, which may come from the low stability of HBC undergoing the dissociation of OH bridge via the Lewis acid (aluminum sites in the solid support) catalytic activities under the ion-exchanging process. The catalytic pathways for the production of DTBQ and byproducts are proposed on the basis of spectroscopic characterizations and activity measurements. The main byproduct observed in NaY supports was formed from a DTBC-mononuclear copper intermediate and followed the pathway of electron transfer, oxygen insertion, ring-opening, and oxidation reaction. Furthermore, the rigid and bulky structure of HPC molecule (planar phen ligands) has more confinement effect in MCM-41 and MCM-48 solids than the flexible HBC molecule (nonplanar bpy), which can prevent an excessive separation of the dinuclear cupric centers in the deoxy state and yield a higher stability and selectivity. The smaller separation of the two Cu(II) ions in HPC may also be responsible for the observed higher oxidation selectivity. However, the bulky structure of four phen ligands in HPC molecules exhibits greater steric hindrance and decreases the contact of the substrate and yields a lower TON. The nanochannels of aluminum-substituted MPS provide the needed confined spaces and surface charge and maintain the separation of the dinuclear cupric centers after removing the hydroxo bridge in the catalytic cycle.