Manipulating the Reaction Pathway of CO2 Photoreduction via the Microenvironment of a Re Molecular Catalyst

Re molecular complexes incorporated into two metal-organic frameworks were investigated to disclose the host- guest interaction by infrared and 1H nuclear magnetic resonance and to explore the microenvironment around the Re complex by absorption and photoluminescence spectra. ZIF-8 provides a confined space to isolated Re via an electrostatic interaction, while UiO-66 exerts a relaxed space to accessible Re via a coordination interaction. For CO2 two-electron photoreduction to CO, the turnover number of 28.6 in Re@ZIF-8 is 10-fold that of 2.7 in Re@UiO-66. The electron transfer is promoted in Re@ZIF-8 by a local electrostatic field with a cross-space pathway, whereas it is retarded in Re@UiO-66 as the solvation shell surrounding Re. In the following CO2 activation, the charged intermediate species could be stabilized in Re@ZIF-8 by spatial confinement, while Re- triethanolamine adducts prevailed in Re@UiO-66 with the accessibility of the Re complex. This work demonstrates a feasibility of diverting the CO2 activation pathway by the microenvironment of a molecular catalyst in the field of artificial photosynthesis.