A Heterogeneous Hydrogen-Evolution Catalyst Based on a Mesoporous Organosilica with a Diiron Catalytic Center Modelling [FeFe]-Hydrogenase

A diiron [FeFe]-hydrogenase model complex tethered with a maleimide group, FeFe1, was covalently grafted on the pore surface of a periodic mesoporous organosilica with thiol groups (SH-PMO) to form an efficient heterogeneous hydrogen (H-2)-evolution catalyst FeFe1@PMO. The coordination structure of the FeFe1 complex and the ordered pore structure were almost completely preserved even after immobilization of FeFe1 on SH-PMO. The FeFe1@PMO promoted photocatalysis for H-2 evolution in water containing a photosensitizer [Ru(bpy)(3)](2+), with a turnover number (TON) of 310 over 120 min. The TON was greater than those of an analogous homogeneous FeFe1 catalyst (TON=180) and conventional diiron complexes immobilized on solid supports (TON=6-18). The increased TON for FeFe1@PMO compared to the homogeneous FeFe1 was attributed to the improvement in the stability of the FeFe1 complex by immobilization on the pore surface of SH-PMO. A [Ru(bpy)(3)](2+) photosensitizer tethered with a maleimide (Ru1) was prepared and co-immobilized on FeFe1@PMO to form an all-solid-state photocatalyst FeFe1-Ru1@PMO. FeFe1-Ru1@PMO evolved H-2 without the additional [Ru(bpy)(3)](2+) photosensitizer, suggesting efficient photoinduced electron transfer from the immobilized Ru1 to the immobilized FeFe1.