Iridium and rhodium complexes within a macroreticular acidic resin: a heterogeneous photocatalyst for visible-light driven H2 production without an electron mediator.

Direct ion exchange of cyclometalated iridium(III) and tris-2,2'-bipyridyl rhodium(III) complexes, of which the former acts as a photosensitizer and the latter as a proton reduction catalyst, within a macroreticular acidic resin has been accomplished with the aim of developing a photocatalyst for H2 production under visible-light irradiation. Ir L(III)-edge and Rh K-edge X-ray absorption fine structure (XAFS) measurements suggest that the Ir and Rh complexes are easily accommodated in the macroreticular space without considerable structural changes. The photoluminescence emission of the exchanged Ir complex due to a triplet ligand charge-transfer ((3)LC) and metal-to-ligand charge-transfer ((3)MLCT) transition near 550 nm decreases with increasing the amount of the Rh complex, thus suggesting the occurrence of an electron transfer from Ir to Rh. The Ir-Rh/resin catalyst behaves as a heterogeneous photocatalyst capable of both visible-light sensitization and H2 production in an aqueous medium in the absence of an electron mediator. The photocatalytic activitity is strongly dependent on the amount of the components and reaches a maximum at a molar ratio of 2:1 of Ir/Rh complexes. Moreover, leaching and agglomeration of the active metal complexes are not observed, and the recovered photocatalyst can be recycled without loss in catalytic activity.