Reduction catalysis by metal complexes confined in a polymer matrix

It is an urgent subject to create renewable energy resources such as artificial photosynthetic system and fuel cell free of an environmental pollution, since global warming is closely related to tremendous consumption of fossil fuels to emit carbon dioxide. In this review, we focus on reduction catalyses indispensable for creating new energy systems, especially in the aspects of molecular catalyst. Recent examples of the molecular catalyses for O-2, CO2, and H+ reductions are reviewed compared with the characteristics of noble metal catalysts. Molecular aggregates composed of a simple metal complex and a functional polymer can be easily prepared without employing complicated materials such as supra-molecular and hybrid complexes. When using molecular aggregates as a catalyst, the efficient catalysis via an multi-electron transfer reduction by the complex often takes place coupled with the intrinsic characteristics of the polymer employed; moreover, they show unique and active catalysis that cannot be achieved by the corresponding neat complex in a solution or in an electrode-coated state. Typical effects of polymer affecting the efficient molecular catalysis are shown to propose approaches for designing and developing catalysts in molecular level. (C) 2003 Elsevier Ltd. All rights reserved.