Transition metal ions: weak links for strong polymers

The discovery of transition metal catalysis in polymerization reactions more than 50 years ago has lead to modern organometallic chemistry and has revolutionized the world of catalysis and polymers. Since then catalyst improvement and functional group tolerant catalysts paved the way for new applications and commercialization of polymers. Due to the commercial success of polymers macromolecular chemistry is a highly developed field. The creation of macromolecular structures utilizing inorganic elements adds a new dimension to the field of polymer materials. Coordination numbers and geometries become additional variables and metal ions give access to redox, magnetic, optical or reactive properties that are not accessible through carbon based polymers. The potential for these materials can be envisioned if we consider the impact of inorganic solid-state materials on technology. The importance of metal ions in biological systems as cofactors in enzymes and metalloproteins for oxygen transport in respiration or for electron-transfer in photosynthesis may give a hint at the potential and the impact on technology that inorganic–organic composite materials may develop. Over 40 elements including main group metal elements (Si, Ge), transition metals or rare earth elements in addition to the 10 elements found in organic polymers (C, H, N, O, B, P, halides) are available for organometallic polymers. Therefore, the variations of organometallic polymers seem endless. Several types of organometallic polymers can be distinguished based on how the metal is integrated in the polymer as outlined by Rehahn (Fig. 1). Metals can be pendent to or they can be present in the polymer backbone. In coordination polymers the coordinative bond between the metal and the ligand is an integral part of the backbone. The polymer backbone can act as polymeric chelate, which embeds the metal ion; breaking the coordinative bond does not affect the polymer backbone. Finally, metals can be part of a network structure with a continuous 3-D topology. Max Planck Institute of Colloids and Interfaces, D-14424 Potsdam, Germany. E-mail: [email protected]; Fax: ++49(0)331-567 9202; Tel: ++49(0)331-567 9211 National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan