Hemilabile Ligands for Non-alternating Copolymerization

Several new ligands have been prepared in our laboratory for the first time or their syntheses are planned. They have been "tailored" to fulfil the criteria of two main topics: 1) Only recently, it has been recognized that homogeneous catalysis is part of the most efficient technological principles, which are able to match economical with ecological advantages. Our challenge is to find structurally precisely defined catalysts for oligomerization and polymerization reactions. The most demanding application is the non-alternating CO/ethylene copolymerization, which is planned to be carried out in cooperation with the ICCOM- CNR in Firenze, Italy, and Prof. C. Bianchini as before the strictly alternating copolymerization. Subsequent insertions of more ethylene monomers and low number-average molecular weights of the polymers would lead to a very good solubility in common organic solvents and therefore to an excellent processing of these advanced materials. The use of water as solvent is a great step towards environmentally benign chemical syntheses and processing and therefore the use of our ligands for water-soluble catalysts is important for the development of "green chemistry". In recent years, water as a reaction solvent has received much attention, because water is safe, cheap, and environmentally friendly. Our hemilabile ligands are further examples that for successes in research leading towards new catalysts, new materials, insight in biocatalysis and for a sustainable environment, controlled ligand design is a crucial element. 2) Homo- and heterobinuclear complexes containing Ru(II), Os(II), and various additional metals attract considerable attention as model catalytic systems for biomimetic photochemical conversion of solar energy. Our challenge is to study bidentate versus bis(bidentate) behavior, saturated versus conjugated backbones, and steric effects. Furthermore, the unprecedented steric control of the efficiency of luminescence due to the difference between bidentate and bis(bidentate) behavior has already led to the first measurement world-wide of long luminescent lifetimes at ambient temperature for this class of compounds. In an international cooperation the photophysical investigations are under way at the University of California at Irvine (UCI) together with the Director of the Laser Spectroscopy Facility Dr. Wytze E. van der Veer, where no measurements of this kind are feasible at the University of Innsbruck. Our photophysical measurements should also be regarded as a breakthrough in transdisciplinary research. This has only been possible by special measurements using a laser equipment working in the nanosecond or picosecond time domain. They have been carried out with one hundred per cent personal commitment in the USA: very fast photophysical processes in the ns or ps time domain, which play an important role in the conversion of light- (solar) energy into chemical energy, can be measured in real time. The coupling of Ru(II) light absorbers to reactive metal centers is of particular interest in developing multifunctional supramolecular complexes. The presence of an efficient light absorber coupled to a reactive metal center allows our complexes to be applicable in related solar energy storage schemes.

The following milestones of the project "Hemilabile Ligands for Non-alternating Copolymerization and Ruthenium(II) Complexes for Photochemical Devices" have been achieved: 1) The VERENA-Award (second place) of the excellent Austrian energy company "VERBUND" has been awarded to the co-worker of the above project Mag. Sylvia Eller. 2) Subsequent to this, the "VERBUND" becomes interested in this topic: the access of the Austrian industry, the companies "VERBUND - Austrian Renewable Power GmbH" and "D. Swarovski und Co.", leads to the approved FFG-project "Photo-Hydrogen". The subject matter of this project is the application of the basic research supported by the FWF. 3) Organization of a workshop with the topic "Photo-Hydrogen" in August 2009 at the institute of the applicant together with the companies "VERBUND - Austrian Renewable Power GmbH" and "D. Swarovski und Co.". 4) The applicant got an invitation to contribute to the Special Issue on The Materials Chemistry of Energy Conversion from the most cited journal in Materials Science "Chemistry of Materials", 2007 ISI Impact Factor: 4.9 (quotation of the invitation: "based on the previously published research of the applicant related to Photochemicals"). 5) The applicant also got a second invitation for a publication that is dedicated to the Editor-in-Chief Prof. U. Belluco of "Inorganica Chimica Acta" (see Reference: Fessler, M.; Czermak, G.; Eller, S.; Trettenbrein, B.; Haringer, S.; Oberhauser, W.; Brüggeller, P., Unusual ligand design: A platinum(II) mediated [2+2] photocycloaddition followed by a nickel(II) induced methoxyactivation, Inorg. Chim. Acta 2010, 363, 2001 - 2008). Further we modulated now RuN4P2 - complexes to produce molecules, that achieve reactivity and solubility in water. The main idea is to stabilize reactive metal centres in the reduced state, obtained by charge transfer after excitation of the Os or Ru centres. We prepared the first examples that are able to stabilize such a reduced state. This fact was proved by cyclovoltammetry. It should be regarded as a real breakthrough in this field, that with these complexes our working group already achieved the aim of solubility in water and photochemical hydrogen generation. However, at this point it is important to note, that on the one hand the amount of hydrogen produced is quite low at the moment. On the other hand, this is a world-wide problem and from a practical standpoint it is clear, that we must learn how to run water-splitting efficiently if we ever are to realize the dream of obtaining clean fuel from sunlight and water on a scale that would provide enough energy to power our planet (see Reference: Eisenberg, R.; Gray, H. B. Inorg. Chem. 2008, 47, 1697 - 1699). Therefore, in order to achieve an improvement of our system a few ligands are not enough, but a whole "Ligand Library" should be studied. In this context it is well-known that for successes in research leading towards new catalysts, new materials, insight in biocatalysis and for a sustainable environment, controlled ligand design is a crucial element. The common feature of our "Ligand Library" is that all ligands contain four phosphorus atoms connected by a central backbone consisting of four carbon atoms.