Conception et développement de catalyseurs moléculaires à base de diaminotriazine pour la production d'hydrogène par la lumière = Design and development of diaminotriazine based molecular catalysts for light-driven hydrogen production

Chemistry ofpolypyridine ligands is an active and important field ofresearch as polypyridines are one of the most versatile chelating ligands for transitions metal ions, generating diverse molecular architectures with useful physical properties.A vast literature is reported on metal complexes of polypyridines and their applications in supramolecular functional devices, catalysis, liquid crystals, artificial photosynthesis, and host-guest interactions.Although, there are several reports on polypyridine chemistry, the development in this are a is limited due to the low yield and synthetic inaccessibility associated with polypyridines.Furthermore, their crystal structures cannot be predicted because they lack functional groups that conduct self-assembly.With the depletion of fossil fuels and the phenomenon of global warming, the necessities for the development of clean and sustainable energy resources are imperative.Hydrogen is a clean, environmentally benign, and sustainable energy carrier as water is the only pro du ct of its combustion.Hydrogen as a fuel possesses high energy output relative to its mass.However, molecular hydrogen is very rare in the Earth's atmosphere c.a. 1 ppm by volume.Therefore, it needs to be produced from suitable sources.Sunlight-triggered hydrogen evolution reaction (HER) has proven to be an interesting solution to harvest the abundant and inexhaustible power of solar energy in the form of chemical bonds in hydrogen.A typical hydrogen evolution reaction is based on visible light-induced sensitization of photosensitizers from which the electrons are transferred to the photo catalytic centre to produce hydrogen with the help of a sacrificial electron donor (SEO).Ruthenium and cobalt molecular complexes are the most widely studied and reported complexes as photosensitizers (PSs) and photocatalysts (PCs) respectively.For efficient electron transfer, the PS and the PC must be in close proximity.Direct contact in the form of covalent or coordination bonds can increase the benefits, but such systems are usually difficult and expensive to synthesize.Sometimes, weaker contacts have also proven to be effective.Nevertheless, the design and development of efficient and non-expensive molecular catalysts and the modification of the catalysts by low-cost ligand design remains the principal focus of research in this area.Our work demonstrates a simple and inexpensive technique to prepare molecular photocatalysts (PCs).The strategy used to prepare these PCs is based on the concept of metallotectons.Metallotectons are molecular complexes that can form supramolecular networks by ligands possessing standard patterns of coordination like bipyridine, terpyridine and quarterpyridine, and ligands containing functional groups that can form strong hydrogen bonds.Such type of ligands are called as tectoligands.In our study, we have used ligands which are bipyridine-like, terpyridine-like and quaterpyridine-like.These ligands possess diaminotriazinyl groups (DAT), that allow them to self-assemble with several transition metal ions by coordination and hydrogen bonds.The most attractive feature of the diaminotriazine group is that, it can be introduced in a single step.To the best of our knowledge, these molecular complexes are the first examples of coordination chemistry based molecular catalysts for the hydrogen evolution reaction (HER).In addition to their interesting catalytic properties, these molecular complexes also have ability to self-assemble via hydrogen bonds to produce fascinating supramolecular networks.

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