Light-activated Nickel catalysts – LightNing

The targeted objectives will be attained thanks to a collaborative project between two partners implying synthetic chemists and spectroscopists.

Numerous potential photoreducible Ni(II) complexes have been synthesized and characterized. Most of them are efficiently reduced into Ni(I)/Ni(0) species under light irradiation.

The study of the photoreduction of the complexes and their application in catalysis are in progress

Manuscript in préparation

The search for innovative metal-based catalysts is a hot topic of current research both in industrial and academic laboratories. Although catalysis is inherently a pillar of green chemistry (9th principle), a major issue to be addressed is the development of catalytic processes favouring the use of non-precious transition metals. In this context, nickel catalysis is at the forefront of research. Nickel attracts considerable interest for various important transformations, in particular homocoupling ans cross-couplings. In such processes, the ability of low-valent Ni(0) or Ni(I) species to effectively promote the first step of the reaction, i.e. the oxidative addition into C-X bonds, is a key feature of Ni reactivity. In the area of catalyst development, a reactivity vs stability dilemma exists, as extremely reactive catalysts are difficult to store/handle thus limiting the scope of their use. This is particularly true for low-valent Ni(I) and Ni(0) species with open coordination sites which are extremely reactive, in particular towards oxygen, and thus typically require handling in a glovebox. The LightNing project aims at developing the first generation of Ni(II) precatalysts that could be photoreduced under particularly mild conditions to generate selectively the low-valent Ni(I) or Ni(0) catalytic species. This contrasts with current activation processes which typically employ an excess of highly reactive reducing species leading to poor control over the reduction process. The general strategy will consist in exploiting the ability of triplet states of aromatic ketones, such as benzophenones, to mediate the reduction of transition metal ions. The expected key benefits of this original strategy are: 1) manipulation of air stable precatalysts, easy to prepare, cheap and that integrate the organic photosensitizer in their structure ; 2) high photoreduction efficiency and accurate control of the reduction process; 3) selective reduction to Ni(I) or Ni(0) catalytic species; 4) greener/safer catalysts. The main objectives are to: 1) develop straightforward access to cheap photoreducible Ni(II) precatalysts; 2) optimize the photoreduction processes and understand the mechanisms; 3) provide highly reactive Ni catalysts for key cross-coupling reactions. The project (42 months), coordinated by Jean-Marc Vincent (DR, CNRS), will be conducted in the framework of a collaborative project implying 2 partners of the Universities of Bordeaux and Grenoble-Alpes having strong and complementary expertise in catalysis, coordination chemistry, photochemistry, electrochemistry and spectroscopies. A PhD and a post-doctoral fellow (18 months) will be recruited to strengthen the consortium. LightNing is a fundamental research (TRL 1-2) project which addresses key societal challenges with the development of more sustainable catalytic processes which should benefit to experimentalists by providing safe, highly reactive but easy to prepare / handle catalysts. Overall, the project corresponds to the OPR « Systèmes catalytiques » belonging to Défi 3 “Stimuler le Renouveau Industriel”, Axis 3 “Chimie moléculaire, chimie durable et procédés associés”. The results of the LightNing project should have a strong impact in the area of homogeneous catalysis, an area where both Ni catalysis and light-mediated processes are experiencing an impressive renewal/development. The outcomes of LightNing will be valorised by publications in high impact peer-reviewed international journals and presentations in international meetings. Most of the target precatalysts should be obtained by straightforward syntheses from inexpensive starting materials, and thus will be compatible with large-scale preparation for possible commercialization. Mid- to long-term developments of this program could ultimately lead to collaboration with an industrial partner.