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Collaboration led by RASEI members Obadiah Reid and Garry Rumbles solves a long-standing puzzle in important organic chemical transformation.

In the world of organic chemistry, making new molecules, the building blocks for everything from advanced electronic materials to pharmaceuticals, is a bit like being a chef. Chemists are always looking to improve the recipe, to make it faster, cheaper, more efficient, and produce less waste. In recent years one of the most exciting new ‘cooking techniques’ is nickel photocatalysis, which uses abundant, low-cost nickel and the power of light to enable chemists to build complex molecules under mild conditions.

This technique has emerged as something of a game-changer in building molecules, but it comes with a significant puzzle. The nickel catalyst, as it is normally added to a reaction, is in a dormant state (called a ‘pre-catalyst’). To get the reaction moving, the catalyst needs to be ‘woken up’. For years, scientists were not sure what the wake-up call was. The activation from pre-catalyst to the functioning catalyst was something of a black box, with numerous theories for what was happening. This led to the assumption that each reaction was unique, and each reaction required its own individual and complicated startup sequence. This has often required a lot of work to find the right ‘On switch’.

This collaborative study, led by RASEI researchers Obadiah Reid and Garry Rumbles at the National Renewable Energy Laboratory (NREL), brings together expertise from the SLAC National Accelerator Laboratory, Brookhaven National Laboratory, Argonne National Laboratory and Northeastern University. Together, the scientists have identified key features of the transformation from pre-catalyst to active catalyst. In the report, just published in Nature Communications, the team shows that there is a universal ‘On switch’ to start these powerful reactions, and the key to this transformation is light.

Imagine a high-tech machine delivered in a locked crate. You know that once you get it out and get it running, it can do amazing things, but you don’t have the key. For years, chemists were essentially trying to pick the lock in different ways every time they wanted to use it. This study describes a universal key for getting the crate open.

It was found that light, either directly, or transferred from another light-absorbing molecule, provide a jolt of energy that breaks a bond in the nickel pre-catalyst structure. This process, which is called photolysis, activates the nickel complex, getting it ready to do the chemistry. This initial step is something that has previously been proposed but never fully proven.

The team brought together a sophisticated array of tools to effectively investigate this mechanism, including incredibly fast laser systems that can watch chemical changes happen in fractions of a second. This allowed them to witness the ‘unlocking’ process in real-time and identify the exact sequence of events. They observed that after the initial light-induced bond breaking, the catalyst can then interact with molecules in the surrounding solvent, forming a temporary ‘reservoir’ that holds the catalyst in a state ready for the main reaction.

Building this body of evidence and developing these findings required a significant team effort, bringing together scientists from across the country, from multiple national labs and universities. RASEI Scientists at ÃÛÌÒ´«Ã½Æƽâ°æÏÂÔØ and NREL used advanced spectroscopy to track the catalyst’s behavior, while researchers at SLAC used high-powered X-rays to confirm changes in the structure of the nickel complex. This combination of knowledge and experience with cutting-edge instrumentation was essential in providing a complete understanding of these reactions begin.

Development of a unified explanation for how one of the most important tools in an organic chemist’s toolbox is initiated has important implications. Understanding this fundamental activation step allows chemists to move from guessing to designing. Not only does this support improvement in the activation of existing reactions, it also provides opportunities to design new transformations, all of which will streamline the manufacture of chemical commodities, such as pharmaceuticals and materials.