Cooking up cooler carbon bonds

If chemists want to make an organic compound, they have to connect carbon atoms. This is because organic compounds, such as many modern drugs but also the components of LCD screens, are defined by their carbon backbones. There are plenty of mechanisms to make these carbon-carbon bonds, but these reactions often require toxic metals, high temperatures or both.

A group of organic chemists from the University of Groningen led by Prof. Ben Feringa have discovered a way to make carbon-carbon bonds under mild conditions, using a special catalyst (a compound that speeds up a chemical reaction without being used up).

Traditionally, the first step in the reaction is to fit organic compounds with a lithium atom, but these ‘organolithium compounds’ are too reactive to be used in selective reactions, so the lithium is then replaced by metals like tin or zinc, or a compound like fluoroborate. Once this has been achieved, specific carbon-carbon bonds can be forged between different organocompounds with the aid of catalysts.

Feringa’s group has managed to tame the reaction of organolithium compounds using palladium as a catalyst. The organic group is transferred from the lithium atom to the palladium before connecting to a second organic molecule. This system makes it possible to make different carbon-carbon bonds under controlled and relatively mild conditions. Where traditional organic chemistry requires high temperatures for a long time, the palladium-catalysed reactions take less time at lower temperatures.

In a paper that appeared on the Nature Chemistry website (9 June), the Groningen chemists describe a reaction that takes one hour at 20 degrees Celsius with their new palladium system rather than the 48 hours at 90 degrees that the traditional method needs. A second advantage is that the palladium system reduces the need for organotin compounds. As tin is a toxic metal, this makes the reactions much greener.

Finally, organolithium compounds are easy to make and much cheaper than other organometals. By taming the lithium, the Feringa group has created a recipe for cleaner and cheaper carbon-carbon bonds.