Life on earth is built on carbon. Chains of carbon atoms, variously arranged, constitute the backbone of most of the molecules that form and regulate living systems. These molecules, large and small, of course contain several other elements too. But the greatest challenge to chemists, when they seek to replicate and even improve on nature’s ability to construct carbon-based (organic) molecules has long been finding ways to make and break the chemical bonds between carbon atoms. Over the years, synthetic organic chemists have amassed a vast armamentarium of such reactions to use when building new molecular structures.
Many organic reactions are, however, rather prone to the formation of unwanted side-products owing to the fierce conditions or highly activated molecules required. The 2010 Nobel Prize in Chemistry rewards three chemists who have developed new methods for making carbon-carbon bonds, highly selectively, under relatively gentle conditions. All three have their reactions named after them. The Heck, Negishi and Suzuki reactions all depend on using palladium, a silvery metal, to unite two molecules, resulting in the formation of a new single bond between them. Over the last 30 years or so, these reactions have become staple and much-valued additions to the organic chemists’ toolkit.
Richard Heck developed his palladium-based coupling reaction during the 1960s, publishing a series of single-author papers on the subject, before producing what became the standard protocol for the Heck reaction in 1972. In this, palladium acts as a catalyst, first taking hold of one molecule, then the other, and then joining and releasing the coupled pair while remaining itself unchanged by the procedure: a little like a dating agency. In the Heck reaction, the first molecule always contains carbon bonded to a halogen atom, such as chlorine, and the second always contains a carbon-carbon double bond. Remarkably, the reaction works at room temperature.
Ei-ichi Negishi and Akira Suzuki, who incidentally had both worked with Herbert Brown, the 1979 Nobel Laureate in Chemistry, extended the range of applicability of the Heck reaction, principally by developing ways of varying the second component molecule. The double-bond-containing molecule is replaced by an organozinc molecule in the Negishi reaction, and by an organoboron molecule in the Suzuki reaction. Together, these three reactions, and the variants that have since followed, have dramatically improved both the potential and the efficiency of synthetic organic chemistry and contributed substantially to the building of the complex molecules which contribute to so many areas of our daily lives, from agriculture to medicine.