Chemists have developed a solvent- and metal-free coupling reaction for creating carbon-carbon bonds. 

Rafael Luque and Duncan Macquarrie, at the University of York, UK, used an amine base called 1,4-diazabicyclo(2.2.2)octane (DABCO) to promote the Sonogashira coupling of phenyl acetylene and electron-deficient iodoarenes. Sonogashira reactions are usually catalysed by a palladium(0) complex and a copper halide salt but Luque says that it can be difficult to remove all traces of the metals from reaction mixtures. 

'The idea of a metal-free coupling reaction has always been the dream of every organic chemist,' says Luque. 'Furthermore, if apart from being metal free, the reaction is also efficient, cost-effective (compared to transition metal protocols) and more environmentally friendly, we have a great advantage for the future.' 

Using only DABCO as the catalyst, Luque formed the coupled products with good yields, selectivities and reaction times, especially when the reactions were done in the microwave. He says he hopes to extend the scope of the protocol to more hindered substrates and investigate the used of related bases in the place of DABCO. 

'The protocol clearly works very well for electron-deficient iodoarenes,' comments Luque, 'but it does not work too well with electron-rich arenes or any other haloarenes. The main challenge will be to extend the protocol's scope to improve the range of target compounds that can be synthesised.' 

Joanne Thomson