Reactions involving organometallic catalysts can now be watched as they happen, thanks to research cooked up at the University of Victoria in Canada. 

Scott McIndoe and colleagues have been investigating the processes involved in catalytic reactions. 'We know what goes into the pot, and what comes out, but often the identities of the active catalytic species are shrouded in doubt,' said McIndoe. Electrospray ionisation mass spectrometry (ESI-MS), with its 'remarkable sensitivity, speed and ability to cope with complex mixtures', would be the ideal tool for looking at the catalytic species, except that most organometallic species are neutral and it is difficult to ionise them. 'We needed a ligand with functionality that would very readily acquire a charge but otherwise not interfere with the reaction of interest,' explained McIndoe.

The researchers chose phosphine ligands based on 1,8-bis(dimethylamino)naphthalene, or Proton Sponge^TM, which, as its commercial name suggests, bonds very readily to protons. This gives the compound an electrical charge allowing it to be detected by ESI-MS. 

Richard O'Hair, an expert in mass spectrometry at the University of Melbourne, Australia, said the ligands were cleverly designed. 'These phosphine ligands show considerable promise to directly monitor metal catalysts and their reactions,' he said. 

Bill Henderson, professor of chemistry at the University of Waikato in New Zealand, said, 'an added bonus is that the ligand solubility can be tuned by altering the protonation state, with the unprotonated ligand dissolving in typical organic solvents, while the protonated ligand is soluble in water.' 

But the picture provided by ESI-MS is by no means complete. McIndoe points out that the method does not distinguish active catalytic states from resting states, and plans to address this by studying reactivity in the gas phase.  

Colin Batchelor