When is a catalyst not a catalyst?
This riddle has come to vex certain corners of the catalysis community. But once solved, it could potentially point to new kinds of chemistry, as James Mitchell Crow discovers
The story typically starts with a known catalytic reaction - a carbon-carbon bond forming cross-coupling reaction, say - that relies on a noble metal catalyst such as palladium or platinum. With the growing awareness that such metals are a finite resource, as well as expensive, seeking ways to carry out the same key reactions with a more abundant metal such as copper or iron - or even ditching the metal altogether - has become a hot topic of research.
In many cases, alternative catalysts to noble metals have been successfully found. But a spate of recent examples present a cautionary tale that all might not necessarily be as it first appears - that a trace impurity in the reaction mixture might be the catalytically active species. And even experienced chemists can be caught out.