New ligand on the block

UK scientists have found an alternative to the cyclopentadienyl (Cp) ligand, historically the dominating anion in olefin polymerisation catalysis.

The recent shifting emphasis in catalyst developments, where specific reactivity such as tolerance to functional groups, now takes priority, has challenged Cp’s position as the ligand of choice.

Martyn Coles and colleagues from the University of Sussex have incorporated boron into alkoxide ligands to make a new boroxide ligand.

When bound to titanium or hafnium these ligands take electron density away from the metal centre, one of the criteria for an active group four metal catalyst.

Having a boron atom present has geometrical benefits as well, because it isolates organic groups from the metal.

This is the first time that a boroxide anion has coordinated to an early transition metal, and shows that these ligands can make metal centres electrophilic, and ideal for active catalysis.

Coles and his group will continue developing their catalysts, with an eye to making an ethylene polymerisation catalyst suitable for industrial use.

Lorna Jack