Rotational rigidity at room temperature

Metal arylphosphine complexes that are rigid above room temperature have been studied for the first time by a team from the University of Bristol, UK.

Arylphosphine ligands are widely used in coordination chemistry and their metal complexes catalyse a staggering range of reactions. Their chiral, propeller-like, stereochemistry is largely destroyed by rapid P-C bond rotation.

Bond rotation in these metal arylphosphine complexes is so slow that diastereomeric rotamers of these compounds have been observed above room temperature for the first time.

Paul Pringle and Guy Orpen’s group studied the conformation of the ligands by variable temperature NMR spectroscopy and found chiral rotational isomers at temperatures as high as 100?C.

This rigidity cannot be seen in a lab timescale of minutes but the fact that it is revealed by NMR means it would have an impact in the time taken for a chemical reaction.

Pringle and Orpen believe this could have implications for catalysis, where such a rigid stereochemistry could give great control over the reaction products.

Neil Withers