Nitrenium hugs stabilise positively rare complexes


Gandelman's team have successfully made rhodium (pictured) and platinum forms of the unusual complexes

Everyone knows that like charges repel one another. But unusual coordination compounds bearing cationic ligands bound to cationic metals have been prepared by scientists in Israel, opening up fresh opportunities for organic transformations.

When two positively charged chemical species are brought together they experience counteracting forces. One is Coulombic repulsion, and the other is attraction due to the bonding interactions between the nuclei of one cation and the electrons of the other. Thermodynamically unstable bonds ensue from the interplay of these opposing interactions.

Rather than being thermodynamically stable, the transition metal complexes made by Mark Gandelman from the Israel Institute of Technology in Haifa and colleagues manage to be kinetically stable. Pincer-type ligands with nitrenium moieties at their centre, that are essentially the nitrogen analogues of N-heterocyclic carbenes, are central to the complexes' creation. Computational investigations reveal that the coordination geometry of the pincer ligand provides the kinetic barrier to dissociation of the nitrogen–metal bond; the two phosphine arms aid coordination by bringing the metal within close proximity of the central nitrogen.

The tridentate pincer ligands provide a kinetic barrier to dissociation of the nitrogen–metal bond

For Gandelman, these compounds aren’t just incredibly rare, they have great potential for catalytic transformations requiring electrophilic species. ‘Cationic metals are good for electrophilic catalysis; cationic ligands also proved good for such catalysis, so we have a situation that can benefit from both – cationic ligand bound to cationic metal.'

Organic chemist Gerard van Koten, of Utrecht University in the Netherlands, agrees that this clever chemistry has much scope for application. ‘The novel nitrenium metal–d8 complexes, containing an extremely rare L+–M+ interaction, are a spectacular demonstration of the power of the tridentate pincer ligand platform; the small kinetic stability of the central nitrenium cation–metal cation interaction is greatly enhanced by the flanking interactions of two ligand-to-metal bonds. These complexes provide a model for novel types of highly electrophilic, cationic metal catalysts.’


Related Content

Phosphorus fragments trapped

11 April 2010 News Archive

news image

Carbenes have been used to trap and stabilise rare and elusive forms of phosphorus

What can U do?

21 January 2014 Premium contentFeature

news image

Actinide chemistry is reaching beyond nuclear and revealing surprising behaviour, finds Andy Extance

Most Read

Lawrencium experiment could shake up periodic table

9 April 2015 Research

news image

Measurement of first ionisation energy confirms electronic configuration but opens up an important debate

Super-fast charging aluminium batteries ready to take on lithium

7 April 2015 Research

news image

New battery charges in under a minute and still performs perfectly after being recharged thousands of times

Most Commented

Women twice as likely to be hired for academic posts as men

17 April 2015 News and Analysis

news image

Experiment shows that faculty staff are more likely to pick women for job roles based on hypothetical CVs

Big problems with little particles?

9 April 2015 Feature

news image

There is a risk that poor toxicology studies could start undermining the success of nanomaterials, reports Elinor Hughes