Poly-NHCs ligands pincer

Lots of previously unreported poly-NHC ligands have been disclosed in the literature during the last 5 years. However, most of the investigations can be categorized according to a small number of target compound classes, namely (i) chiral poly-NHC ligands (ii) pincer or pseudopincer poly-NHC... 

The development of CTOwn ether functionalised imidazolinm salts starts from the consideration that it is possible to link one polyether chain with two imidazolinm nnits at the end points. Since a transition metal can coordinate two imidazoUnm salts in trans fashion [131,162,208], two of these (poly)ether fnnctionaUsed bis-carbenes can form a macrocychc crown ether type hgand system with two transition metal carbene linkages. In favonrable cases, a pincer type C,0,C ms-coordination to the same transition metal is conceivable, bnt may not be very likely when the great affinity of late transition metals to NHC ligands and the aversion of these same late transition metals to ether donor Ugands is taken into account. However, hanilabile stabilisation of transition metal complexes in catalytic processes can certainly be hoped for. 

Figure 2 Recently developed poly-NHC pincer and pseudopincer ligand architectures.

---