Anionic N-heterocyclic carbenes (NHCs): a versatile route to saturated NHCs bearing pendant weakly coordinating anions.

A versatile methodology is reported for the synthesis of anionic NHCs featuring a 5-, 6-, or 7-membered saturated heterocyclic core. Lewis acid promoted exocyclic ring closure generates systems in which the pendant borate functionality is incorporated via a CH2 linker, allowing for electronic and steric isolation of the anionic component. Hence, a library of NHCs can be accessed which incorporate metal binding environments essentially identical to the neutral parent donors, but with significantly altered solubility profiles.