Metalation behavior of a bis-saturated NHC ligand with a flexible m-xylyl linker

摘要

Saturated N-heterocyclic carbenes have unique ligand properties that differ even from their unsaturated analogs. While the unsaturated version has been extensively used in multidentate ligand scaffolds, the incorporation of the saturated version is less common. Here we report the straightforward synthesis of a new bis-saturated N-heterocyclic carbene ligand wherein the carbene moieties are linked by a flexible meta-xylyl unit. Carbene metal complexes of the proligand can be generated by direct metalation, transmetallation or base assisted metalation all of which lead to monodentate coordination modes of silver or iridium. Attempts at direct metalation using zirconium tetrakis-dimethylamide did not lead to complex formation but to the chloroform adduct or amide addition product. As yet, a method to generate pincer complexes from this ligand has not been found. The flexible nature of the xylyl linker as well as the higher sigma-bacisity and -acidity are postulated to contribute to these results.