Multidentate NHC ligands

Figure 3.20 Architectures of complexes of multidentate, pyridine functionalised NHC ligands.

The many synthetic methods available for preparing NHCs have allowed for their ready incorporation into an increasingly diverse set of multidentate ligands. The topic of chelating ligands containing NHCs has been covered in several reviews.Heteroleptic variations have included phosphines, amines, imines, pyridines, oxazolines, amides, alkoxides, aryloxides, thioethers, and other donors. 

Several of the factors that appear to be important in preventing reductive elimination include the use of multidentate ligands, the employment of ancillary ligands that restrict the bite angle and the steric size of the substituents on the NHC and the electronics of these substituents. 

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