NHCs with saturated backbone

Precursors for NHCs with Saturated Backbone (Imidazolidin-2-ylidenes)... 

Based on these findings, another starting point for modifications besides modifying the labile coligand is the NHC ligand itself, especially since there are many more carbenes known and accessible. One of the many possible modifications turned out to be very successful and can—based on its catalytic activity and catalyst lifetime—be considered as the third generation of NHC catalysts in olefin metathesis. The recipe for success is to use NHCs with saturated backbones, i.e., imidazolidin-2-ylidenes. ... 

Another possibility to anchor the NHC unit to a polymeric support is to attach the linker unit to the imidazole backbone rather than using the wingtip group for it. This approach was realised by Connon and Blechert with a saturated functionalised NHC ligand (see Figure 4.76) [245]. There is no real advantage to this approach other than having a saturated NHC as opposed to an unsaturated one. 

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