A new method of functionalization of widely-used methylene-bridged bis(NHC) ligand systems is presented, which still allows a fine-tuning of the electronic and steric properties of the bidentate ligand as compared with the other methods of modifying the wingtip and imidazole backbone of the bis(NHC) ligand. On one hand, three hydroxy-methyl-functionalized imidazolium salts with different wingtip groups (L1-L3 ) as well as three different transition-metals bis(NHC)complexes (Pd, Pt, Ir) C1  -C3  could be successfully synthesized. On the other hand,the hydroxyl substituent of complex C1  could be quantitatively converted to chloro-substituent bis(NHC) Pd-complex G1  , which further demonstrates the tunability of this ligand system. Notably, the introduction of the hydroxyl group into methylene-bridged bis(NHC) ligand systems provide the possibility to further extend the application of the widely-used methylene-bridged bis(NHC) complexes to different areas of research such as recyclable catalysts and water-soluble catalysts. In our preliminary work, two different synthetic routes were tested to immobilize the bis(NHC) Pd-complex C1  on polystyrene via the functional group. The obtained heterogeneous catalyst H1  was applied in Suzuki-Miyaura cross-coupling reactions and could be recycled without obvious loss of activity in four runs. Furthermore, the water-soluble homogeneous catalysts C1  itself, could be employed for Suzuki-Miyaura cross-coupling reactions in water. It is reasonable to say this ligand system could provide a useful tool to further extend the widely-used methylene-bridged bis(NHC) complexes to many more applications.

Hydroxylmethyl functionalizing the methylene-bridge of bis(NHC)-ligands: Water-soluble or immobilized molecular catalysts, yet tunable

248th National Meeting (2014)

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