Complexes bearing NR,NH-substituted N-heterocyclic carbenes can be prepared by reaction of 2-chloro-N-alkylbenzimidazoles with complexes of zero-valent transition metals followed by protonation with NH4BF4. The reaction proceeds by an initial oxidative addition of the C�Cl bond to the transition metal. The intermediate obtained this way reacts with acids under protonation of the ring nitrogen atom and formation of an NR,NH-substituted NHC ligand. In the absence of protons, the intermediate formed by the oxidative addition dimerizes with formation of new bonds between the free ring nitrogen atoms of one molecule and a metal atom of a neighboring molecule. Alternatively, the anionic ring nitrogen atom of the C2-metallated benzimidazole can attack solvent molecules like CH2Cl2 with formation of a new N�C bond and an NR,NR'-NHC ligand. The utility of the oxidative addition reaction for the C-metallation of nucleosides will be discussed.

Synthesis of NHC complexes by oxidative addition of 2-halogenato-<i>N</i>-alkylbenzimidazoles

243rd National Meeting (2012)

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Synthesis of NHC complexes by oxidative addition of 2-halogenato-N-alkylbenzimidazoles