The majority of NHC complexes have been prepared from cyclic azolium precursors which upon C2 deprotonation yield the free NHC which then coordinates to a given metal center. We found that neutral azoles like N-methyl-2-chlorobenzimidazole react with Ni0, Pd0 or Pt0 under oxidative addition to give complexes with an anionic NHC ligand featuring an unsubstituted ring-nitrogen atom 1  . Protonation of such ligands yields NHC ligands with an NH,NMe-substitution pattern as in 2  and reaction with dihydrogen leads to a heterolytic cleavage of H2 and complex 3 . This oxidative addition can also be utilized to generate carbene complexes by C-metallation of biomolecules like 8-bromocaffeine or 6-bromoadenine.

Synthesis of complexes with protic NHC ligands by oxidative addition of neutral azoles or N-alkylazoles to transition metals

247th National Meeting (2014)

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