Oxidative addition of 2-halogenoazoles-direct synthesis of palladium(II) complexes bearing protic NH,NH-functionalized NHC ligands

The chemistry of N-heterocyclic carbenes (NHCs) is dominated by N,N'-dialkylated or -diarylated derivatives. Such NHC ligands are normally obtained by C2-deprotonation of azolium cations or by reductive elimination from azol-2-thiones. A simple one-step procedure is described that leads to complexes with NH,NH-functionalized NHC ligands by the oxidative addition of 2-halogenoazoles to complexes of zero-valent transition metals.