Research into new and efficient catalytic systems based on Earth-abundant metals represents a significant challenge for chemistry.¹ A key prerequisite to reach this goal is the availability of suitable ligands to stabilize the metal center. This field has been considerably stimulated by the discovery of N-heterocyclic carbenes (NHCs) as ligands that impart unique properties.² Triazolylidenes are a subclass of NHCs that are excellent σ-donors and have great electronic flexibility,³ which allows for the stabilization of a wide variety of oxidation states of transition metals. Furthermore, their convenient synthetic modification provides access to heteroatom-functionalized NHCs for chelation.

Here we will present a facile and versatile synthesis of mesoionic ligands bearing a potentially chelating hydroxide moiety on the triazole scaffold as well as a new class of nickel(II) complexes containing these C,O-bidentate chelating mesoionic carbenes starting from a cheap and simple metal precursor. These nickel complexes show excellent activity and selectivity in CO₂ reduction, demonstrating great benefit of the hydroxyl group as chelating moiety for both the synthesis and the catalytic application of Earth-abundant metal complexes.

[1] R.M. Bullock, “Catalysis without precious metals”, 2011, Wiley-VCH, Weinheim, Germany.
[2] K.H. Dötz, J. Stendel, Chem. Rev. 2009, 109, 3227; F.E. Hahn, M.C. Jahnke, 2008, 47, 3112; W.A Herrmann, Angew. Chem. Int. Ed., 2002, 41, 1290.
[3] J.D. Crowley, A. Lee, K. J. Kilpin, Aust. J. Chem., 2011, 64, 1118; K.F. Donnelly, A. Petronilho, M. Albrecht, Chem. Commun., 2013, 49, 1145.