Piano-stool N-heterocyclic carbene iron complexes: Synthesis, reactivity and catalytic applications

This review summarises the advances of N-heterocyclic carbenes (NHCs) as ligands to iron half-sandwich complexes, often referred to as piano-stool complexes because of their structural motif. The review introduces various synthetic routes towards this sub-class of NHC iron-complexes including in particular direct and transmetallation strategies as well as the synthesis of the carbene directly within the iron coordination sphere. Many of these complexes have demonstrated promising reactivity that is relevant to the arenas of catalysis and materials chemistry. In particular, bond activation (e.g. C-H, Si-H, H-H) processes provide exciting new opportunities to exploit these systems for stoichiometric and catalytic transformations. Substantial advances have been achieved specifically in the catalytic reduction of unsaturated substrates, and this topic is emphasised in particular. (C) 2017 Elsevier B.V. All rights reserved.