Iron tris-mesityl: a homoleptic iron(ii) ferrate species for directed C-H activation

C-H activation is a vital synthetic tool due to its superior atom economy and improved step efficiency making it amendable to late-stage functionalisation. In recent years iron has been gaining traction within this field due to its high abundance, low cost and low toxicity. Iron(0) phosphines for C-H activation via oxidative addition are well documented, however, only a handful of iron(ii) complexes competent at C-H activation via ligand-to-ligand hydrogen atom transfer (LLHT) or σ-bond metathesis have been identified. Herein we report the first homoleptic iron species capable of facilitating C-H activation, introducing a new class of well-defined iron(ii) complexes for this purpose, and detail the synthesis and characterisation of a range of tris-cyclometalated iron complexes using a variety of pyridine derived substrates. Density functional theory (DFT) calculations reveal that the C-H activation proceeds through a σ-bond metathesis pathway.