We devote significant time to in studying systems able accommodate both metal-based and ligand-based redox processes in the context of base metals (i.e. iron, cobalt and manganese). This strategy often allows the development of difficult catalytic transformations or of inert bond activation.

Alkyne trimerization and [2+2]-cycloaddition. Pyrimidinediimine scaffolds are π-acidic analogues of the well-established pyridine-based analogues but with increase robustness under reductive catalytic conditions. The reduced propensity towards deactivation has enabled the development of examples of the most active cycloaddition catalysts based on iron. A first general 1,3,5-selective alkyne trimerization reaction proceeds via an iron 1,3-metallacycle intermediate which could be isolated and characterised. Pyrimidinediimine iron complexes also enabled the development of a highly efficient [2+2] cycloaddition of unactivated olefins to yield cyclobutene rings fused with N-heterocycles of pharmaceutical relevance (pyrrolidines, piperiazies and azepanes). Many of building-blocks resulting from this method cannot be obtained through alternative synthetic methods and have led to the development of unique molecular motifs (Figure 1C). The investigation of the catalytic active species through spectroscopic and computational methods have allowed a lowering of the catalyst loading down to 0.5 mol% in some cases. The resulting motifs are amenable towards downstream functionalisation to yield unique cage-like tricyclic β-lactams.

Hydroelementation catalysis. This stability of pyrimidinediimine complexes under reductive conditions was applied in cobalt-catalysed hydroboration. Intriguingly, we could establish that the “inert” gas employed (argon vs. nitrogen) has a determining role in the identity of the active species which further influences the catalytic activity observed. Another class of iron-based pincer ligands (PNN scaffold) are highly active in olefin hydrogenation at very low catalyst loadings (0.1 mol%) and low H2 pressures. If parahydrogen is employed, hyperpolarisation transfer is observed with enhancement factors up to ca. 2500 in 1H and 19F NMR spectroscopy.