Phosphinoquinoline supported Co^II, Ni^II, and Fe^II complexes: divergent behaviour upon reduction

The reduction of [CoLBr2], a Co^II complex supported by a diisopropylphosphinoquinoline (L) ligand, induced a ligand coupling giving access to a (PNNP) supported Co^II complex which was isolated in 70% yield. This complex was formed using a minimum of 2 equivalents of a reductant (either Mn or KC₈). The fate of [CoLBr2] in the presence of 1 equivalent of a reductant was more difficult to study; nevertheless, a Co^I complex was characterised in the solid state. In order to determine whether this ligand coupling could occur with other 3d metals, L supported Fe^II and Ni^II complexes were synthesised. While no compound could be identified upon reduction of [FeLBr2], both [NiLBr2] and [NiL2Br](Br) led to the reduction at the metal center allowing the isolation of an original Ni⁰ trimer in a satisfactory yield. This study shows the different behaviours of these 3d metal complexes in the presence of a reductant.