Metal-ligand cooperation behaviour of Fe and Co complexes bearing a tetradentate phenanthroline-based PNNP ligand

This perspective article describes the synthesis of a series of Fe and Co complexes coordinated with a phenanthroline-based meridional PNNP ligand (2,9-bis((diphenylphosphino)methyl)-1,10-phenanthroline). PNNP-iron(II) dichloride and -cobalt(I) chloride, [FeCl2(PNNP)] and [CoCl(PNNP)], underwent abstraction of the benzylic H-atom upon treatment with NaOtBu, forming the corresponding deprotonated products [FeCl(PNNP')] (1) and [Co(PNNP')] (2), respectively, each of which bears an asymmetrical PNNP' ligand with a dearomatized phenanthroline backbone as a good metal-ligand cooperation (MLC) scaffold. Complex 2 achieved facile H-H bond cleavage mediated by unique long-range MLC, where the PNNP backbone acts as a H-atom reservoir.