Metal-ligand cooperativity across two sites of a square planar iron() complex ligated by a tetradentate PNNP ligand

An iron( ii ) complex with a square planar geometry and S = 1 ground state was synthesized using a rigid tetradentate bisphosphine-bisamide [PNNP] 2− ligand. This complex was shown to bind an equivalent of PMe 3 to produce a five-coordinate low spin complex, and to react with two equivalents of borane reagents via addition of two B-H bonds across the metal-amide bonds in a metal-ligand cooperative fashion. A square planar (PNNP)Fe II complex is shown to readily activate two B-H bonds across the Fe-amide linkages in an overall four-electron process facilitated by metal-ligand cooperativity.