Iron Coordination Chemistry of Phenylpyruvate:  An Unexpected κ 3-Bridging Mode That Leads to Oxidative Cleavage of the C2−C3 Bond

One mononuclear iron(II)−phenylpyruvate complex [TpPh2FeII(PPH)] (1) of the tridentate face-capping TpPh2 ligand and two dinuclear iron(II)−phenylpyruvate enolate complexes [(6-Me3-TPA)2FeII 2(PP)]2+ (2) and [(6-Me3-TPA)2FeII 2(2-NO2-PP)]2+ (3) of the tetradentate 6-Me3-TPA ligand are reported to demonstrate two different binding modes of phenylpyruvate to the iron(II) centers. Phenylpyruvate binds in a κ 2-(O,O) manner to the mononuclear FeII(TpPh2) center of 1 but bridges in a κ 3-(O,O,O) fashion to the two FeII(6-Me3-TPA) centers of 2 and 3. Mononuclear complex 1 reacts with O2 to undergo oxidative decarboxylation and ortho-hydroxylation of one of the aromatic rings of the TpPh2 ligand. In contrast, dinuclear complexes 2 and 3 react with O2 to undergo oxidative cleavage of the C2−C3 bond of phenylpyruvate.