Electronic and mechanistic studies of a biomimetic small-molecule catalyst capable of oxygen-dependent alkane oxidations

The productive, controlled activation of O2 via small-molecule catalysts remains a significant challenge to bioinorganic chemistry. With enzymes, global folding energies dictate the positioning of ligands to optimize chemical pathways. Synthetic iron catalytic complexes, with open or labile coordination sites, frequently give rise to Fenton-like radical-based reactions. To minimize such peroxide/hydroxyl radicals, we developed a synthetic model for the 2-oxoglutarate-dependent dioxygenases, [FeII(N2O1)]- (N2O1 = 2-((2-dimethylamino)ethyl)-(methyl)amino)acetic acid) . We present herein an iron-based synthetic analogue system capable of utilizing dioxygen to perform velut vivum C ‒ H activation at ambient temperatures and pressures. The relationships between a range of α-ketocarboxylate adducts producing metal-to-ligand charge transfer band energies and their corresponding π → π* energy gaps (DFT simulated) are described. Electronic (MCD) and computational (DFT) methods are combined to elucidate the electronic structures of a subset of these adducts. Catalytic efficiency of 15 α-ketocarboxylates is investigated and includes the use of oxalate. The latter represents an original example of a small-molecule synthetic catalyst capable of activating O2 while using oxalate as a cofactor for C ‒ H oxidation. A series of varying N,N,Ox (x = 1 ̶ 3) carboxylate-ligated ferrous, ferric, and chromic complexes was assessed for chemical and electronic influences of increasing carboxylate metal ligation. Electrochemical and spectroscopic characterization, and initial reactivities were examined. The use of the same ligand set but with differing ‘d-electron count’ explores mechanistically dramatic changes to chemical reactivity in the presence of a terminal oxidant. A methodology for the functionalization of the N2Ox (x = 1 ̶ 3) ligand series, using an alkynyl moiety, was also developed. Such could allow ‘click’ chemistry for converting homogeneous catalysts to heterogeneous versions. Using a globally uniform and diffuse low loading resin will provide enhanced catalyst lifetime by diminishing inactivation pathways and support its use in flow chemistry reactors using O2 from air as the oxidant