Synthesis, characterization, and reactivity of iron complexes with N-donor ligands in relation to oxygenation of hydrocarbons

This study examines structural and functional aspects of reactivity of Gif-type reagents, which depend on dioxygen and zinc in pyridine/pivalic acid mixtures. In these solutions, the μ-oxo bridged [Fe₃O(O ₂CCMe₃)₆(py)₃] is reduced by Zn to generate [Fe(II)(O₂CCMe₃)₂(py)₄], which readily reverts to [Fe₃O(O₂CCMe₃) ₆(PY)₃], and eventually to [Fe₃O(O₂CCMe ₃)₆(PY)₃]+, upon exposure to dioxygen. All three species mediate Gif-like oxygenation of substrates supported by O₂/Zn and to a smaller extent by H₂O₂. Product profiles are indicative of competition between dioxygen and protonated pyridine to capture tert- and sec-alkyl radicals. The tert/sec selectivities and other diagnostic parameters are consistent with those of other Gif-type oxygenations, suggesting the involvement of HO· and a more selective, substrate-based tert-alkoxyl radical. All-ferric [Fe(III)₃O(O₂C-CMe ₃)₆(L)₃]+ (L = H₂O, py) are converted by H₂O₂ to the hexairon(III) peroxo compounds [Fe₆(O₂)(O)₂(O₂CCMe ₃)₁₂(L)₂] (L = Me₃CCO₂H, py), (between 7–80% yield) which feature a [Fe₆(η 2-μ4-O₂)(μ3-O) ₂] core, and are not involved in Gif oxygenations.; The second part of this dissertation explores the synthesis and reactivity of a series of metal complexes containing novel ligands (L1H ₃):[(4-tert-Butyl-C₆H₄)-NH-( ortho-C₆H₄)]₃N and (L2H ₃):[(3,5-di-tert-Butyl-C₆H₃)-NH-( ortho-C₆H₄)]₃N. The ferrous species [(L1)Fe(II)-NCMe][Ph₄P] is a crystallographically characterized representative of a series of complexes of type [(L1 )Fe(II)-solv]− (solv = NCCH₃, DMF, THF). These complexes are exceedingly air sensitive and can be readily oxidized by dioxygen to afford [(L)Fe(III)-solv], [(L)Fe(III)-OH]− (K+ or PPh₄+ salts) and [(L 1_re-1)Fe(III)-O-Fe(III)(L1_re-1)] depending on the solvent used. The most intriguing product is [(L1 _re-1)Fe(III)-O-Fe(III)(L1_re-1)], which features ligand rearrangement amounting to a formal 1,4-phenyl migration. This is also accompanied by one-electron oxidation of the ligand, localized onto an aromatic amine/imine moiety. The ligand is also capable of sustaining a two-electron oxidation, as observed in the reaction of [(L)Fe(III)-solv] with FeCl₃, to afford [(L1_re-2H)(Cl)Fe(II)-(μ-Cl) ₂-Fe(II)(Cl)(L1_re-2H)]. Ligand rearrangement is also observed with other redox active metals. For instance, [(L)Mn(II)-THF] − is oxidized by dioxygen to [(L1_re-1)Mn(III)-(μ-O) ₂-Mn(III)(L1_re-1)]. Changing metal center to CrCl₃ afforded [(L)Cr(III)-THF] and [(L1 _re-1)(Cl)Cr(III)-THF].; Regardless of the metal center employed, reactions of ligand (L 2H₃) afforded the mononuclear complexes [(L2 _re)M(III)-THF], where M = Fe...