Three iron complexes of a pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy(3)H, H is the dissociable amide proton) have been synthesized. All three species, namely, two nitrosyls [(PaPy(3))Fe(NO)](ClO(4))(2) (2) and [(PaPy(3))Fe(NO)](ClO(4)) (3) and one nitro complex [(PaPy(3))Fe(NO(2))](ClO(4)) (4), have been structurally characterized. These complexes provide the opportunity to compare the structural and spectral properties of a set of isostructural [Fe-NO](6,7) complexes (2 and 3, respectively) and an analogous genuine Fe(III) complex with an "innocent" sixth ligand ([(PaPy(3))Fe(NO(2))](ClO(4)), 4). The most striking difference in the structural features of 2 and 3 is the Fe-N-O angle (Fe-N-O = 173.1(2) degrees in the case of 2 and 141.29(15) degrees in the case of 3). The clean (1)H NMR spectrum of 2 in CD(3)CN reveals its S = 0 ground state and confirms its [Fe-NO](6) configuration. The binding of NO at the non-heme iron center in 2 is completely reversible and the bound NO is photolabile. Mössbauer data, electron paramagnetic resonance signal at g approximately 2.00, and variable temperature magnetic susceptibility measurements indicate the S = (1)/(2) spin state of the [Fe-NO](7) complex 3. Analysis of the spectroscopic data suggests Fe(II)-NO(+) and Fe(II)-NO(*) formulations for 2 and 3, respectively. The bound NO in 3 does not show any photolability. However, in MeCN solution, it reacts rapidly with dioxygen to afford the nitro complex 4, which has also been synthesized independently from [(PaPy(3))Fe(MeCN)](2+) and NO(2)(-). Nucleophilic attack of hydroxide ion to the N atom of the NO ligand in 2 in MeCN in the dark gives rise to 4 in high yield.

Although Co(III)-alkyl peroxo species have often been implicated as intermediates in industrial oxidation of hydrocarbons with cobalt catalysts, examples of discrete [LCo III -OOR] complexes and studies on their oxidizing capacities have been scarce. In this work, twelve such complexes with two different ligands, L, and various primary, secondary, and tertiary R groups have been synthesized, and seven of them have been characterized by X-ray crystallography. The dianion (L 2-) of the two ligands N, N-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide (Py 3 PH 2 , 1) and N, N-bis[2-(1-pyrazolyl)ethyl]pyridine-2,6-dicarboxamide (PyPz 2 -PH 2 , 2) bind Co(III) centers in pentadentate fashion with two deprotonated carboxamido nitrogens in addition to three pyridine or one pyridine and two pyrazole nitrogens to afford complexes of the type [LCo III (H 2 O)] and [LCo III (OH)]. Reactions of the [LCo III (OH)] complexes with ROOH in aprotic solvents of low polarity readily afford the [LCo III -OOR] complexes in high yields. This report includes syntheses of [Co(Py 3and [Co(PyPz 2 P)(OOR)] complexes with R ) t Bu (13), Cm (14), CMe 2 CH 2 Ph (15), Cy (16), i Pr (17) or n Pr (18). The structures of 8-12 and 16 have been established by X-ray crystallography. Complexes 10 and 16 are the first examples of structurally characterized compounds containing the [Co-OOCy] unit, proposed as a key intermediate in cobalt-catalyzed oxidation of cyclohexane. The metric parameters of 7-12 and 16 have been compared with those of other reported [LCo III -OOR] complexes. When these [LCo III -OOR] complexes are warmed (60-80 °C) in dichloromethane in the presence of cyclohexane (CyH), cyclohexanol (CyOH) and cyclohexanone (CyO) are obtained in good yields. Studies on such reactions (referred to as stoichiometric oxidations) indicate that homolysis of the O-O bond in the [LCo III -OOR] complexes generates RO • radicals in the reaction mixtures which are the actual agents for alkane oxidation. [LCo-O• ], the other product of homolysis, does not promote any oxidation. A mechanism for alkane oxidation by [LCo III -OOR] complexes has been proposed on the basis of the kinetic isotope effect (KIE) value (5 at 80 °C), the requirement of dioxygen for oxidation, the dependence of yields on the stability of the RO • radicals, and the distribution of products with different substrates. Both L and R modulate the capacity for alkane oxidation of the [LCo III -OOR] complexes. The extent of oxidation is noticeably higher in solvents of low polarity, while the presence of water invariably lowers the yields of the oxidized products. Since [LCo III -OOR] complexes are converted into the [LCo III (OH)] complexes at the end of single turnover in stoichiometric oxidation reactions, it is possible to convert these systems into catalytic ones by the addition of excess ROOH to the reaction mixtures. The catalytic oxidation reactions proceed at respectable speed at moderate temperatures and involve [LCo III -OOR] species as a key intermediate. Turnover numbers over 1...