Dioxygen Adducts of Lacunar Cobalt(II) Cyclidene Complexes

Busch, Daryle H.; Jackson, Patricia J.; Kojima, Masayasu; Chmielewski, Piotr J.; Matsumoto, Naohide; Stevens, James C.; Wu, Wei; Nosco, Dennis L.; Herron, Norman; Ye, Naidong; Warburton, P. Richard; Masarwa, Mohamad; Stephenson, N. C.; Christoph, Gary G.; Alcock, Nathaniel W.

doi:10.1021/ic00083a015

Cited by 29 publications

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“…For both complexes, C6 and C8, the binding rate constants increased by two and three orders of magnitude, and the affinities by four orders of magnitude, with C8 having both a higher carbon monoxide affinity and rate of binding than for the C6 complex. These conclusions parallel what has been reported for the dioxygen affinities of cobalt(II) cyclidene complexes. ,,, …”

Section: Resultssupporting

confidence: 90%

“…The width of the cavity, as measured between the two bridgehead nitrogens, increases rather smoothly from 5.4 Å to 7.8 Å, when the bridging group (R 1 ) is increased in length by the addition of methylene units, starting with tetramethylene and proceeding to octamethylene. This structural change produces a large variation in the steric hindrance encountered by a small molecule binding at the metal center. ,,− The corresponding equilibrium constants and rate constants for carbon monoxide binding are shown in Table .…”

Section: Resultsmentioning

confidence: 99%

“…In summary, the cyclidene family of complexes is particularly useful for the exploration of the fundamental structure−function relationships of dioxygen carriers for the following reasons. (1) Small molecule binding depends strongly on ligand substituents. ,,− (2) Cyclidene structures are easily varied in several appropriate ways. (3) Much highly detailed structural information is available on cyclidene complexes. , (4) And because of its preferred conformation, the 16-membered cyclidene ring is especially facilitative of formation of a lacuna 26 within which the small molecule can bind.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of CO Binding to Lacunar Iron(II) Cyclidene Complexes

et al. 1997

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The kinetics of carbon monoxide binding and dissociation have been studied for a series of lacunar iron-(II) cyclidene complexes to elucidate the dependence of dynamic parameters on the various structural features of these versatile compounds. Ligand substituents have large effects on the binding and dissociative rate constants, and remarkably, four distinctly different steric effects have been observed. (1) Changing cavity size alters the rate of CO binding by as much as 4 orders of magnitude, presumably by constraining access to the metal ion. (2) Decreases in cavity size also can increase the rate of CO dissociation by a factor of 10 or so. (3) Placing bulky groups in the path CO must follow to enter the cavity decreases the rate of binding because of steric effect (1), but these same obstructions may also decrease the rate of dissociation by blocking the escape path and, possibly, fostering geminate recombination. (4) Proximal ligand strain both decreases the rate of binding and increases the rate of CO dissociation. In contrast, changes in the iron(III)/(II) redox potential, which accompany ligand substitutions, were found to have only a small impact on CO binding kinetics. The effects on the rate constants of the basicity of the axial base and of solvent polarity were also investigated.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dynamics of CO Binding to Lacunar Iron(II) Cyclidene Complexes

et al. 1997

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“…8,9 In models of biological oxygen carriers, Cavin et al, for example, have extensively examined the oxygen carrier properties of cobalt(II) complexes with SALEN ligands. 10 In addition, the synthetic complexes have potential applications in dioxygen separation and storage.…”

Section: Introductionmentioning

confidence: 99%

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

et al. 2016

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The reactivity of mononuclear metal-hydroperoxo adducts has fascinated researchers in many areas due to their diverse biological and catalytic processes. In this study, a mononuclear cobalt(III)-peroxo complex bearing a tetradentate macrocyclic ligand, [CoIII(Me3-TPADP)(O2)]+ (Me3-TPADP = 3,6,9-trimethyl-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane), was prepared by reacting [CoII(Me3-TPADP)(CH3CN)2]2+ with H2O2 in the presence of triethylamine. Upon protonation, the cobalt(III)-peroxo intermediate was converted into a cobalt(III)-hydroperoxo complex, [CoIII(Me3-TPADP)(O2H)(CH3CN)]2+. The mononuclear cobalt(III)-peroxo and -hydroperoxo intermediates were characterized by a variety of physicochemical methods. Results of electrospray ionization mass spectrometry clearly show the transformation of the intermediates: the peak at m/z 339.2 assignable to the cobalt(III)-peroxo species disappears with concomitant growth of the peak at m/z 190.7 corresponding to the cobalt(III)-hydroperoxo complex (with bound CH3CN). Isotope labeling experiments further support the existence of the cobalt(III)-peroxo and -hydroperoxo complexes. In particular, the O-O bond stretching frequency of the cobalt(III)-hydroperoxo complex was determined to be 851 cm−1 for 16O2H samples (803 cm−1 for 18O2H samples) and its Co-O vibrational energy was observed at 571 cm−1 for 16O2H samples (551 cm−1 for 18O2H samples; 568 cm−1 for 16O22H samples) by resonance Raman spectroscopy. Reactivity studies performed with the cobalt(III)-peroxo and -hydroperoxo complexes in organic functionalizations reveal that the latter is capable of conducting oxygen atom transfer with an electrophilic character, whereas the former exhibits no oxygen atom transfer reactivity under the same reaction conditions. Alternatively, the cobalt(III)-hydroperoxo complex does not perform hydrogen atom transfer reactions, while analogous low-spin Fe(III)-hydroperoxo complexes are capable of this reactivity. Density function theory calculations indicate that this lack of reactivity is due to the high free energy cost of O-O bond homolysis that would be required to produce the hypothetical Co(IV)-oxo product.

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“…As a result, structural and spectroscopic characterization of the cobalt-O 2 complexes has been well established in 1970s. The structural analysis of the cobalt-O 2 complexes by X-ray crystallography revealed that the O 2 group in the intermediates has superoxo character with an end-on ( η 1 ) binding mode, Co(III)-(O 2 − ) 7c,9. Mononuclear cobalt-O 2 complexes with a side-on ( η 2 ) cobalt(III)-peroxo moiety, Co(III)-(O 2 2− ), have also been reported,10 such as [Co(2=phos) 2 (O 2 )] + (2=phos = cis -[(C 6 H5) 2 PCH=CHP(C 6 H5) 2 ]),10a Co(Tp′)(O 2 ) (Tp′ = hydridotris(3- tert -butyl-5-methylpyrazolyl)borate),10b [Co(tmen) 2 (O 2 )] + (tmen = tetramethylenthylenediamine),10c [Co(TIMEN xyl )(O 2 )] + (TIMEN xyl = tris[2-(3-xylenylimidazol-2- ylidene)ethyl]amine) 10d.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Structural, and Spectroscopic Characterization and Reactivities of Mononuclear Cobalt(III)−Peroxo Complexes

Cho

Sarangi

Kang³

et al. 2010

J. Am. Chem. Soc.

134

120

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Metal-dioxygen adducts are key intermediates detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. In this study, mononuclear cobalt(III)-peroxo complexes bearing tetraazamacrocyclic ligands, (17) Å and 1.438(6) Å, respectively. The cobalt(III)-peroxo complexes showed reactivities in the oxidation of aldehydes and O 2 -transfer reactions. In the aldehyde oxidation reactions, the nucleophilic reactivity of the cobalt-peroxo complexes was significantly dependent on the ring size of the macrocyclic ligands, with the reactivity of [Co(13-TMC)(O 2 )] + > [Co(12-TMC)(O 2 )] + . In the O 2 -transfer reactions, the cobalt(III)-peroxo complexes transferred the bound peroxo group to a manganese(II) complex, affording the corresponding cobalt(II) and manganese(III)-peroxo complexes. The reactivity of the cobalt-peroxo complexes in O 2 -transfer was also significantly dependent on the ring size of tetraazamacrocycles, and the reactivity order in the O 2 -transfer reactions was the same as that observed in the aldehyde oxidation reactions.wwnam@ewha.ac.kr. Supporting Information Available. Non-phase shift corrected Fourier transform data, their corresponding EXAFS data, and FEFF best fit parameters for 2 and 4. X-ray crystal structures of 1 and 3, resonance Raman data of 2 and 4, EPR data of 1 -4, COSY NMR spectrum of 2, kinetic data of the reactions of 4 with 2-PPA and para-X-Ph-CHO, UV-vis spectral changes of the O 2 -transfer reactions of 2 and 4, and X-ray crystallographic files of 1 -4 in CIF format. This material is available free of charge via the Internet at

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Dioxygen Adducts of Lacunar Cobalt(II) Cyclidene Complexes

Cited by 29 publications

References 0 publications

Dynamics of CO Binding to Lacunar Iron(II) Cyclidene Complexes

Dynamics of CO Binding to Lacunar Iron(II) Cyclidene Complexes

Reactivity of a Cobalt(III)–Hydroperoxo Complex in Electrophilic Reactions

Synthesis, Structural, and Spectroscopic Characterization and Reactivities of Mononuclear Cobalt(III)−Peroxo Complexes

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