Distinct Reactivity of a Mononuclear Peroxocobalt(III) Species toward Activation of Nitriles

Abstract

A mononuclear side-on peroxocobalt(III) complex with a tetradentate macrocyclic ligand, [Co(TBDAP)(O)] (1), shows a novel and facile mode of dioxygenase-like reactivity with nitriles (R-C≡N; R = Me, Et, and Ph) to produce the corresponding mononuclear hydroximatocobalt(III) complexes, [Co(TBDAP)(R-C(═NO)O)], in which the nitrile moiety is oxidized by two oxygen atoms of the peroxo group. The overall reaction proceeds in one-pot under ambient conditions (ca. 1 h, 40 °C). O-Labeling experiments confirm that both oxygen atoms are derived from the peroxo ligand. The structures of all products, hydroximatocobalt(III) complexes, were confirmed by X-ray crystallography and various spectroscopic techniques. Kinetic studies including the Hammett analysis and isotope labeling experiments suggest that the mechanistic mode of 1 for activation of nitriles occurs via a concerted mechanism. This novel reaction would be significantly valuable for expanding the chemistry for nitrile activation and utilization.

Spectroscopic Determination of the Site in MFI Zeolite where Cobalt(I) Performs Two-Electron Reduction of O2 at Room Temperature

“…The wavenumber of the O–O stretching vibration observed in the present study is typical for mononuclear side-on metal–peroxo complexes (metal = Fe, Co, Ni, Cu). ,− Judging from a well-established relationship between the wavenumber of the O–O stretching vibration of the mononuclear side-on metal dioxygen complexes and the associated O–O distance, the O–O distance of the Co III –peroxo species detected in the present study was estimated to be 1.39 Å (Figure ). This length is typical for a side-on metal–peroxo complex. ,− Other types of ROS can be eliminated from consideration on the basis of the ν O–O of 970 cm –1 ; this value is outside the range for ν O–O of cobalt–superoxo (1248–1135 cm –1 ), − ν O–O of μ-peroxo dicobalt (800 cm –1 ), ν Co–O of bis­(μ-oxo) dicobalt (647–607 cm –1 ), , and ν Co–o of terminal cobalt–oxo (815–770 cm –1 ). , From these results, we can reasonably claim the formation of mononuclear side-on Co III –peroxo species within the zeolite pore via the two-electron reduction of O 2 by the mononuclear Co I species at room temperature. It is worth noting that this is the first example of the spectroscopic detection of a mononuclear metal–peroxo species derived from the O 2 activation by a metal-ion-doped zeolite.…”

“…Previously established relationship between 1/(ν O–O ) 2/3 and R O–O for mononuclear side-on metal–O 2 complexes, i.e., R O–O = 70.7/(ν O–O ) 2/3 + 0.671 . For comparison, experimental data of the previously reported mononuclear metal–peroxo complexes (metal = Fe, Co, Ni, Cu) are also included as red circles. ,− For cobalt peroxo complexes (refs and ), it was reported that the experimental errors of the R O–O value, which are attributed to the librational rotation of the peroxo ligand in the crystal, were exceedingly large; thus, only for the cobalt peroxo complexes, the computationally predicted R O–O were plotted instead of experimental data. ,, Blue arrows indicate the 1/(ν O–O ) 2/3 and R O–O obtained in the present study.…”

Mechanistic insight into hydroxamate transfer reaction mimicking the inhibition of zinc-containing enzymes

“…The average Co-O bond length (2.034 A) in 1 is similar to that of the hydroxamatocobalt(II) complex with 6-(Me 2 Ph) 2 TPA ligand (2.038 A) 34 but is longer than that in 2 (1.856 A) and other hydroximatocobalt(III) complexes. 24,25,[27][28][29]35 1 is the rare example of a structurally characterized hydroxamatocobalt(II) complex, which would be a reactive species towards inhibition of metalloenzymes.…”

“…, which is derived from the reduction of [Co III (TBDAP)(CH 3 C(]NO)O)] + (2). 29 1 was characterized by X-ray crystallography and multiple spectroscopic methods. To the best of our knowledge, 1 represents a rare example of a structurally characterized cobalt(II) complex bearing an acetohydroxamate ligand that has been prepared by the reaction of a hydroximatocobalt(III) complex with a biological reductant.…”

Re(CO)3-Templated Synthesis of α-Amidinoazadi(benzopyrro)methenes

“…has shown that a peroxocobalt(III) complex can activate nitriles to form hydroximatocobalt(III) complexes via oxidation by the peroxo group while Lee and coworkers have activated nitriles using a Ni(II)-(2-mercaptophenyl)phosphine complex to form a thioiminium moiety by nucleophilic attack of a thiol. 29,30 …”