skip to main content

DOE PAGESDOE PAGES

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

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, [Co III(Me 3-TPADP)(O 2)] + (Me 3-TPADP = 3,6,9-trimethyl-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane), was prepared by reacting [Co II(Me 3-TPADP)(CH 3CN) 2] 2+ with H 2O 2 in the presence of triethylamine. Upon protonation, the cobalt(III)- peroxo intermediate was converted into a cobalt(III)-hydroperoxo complex, [Co III(Me 3-TPADP)(O 2H)(CH 3CN)] 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 CH 3CN). 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 16O 2H samples (803 cm -1 for 18O 2H samples) and its Co-O vibrational energy was observed at 571 cm -1 for 16O 2H samples (551 cm -1 for 18O 2H samples; 568 cmmore » -1 for 16O 2 2H 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.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [1]
  1. Daegu Gyeongbuk Inst. of Science and Technology, Daegu (Korea, Republic of). Dept. of Emerging Materials Science
  2. Stanford Univ., CA (United States). Dept. of Chemistry
  3. Univ. of Hyogo (Japan). Picobiology Inst., Graduate School of Life Science
  4. Stanford Univ., CA (United States). Dept. of Chemistry; SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; 2014M1A8A1049320; 15H00960; GM 40392; 20150220; 16-BD-0403; 2016M3D3A01913243
Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 55; Journal Issue: 23; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; National Institutes of Health (NIH)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1361127