Reduction of dioxygen to water by a Co(NO) complex with a 2,2′-bipyridine backbone

• Published in: Chemical communications (Cambridge, England) England), 2021-01, Vol.57 (4), p.516-519
• Main Authors: Nichols, Asa W, Kuehner, Joseph S, Huffman, Brittany L, Miedaner, Peter R, Dickie, Diane A, Machan, Charles W
• Format: Article
• Language: English
• Subjects: Acetic acid; Catalysis; Chemical reduction; Crystallography; Hydrogen peroxide; Iodometry; NMR; Nuclear magnetic resonance; Protonation; Protons; Reducing agents; Selectivity; Titration
• ISSN: 1359-7345; 1364-548X
• DOI: 10.1039/d0cc06763f

We report a Co-based complex for the reduction of O 2 to H 2 O utilizing decamethylferrocene as chemical reductant and acetic acid as a proton donor in methanol solution. Despite structural similarities to previously reported Co(N 2 O 2 ) complexes capable of catalytic O 2 reduction, this system shows selectivity for the four-electron/four-proton reduction product, H 2 O, instead of the two-electron/two-proton reduction product, H 2 O 2 . Mechanistic studies show that the overall rate law is analogous to previous examples, suggesting that the key selectivity difference arises in part from increased favorability of protonation at the distal O position of the key intermediate Co( iii )-hydroperoxide, instead of the proximal one. Interestingly, no product selectivity dependence is observed with respect to the presence of pyridine, which is proposed to bind trans to O 2 during catalysis. The first Co(N 2 O 2 )-based catalyst with intrinsic activity for dioxygen reduction to water instead of hydrogen peroxide is reported.