Oxidative C-N bond cleavage of (2-pyridylmethyl)amine-based tetradentate supporting ligands in ternary cobalt(ii)-carboxylate complexes

Biswarup Chakraborty, Ivy Ghosh, Rahul Dev Jana, Tapan Kanti Paine

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Three mononuclear cobalt(ii)-carboxylate complexes, [(TPA)CoII(benzilate)]+ (1), [(TPA)CoII(benzoate)]+ (2) and [(iso-BPMEN)CoII(benzoate)]+ (3), of N4 ligands (TPA = tris(2-pyridylmethyl)amine and iso-BPMEN = N1,N1-dimethyl-N2,N2-bis((pyridin-2-yl)methyl)ethane-1,2-diamine) were isolated to investigate their reactivity toward dioxygen. Monodentate (η1) binding of the carboxylates to the metal centre favours the five-coordinate cobalt(ii) complexes (1-3) for dioxygen activation. Complex 1 slowly reacts with dioxygen to enable the oxidative decarboxylation of the coordinated α-hydroxy acid (benzilate). Prolonged exposure of the reaction solution of 2 to dioxygen results in the formation of [(DPA)CoIII(picolinate)(benzoate)]+ (4) and [CoIII(BPCA)2]+ (5) (DPA = di(2-picolyl)amine and HBPCA = bis(2-pyridylcarbonyl)amide), whereas only [(DPEA)CoIII(picolinate)(benzoate)]+ (6) (DPEA = N1,N1-dimethyl-N2-(pyridine-2-ylmethyl)-ethane-1,2-diamine) is isolated from the final oxidised solution of 3. The modified ligand DPA (or DPEA) is formed via the oxidative C-N bond cleavage of the supporting ligands. Further oxidation of the -CH2- moiety to -C(O)- takes place in the transformation of DPA to HBPCA on the cobalt(ii) centre. Labelling experiments with 18O2 confirm the incorporation of oxygen atoms from molecular oxygen into the oxidised products. Mixed labelling studies with 16O2 and H2O18 strongly support the involvement of water in the C-N bond cleavage pathway. A comparison of the dioxygen reactivity of the cobalt complexes (1-3) with those of several other five-coordinate mononuclear complexes [(TPA)CoII(X)]+/2+ (X = Cl, CH3CN, acetate, benzoylformate, salicylate and phenylpyruvate) establishes the role of the carboxylate co-ligands in the activation of dioxygen and subsequent oxidative cleavage of the supporting ligands by a metal-oxygen oxidant.

Original languageEnglish
Pages (from-to)3463-3472
Number of pages10
JournalDalton Transactions
Issue number11
StatePublished - 21 Mar 2020
Externally publishedYes

ASJC Scopus subject areas

  • Inorganic Chemistry


Dive into the research topics of 'Oxidative C-N bond cleavage of (2-pyridylmethyl)amine-based tetradentate supporting ligands in ternary cobalt(ii)-carboxylate complexes'. Together they form a unique fingerprint.

Cite this