Kousik Ghosh

One pot synthesis of two cobalt(III) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

Two new cobalt(III) tetrazolato complexes [Co(L1)(PTZ)(N3)] (1) and [Co(L2)(PTZ)(N3)] (2) {where H2L1 = 2((3-(methylamino)propylimino)methyl)-6-methoxyphenol, H2L2 = 2((3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole}, have been synthesized via in situ 1,3-dipolar cycloaddition reaction of 2-cyanopyridine and sodium azide in the presence of cobalt(II) nitrate hexahydrate and respective Schiff bases in the open atmosphere. The structures of both complexes have been confirmed by single crystal X-ray diffraction studies. Features of noncovalent interactions in the solid state of both complexes have been studied by means of DFT and MEP calculations and characterized using Baders theory of “atoms in molecules” (AIM). These complexes act as biomimetic catalysts promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding o-benzoquinone at room temperature. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers of ∼0.030 s−1 in an acetonitrile–methanol (2 : 1) mixture. Both complexes are also reactive towards aerobic oxidation of o-aminophenol in acetonitrile–methanol (2 : 1) with turnover numbers ∼0.095 s−1.

σ-hole halogen bonding interactions in a mixed valence cobalt(III/II) complex and anti-electrostatic hydrogen bonding interaction in a cobalt(III) complex: A theoretical insight

A mixed valence cobalt(III/II) complex, [(μ1,3-OAc)2{(SCN)CoIII(L1)}2CoII]·H2O (1), and an ionic coordination complex of cobalt(III), [CoIII(L2)2][CoIII(L2)(N3)3] (2), have been synthesized and characterized {H2L1 = N,N′-bis(5-bromosalicylidene)-2,2-dimethyl-1,3-propanediamine and HL2 = N(5-bromosalicylidene)-2,2-dimethyl-1,3-propanediamine}. Energetic features of the supramolecular interactions involved in both complexes have been studied through DFT calculations, which indicate that the trinuclear structure of complex 1 has been stabilized via σ-hole halogen bonding interactions in the solid state. On the other hand, counterintuitive anion⋯anion interactions are present in the solid state structure of complex 2, which have been stabilized through anti-electrostatic H-bonds (AEHB). The dissociation scan plot for the AEHB dimer has showed the existence of a significantly high energetic barrier.