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We investigate the redox, spectroscopy and catalytic reactivity of new cobalt(iii) complexes based on phenolate-rich [N2O3] ligands. These complexes are described as [CoIII(LX)MeOH], where X indicates the presence of chloro (1), bromo (2), iodo (3), or tert-butyl (4) substituents in the 3rd and 5th positions of each phenolate ring. These substituents modulate the Co(iii) ← PheO− LMCT bands of the parent complexes with 1 (451) ＞ 2 (453) ＞ 3 (456) ＞ 4 (468 nm) and the redox potentials involved with the Co(iii)/Co(ii) and ligand reduction and with the phenolate/phenoxyl oxidation processes. The influence of the substituents on the phenolate pendant arms was also observed on the kinetic parameters; 1 presented a rate constant of 1.0 × 10−3 s−1 whereas 4 showed a considerably slower rate (5.3 × 10−5 s−1). Species 1 and 4 are electrocatalysts towards proton reduction in the presence of weak acid in acetonitrile. A TON of 10.8 was observed for 1 after 3 h of bulk electrolysis at −2.20 VFc/Fc+ using a mercury pool as the working electrode. [ABSTRACT FROM AUTHOR]

The stabilization of a bivalent oxidation state in cobalt complexes of phenolate-based asymmetric tridentate ligands with iodo and bromo substituents is studied. The complexes [CoII(LIA)2]·2CH3OH (1) and [CoII(LBrA)2]·CH3OH (2) were characterized by means of several spectroscopic and spectrometric techniques. The molecular structure of 1 was determined by diffractometric analysis and reveals the cobalt(lI) ion in a distorted-octahedral geometry. The centrosymmetric metal ion adopts a local D2h symmetry and is surrounded by facially coordinated ligands. Equivalent donor sets in both ligands are trans to each other, and DFT calculations suggest that the fac—trans configuration is favored by a small margin when compared to the fac—cis isomers. Both DFT calculations and EPR spectroscopy agree with a high-spin S = 3/2 electronic configuration given by [a9¹, b19¹, a9¹, b2g², b39²] This oxidation state was indirectly observed by the lack of a pπphenoIate → dσ∗cobapt(III) charge-transfer band, which is found between 430 and 470 nm for similar cobalt(lll) species. On the basis of the geometrical preferences and the oxidation state of archetypical 1 and 2, two metallosurfactants [CoII(LI-ODA)2] (3) and [CoII (LI-NOBA)2].CH2Cl2 (4) were obtained. The redox chemistry of 1-4 is marked by metal- and ligand-centered activity with several follow up processes and film formation on the electrode. Both metallosurfactants exhibit amphiphilic properties and organization, as shown by compression isotherms and Brewster angle microscopy but exhibit dissimilar collapse mechanisms; whereas 3 collapses at constant pressure, 4 exhibits a constant-area collapse. Langmuir—Blodgett films are readily obtained and were characterized by equilibrium contact angle and atomic force microscopy. [ABSTRACT FROM AUTHOR]