A series of new cobalt(II) complexes of Schiff base derived from salicylaldehyde and different cycloalkylamines (cycloalkyl = cyclopentyl-1a, cyclohexyl-1b, and cycloheptyl-1c) was synthesized: [Co(CyPen-Salicyl)₂] (2a), [Co(CyHex-Salicyl)₂] (2b), and [Co(CyHep-Salicyl)₂] (2c). The bis(phenoxyiminato)Co(II) complexes (2a-2c) have been fully characterized by FTIR and UV–vis spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and two of the complexes were further studied by single crystal X-ray crystallography. The X-ray structure analysis of 2a-b shows that the geometry around the metal atom is a distorted tetrahedron, confirming the spectroscopic data. Electrochemical studies suggest that the redox potential of 2a-2c are sensitive to the substituent group, decreasing in order cyclopentyl > cyclohexyl > cycloheptyl. Complexes 2a-2c were used as controlling agents for the polymerization of vinyl acetate (VAc) initiated by AIBN, according to a cobalt-mediated radical polymerization (CMRP) mechanism. The VAc polymerization mediated by 2a-2c suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand. Complex 2b showed the smaller discrepancy between observed and calculated molecular weight, and narrower molecular weight distribution. GRAPHICAL ABSTRACT

Novel dimethyl sulfoxide ruthenium(II) complexes of N-heterocyclic carbenes [RuCl₂(S-dmso)₂(SIMes)] (1), [RuCl₂(S-dmso)₂(IMes)], (2) [RuCl₂(S-dmso)₂(SIDip)] (3), and [RuCl₂(S-dmso)₂(IDip)] (4) were successfully synthesized. The complexes 1–4 were characterized by elemental analysis, FTIR, UV-Vis, ¹H and ¹³C NMR, and computational studies. The polynorbornene (polyNBE) syntheses via ROMP using the complexes 1–4 as pre-catalysts in the presence of ethyl diazoacetate (EDA) were evaluated under different [EDA]/[Ru] and [NBE]/[Ru] ratios, temperatures (25 and 50 °C) and times (5–60 min). Quantitative yields of polyNBEs using [NBE]/[EDA]/[Ru] = 5000/28/1 for 10 min at 25 °C were obtained. The order of magnitude of 10⁵ g mol⁻¹ for M_n and PDI values ranging from 1.2 to 3.5 were measured by SEC. An investigation combining experimental data and computational calculations was performed to elucidate the mechanism of ROMP of NBE mediated by the complexes 1–4 as pre-catalysts. The proposed mechanism suggests the occurrence of a dissociative reaction of the complexes 1–4, losing a dmso ligand as the first step, resulting in a 14-electron species, which reacts with EDA to form the metal-carbene, followed by discoordination of the second dmso molecule for coordination of NBE.