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The synthesis of new moisture-sensitive imine-functionalized N-heterocyclic carbene (NHC) precursor salts [1-(2-[(hydroxyl-benzylidene)-amino]-ethyl)-3-R-3H-imidazole-1-ium bromide; R = methyl (1a), ethyl (1b), and benzyl (1c)] is reported. Subsequent deprotonation of 1a–c and coordination of the in situ generated NHC ligands to CoBr2 led to the isolation of air-stable six-coordinate Co­(III) complexes 2a–c, respectively. All the salts and complexes were fully characterized. Single-crystal X-ray analysis of 2a and 2c showed octahedral Co centers hexacoordinated to two NHC carbons, two imine nitrogen atoms, and two phenolate oxygens in the form [C^N^O­(Co3+)­C^N^O]. The complexes were used in the catalytic transfer hydrogenation (CTH) of a range of ketones in 2-propanol as the solvent and hydrogen donor. Based on a low catalyst concentration of 0.4 mol %, significant conversions in the range of 70–99% were recorded at high turnover frequencies up to 1635 h–1. A mechanism to account for the steps involved in the CTH of cyclohexanone by complex 2a is proposed and supported by data from cyclic voltammetry, low-resolution mass spectrometry, UV, and IR spectroscopic techniques.

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We reported the antimicrobial activities of cobalt and nickel complexes containing imino-NHC ligands. Complex 2 was synthesized by direct reaction of the insitu generated free carbene from 2-[2-(3-benzylimidazol-1-yl)ethyliminomethyl]phenol ligand with NiCl2 diglyme while complexes 3-5 were previously reported as catalysts in the transfer hydrogenation reaction of ketones. The compounds 1-5 were screened for antimicrobial sensitivity test against four gram-negative bacteria Escherichia Coli (E-coli), Shigella, Klebsiella Pneumoniae (K. Pneumoniae) and Salmonella Typhi (S.Typhi) and a gram positive bacteria Staphylocossus aureus (S.aureus). At a varying concentrations of 100, 200, 300, 400 and 500 µg/mL, significant activities were recorded using disc diffusion methods. The cobalt complex 3 was found to have higher activities compared with the corresponding nickel complexes and among the three nickel complexes, nickel complex with pyridine as wingtip was found to be more active than the one with a benzyl group. Similarly, the nickel centre with mononuclear was found to be more active than the tri-nuclear nickel complex.  Except for the cobalt complex 3 no activity was recorded against S. typhi for all the nickel compounds.

The synthesis and antimicrobial application of Co (III) and Fe (III) complexes of imine functionalized N-heterocyclic carbene (Imino-NHC) ligands is reported. The ligand precursors 1-(2-[(hydroxyl-benzylidene)-amino]-ethyl)-3-R-3H-imidazol-1-ium bromide where R = pyridyl (1a) and benzyl (1b) have been reported in our previous work. The in-situ generated ligands of 1a and 1b have been successfully coordinated to CoBr2 and [FeI(Cp)(CO)2] leading to the isolation of air-stable N^C^N^O four coordinate Co(III)  complex 2 and a six-coordinate Fe(III) complex 3. The synthesised complexes were both found to be NMR inactive hence were characterize using FTIR and LRMS. The complexes were screened for antimicrobial activities against four gram-negative bacteria Escherichia Coli (E-coli), Shigella, Klebsiella pneumoniae (K. Pneumoniae) and Salmonella typhi (S. typhi) and a gram positive bacteria Staphylocossus aureus (S. aureus). The antimicrobial test was conducted using disc diffusion methods and based on the concentrations of 100, 200, 300, 400 and 500 µg/ mL, significant activities were recorded for both cobalt and the iron complexes.