Design, synthesis, physicochemical and antimicrobial properties of rhenium(I) tricarbonyl complexes of 3-(phenylimino)indole-2-one

Abstract

Modern medical application of luminescent d6 transition metal complexes to cell imaging has aroused great interest. Using the method of Coogan and co-workers, with slight modifications, the reactions of the Schiff base of isatin and aniline (L1; C14H10N2O; 41%) with Re(CO)5X (X = Cl; a and Br; b) in toluene yielded the complexes [Re(C14H10N2O)(CO)3X] (2a, 2b; 96% and 90% respectively). Refluxing in dry toluene under nitrogen and recrystallization afforded 2bcrystallizing as a solvate compound [Re(C14H10N2O)(CO)3Br].C2H5OH (3; 72%) in ethanol. The reaction of Complex 2b with AgBF4 in diethyl ether under nitrogen yielded [Re(C14H10N2O)(C4H10O)(CO)3]+BF4- (4). Characterization was done by Fourier Transform Infra-red Spectroscopy (FTIR), Electronic spectra, Magnetic susceptibility measurements and melting point determinations. The NMR and Mass Spectra analyses were also done for L1 and 2a. In-vitro antimicrobial studies was done using three gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis and haemolytic Staphylococcus aureus), three gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli and Klebsiella sp.) and three fungi (Aspergillus niger, Trichoderma viride and Penicillium citrinum). Complex 2a showed a broad-spectrum activity, 2b had activities against all gram-negative bacteria (and it was the most active against Pseudomonas aeruginosa) and 2c was active against all tested gram-positive bacteria. Complex 2b had the minimum inhibitory concentration (MIC) value of 1.25 μg/mL against Pseudomonas aeruginosa. The tested complexes showed selective activities in a distinct manner from the ligand and mostly with higher zones of inhibition against the tested organisms than tetracycline (standard clinical antibiotic) against the tested bacteria. All compounds were inactive against the tested fungi.