Rhodium(I) complexes with N-heterocyclic carbene ligands: synthesis, biological properties and catalytic activity in the hydrosilylation of aromatic ketones

New rhodium(I) N-heterocyclic carbene (NHC) complexes 3a–f were synthesized in good yields by the reactions of rhodium dimer [Rh(OMe)(cycloocta-1,5-diene:COD)]2 with benzimidazolium salts 2a–f in tetrahydrofuran. All the complexes were characterized by IR, 1H-NMR, and 13C-NMR spectroscopy, DART-TOF mass spectrometry (for 3b, 3d and 3f) and elemental analysis. All complexes were used as catalysts in the hydrosilylation of acetophenone derivatives with triethylsilane at 80 °C for 1 h. These Rh(I) NHC showed good catalytic performance for the hydrosilylation of acetophenone derivatives by using 1 mol % of the rhodium complexes. In addition the new rhodium(I) NHC complexes were tested against MCF7 and MDA-MB-231 cancer cells, Micrococcus luteus LB 14110, Listeria monocytogenes ATCC 19117, Salmonella Typhimurium ATCC 14028, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa and Candida albicans microorganisms. The synthesized rhodium(I) NHC complex 3f was found the most active against MCF7 cancer cells (half-growth inhibition concentration (IC50) = 0.3 µg mL−1), as well as the most potent antimicrobial against L. monocytogenes ATCC 19117 (inhibition zone (IZ) = 29 mm). Moreover, the antioxidant activity determination of these complexes was studied with the DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) and compared with gallic acid and butylated hydroxytoluene.