Halide Control of N,N-Coordination versus N,C-Cyclometalation and Stereospecific Phenyl Ring Deuteration of Osmium(II) p-Cymene Phenylazobenzothiazole Complexes

Abstract

We report the synthesis of halido Os(II) p-cymene complexes bearing bidentate chelating phenylazobenzothiazole (AZBTZ) ligands. Unlike the analogous phenylazopyridine (AZPY) complexes, AZBTZ-NMe2 is capable of both N,N-coordination to Os(II) and cyclometalation to form N,C-coordinated species. N,C-Coordination occurs via an azo nitrogen and an ortho carbon on the aniline ring, as identified by 1H NMR and X-ray crystallography of [Os(p-cym)(N,N-AZBTZ-NMe2)Cl]PF6 (1a), [Os(p-cym)(N,N-AZBTZ-NMe2)Br]PF6 (2a), [Os(p-cym)(N,C-AZBTZ-NMe2)Br] (2b), and [Os(p-cym)(N,C-AZBTZ-NMe2)I] (3b). The N,C-coordinated species is more stable and is not readily converted to the N,N-coordinated complex. Analysis of the crystal structures suggests that their formation is influenced by steric interactions between the p-cym and AZBTZ-NMe2 ligands: in particular, larger monodentate halide ligands favor N,C-coordination. The complexes [Os(p-cym)(N,N-Me2-AZBTZ-NH2)Cl]PF6 (4) and [Os(p-cym)(N,N-Me2-AZBTZ-NH2)I]PF6 (5) were synthesized with methyl groups blocking the ortho positions on the aniline ring, forcing an N,N-coordination geometry. 1H NMR NOE experiments confirmed hindered rotation of the arene ligand and steric crowding around the metal center. Complex 2b exhibited unexpected behavior under acidic conditions, involving regiospecific deuteration of the aniline ring at the meta position, as observed by 1H NMR and high-resolution ESI-MS. Deuterium exchange occurs only under acidic conditions, suggesting an associative mechanism. The calculated partial charges on 2b show that the meta carbon is significantly more negatively charged, which may account for the regiospecificity of deuterium exchange.

Fast Hydrolysis and Strongly Basic Water Adducts Lead to Potent Os(II) Half-Sandwich Anticancer Complexes

“…Interestingly, for the Os-CN analogue, the Os center receives 0.08 electrons from its ligands, indicating that the osmium center is significantly more basic (Tables S8 and S9). These results on distinct electronic fluxes of the first coordination sphere of NN versus CN coordination of Os­(II) half-sandwich complexes agree with the observations of Needham et al…”

“…Interestingly, for the Os-CN analogue, the Os center receives 0.08 electrons from its ligands, indicating that the osmium center is significantly more basic (Tables S8 and S9). These results on distinct electronic fluxes of the first coordination sphere of NN versus CN coordination of Os(II) half-sandwich complexes agree with the observations of Needham et al 55 We determined the pK a of the carboxylic acid groups (pK a2 ) in aqua adducts 1A and 2A and also in DMSO adducts 1DMSO and 2DMSO (Figure 4 and Table 1). Chart S2 summarizes the speciation in aqueous solution of complexes OH equilibria (pK a1 ), that is, the species in solution were indeed 1DMSO−5DMSO (Figure 4, Figure S20, and Table 1).…”

Anticancer and Antibacterial Activity of Transition Metal Complexes

“…Zeise's salt is one of the first synthesized platinum‐based organometallic complex . Many metal complexes have been synthesized thereafter that contain disparate transition metals, for example titanium,, zirconium, vanadium, niobium,, tantalum, iridium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, palladium, osmium, rhodium, and platinum . Transition metal complexes have multiple utilization in a wide range of areas such as catalysis, optics,, electroluminescent devices,, agricultural and biocidal use, and mostly in biological fields including anticancer, antibacterial, and antifungal applications.…”