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Ligands containing benzothiazole moiety upon reaction with arene platinum group metal precursors in dry methanol yielded cationic complexes 1–9 having N∩N bonding mode. The general formulation of t...

Arene metal precursors on treatment with thiosemicarbazone ligands (L1, L2, and L3) yielded a series of cationic mono- and binuclear complexes (1–9) with N∩S bonding mode. In general, the complexes have been formulated as [(p-cymene)Ru(L)Cl]+ and [Cp*2M2(L)2]4+ where L = L1, L2, L3, M = Rh/Ir. Contrary to previous results [1], ruthenium complexes portrayed mononuclear bidentate chelation while rhodium and iridium complexes revealed dinuclear bridging coordination through sulfur and imine nitrogen atoms. All these complexes have been characterized by various spectroscopic techniques and antibacterial studies have been carried out for the complexes as well as the ligands, where 5 and 8 showed good inhibitory antibacterial activity.

A series of complexes ( 1 – 9 ) were synthesized by the reaction of halide bridged metal precursors with the three pyrazine thiourea ligands L1 , L2 and L3 to yield cationic as well as neutral complexes and characterized by various spectroscopic techniques. The cationic complexes are represented by the general formula [(arene)M(L)Cl] + , where L = L1 , L2 and L3 , arene = p -cymene, Cp* and M = Ru, Rh and Ir. All the cationic complexes were isolated with chloride/PF 6 as the counter ion. Reactions of rhodium and iridium dimers with L2 yielded neutral complexes 5 and 6 with the general formula [(arene)M(L)Cl 2 ]. The neutral complexes 5 and 6 were further reacted with NaN 3 to yield azido complexes 10 and 11 . These complexes were, in turn, reacted with acetylene derivatives to yield triazolo complexes 12 – 15 where only a few triazolo complexes of Cp* have been reported. X-ray diffraction studies revealed the complexes having a typical piano stool geometry around the metal center with the thiourea adducts binding to the metal center in a chelating (N, S) manner. Furthermore, the complexes 1 – 9, as well as the ligands were screened for potential anti-bacterial agents out of which complexes 3 and 5 exhibited anti-bacterial activity. Colorimetric sensing studies showed the agglomeration of the silver NPs upon addition of the ligands while the complexes were unresponsive.

Complexes 1–9 were prepared by the reaction of [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) with thiourea derivative ligands L1, L2 and L3. These complexes have been isolated as cationic bidentate (N, S), neutral bidentate (N, S) as well as neutral mono-dentate (S) complexes. Anti-bacterial activity studies were carried out for these complexes as well as the ligands against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli; Klebsiella pneumoniae) in which all the complexes (except complexes 2 and 6) as well as the ligands (except L3) showed anti-bacterial activity. In addition to the biological studies, colorimetric sensing study using silver nanoparticles was also carried out where, ligands L1 and L3 showed agglomeration effects.

The reaction of [(arene)MCl2]2 with ligands 4-hydroxy-benzhydrazide (L1) and 3-methoxy-benzhydrazide (L2) leads to formation of cationic complexes 1-6 having the general formula [(arene)M(L)Cl]+ {arene = p-cymene, M = Ru; arene = Cp*; M = Rh/Ir; L = L1 and L2}. The reaction of [CpRu(PPh3)2Cl] with L1 and L2 yielded cationic complexes that have been formulated as [CpRu(L)PPh3]Y {Y = Cl (7), Y = PF6 (8)}. The molecular structures of 1, 2 and 4 revealed that these complexes adopt typical three-legged “piano stool” geometry. The arene ring occupies the apex of the stool, terminal chloride and N,O-bidentate ligands are coordinated to the metal center at the base of the stool. The antibacterial activity of the ligands and complexes was evaluated on Gram-positive S. aureus, B. thuringiensis and Gram-negative E. coli, P. aeruginosa strains; some complexes exhibit moderate antibacterial activity towards gram-positive bacteria. The antioxidant studies of these complexes have been carried out, and the results showed that these complexes have strong DPPH-scavenging properties.

Ligands containing benzothiazole moiety upon reaction with arene platinum group metal precursors in dry methanol yielded cationic complexes 1–9 having N∩N bonding mode. The general formulation of the complexes is presented as [(arene)M(κ2N∩N-L)Cl]+, where L = L1, L2 and L3, M = Ru, Rh and Ir, and arene = p-cymene and pentamethylcyclopentadiene (Cp*). All these complexes were characterized by various spectroscopic techniques and were found to be air-stable. The biological activity studies of these complexes and ligands such as antibacterial and cytotoxicity studies showed that complexes 5, 6 and 9 have the highest antibacterial activity and ligand L1 has the highest cytotoxicity activity.

The benzamide derivative ligands of benzothiazole (L1) and benzimidazole (L2) upon reaction with halide bridged metal precursors of platinum group yielded a series of complexes (1-6) formulated as [(arene)M(κ1(N)-L)Cl2], where, L = L1 and L2, M = Ru, Rh and Ir, arene = Cp*, p-cymene. Structural studies revealed the bonding of the ligands to the metal centers takes through the nitrogen donor atom of the benzothiazole and benzimidazole moiety in a monodentate fashion. Further reaction of rhodium and iridium complexes with NaN3 in methanol yielded di-azido κ1(N3) monodentate complexes by substituting two chlorides. In the case of ruthenium, azido complexes could not be isolated. Additional treatment of the di-azido complexes with diethyl acetylene dicarboxylate (DEAD) yielded two different bonded triazolo complexes of rhodium (11 and 13) and iridium (12 and 14). In rhodium triazolo complexes, the ligands displayed a chelating mode of bonding through the carbonyl oxygen and the nitrogen atom of the benzothiazole/benzimidazole ring while in iridium triazolo complexes, the ligands retained a monodentate bonding through the nitrogen atom of the benzothiazole/benzimidazole ring and formed two triazole rings. All these complexes were characterized by various spectroscopic techniques. NMR analysis revealed the triazolo ring coordinated to the metal center via the central nitrogen in both the rhodium and iridium triazolo complexes. These complexes as well as the ligands have been studied for antibacterial, antioxidant activity as well as DNA binding studies where a few of the compounds have shown good activity. Amongst these compounds, complex 7 possessed the highest antibacterial and radical scavenging activity while ligand L1 and complexes 1 and 2 showed good affinity as DNA binders.

Halide bridged metal precursors of platinum group on reaction with thiocarbamate derivative ligands (L1 and L2) yielded a series of neutral mono-dentate complexes (1–6) formulated as [(arene)M(κ1(S)-L)Cl2] where, L = L1 and L2, M = Ru, Rh and Ir, arene = p-cymene, Cp∗. Structural studies revealed the ligands coordinated to the metal centers through the thione sulfur in a mono-dentate fashion. These neutral complexes (1–6) were further reacted with NaN3 in methanol which resulted in the formation of highly strained κ2(N,S) azido complexes (7–12). Further treatment of the azido complexes with diethyl acetylene dicarboxylate (DEAD) yielded in the case of rhodium and iridium triazolo complexes (13–16). All these complexes were characterized by various spectroscopic techniques. NMR analysis revealed the triazolo ring coordinated to the metal center via the central nitrogen. Besides the varied coordination of the complexes, these complexes as well as the ligands exhibited antibacterial activity against some bacterial strains under study as well as profound antioxidant potency.

Metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp∗; M = Ru, Rh and Ir) on reacting with 9-fluorenone derivative ligands L1, L2 and L3 resulted in the formation of mononuclear bidentate cationic N∩N bonded complexes. The biological studies of these complexes such as antibacterial activity studies (against Gram-positive and Gram-negative bacteria) revealed significant antibacterial activity with complexes 4, 7 and 9 having the highest activity potency (in-vitro). Whilst for DNA-binding studies, the results revealed that complexes 4 and 5 displayed significant changes in their spectral features upon addition of SM-DNA, thus, indicating that these complexes bind to DNA with a significant affinity.

Complexes 1–9 were synthesized by reacting metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) and benzhydrazone derivative ligands L1, L2 and L3 which resulted in the formation of cationic complexes with PF6 as the counter ion. Ruthenium complexes exhibited N∩O bonding mode while rhodium and iridium complexes exhibited N∩N bonding mode with the migration of the N H proton to the adjacent C O (keto) group forming enol. Anti-bacterial activity studies (against Gram-positive and Gram-negative bacteria) as well as anti-cancer [HCT116 p53 wild type (p53+/+) and HCT116 p53 null (p53−/−)] were carried out for all the complexes as well as ligands where interestingly, ligand L2 and complex 5 showed high activity potency (in-vitro) for both biological studies. Amongst Ru, Rh and Ir, rhodium complexes showed more anticancer activity.