Synthesis and characterization of Ru(arene) complexes of bispyrazolylazines: Catalytic hydrogen transfer of ketones

Dehydrogenative Syntheses of Biazoles via a "Pre-Join" Approach

The structural motif of biazoles is the predominant substructure of many natural products, pharmaceuticals, and organic materials. Considerable efforts have focused on synthesizing these compounds; however, a limited number of processes have been reported for the efficient formation of biazoles. Herein, we report a "pre-join" approach for the dehydrogenative synthesis of biazoles, which are challenging to prepare using conventional methods. A bench-stable and easily synthesized pyrazine-based group is critical for this transformation. This strategy enables the homocoupling of biazoles and the heterocoupling of two different azoles. Due to the broad substrate scope, this strategy exhibits potential for use in other fields, such as medicine, materials, and natural product chemistry.

DFT Investigation of the η6 ⇌ η6-Inter-ring Haptotropic Rearrangement of the Group 8 Metals Complexes [(graphene)MCp]+ (M = Fe, Ru, Os)

Metalcyclopentadienyl complexes (MCp)⁺ (M = Fe, Ru, Os) bound to the large polyaromatic hydrogenated hydrocarbon (PAH) C₉₆H₂₄ used as a model for pristine graphene have been studied using a density functional theory (DFT) generalized gradient approximation (PBE functional) to reveal their structural features and dynamic behavior. The inter-ring haptotropic rearrangements (IRHRs) for these complexes were shown to occur via two transition states and one intermediate. The energy barriers of the η⁶ ⇌ η⁶ IRHRs of the (MCp)⁺ unit were found to be 30, 27, and 29 kcal/mol for M = Fe, Ru, and Os, respectively. These values are significantly lower than the values found previously for smaller PAHs. Both polar and nonpolar solvents were found not to affect significantly the energy barrier heights. Investigated transition metal complexes could be used in general as catalysts in the design of novel derivatives or materials with promising properties. Metalcyclopentadienyl complexes (MCp)⁺ of PAHs show catalytic properties mainly due to their structural details as well as their important characteristic of inter-ring haptotropic rearrangement. IRHRs take place usually by intramolecular mechanisms. During IRHRs, the ML_n organometallic groups (OMGs) undergo shifting along the PAH plane and could coordinate additional reagents, which is important for catalysis. Large PAHs such as graphene, fullerenes, and nanotubes possess intrinsic anticancer activity, and numerous arene complexes of Ru and Os have been proven to have anticancer properties as well. We suppose that coordinating Ru or Os to very large PAHs could synergistically increase the anticancer activity of resulting complexes.

Arene-Ruthenium(II) Complexes Containing 11H-Indeno[1,2-b]quinoxalin-11-one Derivatives and Tryptanthrin-6-oxime: Synthesis, Characterization, Cytotoxicity, and Catalytic Transfer Hydrogenation of Aryl Ketones

A series of novel mono- and binuclear arene-ruthenium(II) complexes [(p-cym)Ru(L)Cl] containing 11H-indeno[1,2-b]quinoxalin-11-one derivatives or tryptanthrin-6-oxime were synthesized and characterized by X-ray crystallography, IR, NMR spectroscopy, cyclic voltammetry, and elemental analysis. Theoretical calculations invoking singlet state geometry optimization, solvation effects, and noncovalent interactions were done using density functional theory (DFT). DFT calculations were also applied to evaluate the electronic properties, and time-dependent DFT was applied to clarify experimental UV-vis results. Cytotoxicity for cancerous and noncancerous human cell lines was evaluated with cell viability MTT assay. Complexes demonstrated a moderate cytotoxic effect toward cancerous human cell line PANC-1. The catalytic activity of the complexes was evaluated in transfer hydrogenation of aryl ketones. All complexes exhibited good catalytic activity and functional group tolerance.

Heteroleptic ruthenium(II) 2,2′-bipyridine complexes incorporating substituted pyrazol-1-yl-pyridazine ancillaries

Condensation of 3,6-dichloropyridazine or 3,6-dichloro-4,5-dimethyl- pyridazine with 3-methyl-1H-pyrazole or 4-methyl-1H-pyrazole with the assistance of sodium metal in tetrahydrofuran at reflux afforded three 3,6-bis(pyrazolyl)- pyridazine-type ligands: 3,6-bis(3-methylpyrazolyl)pyridazine (L1), 3,6-bis(4-methyl- pyrazolyl)pyridazine (L2) and 4,5-dimethyl-3,6-bis(4-methylpyrazolyl)pyridazine (L3). Reactions of cis-[RuCl2(bpy)2] · 2H2O (bpy = 2,2′-bipyridine) and L1, L2 or L3 in the presence of NH4PF6 produced the heteroleptic cationic ruthenium(II) complexes [Ru(L1)(bpy)2](PF6)2 (1), [Ru(L2)(bpy)2](PF6)2 (2) and [Ru(L3)(bpy)2](PF6)2 (3), respectively. The three complexes have been characterized by UV/Vis and luminescence spectroscopy. The crystal structures of 1 · EtOH, 2 · EtOH and 3 have been determined by single-crystal X-ray diffraction.

1IL and 3MLCT excited states modulated by H+: the structure and photophysical properties of [(2-bromo-5-(1H-pyrazol-1-yl)pyrazine)Re(CO)3Br]

The photophysical characterization of pyrazolyl–pyrazine Re(i) complex, shows a ¹IL and ³MLCT excited states, being just the ³MLCT able to react with trifluoroacetic acid to yield the protonated and long-lived ³ILH⁺ species. These findings make the compound a potential sensor for protons in solution in the presence of light.