The direct reaction of a series of substituted (1H-pyrazol-1yl)pyridazine (L I : 6-(1H-pyrazolyl)pyridazine; L II : 3-chloro-6-(1H-pyrazole-1-yl)-pyridazine; L III : 6-(1H-3,5-dimethylpyrazolyl)pyridazine-3-carboxylic acid; L IV : 3,6-bis-N-pyrazolyl-pyridazine; and L V : 3,6-bis-N-3methylpyrazolyl-pyridazine) with the bromotricarbonyl(tetrahydrofuran)rhenium(I) dimer leads to the monometallic complexes [(L X )Re(CO) 3 Br] (I−V), which displays a nonregular octahedral geometry around the Re I center and a fac-isomerism for the carbonyl groups, whereas pyridazine and pyrazolyl rings remain highly coplanar after coordination to rhenium. Cyclic voltammetry shows one irreversible oxidation and one irreversible reduction for each compound as measured in N,N-dimethylformamide. Oxidation ranges from 0.94 V for III to 1.04 V for I and have been attributed to the Re I /Re II couple. In contrast, the reductions are ligand centered, ranging from −1.64 V for II to −1.90 V for III and V. Density functional theory calculations on the vertical one electron oxidized and one electron reduced species, using the gas-phase optimized geometry for the neutral complex confirm this assignment. Compounds I−V show two absorption bands, one around 410 nm (metal-to-ligand charge transfer (MLCT), Re dπ → π*) and the other at ∼300 nm (intraligand, π → π*). Excitation at 400 nm at 77 K leads to unstructured and monoexponential emission with large Stokes shift, whose maxima vary between 570 (III) and 636 (II) nm. The quantum yields for these emissions in solution are intensified strongly going from air to argon equilibrated solution. Singlet oxygen quantum yields change from 0.03 (III) to 0.21 (IV). These data are consistent with emission from 3 MLCT. The emission undergoes a bathochromic shift when R 1 is a π-donating group (Cl or N-pyrazolyl) and a hypsochromic shift for a π-acceptor (COOH). The bimolecular emission quenching rate constant by triethylamine (TEA) for II, IV, and V is 1.09, 0.745, and 0.583 × 10 8 M −1 s −1 , respectively. Photolysis in dichloromethane−CO 2 saturated solution with TEA as a sacrificial electron donor leads in all cases to formic acid generation.

The coordination of the ligands with respect to the central atom in the complex bromidotricarbonyl[diphenyl(pyridin-2-yl)phosphane-κ2 N,P]rhenium(I) chloroform disolvate, [ReBr(C17H14NP)(CO)3]·2CHCl3 or [κ2-P,N-{(C6H5)2(C5H5N)P}Re(CO)3Br]·2CHCl3, (I·2CHCl3), is best described as a distorted octahedron with three carbonyls in a facial conformation, a bromide atom, and a biting P,N-diphenylpyridylphosphine ligand. Hirshfeld surface analysis shows that C—Cl...H interactions contribute 26%, the distance of these interactions are between 2.895 and 3.213 Å. The reaction between I and piperidine (C5H11N) at 313 K in dichloromethane leads to the partial decoordination of the pyridylphosphine ligand, whose pyridyl group is replaced by a piperidine molecule, and the complex bromidotricarbonyl[diphenyl(pyridin-2-yl)phosphane-κP](piperidine-κN)rhenium(I), [ReBr(C5H11N)(C17H14NP)(CO)3] or [P-{(C6H5)2(C5H5N)P}(C5H11N)Re(CO)3Br] (II). The molecule has an intramolecular N—H...N hydrogen bond between the non-coordinated pyridyl nitrogen atom and the amine hydrogen atom from piperidine with D...A = 2.992 (9) Å. Thermogravimetry shows that I·2CHCl3 losses 28% of its mass in a narrow range between 318 and 333 K, which is completely consistent with two solvating chloroform molecules very weakly bonded to I. The remaining I is stable at least to 573 K. In contrast, II seems to lose solvent and piperidine (12% of mass) between 427 and 463 K, while the additional 33% loss from this last temperature to 573 K corresponds to the release of 2-pyridylphosphine. The contribution to the scattering from highly disordered solvent molecules in II was removed with the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18] in PLATON. The stated crystal data for M r, μ etc. do not take this solvent into account.

No abstract

No abstract

The reaction of 6-(1H-3,5-dimethylpyrazolyl)pyridazine-3-carboxylic acid with oxalyl chloride and then 2,4-dimethyl-3-ethylpyrrole leads to [6-(3,5-dimethyl-1Hpyrazol-1-yl)pyridazin-3-yl](4-ethyl-3,5-dimethyl-1H-pyrrol-2-yl)methanone (ppyEt). The reaction of ppyEt with bromotricarbonyl(tetrahydrofuran)-rhenium(I) dimer leads to [(ppyEt)Re(CO)3Br] compound. The molecule of [(ppyEt)Re(CO)3Br] displays a non-regular octahedron around the rhenium(I) center with a bromide. The molecule defines an intramolecular hydrogen bond between the 4-ethyl-3,5-dimethyl-1H-pyrrol-2-yl hydrogen atom and one nitrogen from the pyridazin-3-yl fragment with D•••A 2.833(17) Å. The coplanarity of the 4-ethyl-3,5-dimethyl-1H-pyrrol-2-yl-carbonyl is attributed to this intramolecular bond, in addition to C-H•••O≡C and N-H•••O≡C interactions as suggested by NCI calculations.