A series of tricarbonylrhenium(I) complexes with the N-methyl-2-pyridinecarboxyamide ligand: Synthesis, structure, spectroscopic characterization and computational studies

Tricarbonyl rhenium(i) complexes with 8-hydroxyquinolines: structural, chemical, antibacterial, and anticancer characteristics

Twelve tricarbonyl rhenium(i) complexes in the '2 + 1' system with the anionic bidentate N,O-donor ligand (deprotonated 8-hydroxyquinoline (HQ) or its 2-methyl (MeHQ) or 5-chloro (ClHQ) derivative) and neutral N-donor diazoles (imidazole (Him), 2-methylimidazole (MeHim), 3,5-dimethylpyrazole (Hdmpz), and 3-phenylpyrazole (HPhpz)) were synthesized: [Re(CO)3(LN,O)LN] (LN,O = Q-, MeQ-, ClQ-; LN = Him, MeHim, Hdmpz, HPhpz). Their crystal structures were determined by the scXRD method, compared with the DFT-calculated ones, and characterized by analytical (EA) and spectroscopic techniques (FT-IR, NMR, and UV-Vis) interpreted with DFT and TD-DFT calculations. Most of the Re(i) complexes did not show relevant antibacterial activity against Gram-negative and Gram-positive bacterial strains. Only [Re(CO)3(MeQ)Him] demonstrated significant action 4-fold better against Gram-negative Pseudomonas aeruginosa than the free MeHQ ligand. The cytotoxicity of the compounds was estimated using human acute promyelocytic leukemia (HL-60), ovarian (SKOV-3), prostate (PC-3), and breast (MCF-7) cancer, and breast non-cancerous (MCF-10A) cell lines. Only HQ and ClHQ ligands and [Re(CO)3(Q)Hdmpz] complex had good selectivity toward MCF-7 cell line. HL-60 cells were sensitive to all complexes (IC50 = 1.5-14 μM). Still, pure HQ and ClHQ ligands were slightly more active than the complexes.

Understanding the Deactivation Pathways of Iridium(III) Pyridine-Carboxiamide Catalysts for Formic Acid Dehydrogenation

The degradation pathways of highly active [Cp*Ir(κ² -N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO₃ ), 2 undergoes partial protonation of the amide moiety, inducing rapid κ² -N,N to κ² -N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the κ² -N,N key intermediate of FA dehydrogenation (I_NH ), bearing a N-protonated pica, can easily transform into the κ² -N,O analogue (I_NH2 ; ΔG^≠ ≈11 kcal mol^-1 , ΔG ≈-5 kcal mol^-1 ). Intramolecular hydrogen liberation from I_NH2 is predicted to be rather prohibitive (ΔG^≠ ≈26 kcal mol^-1 , ΔG≈23 kcal mol^-1 ), indicating that FA dehydrogenation should involve mostly κ² -N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c. DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible.

Dicarbonyl cis-[M(CO)2(N,O)(C)(P)] (M = Re, 99mTc) Complexes with a New [2 + 1 + 1] Donor Atom Combination

The synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO)₂(quin)(cisc)(PPh₃)] complex, 4, where quin is the deprotonated quinaldic acid, cisc is cyclohexyl isocyanide, and PPh₃ is triphenylphosphine, is presented. The synthesis of 4 proceeds in three steps. In the first, the intermediate fac-[Re(CO)₃(quin)(H₂O)] aqua complex 2 is generated from the fac-[NEt₄]₂[Re(CO)₃Br₃] precursor, together with the brominated products fac-[Re(CO)₃(quinH)(Br)] 1a and fac-[NEt₄][Re(CO)₃(quin)(Br)] 1b, in low yield. In the following step, replacement of the aqua ligand of complex 2 by the monodentate isocyanide ligand leads to the formation of fac-[Re(CO)₃(quin)(cisc)], 3. In the third step replacement of the species trans to the isocyanide carbonyl group of 3 by a phosphine generates complex 4. The Re complexes 2-4 were prepared in high yield and fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography. At the technetium-99m (^99mTc) tracer level, the analogous complexes 3' and 4' were produced in high radiochemical purity, characterized by comparative reverse phase high-performance liquid chromatography and showed high resistance to transchelation by histidine or cysteine. This new [N,O][C][P] donor atom combination with the cis-[M(CO)₂]⁺ core (M = Re, ^99mTc) is a promising scaffold for the development of novel diagnostic and therapeutic targeted radiopharmaceuticals.

Crystal structure of a second polymorph of tricarbon-yl(N-methyl-pyridine-2-carboxamide-κ2N1,O)(thio-cyanato-κN)rhenium(I)

A new polymorph of the title compound, [Re(NCS)(C7H8N2O)(CO)3], crystallizing in the space group P21/n, has been obtained and structurally characterized by the experiment and DFT calculations. In this complex, the rhenium(I) cation is octa-hedrally coordinated by three carbonyl groups in a facial configuration, the N,O-bidentate N-methyl-pyridine-2-carboxamide ligand and the N-bonded thio-cyanate anion. Neighbouring mol-ecules are linked into a three-dimensional network by inter-molecular N-H⋯S and C-H⋯S inter-actions.

Crystal structure of fac-tricarbon-yl(cyclo-hexyl isocyanide-κC)(quinoline-2-carboxyl-ato-κ(2) N,O)rhenium(I)

In the title compound, [Re(C10H6NO2)(C7H11N)(CO)3], the Re(I) atom is coordinated by three carbonyl ligands in a facial arrangement and by the N, O and C atoms from a chelating quinaldate anion and a monodentate isocyanide ligand, respectively. The resultant C4NO coordination sphere is distorted octa-hedral. A lengthening of the axial Re-CO bond trans to the isocyanide ligand is indicative of the trans effect. Individual complexes are stacked into rods parallel to [001] through displaced π-π inter-actions. Weak C-H⋯O hydrogen-bonding inter-actions between the rods lead to the formation of layers parallel to (010). These layers are stacked along [010] by C-H⋯H-C van der Waals contacts.