Synthesis and Transition Metal Complexes of NovelN,N,O Scorpionate Ligands Suitable for Solid Phase Immobilisation

Exploring the Antitumor Potential of Copper Complexes Based on Ester Derivatives of Bis(pyrazol-1-yl)acetate Ligands

Bis(pyrazol-1-yl)acetic acid (HC(pz)₂COOH) and bis(3,5-dimethyl-pyrazol-1-yl)acetic acid (HC(pz^Me2)₂COOH) were converted into the methyl ester derivatives 1 (L^OMe) and 2 (L^2OMe), respectively, and were used for the preparation of Cu(I) and Cu(II) complexes 3–10. The copper(II) complexes were prepared by the reaction of CuCl₂·2H₂O or CuBr₂ with ligands 1 and 2 in methanol solution. The copper(I) complexes were prepared by the reaction of Cu[(CH₃CN)₄]PF₆ and 1,3,5-triaza-7-phosphaadamantane (PTA) or triphenylphosphine with L^OMe and L^2OMe in acetonitrile solution. Synchrotron radiation-based complementary techniques (XPS, NEXAFS, and XAS) were used to investigate the electronic and molecular structures of the complexes and the local structure around copper ions in selected Cu(I) and Cu(II) coordination compounds. All Cu(I) and Cu(II) complexes showed a significant in vitro antitumor activity, proving to be more effective than the reference drug cisplatin in a panel of human cancer cell lines, and were able to overcome cisplatin resistance. Noticeably, Cu complexes appeared much more effective than cisplatin in 3D spheroid cultures. Mechanistic studies revealed that the antitumor potential did not correlate with cellular accumulation but was consistent with intracellular targeting of PDI, ER stress, and paraptotic cell death induction.

Bis(4-carboxylpyrazol-1-yl)acetic acid: a scorpionate ligand for complexes with improved water solubility

Bis(4-carboxylpyrazol-1-yl)acetic acid (H₃bcpza) (2), obtained in a one-pot synthesis, contains carboxyl groups that differ in their pK_a values. The ligand exhibits heteroscorpionate κ³-N,N,O-coordination whereupon the peripheral carboxyl groups are not involved in metal binding. The corresponding carbonyl complexes [Mn(H₂bcpza)(CO)₃] (4), [Re(H₂bcpza)(CO)₃] (5) and [Ru(H₂bcpza)Cl(CO)₂] (6a/6b) are partially soluble in water but readily soluble in PBS buffer.

A New Dimeric Copper(II) Complex of Hexyl Bis(pyrazolyl)acetate Ligand as an Efficient Catalyst for Allylic Oxidations

A new dimeric copper(II) bromide complex, [Cu(L^OHex)Br(μ-Br)]₂ (1), was prepared by a reaction of CuBr₂ with the hexyl bis(pyrazol-1-yl)acetate ligand (L^OHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol and an easy preparation of its tungsten complex

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol, C24H26N4O, features in the solid state an intramolecular O—H...N hydrogen bond. A heteroscorpionate tungsten complex, cis-[2,2-bis(3,5-dimethylpyrazolyl)-1,1-diphenylethanolato]chloridodioxidotungsten(VI) tetrahydrofuran monosolvate, [W(C24H25N4O)ClO2]·C4H8O, was prepared by the simple mixing of solutions of the ligand and WOCl4 in tetrahydrofuran. The tungsten complex was isolated after standing for several weeks. The complex exhibits a κ3 N,N′,O-coordination of the ligand. This simple synthetic procedure allows access to the cis isomer in high yield without additional purification steps. The Hirshfeld surface analysis shows a change of the intermolecular contacts due to the coordination of the WO2Cl unit with the ligand molecule.

Synthesis and solution stability of water-soluble κ2N,κO-bis(3,5-dimethylpyrazolyl)ethanol manganese(i) tricarbonyl bromide (CORM-ONN1)

The reaction of (OC)₅MnBr with bis(3,5-dimethyl-1-pyrazolyl)methane yields [{(Pz^Me2)₂CH₂}Mn(CO)₃Br] (1). The use of tridentate heteroscorpionates such as bis(3,5-dimethyl-1-pyrazolyl)acetic acid and 2,2-bis(3,5-dimethyl-1-pyrazolyl)ethanol leads to the formation of mononuclear [(OC)₃Mn{(Pz^Me2)₂CH-CO₂}] (2) and [(OC)₃Mn{(Pz^Me2)₂CH-CH₂OH}]Br (3, CORM-ONN1). Salt-like photoCORM 3 is soluble in aqueous media up to a concentration of 200 μM, non-toxic up to an approx. 65 μM solution and releases all carbonyl ligands upon irradiation. The molecular complexes 1 and 2 are insoluble in aqueous solutions. CORM-ONN1 (3) slowly degrades in methanol yielding iCORM 4, consisting of the complex cation [{(Pz^Me2)₂CH-CH₂OH}{(Pz^Me2)₂CH-CH₂O}Mn]⁺ and the [Mn(CO)₅]^- counter anion with the cations linked to a dimeric unit by intermolecular hydrogen bridges between the alcohol and alkoxide functionalities.

Acetoxymethyl Concept for Intracellular Administration of Carbon Monoxide with Mn(CO)3 -Based PhotoCORMs

Targeted administration of carbon monoxide with CO releasing molecules (CORMs) inside of cells proved to be very challenging. Consequently, there are only very few reports on intracellular uptake of CORMs requiring high extracellular CORM loading because an equilibrium between extra- and intracellular concentrations can be assumed. Here we present a strategy for a targeted intracellular administration of manganese(I)-based CORMs that are altered inside of cells to trap these complexes. Thereafter, carbon monoxide can be liberated by irradiation (photoCORMs). To achieve this innovative task, acetoxymethyl (AM) groups are attached at the periphery of the hydrophobic manganese(I) carbonyl complexes to not influence the CO release behavior. Inside of cells these AM substituents are cleaved by esterases yielding hydrophilic manganese(I) carbonyl compounds which are captured inside of cells. This objective is realized by using the bidentate bases 4-(acetoxymethoxycarbonyl)phenyl-bis(3,5-dimethylpyrazolyl)methane (1) and 4-(acetoxymethoxy)phenyl-bis(3,5-dimethylpyrazolyl)methane (4) at facial (OC)₃ MnBr fragments yielding CORM-AM1 (2) and CORM-AM2 (5), respectively. Besides synthesis, crystal structures and spectroscopic properties we present targeted administration and intracellular accumulation of these AM-containing CORMs.

Immobilization of a Boron Center-Functionalized Scorpionate Ligand on Mesoporous Silica Supports for Heterogeneous Tp-Based Catalysts

To develop novel immobilized metallocomplex catalysts, allyltris(3-trifluoromethylpyrazol-1-yl)borate (allyl-Tp^CF3) was synthesized. A boron-attached allyl group reacts with thiol to afford the desired mesoporous silica-immobilized Tp^CF3. Cobalt(II) is an efficient probe for estimating the structures of the immobilized metallocomplexes. The structures of the formed cobalt(II) complexes and their catalytic activity depended on the density of the organic thiol groups and on the state of the remaining sulfur donors on the supports.

Ruthenium(ii) p-cymene complexes of a benzimidazole-based ligand capable of VEGFR2 inhibition: hydrolysis, reactivity and cytotoxicity studies

Ru(ii)-p-Cymene complexes of a bispyrazole-benzimidazole ligand inhibit vascular endothelial growth factor 2, reduce the cellular glutathione pool and inhibit cell migration.

Transition metal complexes bearing a 2,2-bis(3,5-dimethylpyrazol-1-yl)propionate ligand: one methyl more matters

The new N,N,O ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)propionic acid (2,2-Hbdmpzp) (2) and its transition metal complexes [Mn(2,2-bdmpzp)(CO)(3)] (3), [Re(2,2-bdmpzp)(CO)(3)] (4), [Cu(2,2-bdmpzp)(2)] (5), and [Ru(2,2-bdmpzp)Cl(L)(PPh(3))] [L = PPh(3) (6), N(2) (7), CO (8a/b), SO(2) (9a/b)] have been synthesized, characterized and compared to analogous complexes bearing a bis(3,5-dimethylpyrazol-1-yl)acetic acid. It was found that the additional methyl group has a remarkable influence on the stability and reactivity of transition metal complexes.