1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene,unprecedented intramolecular C–H activation,and reactivity studies

The structure, bonding, and reactivity of small, highly unsaturated ring systems is of fundamental interest for inorganic and organic chemistry. Four-membered metallacyclobuta-2,3-dienes, also referred to as metallacycloallenes, are among the most exotic examples for ring systems as these represent organometallic analogs of 1,2-cyclobutadiene, the smallest cyclic allene. Herein, the synthesis of the first examples of 1-zirconacyclobuta-2,3-dienes of the type [Cp′₂Zr(Me₃SiC₃SiMe₃)] (Cp′₂ = rac-(ebthi), (ebthi = 1,2-ethylene-1,1′-bis(η⁵-tetrahydroindenyl)) (2a); rac-Me₂Si(thi)₂, thi = (η⁵-tetrahydroindenyl), (2b)) is presented. Both complexes undergo selective thermal C–H activation at the 7-position of the ansa-cyclopentadienyl ligand to produce a new type of “tucked-in” zirconocene system, 3a and 3b, that possesses a η³-propargyl/allenyl ligand. Both types of complexes react with carbonyl compounds, producing enynes in the case of 2a and 2b, as well as η¹-allenyl complexes for 3a and 3b. Computational analysis of the structure and bonding of 2a and 3a reveals significant differences to a previously described related Ti complex. All complexes were fully characterised, including X-ray crystallography and experimental results were supported by DFT analysis.

A detailed study of structure, bonding and reactivity of new 1-zirconacyclobuta-2,3-dienes is presented in comparison to a lighter Ti analog. We found a unique C–H activation at the widely used rac-(ebthi) ligand for that only occurs for Zr.     

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure,Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm,Eu, Tb,Dy, Ho,Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.     

A comparative study of the coordination behavior of cyclo-P5 and cyclo-As5 ligand complexes towards the trinuclear Lewis acid complex (perfluoro-ortho-phenylene)mercury

Reactions of the cyclo-E₅ sandwich complexes [Cp*Fe(η⁵-P₅)] (1) and [Cp*Fe(η⁵-As₅)] (2) with the planar Lewis acid trimeric (perfluoro-ortho-phenylene)mercury [(o-C₆F₄Hg)₃] (3) afford compounds that show distinctly different assemblies in the solid state. The phosphorus containing ligand 1 forms dimeric coordination units with two molecules of 3, with one P atom of each cyclo-P₅ ligand positioned in close proximity to the center of a molecule of 3. In contrast to the coordination behavior of 1, the arsenic analog 2 shows simultaneous interaction of three As atoms with the Hg atoms of 3. A DFT study and subsequent AIM analyses of the products suggest that electrostatic forces are prevalent over donor–acceptor interactions in these adducts, and may play a role in the differences in the observed coordination behavior. Subsequently, a series of [Cp^RFe(η⁵-P₅)] (Cp^R = C₅H_5–n tBu_n, n = 1–3, 6a–c) sandwich complexes was prepared and also reacted with [(o-C₆F₄Hg)₃]. In the solid state the obtained products 7a–c with increasing steric demand of the Cp^R ligands show no significant change in their assembly compared to the Cp* analog 4. All of the products were characterized by single crystal X-ray structure analysis, mass spectrometry and elemental analysis as well as NMR spectroscopy and IR spectrometry.     

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic,Structural, and Physical Studies

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO₃)₃·nH₂O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln₂(O₂CMe)₄(NO₃)₂(mepaoH)₂] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the Ln^III—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O₂CMe)₃·4H₂O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy₂(O₂CMe)₆(mepaoH)₂] (6). Treatment of 6 with one equivalent of HNO₃ gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two Ln^III centers are bridged by two bidentate bridging (η¹:η¹:μ₂) and two chelating-bridging (η¹:η²:μ₂) acetate groups. The Ln^III atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate Ln^III centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the Tb^III atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular Gd^III…Gd^III exchange interactions in 3; the J value is −0.09(1) cm⁻¹ based on the spin Hamiltonian Ĥ = −J(Ŝ_Gd1·Ŝ_Gd2).     

Characterization and chemical reactivity of room-temperature-stable MnIII–alkylperoxo complexes

While alkylperoxomanganese(iii) (Mn^III–OOR) intermediates are proposed in the catalytic cycles of several manganese-dependent enzymes, their characterization has proven to be a challenge due to their inherent thermal instability. Fundamental understanding of the structural and electronic properties of these important intermediates is limited to a series of complexes with thiolate-containing N₄S⁻ ligands. These well-characterized complexes are metastable yet unreactive in the direct oxidation of organic substrates. Because the stability and reactivity of Mn^III–OOR complexes are likely to be highly dependent on their local coordination environment, we have generated two new Mn^III–OOR complexes using a new amide-containing N₅⁻ ligand. Using the 2-(bis((6-methylpyridin-2-yl)methyl)amino)-N-(quinolin-8-yl)acetamide (H^6Medpaq) ligand, we generated the [Mn^III(OO^tBu)(^6Medpaq)]OTf and [Mn^III(OOCm)(^6Medpaq)]OTf complexes through reaction of their Mn^II or Mn^III precursors with ^tBuOOH and CmOOH, respectively. Both of the new Mn^III–OOR complexes are stable at room-temperature (t_1/2 = 5 and 8 days, respectively, at 298 K in CH₃CN) and capable of reacting directly with phosphine substrates. The stability of these Mn^III–OOR adducts render them amenable for detailed characterization, including by X-ray crystallography for [Mn^III(OOCm)(^6Medpaq)]OTf. Thermal decomposition studies support a decay pathway of the Mn^III–OOR complexes by O–O bond homolysis. In contrast, direct reaction of [Mn^III(OOCm)(^6Medpaq)]⁺ with PPh₃ provided evidence of heterolytic cleavage of the O–O bond. These studies reveal that both the stability and chemical reactivity of Mn^III–OOR complexes can be tuned by the local coordination sphere.

A pair of room-temperature-stable Mn^III–alkylperoxo complexes were characterized and shown to oxidize PPh₃. Thermal decomposition studies provide evidence of both homolysis and heterolysis of the Mn^III–alkylperoxo O–O bond.     

Structural Characterization of Cis– and Trans–Pt(NH3)2Cl2 Conjugations with Chitosan Nanoparticles

The conjugation of chitosan 15 and 100 KD with anticancer drugs cis– and trans–Pt (NH₃)₂Cl₂ (abbreviated cis–Pt and trans–Pt) were studied at pH 5–6. Using multiple spectroscopic methods and thermodynamic analysis to characterize the nature of drug–chitosan interactions and the potential application of chitosan nanoparticles in drug delivery. Analysis showed that both hydrophobic and hydrophilic contacts are involved in drug–polymer interactions, while chitosan size and charge play a major role in the stability of drug–polymer complexes. The overall binding constants are K_{ch–15–cis–Pt} = 1.44 (±0.6) × 10⁵ M⁻¹, K_{ch–100–cis–Pt} = 1.89 (±0.9) × 10⁵ M⁻¹ and K_{ch–15–trans–Pt} = 9.84 (±0.5) × 10⁴ M⁻¹, and K_{ch–100–trans–Pt} = 1.15 (±0.6) × 10⁵ M⁻¹. More stable complexes were formed with cis–Pt than with trans–Pt–chitosan adducts, while stronger binding was observed for chitosan 100 in comparison to chitosan 15 KD. This study indicates that polymer chitosan 100 is a stronger drug carrier than chitosan 15 KD in vitro.     

Meloxicam and Study of Their Antimicrobial Effects against Phyto- and Human Pathogens

Recently, the design of new biological metal-ligand complexes has gained a special interest all over the world. In this research, new series of mixed ligand complexes from meloxicam (H₂mel) and glycine (Gly) were synthesized. Structures of the compounds were investigated employing elemental analyses, infrared, electronic absorption, ¹H NMR, thermal analyses, effective magnetic moment and conductivity. The estimated molar conductivity of the compounds in 1 × 10⁻³ M DMF solution indicates the non-electrolyte existence of the examined complexes. Additionally, the effective magnetic moment values refer to the complexes found as octahedral molecular geometry. The data of the infrared spectra showed the chelation of H₂mel and Gly with metal ions from amide oxygen and nitrogen of the thyizol groups of H₂mel and through nitrogen of the amide group and oxygen of the carboxylic group for Gly. Thermal analyses indicated that the new complexes have good thermal stability and initially lose hydration water molecules followed by coordinated water molecules, Gly and H₂mel. The kinetic parameters were calculated graphically using Coats–Redfern and Horowitz–Metzeger methods at n = 1 and n ≠ 1. The density functional theory (DFT) calculations were performed at B3LYP levels. The optimized geometry of the ligand and its complexes were obtained based on the optimized structures. The data indicated that the complexes are soft with η value in the range 0.114 to 0.086, while η = 0.140 for free H₂mel. The new prepared complexes were investigated as antibacterial and antifungal agents against some phyto- and human pathogens and the minimum inhibitory concentration (MIC) data showed that complex (A) has the lowest MIC for Listeria and E. coli (10.8 µg/mL).     

The Theoretical and Experimental Investigation of the Fluorinated Palladium β-Diketonate Derivatives: Structure and Physicochemical Properties

To search for new suitable Pd precursors for MOCVD/ALD processes, the extended series of fluorinated palladium complexes [Pd(CH₃CXCHCO(R))₂] with β-diketone [tfa−1,1,1-trifluoro-2,4-pentanedionato (1); pfpa−5,5,6,6,6-pentafluoro-2,4-hexanedionato (3); hfba−5,5,6,6,7,7,7-heptafluoro-2,4-heptanedionato (5)] and β-iminoketone [i-tfa−1,1,1-trifluoro-2-imino-4-pentanonato (2); i-pfpa−5,5,6,6,6-pentafluoro-2-imino-4-hexanonato (4); i-hfba-5,5,6,6,7,7,7-heptafluoro-2-imino-4-heptanonato (6)] ligands were synthesized with 70–80% yields and characterized by a set of experimental (SXRD, XRD, IR, NMR spectroscopy, TG) and theoretical (DFT, Hirshfeld surface analysis) methods. Solutions of Pd β-diketonates contained both cis and trans isomers, while only trans isomers were detected in the solutions of Pd β-iminoketonates. The molecules 2–6 and new polymorphs of complexes 3 and 5 were arranged preferentially in stacks, and the distance between molecules in the stack generally increased with elongation of the fluorine chain in ligands. The H…F contacts were the main ones involved in the formation of packages of molecules 1–2, and C…F, F…F, NH…F contacts appeared in the structures of complexes 4–6. The stability of complexes and their polymorphs in the crystal phases were estimated from DFT calculations. The TG data showed that the volatility differences between Pd β-iminoketonates and Pd β-diketonates were minimized with the elongation of the fluorine chain in the ligands.     

Spectroscopic and Molecular Docking Studies of Cu(II), Ni(II), Co(II), and Mn(II) Complexes with Anticonvulsant Therapeutic Agent Gabapentin

New Cu(II), Ni(II), Co(II), and Mn(II) complexes of the gabapentin (Gpn) bidentate drug ligand were synthesized and studied using elemental analyses, melting temperatures, molar conductivity, UV–Vis, magnetic measurements, FTIR, and surface morphology (scanning (SEM) and transmission (TEM) electron microscopes).The gabapentin ligand was shown to form monobasic metal:ligand (1:1) stoichiometry complexes with the metal ions Cu(II), Ni(II), Co(II), and Mn(II). Molar conductance measurements in dimethyl-sulfoxide solvent with a concentration of 10⁻³ M correlated to a non-electrolytic character for all of the produced complexes. A deformed octahedral environment was proposed for all metal complexes. Through the nitrogen atom of the –NH₂ group and the oxygen atom of the carboxylate group, the Gpn drug chelated as a bidentate ligand toward the Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺ metal ions. This coordination behavior was validated by spectroscopic, magnetic, and electronic spectra using the formulas of the [M(Gpn)(H₂O)₃(Cl)]·nH₂O complexes (where n = 2–6).Transmission electron microscopy was used to examine the nanostructure of the produced gabapentin complexes. Molecular docking was utilized to investigate the comparative interaction between the Gpn drug and its four metal [Cu(II), Ni(II), Co(II), and Mn(II)] complexes as ligands using serotonin (6BQH) and dopamine (6CM4) receptors. AutoDock Vina results were further refined through molecular dynamics simulation, and molecular processes for receptor–ligand interactions were also studied. The B3LYP level of theory and LanL2DZ basis set was used for DFT (density functional theory) studies. The optimized geometries, along with the MEP map and HOMO → LUMO of the metal complexes, were studied.     

In silico design to enhance the barrier height for magnetization reversal in Dy(iii) sandwich complexes by stitching them under the umbrella of corannulene

Lanthanide based single molecular magnets (SMMs), particularly dysprocenium based SIMs, are well known for their high energy barrier for spin reversal (U_eff) and blocking temperatures (T_B). Enhancing these two parameters and at the same time obtaining ambient stability is key to realising end-user applications such as compact storage or as qubits in quantum computing. In this work, by employing an array of theoretical tools (DFT, ab initio CASSCF and molecular dynamics), we have modelled six complexes [(η⁵-corannulene)Dy(Cp)] (1), [(η⁵-corannulene)Dy(C₆H₆)] (2), [(η⁶-corannulene)Dy(Cp)] (3), [(η⁶-corannulene)Dy(C₆H₆)] (4), [(exo-η⁵-corannulene)Dy(endo-η⁵-corannulene)] (5), and [(endo-η⁵-corannulene)Dy(endo-η⁵-corannulene)] (6) containing corannulene as a capping ligand to stabilise Dy(iii) half-sandwich complexes. Our calculations predict a strong axiality exerted by the Dy–C interactions in all complexes. Ab initio calculations predict a very large barrier height for all six molecules in the order 1 (919 cm⁻¹) ≈ 3 (913 cm⁻¹) > 2 (847 cm⁻¹) > 4 (608 cm⁻¹) ≈ 5 (603 cm⁻¹) ≈ 6 (599 cm⁻¹), suggesting larger barrier heights for Cp ring systems, followed by six-membered arene systems and then corannulene. DFT based molecular dynamics calculations were performed on complexes 3, 5 and 6. For complexes 3 and 5, the geometries that are dynamically accessible are far fewer. The range of U_eff computed for molecular dynamics snapshots is high, indicating a possibility of translating the large U_eff obtained into attractive blocking temperatures in these complexes, but the converse is found for 6. Furthermore, an in-depth C–H bond vibrational analysis performed on complex 3 suggests that the vibration responsible for reducing the blocking temperature in dysprocenium SIMs is absent here as the C–H bonds are stronger and corannulene steric strain prevents the C(Cp)–Dy–C(Cor) bending. As [(η⁶-corannulene)TM(X)]⁺ (TM = Ru, Zr, Os, Rh, Ir and X = C₅Me₅, C₆Me₆) are known, the predictions made here have a higher prospect of yielding stability under ambient conditions, a very large U_eff value and a high blocking temperature – a life-giving combination to new generation SMMs.

Bringing half-sandwich Dy(iii) SIMs under the umbrella of corannulene was found to offer stability, greater barrier height and may offer higher blocking temperatures.     

Imine Palladacycles: Synthesis,Structural Analysis and Application in Suzuki–Miyaura Cross Coupling in Semi-Aqueous Media

Treatment of the imines a–c with palladium(II) acetate in acetic acid yielded the μ-acetate dinuclear complexes 1a–c, which readily reacted with sodium chloride or bromide to provide μ-halide analogues. The reaction of the latter with nitrogen, phosphorus and oxygen donor nucleophiles yielded new imine palladacycles following the cleavage of the Pd₂X₂ unit. The complexes were fully characterized by microanalysis, ¹H, ¹³C and ³¹P NMR spectroscopies, as appropriate. The compounds were applied as catalysts in the Suzuki–Miyaura coupling reaction in aqueous and semi-aqueous media.     

pH-Responsive N^C-Cyclometalated Iridium(III) Complexes: Synthesis,Photophysical Properties,Computational Results,and Bioimaging Application

Herein we report four [Ir(N^C)₂(L^L)]ⁿ⁺, n = 0,1 complexes (1–4) containing cyclometallated N^C ligand (N^CH = 1-phenyl-2-(4-(pyridin-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole) and various bidentate L^L ligands (picolinic acid (1), 2,2′-bipyridine (2), [2,2′-bipyridine]-4,4′-dicarboxylic acid (3), and sodium 4,4′,4″,4‴-(1,2-phenylenebis(phosphanetriyl))tetrabenzenesulfonate (4). The N^CH ligand precursor and iridium complexes 1–4 were synthesized in good yield and characterized using chemical analysis, ESI mass spectrometry, and NMR spectroscopy. The solid-state structure of 2 was also determined by XRD analysis. The complexes display moderate to strong phosphorescence in the 550–670 nm range with the quantum yields up to 30% and lifetimes of the excited state up to 60 µs in deoxygenated solution. Emission properties of 1–4 and N^CH are strongly pH-dependent to give considerable variations in excitation and emission profiles accompanied by changes in emission efficiency and dynamics of the excited state. Density functional theory (DFT) and time-dependent density functional theory (TD DFT) calculations made it possible to assign the nature of emissive excited states in both deprotonated and protonated forms of these molecules. The complexes 3 and 4 internalize into living CHO-K1 cells, localize in cytoplasmic vesicles, primarily in lysosomes and acidified endosomes, and demonstrate relatively low toxicity, showing more than 80% cells viability up to the concentration of 10 µM after 24 h incubation. Phosphorescence lifetime imaging microscopy (PLIM) experiments in these cells display lifetime distribution, the conversion of which into pH values using calibration curves gives the magnitudes of this parameter compatible with the physiologically relevant interval of the cell compartments pH.     

Synthesis of Platinum(II) N-Heterocyclic Carbenes Based on Adenosine

Organometallic derivatization of nucleosides is a highly promising strategy for the improvement of the therapeutic profile of nucleosides. Herein, a methodology for the synthesis of metalated adenosine with a deprotected ribose moiety is described. Platinum(II) N-heterocyclic carbene complexes based on adenosine were synthesized, namely N-heterocyclic carbenes bearing a protected and unprotected ribose ring. Reaction of the 8-bromo-2′,3′,5′-tri-O-acetyladenosine with Pt(PPh₃)₄ by C8−Br oxidative addition yielded complex 1, with a Pt^II centre bonded to C-8 and an unprotonated N7. Complex 1 reacted at N7 with HBF₄ or methyl iodide, yielding protic carbene 2 or methyl carbene 3, respectively. Deprotection of 1 to yield 4 was achieved with NH₄OH. Deprotected compound 4 reacted at N7 with HCl solutions to yield protic NHC 5 or with methyl iodide yielding methyl carbene 6. Protic N-heterocyclic carbene 5 is not stable in DMSO solutions leading to the formation of compound 7, in which a bromide was replaced by chloride. The cis-influence of complexes 1–7 was examined by ³¹P{¹H} and ¹⁹⁵Pt NMR. Complexes 2, 3, 5, 6 and 7 induce a decrease of ¹J_Pt,P of more than 300 Hz, as result of the higher cis-influence of the N-heterocyclic carbene when compared to the azolato ligand in 1 and 4.     

Synthesis,Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of (Z)-1-R-2-(4′,4′-Dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates

The coordination chemistry of the title ligands with Mo metal centers was investigated. Thus, the synthesis and characterization (NMR, X-ray diffraction) of four mononuclear formally Mo(6+) complexes of (Z)-1-R-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates (L: R = –Ph, –Ph-p-NO₂, –Ph-p-OMe and –t-Bu), derived from the part enols (LH), is described. The resulting air-stable MoO₂L₂ complexes (1–4) exist, as shown by single-crystal X-ray diffraction experiments, in the cis-dioxido-trans(N)-κ²-N,O-L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes 1–4 represent the first Mo complexes of this ligand class and, indeed, of Group 6 metals in general. Structural and spectroscopic comparisons were made between these and related Mo(6+) compounds. Complex 1 (R = –Ph) was studied for its ability to selectively catalyze the production of poly-norbornene from the monomer in the presence of MAO. This, unfortunately, only resulted in the synthesis of insoluble, presumably highly cross-linked, polymeric and/or oligomeric materials. However, complexes 1–4 were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the O-transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.     

Antioxidant Activity of Ruthenium Cyclopentadienyl Complexes Bearing Succinimidato and Phthalimidato Ligands

In these studies, we investigated the antioxidant activity of three ruthenium cyclopentadienyl complexes bearing different imidato ligands: (η⁵-cyclopentadienyl)Ru(CO)₂-N-methoxysuccinimidato (1), (η⁵-cyclopentadienyl)Ru(CO)₂-N-ethoxysuccinimidato (2), and (η⁵-cyclopentadienyl)Ru(CO)₂-N-phthalimidato (3). We studied the effects of ruthenium complexes 1–3 at a low concentration of 50 µM on the viability and the cell cycle of peripheral blood mononuclear cells (PBMCs) and HL-60 leukemic cells exposed to oxidative stress induced by hydrogen peroxide (H₂O₂). Moreover, we examined the influence of these complexes on DNA oxidative damage, the level of reactive oxygen species (ROS), and superoxide dismutase (SOD) activity. We have observed that ruthenium complexes 1–3 increase the viability of both normal and cancer cells decreased by H₂O₂ and also alter the HL-60 cell cycle arrested by H₂O₂ in the sub-G1 phase. In addition, we have shown that ruthenium complexes reduce the levels of ROS and oxidative DNA damage in both cell types. They also restore SOD activity reduced by H₂O₂. Our results indicate that ruthenium complexes 1–3 bearing succinimidato and phthalimidato ligands have antioxidant activity without cytotoxic effect at low concentrations. For this reason, the ruthenium complexes studied by us should be considered interesting molecules with clinical potential that require further detailed research.     

Osmium(ii) tethered half-sandwich complexes: pH-dependent aqueous speciation and transfer hydrogenation in cells

Aquation is often acknowledged as a necessary step for metallodrug activity inside the cell. Hemilabile ligands can be used for reversible metallodrug activation. We report a new family of osmium(ii) arene complexes of formula [Os(η⁶-C₆H₅(CH₂)₃OH)(XY)Cl]^+/0 (1–13) bearing the hemilabile η⁶-bound arene 3-phenylpropanol, where XY is a neutral N,N or an anionic N,O⁻ bidentate chelating ligand. Os–Cl bond cleavage in water leads to the formation of the hydroxido/aqua adduct, Os–OH(H). In spite of being considered inert, the hydroxido adduct unexpectedly triggers rapid tether ring formation by attachment of the pendant alcohol–oxygen to the osmium centre, resulting in the alkoxy tethered complex [Os(η⁶-arene-O-κ¹)(XY)]ⁿ⁺. Complexes 1C–13C of formula [Os(η⁶:κ¹-C₆H₅(CH₂)₃OH/O)(XY)]⁺ are fully characterised, including the X-ray structure of cation 3C. Tether-ring formation is reversible and pH dependent. Osmium complexes bearing picolinate N,O-chelates (9–12) catalyse the hydrogenation of pyruvate to lactate. Intracellular lactate production upon co-incubation of complex 11 (XY = 4-Me-picolinate) with formate has been quantified inside MDA-MB-231 and MCF7 breast cancer cells. The tether Os–arene complexes presented here can be exploited for the intracellular conversion of metabolites that are essential in the intricate metabolism of the cancer cell.

New Os(ii) half-sandwich complexes bearing a pendant alcohol prompt reversible tether-ring formation upon aquation, protecting Os against deactivation. Excitingly, these complexes mediate hydrogenation of pyruvate to lactate inside cancer cells.     

A (μ-hydrido)diborane(4) anion and its coordination chemistry with coinage metals

A tetra(o-tolyl) (μ-hydrido)diborane(4) anion 1, an analogue of [B₂H₅]⁻ species, was facilely prepared through the reaction of tetra(o-tolyl)diborane(4) with sodium hydride. Unlike common sp²–sp³ diborane species, 1 exhibited a σ-B–B bond nucleophilicity towards NHC-coordinated transition-metal (Cu, Ag, and Au) halides, resulting in the formation of η²-B–B bonded complexes 2 as confirmed by single-crystal X-ray analyses. Compared with 1, the structural data of 2 imply significant elongations of B–B bonds, following the order Au > Cu > Ag. DFT studies show that the diboron ligand interacts with the coinage metal through a three-center-two-electron B–M–B bonding mode. The fact that the B–B bond of the gold complex is much prolonged than the related Cu and Ag compounds might be ascribed to the superior electrophilicity of the gold atom.

A tetra(o-tolyl)(μ-hydrido)diborane(4) anion is facilely prepared via the reaction of tetra(o-tolyl)diborane(4) with NaH. It exhibits a σ-B–B bond nucleophilicity towards NHC-metal halides to give the corresponding η²-B–B bonded metal complexes.     

Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis, characterization and catalytic oligomerisation of ethylene

New N-functionalised 2-phosphinobenzaldimino (P^N) ligands bearing 3-picolyl, furfuryl, thiophene-2-methyl, thiophene-2-ethyl, and benzyl groups have been prepared in good yield. The 2-phosphinobenzaldimino ligands were reacted with PdCl₂(COD) to give the corresponding metal complexes of the type Pd(L)Cl₂ (L = 2-phosphinobenzaldimino (P^N) ligand). All compounds were fully characterized using spectroscopic and analytical techniques, including ¹H, ¹³C, and ³¹P NMR and IR spectroscopies, mass spectrometry and elemental analysis. Selected neutral palladium complexes were evaluated as catalyst precursors in ethylene oligomerisation reactions, after activation with a co-catalyst (MMAO, EtAlCl₂, or Et₂AlCl).     

Group 9 half-sandwich complexes containing the unique P,P′-diphenyl-1,4-diphospha-cyclohexane ligand: Synthesis, X-ray structure analyses and spectroscopic studies

We wish to report the synthesis and characterization of Group 9 metal complexes with the novel P,P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc) ligand. The complexes are readily prepared by direct ligand substitution reactions from the dichloro-bridged binuclear complexes, [{η⁵-Cp*M(Cl)₂}₂]. The complexes include: [η⁵-Cp*Rh(Cl)₂]₂(μ-dpdpc) (1), [η⁵-Cp*Ir(Cl)₂]₂(μ-dpdpc) (2), and [η⁵-Cp*Rh(Cl)(dpdpc)]PF₆ (3). The structures for all three complexes are supported by ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy as well as elemental analysis. The molecular structures of 1 and 3 have also been established by single-crystal X-ray analysis.     

Cooperative B–H bond activation: dual site borane activation by redox active κ2-N,S-chelated complexes

Cooperative dual site activation of boranes by redox-active 1,3-N,S-chelated ruthenium species, mer-[PR₃{κ²-N,S-(L)}₂Ru{κ¹-S-(L)}], (mer-2a: R = Cy, mer-2b: R = Ph; L = NC₇H₄S₂), generated from the aerial oxidation of borate complexes, [PR₃{κ²-N,S-(L)}Ru{κ³-H,S,S′-BH₂(L)₂}] (trans–mer-1a: R = Cy, trans–mer-1b: R = Ph; L = NC₇H₄S₂), has been investigated. Utilizing the rich electronic behaviour of these 1,3-N,S-chelated ruthenium species, we have established that a combination of redox-active ligands and metal–ligand cooperativity has a big influence on the multisite borane activation. For example, treatment of mer-2a–b with BH₃·THF led to the isolation of fac-[PR₃Ru{κ³-H,S,S′-(NH₂BSBH₂N)(S₂C₇H₄)₂}] (fac-3a: R = Cy and fac-3b: R = Ph) that captured boranes at both sites of the κ²-N,S-chelated ruthenacycles. The core structure of fac-3a and fac-3b consists of two five-membered ruthenacycles [RuBNCS] which are fused by one butterfly moiety [RuB₂S]. Analogous fac-3c, [PPh₃Ru{κ³-H,S,S′-(NH₂BSBH₂N)(SC₅H₄)₂}], can also be synthesized from the reaction of BH₃·THF with [PPh₃{κ²-N,S-(SNC₅H₄)}{κ³-H,S,S′-BH₂(SNH₄C₅)₂}Ru], cis–fac-1c. In stark contrast, when mer-2b was treated with BH₂Mes (Mes = 2,4,6-trimethyl phenyl) it led to the formation of trans- and cis-bis(dihydroborate) complexes [{κ³-S,H,H-(NH₂BMes)Ru(S₂C₇H₄)}₂], (trans-4 and cis-4). Both the complexes have two five-membered [Ru–(H)₂–B–NCS] ruthenacycles with κ²-H–H coordination modes. Density functional theory (DFT) calculations suggest that the activation of boranes across the dual Ru–N site is more facile than the Ru–S one.

Redox-active ruthenium complexes supported by hemilabile κ²-N,S-chelated ruthenacycles undergo unusual dual site B–H bond activation through metal–ligand cooperation with free and bulky boranes.