Unusual Reactivity of a Heterobimetallic Al─Zn Complex With a Carbodiimide.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Single molecular precursors are appropriate starting materials for synthesis of semiconductor nanoparticles (NPs), which allow for the control of atomic ratio, monodispersity, composition and particle size of nanoscaled metallic sulfide nanoparticles. In the present study, we have reported the synthesis of nanostructured chalcogenides pharmacologically active active zinc sulfide nanoparticles (ZnS NPs) using Zn (II) ion inserted thiosemicarbazone ligand as a single molecular precursor .The precursors were thermally pyrolysized using high energy microwave radiations to obtain very fine ZnS nanoparticles. In this synthesis, we use DMSO as a nonpolar solvent for the synthesis of all compounds. The heating of Zinc complex in the non- aqueous environment of DMSO plays a very crucial role in decreasing reaction time, reducing the chances of side reactions and proper conversion of Zn complex into ZnS nanoparticles. In this reaction Zn complex of thiosemicarbazone ligand provides both Zn2+ and S2- ions for synthesis of ZnS nanoparticles. The microwave synthesis of ZnS NPs from Zn complex is a very simple, fast, highly effective, efficient and low cost method. All synthesized compounds were characterized by various structural, electronic, vibrational, optical, morphological and pharmacological characterizations. The prepared ZnS NPs were found to crystallize in cubic phase, which generally forms at low temperatures, with the dimensions dependent upon the molar ratio of molecular precursors used. Synthesized ZnS nanomaterials had surface sulfur vacancies that extend their absorption spectra towards the visible region and decreased the bond gap. This allowed ZnS nanoparticles to demonstrate various pharmacological activities like antibacterial, antioxidant and anti-inflammatory activities under normal conditions. Powered X-ray diffraction studies confirms the formation of well -defined equispaced crystalline ZnS NPS. TEM and FE SEM microscopic studies confirmed the elongated tubules structure of ZnS NPs with an average particle size of 60 nm. Sharpe electronic absorption band at 390 nm indicates the synthesis of good quality ZnS NPs. The FT-IR spectral studies confirmed the presence of Zn-S stretching, N-H bending and C=N stretching, vibrations in molecular precursor as Zn(II) complex. The thermal analysis of molecular precursor was performed to investigate the thermal stability of zinc complex. The Zn complex was stable up-to 3800 c. All synthesized compounds demonstrated excellent pharmacological activities like antibacterial, antioxidant and antiinflammatory activities as compared to standards used in analysis of compounds. The microwave synthesis of ZnS nanoparticles via single molecular precursor in proper stoichiometric ratios is an excellent and an efficient method for synthesizing highly effective bioactive agents which can be considered as good drug candidate for the treatment of various diseases in future

The title Zn (II) complex was synthesized by reacting the compound Bis-[(E)-3{2-(1-4-chlorophenyl) ethylidiene}hydrazinyl]-N-(4-methylphenyl)-3-oxo propanamide with Zn (II) chloride dihydrate in alkaline dimethylsulphoxide and ethanol solution under reflexing condition for 8 h. The resultant compound was filtered and recrystallized from ethanol. The hydrazone Schiff base ligand and its Zn (II) complex were characterized by using UV-Vis spectroscopy and XRD, TEM and SEM analysis. The antibacterial activities of ligand and its Zn complex were examined using disc diffusion method. The spectra results showed that the hydrazone ligand undergoes keto-enoltautomerism forming a bidentated ligand (N,N) towards Zn+2 (II) ion. It is very interesting that on sides of the two hydrazone ligands which coordinate to the Zn+2 ions, an additional two thiosemicarbazine moiety were also coordinated with Zn+2 ions in the crystalline powder, resulting in a hexa coordinated octahedral Zn (II) complex. Both hydrazone Schiff base ligand and its Zn (II) complex were found to exhibit good antibacterial activity even when the concentrations were high. Molecular docking analysis also deciphered that Zinc complex and carbohydrazone ligand both were found to be fitted into the active sites of molecular targets and Zn complex showed better binding affinities towards macromolecules compared to ligand.

The binding site of new complex Zn(ii) of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and HAS.

Novel synthetic methods for Ti−Mo, Ti−W, and Ti−Ru heterobimetallic complexes are established by the reaction of a certain titanium(III) alkoxide and the corresponding metal carbonyl dimer, [CpM(CO)n]2 [M = Mo, W (n = 3); M = Ru (n = 2)]. Thus, a novel monomeric titanium complex, Cp2Ti(OtBu) (1), which is synthesized from Cp2TiCl and KOtBu and characterized by spectroscopy and crystallography, smoothly reacts with [CpM(CO)3]2 (M = Mo (2a), W (2b)) to give heterobimetallic complexes, Cp2Ti(OtBu)(μ-OC)M(CO)2Cp (M = Mo (3a) and W (3b)), of which two metallic moieties are linked by the isocarbonyl bridge. Similar reaction of 1 with [CpRu(CO)2]2 (4) does not occur thermally, but is accomplished under photoirradiation to afford Cp2(OtBu)Ti−Ru(CO)2Cp (5), of which two metallic moieties are linked by a direct metal−metal bond. Use of 1 is particularly important for these reactions; other titanium alkoxides such as [Cp2Ti(OMe)]2 and Cp2Ti[O(2,6-tBu2-4-Me)C6H2] do not react with the metal carbonyl dimers. An interesting feature of these new heterobimetallic complexes, 3a, 3b, and 5, is the existence of the thermal fragmentation process to regenerate the starting materials: 3a or 3b is actually in equilibrium with a mixture of 1 and 2a or 1 and 2b, respectively [ΔG0298K= −4.1 ± 0.2 kcal mol-1 (3a), −4.3 ± 0.2 kcal mol-1 (3b)]. The Ti−Ru compound 5 thermally undergoes fragmentation to regenerate 1 and 4. The formation of these heterobimetallic complexes is formally considered as the metal−metal bond cleavage of metal carbonyl dimers by a Ti(III) reducing reagent; possible mechanisms are discussed.

Novel series of nanosized mono- and homobi-nuclear metal complexes of sulfathiazole azo dye ligand: Synthesis, characterization, DNA-binding affinity, and anticancer activity

In the current research, we have reported the synthesis of eight new Co (II), Ni (II), Cu (II) and Zn (II) metal complexes from aldehyde derivatives and 3,5‐dichlorobenzohydrazide‐based hydrazone ligands (HL1HL2) in an effort to identify a combating agent for infectious ailments. Further, numerous physical and spectral studies were carried out to characterize the compounds and the spectral analysis indicates octahedral geometry around central metal ions in the complexes. The anti‐tuberculosis (TB) activity indicates that the complexes (3–10) are highly active for TB ailment and Zn (II) complex (10) has double efficacy to control the TB dysfunction with MIC value (0.006 ± 0.001 μmol/mL) in comparison with streptomycin (0.010 ± 0.001 μmol/mL) while complexes (6), (8), and (9) are comparably active (0.013 ± 0.001–0.014 ± 0.002 μmol/mL MIC) to inhibit the TB malformation. The antimicrobial investigation affirmed that zinc complex (10) has higher efficacy to control the microbial ailments with 0.0064–0.0129 μmol/mL MIC value. The anti‐inflammatory activity also revealed that the complexes (3–10) are highly active for inflammation and the Zn complex (10) has comparable IC50 value (7.58 ± 0.02 μM) with diclofenac sodium to hinder the inflammation diseases. Furthermore, the computational techniques such as molecular docking, density functional theory, molecular electrostatic potential and absorption, distribution, metabolism, excretion and toxicity studies were conducted against highly active ligand (2) and its complexes (7–10) which advocates that the biological activity of the hydrazone ligands was increased on complexation and the complex (10) has higher potency to control infectious ailments that behave as effective infection inhibitor without any toxic effects. Hence, the present research gives a new insight for in vivo investigation.

Synthesis of some oligopyridine–galactose conjugates and their metal complexes: a simple entry to multivalent sugar ligands

The readily accessible dianionic β-diketiminato lanthanide amido complexes LnLN(SiMe3)2(THF) (L = {(2,6-(i)Pr2C6H3)NC(CH2)CHC(CH3)N(2,6-(i)Pr2C6H3)}(2-)) show an unprecedented reactivity toward carbodiimides. The reaction with N,N'-dicyclohexylcarbodiimide (DCC) led via [4 + 2] cycloaddition to γ-amidine-functionalized dianionic β-diketiminato lanthanide amido complexes, LnL(1)N(SiMe3)2 (L(1) = {[(NHC6H11)(NC6H11)C]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(2-), Ln = Sm(1), Yb(2), Y(3), Gd(4)). Conversion of a mixture of SmLN(SiMe3)2(THF) and NaN(SiMe3)2 with carbodiimide furnished the heterobimetallic complexes of Sm/Na with a novel amidinate-functionalized trianionic β-diketiminate ligand, [Na(DME)2](μ-L(2))[SmN(SiMe3)2] (L(2) = {[C(N(i)Pr)2]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(3-), DME = dimethoxyethane) (5) for N,N'-diisopropylcarbodiimide (DIC) and [Na(DME)3](+)[SmL(3)N(SiMe3)2](-) (L(3) = {[C(NCy)2]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(3-)) (6) for DCC. Molecular structures of complexes 1-6 were determined by an X-ray single crystal structure analysis. Complexes 1-4 were found to be highly active initiators of the ring-opening polymerization (ROP) of L-lactide (L-LA). The activity depended on the central metal with the increasing sequence of Yb < Y < Gd < Sm. Notably, the binary 1/BnOH (benzyl alcohol) system exhibited an "immortal" nature and proved able to convert 2000 equivalents of L-LA with up to 100 equivalents of BnOH per initiator. All the polylactides (PLAs) obtained showed monomodal, narrow molar mass distributions (M(w)/M(n) = 1.08-1.13) with the M(n) (average number molar mass) decreasing with increasing amount of BnOH proportionally.

Chapter 1 gives a general introduction into d-block elements, including some of the fundamental concepts, such as the 18 electron rule and metal-metal bonding. It also includes an overview of low oxidation state metal complexes, in addition to some of the ligands that have been used to stabilize such complexes. Finally, dimeric magnesium(I) complexes are introduced showing their use as effective reducing agents in organic and inorganic synthesis. Chapter 2 focuses on the preparion of extrememly bulky amido d-block metal(II) halide complexes, including those of chromium, manganese, iron, cobalt, zinc, cadmium and mercury. The synthesis, structure and magnetic propreties of these complexes were explored and compared to related terphenyl d-block metal(II) halide complexes. These amido d-block metal(II) halide complexes could potentially serve as precursors for low coordinate, low oxidation state d-block chemistry. Low coordinate, low oxidation state manganese complexes are discussed in Chapter 3. These include the characterisation of the first two-coordinate manganese(I) dimer [{(Ar*(SiMe3)NMn}₂] (Ar* = 2,6-{Ph₂CH}₂-4-Me-C₆H₂), synthesised by the reduction of [Ar*(SiMe3)NMn(THF)(µ-Br)}₂] with the magnesium(I) reducing agent [{(MesNacnac)Mg}₂] (MesNacnac = [(MesNCMe)₂CH]–, Mes = mesityl). The reduction of the bulkier precursor complex [Ar†(SiⁱPr₃)NMn(THF)(µ-Br)}₂] (Ar† = 2,6-{Ph₂CH}₂-4-ⁱ Pr-C6H₂) with the same magnesium(I) reducing agent yielded the unprecedented Mn(0)Mg(II) heterobimetallic complex [Ar†(SiⁱPr₃)NMnMg(MesNacnac)] posessing an unsupported Mn-Mg bond. The complex was utilized as an “inorganic Grignard reagent”, in the prepaption of the asymmetric manganese(I) dimer [Ar†(SiⁱPr₃)NMnMn(SiMe₃)Ar*] and the related mixed valence, bis(amido)-heterobimetallic complex [CrMn{Ar†(SiⁱPr₃)N}{Ar*(SiMe₃)N}]. It is also shown to act as a two-electron reducing agent in reactions with unsaturated substrates. Chapter 4 concentrates on low oxidation state group 12 complexes with metal-metal bonds. This includes the synthesis and characterisation of a homologous series of two-coordinate amido group 12 metal(I) dimers [{(Ar†(SiMe₃)NM}₂] (M = Zn, Cd, Hg). The reduction of the extrememly bulky amido zinc(II) bromide complex [Ar*(SiⁱPr₃)NZnBr] with [{(MesNacnac)Mg}₂] gave the novel Zn(0)Mg(II) heterobimetallic complex [Ar*(SiⁱPr₃)NZnMg(MesNacnac)], which bears the first example of a Zn-Mg bond in a molecular complex. The complex was utilized as a transfer reagent in the preparation of the unprecendented trimetallic zinc complex [{Ar*(SiⁱPr₃)NZn}₂Zn], which bears a string of two-coordinate zinc atoms. The related group 12 trimetallic complexes [{Ar*(SiiPr₃)NZn}₂M] (M = Cd, Hg) were also isolated. Chapter 5 investigates the synthesis, structure and reactivity of low coordinate, low oxidation state cobalt complexes. A series of low coordinate, high-spin cobalt(I) complexes bearing the extremely bulky amide ligand Ar*(SiPh₃)N– are described. These include the benzene capped cobalt(I) complex [Ar*(SiPh₃)NCo(η⁶-benzene)], which readly looses its benzene ligand upon dissolution in THF or fluorobenzene, to give the dimeric cobalt(I) complex [{Ar*(SiPh₃)NCo}₂]. The first neutral two-coordinate cobalt(I) complex [Ar*(SiPh₃)NCo(IPriMe)] (IPriMe = :C{N(ⁱPr)C(Me)}₂) was also isolated by exchange of the benzene ligand with the N-heterocyclic carbene IPriMe. Finally, Chapter 6 discusses transition metal tetrelyne complexes, which are heavier group 14 analogues of transition metal carbyne complexes. The synthesis and structure of the two singly bonded Mo-Ge complexes [Cp(CO)₃Mo–GeN(Ph)Ar*] (Cp = η5-C₅H₅) and [Cp(CO)₃Mo–GeN(SiMe₃)Ar*] is discussed. The latter readily eliminates a molecule of CO when heated or irradiated with UV light to give the unprecedented amino-germylyne complex [Cp(CO)₃Mo≡GeN(SiMe₃)Ar*]. The spectroscopic and structural data for this complex, in combination with the results of computational studies, show that this compound is best viewed as having a bent Mo−Ge “triple” bond, with little multiple bond character to its Ge−N interaction. Awards: Winner of the Mollie Holman Doctoral Medal for Excellence, Faculty of Science, 2015.

Transition metal heterobimetallic catalysts provide an alternative to classic transition metal ligand catalyst design. The resurgence in popularity of heterobimetallic complexes prompted our use of density functional theory to examine the mechanism and reactivity of alkene hydrogenation catalyzed by the transition metal heterobimetallic complex Cp2Ta(CH2)2Ir(CO)(PPh3) and the transition metal/main group complex Ph2P(CH2)2Ir(CO)(PPh3). Calculations indicate that the Ir–Ta and Ir–P catalysts operate by different mechanisms. For the Ir–Ta complex, initial H2 oxidative addition to the Ir metal center followed by reductive elimination of an Ir–H and μ-CH2 bridge transforms the starting heterobimetallic complex into an active Ir–H catalyst. This catalyst precursor transformation occurs because the cationic Cp2Ta group provides a low activation barrier for reductive elimination. This transformation does not occur for the Ir–P catalyst because the reductive elimination activation barrier is significantly higher in energy. The active heterobimetallic Ir–H likely catalyzes multiple turnovers of alkene hydrogenation before reforming the original heterobimetallic Ir–Ta complex. The Ir–H catalytic cycle involves a series of classic organometallic reaction steps: alkene migratory insertion, H2 oxidative addition, and reductive elimination. In the Ir–P mechanism, the Ph2P(CH2)2 group remains as a spectator ligand throughout the active catalytic cycle. The Ir–P catalytic cycle involves H2 oxidative addition, phosphine ligand dissociation, ethylene migratory insertion, and reductive elimination.

A new series of transition metal complexes of bidentate Schiff base compound derived from 2‐hydroxy‐1‐(2‐methoxyethylimino)‐naphthalene (HL) were synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), and UV–vis spectroscopies. X‐ray single crystal structures of Zn(II), Mn(III), and Co(III) complexes (1–4) have also been determined, and it was indicated that these Zn(II) and Co(III) complexes (1, 4) are in an octahedral geometry. Whereas, it was found that the Zn complex (2) is in quite a regular tetrahedral environment. Also, the Mn center in complex (3) is ligated by two azomethine nitrogen atoms, two ligand oxygen atoms, and one Cl atom of metal salt forming five coordinated tetragonal pyramid geometry around the Mn atoms. The cyclic voltammetry of the complexes specifies an irreversible redox behavior for all complexes (1–4). Next, DFT/B3LYP theoretical method was used to determine the optimal geometrical configurations and comparison between experimental and theoretical data, as well as for calculations of molecular electrostatic potential, highest‐occupied molecular orbital (HOMO)‐lowest‐unoccupied molecular orbital (LUMO) energy values of selected compounds. The study of non‐covalent interactions was done by Hirshfeld surface analysis using CrystalExplorer program. Furthermore, molecular docking inspection was carried out to study the binding affinity of the tested complexes towards protein B‐cell lymphorna (PDB ID: 4LXD). Using the results obtained from the molecular docking and the summarized interaction of the binding processes, these structures show the validity of effective inhibition against liver cancer.

Molecular docking and inhibitory effects of a novel cytotoxic agent with bovine liver catalase

Zinc K-edge X-ray absorption fine structure (XAFS) experiments were performed in the solid and solution states at low temperature (10 K), on dimeric and monomeric anti-inflammatory Zn(II) complexes of indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid=IndoH] of the formula [Zn2(Indo)4L2] [L=pyridine (Py), N,N-dimethylacetamide (DMA)], [Zn(Indo)2L2] [L=ethanol (EtOH), methanol (MeOH)], and Zn(II) acetate dihydrate [Zn(OAc)2(OH2)2]. The bond distances and angles obtained from multiple-scattering fits to the XAFS data of the Zn(II) dimeric complexes in the solid and solution states exhibit excellent correspondence with those obtained from single crystal diffraction studies. The Zn...Zn separations of 2.97 and 2.96 A and carboxylate group O-C-O angles of 125 degrees for powdered [Zn2(Indo)4(Py)2] and [Zn2(Indo)4(DMA)2] agree well with the XRD values of 2.969(1) and 2.9686(6) A and 125.8(4) degrees and 126.1(2) degrees, respectively. The calculated Zn-O(RCOO) and Zn-L bond distances of 2.03 and 2.04 A, or 2.02 and 1.98 A for Py or DMA complexes, respectively, also agree well with crystallographic data. The X-ray powder diffraction data on samples of the monomers exhibited additional reflections apart from those due to the crystallographically characterized cis-[Zn(eta2-O,O'-Indo)2L2], but microanalyses were consistent with this formulation. Therefore, mixed models that contained the cis complex and a second component consisting of a trans-six-coordinate complex, a five-coordinate complex, or a four-coordinate complex were used to model the XAFS. The best fits to the XAFS data were obtained with a mixture of the cis-six-coordinate complex and a four-coordinate complex containing two monodentate Indo ligands. The bond lengths for the six-coordinate structure were consistent with those determined on a single crystal, and those for the four-coordinate complexes were consistent with related four-coordinate structures with two monodentate carboxylate ligands. Dissolution of the dimer (DMA adduct) in DMF resulted in a mixture of dimer and monomer species as shown by MS XAFS fitting. This is the first time that solution structures have been determined for anti-inflammatory Zn(II) complexes, and this is an important first step in understanding the pharmacology of the complexes.

P6.08 - Cationic porphyrin-phenazine conjugates as quadruplex DNA ligands and potential agents for anticancer therapy