Complexes 1a-4a Research Articles

Structural optimization of pyridine quinoxaline cobalt (II) catalysts for MMA polymerization based on systematical SCSC transformation study

The Schiff base condensation reaction was adopted to synthesize a series of pyridine-based quinoxaline ligands (L1, L2, L3, L4) using 2-acetylpyridine and 1,2-phenylenediamine aromatic amines with different substituents of –OCH3, –F, -Cl, -Br. Then, four symmetrical dinuclear metal complexes (1–4) were obtained by coordination reaction of the synthesized ligands with CoCl2·6H2O, and six unexpectedly systematic and novel solvent-involved asymmetric mononuclear metal complexes (1A-4A, 3B, 4B) were obtained during single crystals cultivating by solvent diffusion method. The microscopic composition of the complexes were proved by a series of characterizations such as elemental analysis, IR and UV–vis. At the same time, by improving the single crystal culture technology, full crystal sample of compounds was obtained and X-ray single crystal diffraction showed a rare single crystal to single crystal structure transition (SCSC) phenomenon in this study. Furthermore, the catalytic properties of the complexes for MMA polymerization was explored, it was found that the catalytic activity of complexes 1–4 containing different types of substituents on pyridyl quinoxaline ligand was in the order of 1 < 2 <3 < 4, indicating that the complex with an electron-withdrawing substituent showed the higher activity than that of electron-donating substituent. Complexes 1A-4A, 3B and 4B showed higher catalytic activity in MMA polymerization than 1–4, which confirmed that the catalytic activity of mononuclear complexes were generally higher than that of binuclear complexes.

Phenoxyamidine Zn and Al Complexes: Synthesis, Characterization, and Use in the Ring-Opening Polymerization of Lactide

Herein, we report the synthesis of new ditopic ligands, which consist of a phenoxy group and N,N,N′-trisubstituted amidines linked by a methylene spacer (L1–L4). Their coordination chemistry has been investigated with Zn(II) and Al(III). Alkane elimination route between the phenol-amidine proligands (L1H–L4H) and Et2Zn led to dinuclear complexes [(L1–L4)ZnEt]2 (1a–4a) in which the Zn centers are chelated by phenoxyamidine ligands and bridged through the oxygen atom of the phenoxy groups. Salt metathesis reaction between two equivalents of the sodium amidine phenate L1Na and ZnCl2 led to a bis-chelate chiral spiro-complex (L12Zn) 1a′. Analogous alkane elimination route between AlMe3 and the phenol-amidine proligands L1H–L4H allowed the preparation of the mononuclear complexes [(L1–L4)AlMe2] (1b–4b). The phenoxyamidine-Al and -Zn complexes have been characterized by NMR spectroscopy, elemental analysis, and/or high-resolution ESI-MS. The solid state structures of the proligands [L1H2][Br] and L2H as well as of six complexes have been established by single crystal X-ray diffraction analysis. Fluxional properties of the proligands L1H–L2H and of the complexes 1a and 2b have been investigated by VT NMR experiments. In the presence of an alcohol source, complexes 1a–4a and 1b–4b were used as initiators for the controlled ring-opening polymerization (ROP) of rac-lactide to afford atactic polylactic acid (PLA).

Zinc and Magnesium Complexes Bearing Oxazoline-Derived Ligands and Their Application for Ring Opening Polymerization of Cyclic Esters.

A family of different substituents aza(oxazoline) ligand-based zinc and magnesium complexes were synthesized. These complexes can catalyze ring opening polymerization of ε-caprolactone (ε-CL) and lactide (LA) to produce poly-ε-caprolactone and polylactide with good conversions. Polymerization studies showed that the zinc complexes 1a–4a had moderate activity toward LA and ε-CL polymerization. In situ IR spectroscopy research of zinc complexes showed that the N-donor group-substituted complexes had higher activity than that of the O-ether donor group. The substituted analogies and the flexibility of the amino backbone had a distinct influence on the activity of LA and ε-CL polymerization. The alternates of zinc with magnesium produced complexes 5a–8a, which achieved an obviously increased polymerization activity. Among these magnesium complexes, 7a showed the highest activity in the polymerization of LA. At [M]/[cat] = 1000, the reaction progress was stabilized in 5 min with up to 97% conversion of a monomer at ambient temperature.

Ruthenium Complexes are pH-Activated Metallo Prodrugs (pHAMPs) with Light-Triggered Selective Toxicity Toward Cancer Cells.

Metallo prodrugs that take advantage of the inherent acidity surrounding cancer cells have yet to be developed. We report a new class of pH-activated metallo prodrugs (pHAMPs) that are activated by light- and pH-triggered ligand dissociation. These ruthenium complexes take advantage of a key characteristic of cancer cells and hypoxic solid tumors (acidity) that can be exploited to lessen the side effects of chemotherapy. Five ruthenium complexes of the type [(N,N)2Ru(PL)]2+ were synthesized, fully characterized, and tested for cytotoxicity in cell culture (1A: N,N = 2,2'-bipyridine (bipy) and PL, the photolabile ligand, = 6,6'-dihydroxybipyridine (6,6'-dhbp); 2A: N,N = 1,10-phenanthroline (phen) and PL = 6,6'-dhbp; 3A: N,N = 2,3-dihydro-[1,4]dioxino[2,3-f][1,10]phenanthroline (dop) and PL = 6,6'-dhbp; 4A: N,N = bipy and PL = 4,4'-dimethyl-6,6'-dihydroxybipyridine (dmdhbp); 5A: N,N = 1,10-phenanthroline (phen) and PL = 4,4'-dihydroxybipyridine (4,4'-dhbp). The thermodynamic acidity of these complexes was measured in terms of two pKa values for conversion from the acidic form (XA) to the basic form (XB) by removal of two protons. Single-crystal X-ray diffraction data is discussed for 2A, 2B, 3A, 4B, and 5A. All complexes except 5A showed measurable photodissociation with blue light (λ = 450 nm). For complexes 1A-4A and their deprotonated analogues (1B-4B), the protonated form (at pH 5) consistently gave faster rates of photodissociation and larger quantum yields for the photoproduct, [(N,N)2Ru(H2O)2]2+. This shows that low pH can lead to greater rates of photodissociation. Cytotoxicity studies with 1A-5A showed that complex 3A is the most cytotoxic complex of this series with IC50 values as low as 4 μM (with blue light) versus two breast cancer cell lines. Complex 3A is also selectively cytotoxic, with sevenfold higher toxicity toward cancerous versus normal breast cells. Phototoxicity indices with 3A were as high as 120, which shows that dark toxicity is avoided. The key difference between complex 3A and the other complexes tested appears to be higher uptake of the complex as measured by inductively coupled plasma mass spectrometry, and a more hydrophobic complex as compared to 1A, which may enhance uptake. These complexes demonstrate proof of concept for dual activation by both low pH and blue light, thus establishing that a pHAMP approach can be used for selective targeting of cancer cells.

Theoretical studies on the substituent effect on the photophysical properties of two series of heteroleptic Ir(III) complexes

The electronic structures and phosphorescence efficiency for two series of Ir(III) complexes with different substituent groups were theoretically investigated by using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The results reveal that the nature of the different substituents can influence the electron density distributions of frontier molecular orbitals and their energies, resulting in the change of transition character and emission color, while the different number of –(CH2CH2O)– units have an impact on the HOMO and LUMO energy levels of the designed complexes 2a–6a and 2b–6b. It can be speculated that the complexes 1a–4a and 1b–5b are considered to be potential candidates as blue-emitting materials. The assumed complexes 6a and 6b also are the potential candidate as an efficient green-emitting material with high photoluminescent quantum yield.

Phosphane‐Ligated Ionic Palladium Complexes: Synthesis, Characterization and Application as Efficient and Reusable Precatalysts for the Homogeneous Carbonylative Sonogashira Reaction under CuI‐Free Conditions

AbstractThe stable ionic PdII complexes 1A–4A were synthesized through the complexation of PdCl2(MeCN)2 with the phosphane‐functionalized ionic liquids (FILs) 1–4 with π‐acceptor character. Single‐crystal X‐ray diffraction analyses showed that 1A–4A were all composed of PdII‐centred square‐planar cations and triflate (OTf–, CF3SO3–) counteranions. The complex cations in 1A–3A possessed structural similarity to trans‐PdCl2(PPh3)2. The cation in 4A was a new PdII‐centered planar complex ligated by the phosphane–carbon anion–carbene (PCC) pincer in a tripodal manner. The stabilities of 1A–4A were improved due to the intensive π‐backbonding interaction between the Pd and P atoms. When complexes 1A–4A were used as precatalysts for homogeneous carbonylative Sonogashira coupling of PhI with phenylacetylene free of CuI, 1A–3A exhibited excellent catalytic behaviour with a TON of up to 1700 at a CO pressure of 0.5 MPa and moderate temperature of 100 °C, whereas 4A exhibited poor activity towards the transformation of PhI due to the high stability of 4A. The recycling experiments of 3A in [Bpy]BF4 (as a solvent) indicated that 3A could be recycled for 5 runs with neither activity loss nor metal leaching into the organic phase. Complex 3A also proved to be a general precatalyst for the carbonylative Sonogashira couplings of a wide range of aryl iodides with phenylacetylene. The selectivity of the desired carbonylation product depended more on electronic effects than the steric effects of the substituents of the aryl iodides.

Toppled Molecular-Domino Sets by Self-Assembly of Self-assembly: The π-Polymers

A series of designed binuclear palladium(II)-based self-assemblies, [Pd2(en)2(L)2](NO3)4, 1a; [Pd2(tmeda)2(L)2](NO3)4, 2a; [Pd2(bpy)2(L)2](NO3)4, 3a; and [Pd2(phen)2(L)2](NO3)4, 4a, are synthesized. These complexes are obtained in good to excellent yields by equimolar combination of the nonchelating bidentate ligand bis(4-pyridylmethyl)piperazine, L, with the corresponding cis-protected palladium(II) component, that is, Pd(N-N)(NO3)2, under suitable reaction conditions. The cis-protecting N-N units used are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridyl (bpy), and 1,10-phenanthroline (phen). The complexes 1a–4a are well-characterized by 1H NMR, H–H COSY, and HSQC, and the molecular compositions have been established by ESI-MS. The molecular structures are confirmed for the complexes [Pd2(tmeda)2(L)2](ClO4)4, 2b; [Pd2(bpy)2(L)2](ClO4)4, 3b; and [Pd2(phen)2(L)2](NO3)4, 4a, by the single-crystal X-ray diffraction technique. In the cases of the complexes 3b and 4a, the crystal packin...

Outstanding luminescence from neutral copper(i) complexes with pyridyl-tetrazolate and phosphine ligands

Strongly luminescent, neutral copper(I) complexes bearing 5-(2-pyridyl)tetrazolate and various phosphine ligands were synthesized. While the cationic copper(I) precursors 1b-4b do not exceed photoluminescence quantum yields (PLQY) of 4-46%, the neutral complexes 1a-4a show PLQYs of up to 89%.

Expanding the scope of ‘Click’ derived 1,2,3-triazole ligands: New palladium and platinum complexes

Using the ‘Click Protocol’ the new ligands 1-(cyclohexyl)-4-(2-pyridyl)-1,2,3-triazole (1), 1-(2-trifluoromethyl phenyl)-4-(2-pyridyl)-1,2,3-triazole (2), 1-(4-hexyl phenyl)-4-(2-pyridyl)-1,2,3-triazole (3), 1-(2-mercaptomethyl phenyl)-4-(2-pyridyl)-1,2,3-triazole (4) and 1-(4-N,N-dimethylamino phenyl)-4-(2-pyridyl)-1,2,3-triazole (5) were prepared by reacting 2-ethynylpyridine with the corresponding azides. In the next step the ligands were reacted with suitable palladium and platinum precursors to yield the cis-dichloro-palladium complexes 1a–4a and platinum complexes 1b–4b. Investigation of the molecular structure of the free ligands 1 and 5 reveals the formation of infinite chains in the 3D structure which are governed by hydrogen bonds between the triazole units. Likewise the 3D structure of 1a shows infinite chains which are held together by multiple remarkably short C–H⋯Cl–Pd contacts. Electrochemical investigation of the free ligands by cyclic voltammetry showed irreversible reduction processes at highly negative potential. Upon metal complexation huge anodic shifts of the reduction potential were observed. To further characterize the electronic properties of all the compounds UV–Vis spectra were also analyzed.

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η5-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η5-C5H5)Fe(L)2ER3 (L2=(CO)2 (a), (Ph2P)2CH2 (b); ER3=CH3 (1a/b); SiMe3 (2a/b), GeMe3 (3a/b), SnMe3 (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a–4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b–4b were reversible. The Eox values found for the series 1a–4a were in the narrow range 1.3–1.5V and in the order Si>Sn≈Ge>C; those for 1b–4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn>Si≈Ge>C. This latter oxidation potential pattern relates directly to the solution 31P NMR chemical shift data illustrating that stronger donation lowers the Eox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.

Pyrazolate‐Based Dinuclear α‐Diimine‐Type Palladium(II) and Nickel(II) Complexes – a Bimetallic Approach in Olefin Polymerisation

AbstractA series of compartmental pyrazole/imine dinucleating ligands HL1–HL4 have been prepared with different backbone substitutents and different steric bulk of the appending arylimine groups, and two of them have been structurally characterised. With PdCl2 all ligands form the anticipated pyrazolate‐bridged bimetallic complexes LPd2Cl3 (1a–4a) that feature square‐planar metal ions, as is confirmed by the X‐ray crystallographic analyses of L1Pd2Cl3 (1a) and L3Pd2Cl3 (3a). With NiBr2(dme), however, oligonuclear systems [LNi2Br3]x (1b–4b) are formed according to mass spectrometric findings, which is corroborated by the crystallographic structure of [L3Ni2Br3]3. Complexes 1a–4a can be described as bimetallic versions of Brookhart‐type α‐diimine palladium complexes, where dissociation into mononuclear species is prevented by the dinucleating scaffold and the proximate metal ions are suitably positioned to work in concert during substrate transformation. Upon activation of the complexes with MAO and exposure to ethylene, polyethylene is formed. Whereas the palladium complexes display moderate activities, nickel complexes are very active. From structure/activity correlations it is evident that the presence of backbone substitutents at the pyrazolate scaffold as well as bulky ortho aryl substituents is advantageous for polymerisation. Overall, activities of the Ni complexes and the microstructure of the polymer obtained (total branching, Tm and molecular weights) are still rather similar to the data reported previously for mononuclear cationic diimine nickel complexes.

Kinetic Studies upon the Influence of Cyclodextrin on the Polymerization of Methacrylamides in Homogenous Aqueous Solution

AbstractSummary: N‐methacryloyl‐1‐aminopropane (1), N‐methacryloyl‐1‐aminobutane (2), N‐methacryloyl‐1‐aminopentane (3), and N‐methacryloyl‐1‐aminohexane (4) are synthesized and treated with an aqueous solution of randomly methylated β‐cyclodextrin (Me‐β‐CD) to form the water‐soluble host‐guest complexes 1a–4a. In case of the aqueous polymerization of the free monomers 1–4 the initial polymerization rate increases with increasing water solubility. The opposite effect is observed in the case of the polymerizations of the Me‐β‐CD‐complexed methacrylamide monomers 1a–4a. The polymerization rates are increased with increasing alkyl chain length of the complexed monomers 1a–4a and decreasing water solubility of the free monomers 1–4.Initial polymerization rate v0 of CD‐complexed monomers 1a–4a (○) vs. water solubilities of monomers 1–4 (▪).magnified imageInitial polymerization rate v0 of CD‐complexed monomers 1a–4a (○) vs. water solubilities of monomers 1–4 (▪).

Synthesis, characterization and in vitro Antiamoebic Activity of 5-nitrothiophene-2-carboxaldehyde thiosemicarbazones and their Palladium (II) and Ruthenium (II) Complexes

Synthesis of new Palladium(II) and Ruthenium(II) complexes of the type, [Pd(L)Cl 2] and [Ru(η 4-C 8H 12)(L)Cl 2] {where, L = thiosemicarbazones derived from 5-nitrothiophene-2-carboxaldehyde and cycloalkylaminothiocarbonyl hydrazines} have been isolated by the reaction of [Pd(DMSO) 2Cl 2] and [Ru(η 4-C 8H 12)(CH 3CN) 2Cl 2] with 5-nitrothiophene-2-carboxaldehyde thiosemicarbazones. The spectral data revealed that the thiosemicarbazones act as bidentate ligands, making use of thionic sulphur and the azomethine nitrogen atom for coordination to the central metal ion. Microdilution method was used for the assessment of antiamoebic activity of all the compounds against HK-9 strain of Entamoeba histolytica. Among all the thiosemicarbazones, 5-NT-4-BPTSCN ( 3) showed significant antiamoebic activity (IC 50 – 2.56 μM). Enhancement of antiamoebic activity resulted by introducing palladium and ruthenium metals in the thiosemicarbazone moiety. All the Pd(II) and Ru(II) complexes of 5-nitrothiophene-2-carboxaldehyde thiosemicarbazones were found more active then their respective ligands. The complexes 1a-4a, 1b and 3b showed antiamoebic activity.