Terdentate Ligand Research Articles

Luminescent Platinum(II) Complexes with Terdentate N∧C∧C Ligands.

The synthesis, structure, and luminescence of Pt(II) complexes of the type [Pt(N∧C∧C)(L)] are reported, where N∧C∧C is a terdentate ligand resulting from the cycloplatination of 2-(3,5-diphenoxyphenyl)pyridine or 2-(4,4″-dimethyl-[1,1':3',1″-terphenyl]-5'-yl)pyridine, and L represents a monodentate ancillary ligand, which can be γ-picoline, 4-pyridinecarboxaldehyde, PPh3, n-butyl or 2,6-dimethylphenyl isocyanide, CO, or the N-heterocyclic carbenes 1-butyl-3-methylimidazol-2-ylidene or 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene. Derivatives bearing CO, isocyanides, or carbenes showed the highest stabilities in solution, whereas the pyridine and PPh3 derivatives establish ligand-exchange equilibria in acetonitrile. Different supramolecular structures are observed in the solid state, which largely depend on the nature of the ancillary ligand. Isocyanides and CO favor π interactions between the aromatic rings, metallophilic Pt···Pt contacts, or a combination of both. In contrast, pyridine ligands may lead to bimolecular assemblies driven by C-H···O, C-H···Pt, or C-H/π hydrogen bonds. Luminescence was examined in fluid solution, poly(methyl methacrylate) matrices, and the solid state at 298 K, and in 2-methyltetrahydrofuran glasses at 77 K. The majority of derivatives show highly efficient emissions from 3ILCT/MLCT or 3ILCT/MLCT/LLCT excited states of monomeric species. The formation of excimers and different types of emissive aggregates are demonstrated, which lead to red-shifted emissions of different origins and characteristics depending on the involved noncovalent interactions.

Synthesis of an Electrodeficient Dipyridylbenzene-like Terdentate Ligand: Cyclometallating Ligand for Highly Emitting Iridium(III) and Platinum(II) Complexes

Cyclometallated iridium(III) and platinum(II) complexes are intensely used in optoelectronics for their photophysical properties and ability to convert excitons from singlet to triplet state, thus improving the device efficiency. In this contribution, we report the multi-steps synthesis of an electrodeficient dipyridylbenzene-like terdentate ligand [N^C^N], namely 2′,6′-dimethyl-2,3′:5′,2″-terpyridine (6), with 18% overall yield. Compound 6 has been employed to synthesize two phosphorescent complexes of platinum(II) and iridium(III), namely compounds 7 and 8, respectively. Both complexes have been characterized by NMR and high resolution mass spectrometry, and demonstrate high luminescence quantum yields in a deaerated solution at room temperature, with 18% and 61% for 7 and 8, respectively. If the iridium(III) complex displays similar emission properties to [Ir(dpyx)(ppy)Cl] (dpyx = 3,5-dimethyl-2,6-dipyridylbenzene and ppy = 2- phenylpyridine), the platinum(II) derivative, with λem = 470 nm, is a rare example of a fluorine atom-free blue emitting [N^C^N]PtCl complex.

Ir(III) Compounds Containing a Terdentate Ligand Are Potent Inhibitors of Proliferation and Effective Antimetastatic Agents in Aggressive Triple-Negative Breast Cancer Cells.

Herein, we report a series of new octahedral iridium(III) complexes Ir1-Ir9 of the type [Ir(N^N^N)(C^N)Cl]PF6 (N^N^N = 4'-(p-tolyl)-2,2':6',2″-terpyridine; C^N = deprotonated 2-arylbenzimidazole backbone) to introduce new metal-based compounds for effective inhibition of metastatic processes in triple-negative breast cancer (TNBC). The results show that the structural modifications within the C^N scaffold strongly impact the antimetastatic properties of these complexes in TNBC cells. Furthermore, testing the antimetastatic effects of the investigated Ir complexes revealed that the highest antimetastatic activity in TNBC cells is exhibited by complex Ir1. This result was in contrast to the effects of the clinically used drug doxorubicin used in conventional chemotherapy of TNBC, which conversely promoted metastatic properties of TNBC cells. Thus, the latter result suggests that doxorubicin chemotherapy may increase the risk of metastasis of breast cancer cells, so the search for new drugs to treat breast cancer that would show better antitumor effects than doxorubicin is justified.

Chelator PBT2 Forms a Ternary Cu2+ Complex with β-Amyloid That Has High Stability but Low Specificity.

The metal chelator PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) acts as a terdentate ligand capable of forming binary and ternary Cu2+ complexes. It was clinically trialed as an Alzheimer's disease (AD) therapy but failed to progress beyond phase II. The β-amyloid (Aβ) peptide associated with AD was recently concluded to form a unique Cu(Aβ) complex that is inaccessible to PBT2. Herein, it is shown that the species ascribed to this binary Cu(Aβ) complex in fact corresponds to ternary Cu(PBT2)NImAβ complexes formed by the anchoring of Cu(PBT2) on imine nitrogen (NIm) donors of His side chains. The primary site of ternary complex formation is His6, with a conditional stepwise formation constant at pH 7.4 (Kc [M-1]) of logKc = 6.4 ± 0.1, and a second site is supplied by His13 or His14 (logKc = 4.4 ± 0.1). The stability of Cu(PBT2)NImH13/14 is comparable with that of the simplest Cu(PBT2)NIm complexes involving the NIm coordination of free imidazole (logKc = 4.22 ± 0.09) and histamine (logKc = 4.00 ± 0.05). The 100-fold larger formation constant for Cu(PBT2)NImH6 indicates that outer-sphere ligand-peptide interactions strongly stabilize its structure. Despite the relatively high stability of Cu(PBT2)NImH6, PBT2 is a promiscuous chelator capable of forming a ternary Cu(PBT2)NIm complex with any ligand containing an NIm donor. These ligands include histamine, L-His, and ubiquitous His side chains of peptides and proteins in the extracellular milieu, whose combined effect should outweigh that of a single Cu(PBT2)NImH6 complex regardless of its stability. We therefore conclude that PBT2 is capable of accessing Cu(Aβ) complexes with high stability but low specificity. The results have implications for future AD therapeutic strategies and understanding the role of PBT2 in the bulk transport of transition metal ions. Given the repurposing of PBT2 as a drug for breaking antibiotic resistance, ternary Cu(PBT2)NIm and analogous Zn(PBT2)NIm complexes may be relevant to its antimicrobial properties.

A Novel Class of Cyclometalated Platinum(II) Complexes for Solution-Processable OLEDs.

Substitution of the chlorido ligand of cyclometalated [Pt (5-R-1,3-di(2-pyridyl) benzene)Cl] (R = methyl, mesityl, 2-thienyl, or 4-diphenylamino-phenyl) by 4-phenylthiazole-2-thiolate leads to related thiolato complexes, which were fully characterized. Their photophysical properties were determined in degassed dichloromethane solution. The emission color of the novel complexes can be easily tuned by the nature of the substituents on the terdentate ligand, as is the case for the parent chlorido complexes. Their luminescence Quantum Yield is high, with that of the compounds with the 2-thienyl or 4-diphenylamino-phenyl substituents being much higher than that of the related chloride complexes. The platinum complex with the cyclometalated 5-(2-thienyl)-1,3-di(2-pyridyl) benzene was used as the emitter for the fabrication of a yellow solution-processable OLED.

Synthesis and Characterisation of Transition Metal Complexes of a Novel 1,5‐benzodiazepine‐Functionalised Tertiary Phosphine

AbstractThe one‐step synthesis (44 % isolated yield) of the 1,5‐benzodiazapine functionalised phosphine 1, C31H31N2OP, is reported. Bridge cleavage of {MCl(μ‐Cl)(η5‐Cp*)}2 (M=Ir, Rh) with 2 equiv. of 1 in CH2Cl2 gave the mononuclear compounds [MCl2(η5‐Cp*)(P‐1)] (M=Ir, 2 a; M=Rh, 2 b) in which 1 functions as a P‐monodentate ligand. Rapid C(sp3)−H bond activation, at room temperature, is observed for 2 a leading to the unusual cyclometallated complex [Ir(η5‐Cp*)(P,N,C‐1)]Cl2 3 (or 3‘) bearing an anionic P/Namine/C‐terdentate ligand. Reaction of [Pt(CH3)Cl(η4‐cod)] with one equiv. of 1 led to [Pt(CH3)Cl(P,N‐1)] 4, suggesting that 3 may form via an intermediate IrIII cationic species in which the ligand is P,N‐bound. The IrI complex [IrCl(η4‐cod)(P‐1)] 5 does not, under similar conditions, show any evidence for C−H activation. Single crystal X‐ray studies on 1, 2 a, 2 b, 3, 3‘, 4, and 5 reveal intramolecular N ⋅⋅⋅ H−O H‐bonding in all cases.

First divalent copper complex of a terdentate thiosemicarbazido-pyrazoline derived from 2,4-pentanedione bis(thiosemicarbazone): Synthesis, structural characterisation and antimicrobial in vitro activity assessment

Reaction of 2,4-pentanedione with thiosemicarbazide in 1:2 ratio produces cyclic pyrazoline thiosemicarbazone (H2L2 with L2 = C7H12N6S2). The obtained ligand has been characterized by elemental analysis, UV–Visible, FTIR, 1H and 13C NMR. The results suggest that the ligand is in pyrazolinic form, and finally the structure has been confirmed by single crystal X-ray diffraction. The [(L2•)Cu(SCN)] copper complex has been prepared by reaction of H2L2 and thiocyanate salt with copper acetates and has been fully characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, as well as UV–Visible, FTIR, and Raman spectroscopies. TGA analysis and magnetic measurements were also performed. Single-crystal X-ray diffraction reveals that the complex is a neutral monomer with copper in distorted tetrahedral environment. The anionic ligand (L2•)− remained in cyclic form and is coordinated as terdentate ligand (SNS). The title complex results from a double deprotonation coupled with a monoelectronic oxidation of H2L2 and it may be seen as a CuII-ligand radical type complex. The copper ion is tetra coordinated (CuN2S2) by two sulfur and one nitrogen of (L2•)− and by thiocyanate nitrogen atoms. The new [(L2•)Cu(SCN)] complex crystallizes in the monoclinic system and C 2/c space group. Full-Potential Linearized Augmented Planewave Method (FLAPW) calculations based on the Density-Functional Theory (DFT) principle are performed to shed light on both electronic and magnetic structures as well. [(L2•)Cu(SCN)] showed a greater activity than its parental ligand H2L2 against two strains of the phytopathogenic fungus Verticillium dahliae while a moderate antibacterial activity was recorded with both against Agrobacterium tumefaciens strains and Pseudomonas syringae pv. syringae.

Novel nickel(II), palladium(II), and platinum(II) complexes having a pyrrolyl-iminophosphine (PNN) pincer: Synthesis, crystal structures, and cytotoxic activity

A pyrrolyl-iminophosphine (PNNH) which would act as a potential terdentate ligand has been prepared by Schiff base reaction. Complexes [M(PNN)X] (M = Ni; X = Cl (1), Pd; X = Cl (2), Br (3), I (4), M = Pt; X = Cl (5)) were prepared. The title complexes were characterized by various spectroscopic (IR, 1H, 13C, and 31P NMR) and elemental analyses. The molecular structures of 1, 2, and 5 have been established by single-crystal X-ray crystallography, demonstrating a distorted square planar geometry comprising two 5-membered metallacyclic rings. Complexes 1 and 2 were found to crystallize in the orthorhombic while complex 5 crystallizes in the monoclinic. Cytotoxicities of the complexes along with PNNH were evaluated against A549 (lung), SK-OV-3 (ovarian), SM-MEL-2 (skin), and HCT15 (colon) human cancer cell lines by sulforhodamine B assay. Notably, the palladium(II) complex (2) shows the highest activity. Apoptosis activity along with the caspase inhibitor Z-VAD (Z-Val-Ala-Asp-fluoromethyl ketone) assay of 2 and 5 against A549 and HCT15 cancer cell lines were investigated to learn a mechanistic pathway for the observed cytotoxicity, practically eliminating an apoptotic cell-death route. Complexes 2 and 5 were studied to DNA cleavage assay and molecular docking simulation. The DNA (pcDNA3.0) cleavage experiment evaluates complex 5 interacting with DNA, more effectively, in comparison to complex 2. Molecular docking simulation of 2 and 5 toward DNA and GRP78 (glucose-regulated protein 78) was performed to predict binding sites of ligand-receptors and a plausible mechanistic aspect of metallodrug-action.

Palladium(II) complexes of hemilabile NNS and NNSe iminophosphorane ligands: Synthesis, characterization, and reactivity

Four terdentate ligands combining (2-indolyl)iminophosphorane with a thioether or selenoether moiety, with general formula 2-C8H6N(Ph2P = NC6H4XR) [X = S, R = CH3 (2), C6H5 (3); X = Se, R = CH3 (4), C6H5 (5)], were synthesized and fully characterized, including the structure of ligand (2) by single-crystal X-ray crystallography. Treatment of ligands 2–5 with PdCl2(CH3CN)2 produces non-symmetrical N,N,X-Pd(II) pincer complexes [PdCl{2-C8H5N(Ph2P = NC6H4XR-κ3-N,N,X)}] [X = S, R = CH3 (6), C6H5 (7); X = Se, R = CH3 (8), C6H5 (9)]. All complexes were fully characterized spectroscopically and by single-crystal X-ray crystallography. In presence of NaPF6 or NaBF4, treatment of 6 with neutral ligands NEt3, Pyridine and PPh3 gives mononuclear cationic complexes 10, 11, 12 where Cl− is replaced by the corresponding ligand. The solid state structure of cationic complexes 10–12 show that κ3-N,N,X pincer coordination is preserved. Reaction of 6 with diphosphane Ph2P(CH2)2PPh2 (dppe) in 1:1 ratio promotes liberation of the sulfur donor atom from Pd(II) and gives the mononuclear cationic complex 13 bearing the ligand in bidentate N,N chelation and the diphosphane in P,P chelation. Solid-state structure of 13 determined by X-ray crystallography confirms the labile character of the thioether group and reveals a strong interaction between the iminic nitrogen and sulfur atom, holding the thioether group very close to the metal center. Reversibility of the process is proven by reformation of the pincer structure upon treatment of 13 with O2 and release of Ph2P(O)(CH2)2P(O)Ph2 (dppeO2). When complexes 7–9 are treated with the same sequence of reactions, 31P NMR monitoring indicates that pincer complexes with selenoether donors undergo the same reversible hemilability.

Assessing the safety of complementary medicines in lactation

A pyrrolyl-iminophosphine (PNNH) which would act as a potential terdentate ligand has been prepared by Schiff base reaction. Complexes [M(PNN)X] (M = Ni; X = Cl (1), Pd; X = Cl (2), Br (3), I (4), M = Pt; X = Cl (5)) were prepared. The title complexes were characterized by various spectroscopic (IR, 1H, 13C, and 31P NMR) and elemental analyses. The molecular structures of 1, 2, and 5 have been established by single-crystal X-ray crystallography, demonstrating a distorted square planar geometry comprising two 5-membered metallacyclic rings. Complexes 1 and 2 were found to crystallize in the orthorhombic while complex 5 crystallizes in the monoclinic. Cytotoxicities of the complexes along with PNNH were evaluated against A549 (lung), SK-OV-3 (ovarian), SM-MEL-2 (skin), and HCT15 (colon) human cancer cell lines by sulforhodamine B assay. Notably, the palladium(II) complex (2) shows the highest activity. Apoptosis activity along with the caspase inhibitor Z-VAD (Z-Val-Ala-Asp-fluoromethyl ketone) assay of 2 and 5 against A549 and HCT15 cancer cell lines were investigated to learn a mechanistic pathway for the observed cytotoxicity, practically eliminating an apoptotic cell-death route. Complexes 2 and 5 were studied to DNA cleavage assay and molecular docking simulation. The DNA (pcDNA3.0) cleavage experiment evaluates complex 5 interacting with DNA, more effectively, in comparison to complex 2. Molecular docking simulation of 2 and 5 toward DNA and GRP78 (glucose-regulated protein 78) was performed to predict binding sites of ligand-receptors and a plausible mechanistic aspect of metallodrug-action.

(Diphenylphosphino)alkylaldehyde affords hydride- or alkyl-[(diphenylphosphino)alkylacyl]rhodium(iii) or (diphenylphosphino)alkylester complexes: theoretical and experimental diastereoselectivity.

The reaction of [RhCl(COD)]2 (COD = 1,5-cyclooctadiene) with racemic PPh2(CH(Ph)CH2CHO) and pyridine (py) led to the oxidative addition of the aldehyde, and a single geometric isomer of [RhHCl(PPh2(CH(Ph)CH2CO))(py)2] (1), with hydride trans to chloride, was obtained as a mixture of two diastereomers in a 95 : 5 ratio; this was in agreement with density functional theory (DFT) calculations. In a chloroform solution, the exchange of hydride by chloride yielded [RhCl2(PPh2(CH(Ph)CH2CO))(py)2] (2) as a mixture of a kinetically preferred species, trans-py-2a, and two diastereomers, cis-Cl-2b' and cis-Cl-2b, with cis pyridines and a chloride trans to acyl; as predicted by the DFT calculations, the latter was the major species. Complex 1 reacted with racemic PPh2(CH(Ph)CH2CHO) or PPh2(o-C6H4CHO) to afford [RhHCl(PPh2(CH(Ph)CH2CO))(κ1-PPh2(CH(Ph)CH2CHO))(py)] (3) or [RhHCl(PPh2(o-C6H4CO))(κ1-PPh2(CH(Ph)CH2CHO))(py)] (4), respectively, both with a dangling alkylaldehyde. Diastereomeric mixtures with the ratios 3a/3a' = 80 : 20 and 4a/4a' = 50 : 50 were obtained. Complex 4 reacted with N-donors to afford cationic [RhH(NN)(PPh2(o-C6H4CO))(κ1-PPh2(CH(Ph)CH2CHO))]BPh4 (NN = 1,10-phenanthroline, 5; 2,2'-bipyridine, 6) or with 8-aminoquinoline (aqui) or 2-(aminomethyl)pyridine to yield imination products with terdentate ligands: [RhH(PPh2(o-C6H4CO))(κ3-PNN)]BF4 (PNN = PPh2(CH(Ph)CH2CNC9H6N), 7 and PPh2(CH(Ph)CH2CNCH2C5H4N), 8, respectively. Compounds 5-8 were obtained as equimolar a/a' mixtures of diastereomers. Moreover, 5a and 5a' could be separated. [RhCl(NBD)]2 reacted with racemic PPh2(CH(Ph)CH2CHO) and N-donors to provide nortricyclyl (Ntyl) derivatives [RhCl(NN)(Ntyl)(PPh2CH(Ph)CH2CO)] (NN = phen, 9 and bipy, 10) as an a/a' = 75 : 25 mixture of diastereomers. By reacting [RhCl(NBD)]2 with PPh2(CH(Ph)CH2CHO) and quinoline-8-carbaldehyde in methanol, the phosphino-ester complex [RhCl(Ntyl)(C9H6NCO)(κ2-PPh2CH(Ph)CH2CO(OCH3)] 11 was obtained. The initial equimolar mixture of two diastereomers readily transformed into a single diastereomer, which was found to be thermodynamically most stable by the DFT calculations. Furthermore, single crystal X-ray diffraction analysis of cis-Cl-2b, 5a, 7a, 10a and 11 is reported.

Chiral palladium pincer complexes for asymmetric catalytic reactions.

Palladium pincer complexes, containing a monoanionic terdentate ligand composed of an anionic aryl carbon atom and two mutually compatible donor sites, have aroused considerable interest since their first reports in the late 1970s. The high stability of the Pd pincer complexes and particularly their high modularity make these species ideal candidates for catalysis. Furthermore, the nature of the meridional coordination of the pincer ligands, and along with this their ability to enforce a stereo-specific environment around the Pd center, provide a good opportunity for developing chiral Pd pincer catalysts. Thus, a broad variety of chiral Pd pincer complexes have been prepared by the introduction of various stereochemical centers in the pincer skeletons. These chiral Pd pincer complexes have been successfully applied to many asymmetric catalytic reactions such as hydrophosphination reactions, allylation of aldehydes and imines, Michael and aldol reactions, Suzuki-Miyaura reactions as well as reactions of nitrile compounds with imines. This review focuses on the synthetic methods and the applications of chiral Pd pincer complexes in asymmetric catalysis.

Structural Insight into Redox Dynamics of Copper Bound N-Truncated Amyloid-β Peptides from in Situ X-ray Absorption Spectroscopy.

X-ray absorption spectroscopy of CuII amyloid-β peptide (Aβ) under in situ electrochemical control (XAS-EC) has allowed elucidation of the redox properties of CuII bound to truncated peptide forms. The Cu binding environment is significantly different for the Aβ1-16 and the N-truncated Aβ4-9, Aβ4-12, and Aβ4-16 (Aβ4-9/12/16) peptides, where the N-truncated sequence (F4R5H6) provides the high-affinity amino-terminal copper nickel (ATCUN) binding motif. Low temperature (ca. 10 K) XAS measurements show the adoption of identical CuII ATCUN-type binding sites (CuIIATCUN) by the first three amino acids (FRH) and a longer-range interaction modeled as an oxygen donor ligand, most likely water, to give a tetragonal pyramid geometry in the Aβ4-9/12/16 peptides not previously reported. Both XAS-EC and EPR measurements show that CuII:Aβ4-16 can be reduced at mildly reducing potentials, similar to that of CuII:Aβ1-16. Reduction of peptides lacking the H13H14 residues, CuII:Aβ4-9/12, require far more forcing conditions, with metallic copper the only metal-based reduction product. The observations suggest that reduction of CuIIATCUN species at mild potentials is possible, although the rate of reduction is significantly enhanced by involvement of H13H14. XAS-EC analysis reveals that, following reduction, the peptide acts as a terdentate ligand to CuI (H13, H14 together with the linking amide oxygen atom). Modeling of the EXAFS is most consistent with coordination of an additional water oxygen atom to give a quasi-tetrahedral geometry. XAS-EC analysis of oxidized CuII:Aβ4-12/16 gives structural parameters consistent with crystallographic data for a five-coordinate CuIII complex and the CuIIATCUN complex. The structural results suggest that CuII and the oxidation product are both accommodated in an ATCUN-like binding site.

The effect of substituents at C2/N1 atoms of salicyladehyde and 2-hydroxyacetophenone based thiosemicarbazones on the nature of nickel(II) complexes with 1,10-phenathroline and terpyridine as co-ligands

Coordination chemistry of nickel(II) with salicyladehyde and 2-hydroxyacetophenone based thiosemicarbazones {(2-OH-5-X-C6H3)-C2(R2)=N3-N2H-C1(=S)-N1HR3, LH2} and 1,10-phenanthroline (phen)/terpyridine (terpy) as a co-ligand has been investigated by varying the substituents at C2 (X = H, Me, MeO; R2 = H, Me) and N1 (R3 = H, Me, Et, Ph) atoms of thiosemicarbazones. Reactions of nickel(II) acetate with various thio-ligands, LH2 {X = H, R2 = H: L1H2 (R3 = H), L2H2 (R3 = Me), L3H2 (R3 = Et), L4H2 (R3 = Ph); X = Me, R2 = H, L5H2 (R3 = Me), L6H2 (R3 = Et); X = H, R2 = Me, L7H2 (R3 = Me), L8H2 (R3 = Et); X = MeO, R2 = H, L9H2 (R3 = Me)} have yielded dinuclear, [Ni2L2(phen)(D)] (D = H2O, L2− = L1–L4, 1–4; MeOH, L5, L6, 5, 6) and tetranuclear [Ni4L4(phen)2] (L2− = L7, 7, L8, 8) complexes in the presence of phen as a co-ligand, while in the presence of terpy as a co-ligand, only mononuclear [NiL(terpy)] (L2− = L2 , 9; L4, 10; L9, 11) complexes were formed. All these complexes have been characterized with the help of analytical data, spectroscopic techniques (IR and UV-visible), magnetic moments and single crystal X-ray crystallography (2, 3, 5, 6, 8–11). Thio-ligands undergo deprotonation of OH and N2H groups during complexation and coordinate to the metal centers as dianions in these complexes. In dinuclear complexes 1–6, one metal center is octahedral and second metal center is square planar (6, 4-coordination pair) and one site is occupied by H2O or MeOH ligands, thus completing six coordination. Tetranuclear complexes, 7 and 8, have 4, 6, 6, 4-coordination pattern and finally mononuclear complexes, 9–11, are octahedral with the thio-ligands forming O, N3, S- chelation and terpyridine coordinating as a terdentate ligand. All complexes are paramagnetic with magnetic moment (μeff) values in the range, 2.92–3.12 BM. Complexes 1–8 represent a less common type of dinuclear coordination pairs/tetranuclear oligomers in the metal-thiosemicarbazone chemistry.

Synthesis and Characterization of a Series of Bis-homoleptic Cycloruthenates with Terdentate Ligands as a Family of Panchromatic Dyes.

A series of six homoleptic bis-cyclometalated ruthenium complexes, Ru(N^N^C)2, is reported where N^N^C is a 6-(2,4-difluoro-3-R3-phenyl)-4-R2-4'-R1-2,2'-bipyridine with R3 = -H or -CF3 and R2 and R1 = -COOEt or -CF3. An effective synthesis of the ligands and the complexes is described. The UV-visible absorption studies demonstrate that these complexes are panchromatic dyes absorbing up to 900 nm. Importantly, the onset of absorption depends only on the substitution on the metalated phenyl, whereas the intensity of absorption throughout the spectra is a function of substituents on both the phenyl and the bipyridine moieties. The same trend is observed in electrochemistry as the redox gap depends only on the substitution on the metalated phenyl, whereas the oxidation and reduction potentials are a function of substituents on both the phenyl and the bipyridine moieties. Preliminary tests as sensitizer for dye-sensitized solar cells demonstrate that the number of anchoring groups on the dye has a major influence on the device efficiency.

Use of a Cyclometalated Iridium(III) Complex Containing a N∧C∧N-Coordinating Terdentate Ligand as a Catalyst for the α-Alkylation of Ketones and N-Alkylation of Amines with Alcohols

A cyclometalated iridium(III) complex containing a N∧C∧N-coordinating terdentate ligand [Ir(dpyx-N,C,N)Cl(μ-Cl)]2 was found to be a general and highly effective catalyst for the α-alkylation of ketones and N-alkylation of amines with alcohols. In the presence of catalyst (1 mol % Ir) and base (0.2-0.5 equiv), a variety of desirable products were obtained in good yields under an air atmosphere. Notably, this research exhibited the new potential of Ir(III) complexes bearing non-Cp* ligand and will facilitate the progress of the hydrogen autotransfer process.

On the stability and biological behavior of cyclometallated Pt(IV) complexes with halido and aryl ligands in the axial positions

A series of cyclometallated platinum(IV) compounds (3a, 3a′ and 3b′) with a meridional [C,N,N′] terdentate ligand, featuring an halido and an aryl group in the axial positions has been evaluated for electrochemical reduction and preliminary biological behavior against a panel of human adenocarcinoma (A-549 lung, HCT-116 colon, and MCF-7 breast) cell lines and the normal bronquial epithelial BEAS-2B cells. Cathodic reduction potentials (shifting from −1.463 to −1.570V) reveal that the platinum(IV) compounds under study would be highly reluctant to be reduced in a biological environment. Actually ascorbic acid was not able to reduce complex 3a′, the most prone to be reduced according its reduction potential, over a period of one week. These results suggest an intrinsic activity for the investigated platinum(IV) complexes (3a, 3a′ and 3b′), which exhibit a remarkable cytotoxicity effectiveness (with IC50 values in the low micromolar range), even greater than that of cisplatin. The IC50 for A-549 lung cells and clog P values were found to follow the same trend: 3b′>3a′>3a. However, no correlation was observed between reduction potential and in vitro activity. As a representative example, cyclometallated platinum(IV) compound 3a′, exercise its antiproliferative activity directly over non-microcytic A-549 lung cancer cells through a mixture of cell cycle arrest (13% arrest at G1 phase and 46% arrest at G2 phase) and apoptosis induction (increase of early apoptosis by 30 times with regard to control). To gain further insights into the mode of action of the investigated platinum(IV) complexes, drug uptake, cathepsin B inhibition and ROS generation were also evaluated. Interestingly an increased ROS generation could be related with the antiproliferative activity of the cyclometallated platinum(IV) series under study in the cisplatin-resistant A-549 lung and HCT-116 cancer cell lines.

Asymmetrical 1,3‐Bis(heteroazolyl)benzene Platinum Complexes with Tunable Second‐Order Non‐Linear Optical Properties

A series of cyclometallated platinum(II) complexes bearing an asymmetrical 1,3‐bis(heteroazolyl)benzene ligand as well as a chloro or phenylacetylene ancillary ligand have been synthesized and characterized. The N^C^N pro‐ligands, (benzoxazolyl)(benzothiazolyl)benzene in complex Pt1 and related compounds, and (benzoxazolyl)(benzimidazolyl)benzene in complex Pt2, were synthesized by a two‐step procedure that includes a Pd‐catalysed C–H bond‐activation reaction. The electronic absorption, luminescence and second‐order non‐linear optical properties of the novel complexes were investigated experimentally and theoretically (TD‐DFT) and compared with those of the known 1,3‐bis(benzoxazolyl)benzeneplatinum complex, the non‐linear optical response of which has been studied for the first time. All the complexes exhibit green luminescence in dichloromethane solution at room temperature, the nature of the heteroazolyl ligand and/or the substituent on the central phenyl ring having no significant impact on the emission signatures. In contrast, functionalization of the terdentate ligands and the nature of the ancillary ligand (chloride or phenylacetylide) allow modulation of the non‐linear optical activity.

Emissive mononuclear Eu(III) and Tb(III) complexes bearing deprotonated 2,2′-bipyridyl-1,2,4-triazole terdentate ligands

A series of new emissive mononuclear Ln(III) complexes with deprotonated 2,2ʹ-bipyridyl-1,2,4-triazole terdentate ligands, [Ln(L)(DMF)2(NO3)2]∙n(solvent) (Ln = Eu (1 and 2), Tb (3 and 4), HL = 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-2,2′-bipyridine, 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine), have been synthesized and characterized. As revealed by X-ray crystallography, each Ln(III) has a distorted tricapped trigonal prism generated by three nitrogens from one 2,2ʹ-bipyridyl-1,2,4-triazolate chelate and six oxygens from two DMF molecules and two chelating nitrates, where 2,2ʹ-bipyridyl-1,2,4-triazole serves as a mono-anionic tridentate chelate via deprotonation of the 1,2,4-triazolyl-NH. Complexes 1–4 are all emissive at room temperature in solution and solid states, and the introduction of two methyl groups into the 2,2ʹ-bipyridyl ring is efficient in enhancing luminescence efficiencies of Ln(III) complexes.

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino‐ or Iminium‐Acyl Moieties or Formation of Hydrido from Hydroxyl (Eur. J. Inorg. Chem. 12/2016)

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino‐ or Iminium‐Acyl Moieties or Formation of Hydrido from Hydroxyl (Eur. J. Inorg. Chem. 12/2016)