Showing papers on "Denticity published in 2016"
TL;DR: Chiral acetyl-protected aminoethyl quinoline ligands are found that enable asymmetric palladium insertion into prochiral C–H bonds on a single methylene carbon center and are applied to catalytic enantioselective functionalization of β-methylene C-H bonds in aliphatic amides.
Abstract: Effective differentiation of prochiral carbon–hydrogen (C–H) bonds on a single methylene carbon via asymmetric metal insertion remains a challenge. Here, we report the discovery of chiral acetyl-protected aminoethyl quinoline ligands that enable asymmetric palladium insertion into prochiral C–H bonds on a single methylene carbon center. We apply these palladium complexes to catalytic enantioselective functionalization of β-methylene C–H bonds in aliphatic amides. Using bidentate ligands to accelerate C–H activation of otherwise unreactive monodentate substrates is crucial for outcompeting the background reaction driven by substrate-directed cyclopalladation, thereby avoiding erosion of enantioselectivity. The potential of ligand acceleration in C–H activation is also demonstrated by enantioselective β-C–H arylation of simple carboxylic acids without installing directing groups.
249 citations
TL;DR: A highly active and selective homogeneous manganese-based C=O bond hydrogenation catalyst that is able to hydrogenate aryl-alkyl, diaryl, dialkyl, and cycloalkyl ketones as well as aldehydes and fine-tuning of a complex coordination environment is easily accomplished.
Abstract: The replacement of expensive noble metals by earth-abundant transition metals is a central topic in catalysis. Herein, we introduce a highly active and selective homogeneous manganese-based C=O bond hydrogenation catalyst. Our catalyst has a broad substrate scope, it is able to hydrogenate aryl-alkyl, diaryl, dialkyl, and cycloalkyl ketones as well as aldehydes. A very good functional group tolerance including the quantitative and selective hydrogenation of a ketone in the presence of a non-shielded olefin is observed. In Mn hydrogenation catalysis, the combination of the multidentate ligand, the oxidation state of the metal, and the choice of the right ancillary ligand is crucial for high activity. This observation emphasizes an advantage and the importance of homogeneous catalysts in 3d-metal catalysis. For coordination compounds, fine-tuning of a complex coordination environment is easily accomplished in comparison to enzyme and/or heterogeneous catalysts.
235 citations
TL;DR: At room temperature under mild photochemical conditions, gold(i) chloro complexes of both phosphane and carbene ligands in combination with aryldiazonium salts afford arylgold(iii) complexes.
153 citations
TL;DR: The synthesis of four different bidentate hybrid NHC-thioether ligands is presented and XPS analysis was identified as a convenient tool to establish the binding mode of NHC ligands.
Abstract: The synthesis of four different bidentate hybrid NHC-thioether ligands is presented. The corresponding palladium nanoparticles are stable in various solvents, depending on the ligand used, and show high chemoselectivity in the hydrogenation of olefins. The solubility of the nanoparticles can be switched multiple times depending on the pH value of the solvent. XPS analysis (which shows a subtle shift in the binding energy) was identified as a convenient tool to establish the binding mode of NHC ligands.
104 citations
TL;DR: Excited state properties, photo-catalysis and cellular imaging of photo-stable bis-NHC Ir(iii) complexes are described.
Abstract: A new class of cyclometalated Ir(III) complexes supported by various bidentate C-deprotonated (C^N) and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized. These complexes display strong emission in deaerated solutions at room temperature with photoluminescence quantum yields up to 89% and emission lifetimes up to 96 μs. A photo-stable complex containing C-deprotonated fluorenyl-substituted C^N shows no significant decomposition even upon irradiation for over 120 h by blue LEDs (12 W). These, together with the strong absorption in the visible region and rich photo-redox properties, allow the bis-NHC Ir(III) complexes to act as good photo-catalysts for reductive C–C bond formation from C(sp3/sp2)–Br bonds cleavage using visible-light irradiation (λ > 440 nm). A water-soluble complex with a glucose-functionalized bis-NHC ligand catalysed a visible-light-driven radical cyclization for the synthesis of pyrrolidine in aqueous media. Also, the bis-NHC Ir(III) complex in combination with a cobalt catalyst can catalyse the visible-light-driven CO2 reduction with excellent turnover numbers (>2400) and selectivity (CO over H2 in gas phase: >95%). Additionally, this series of bis-NHC Ir(III) complexes are found to localize in and stain endoplasmic reticulum (ER) of various cell lines with high selectivity, and exhibit high cytotoxicity towards cancer cells, revealing their potential uses as bioimaging and/or anti-cancer agents.
98 citations
TL;DR: Electrochemical measurements with the Ni(II) complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source.
Abstract: A novel nickel(II) complex [Ni(L)2Cl]Cl with a bidentate phosphinopyridyl ligand 6-((diphenylphosphino)methyl)pyridin-2-amine (L) was synthesized as a metal-complex catalyst for hydrogen production from protons. The ligand can stabilize a low Ni oxidation state and has an amine base as a proton transfer site. The X-ray structure analysis revealed a distorted square-pyramidal NiII complex with two bidentate L ligands in a trans arrangement in the equatorial plane and a chloride anion at the apex. Electrochemical measurements with the NiII complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source. The catalytic current increases with the stepwise addition of protons, and the turnover frequency is 8400 s−1 in 0.1 m [NBu4][ClO4]/MeCN in the presence of acetic acid (290 equiv) at an overpotential of circa 590 mV.
93 citations
TL;DR: A nickel-catalyzed cross-coupling between (hetero)arylborons and unactivated 1-bromo-1,1-difluoroalkanes has been developed and offers a highly efficient nickel-based catalytic system to prepare difluoalkylated arenes which have important applications in medicinal chemistry.
Abstract: A nickel-catalyzed cross-coupling between (hetero)arylborons and unactivated 1-bromo-1,1-difluoroalkanes has been developed. The use of two ligands (a bidentate bipyridine-based ligand, 4,4′-ditBu-bpy, and a monodentate pyridine-based ligand, DMAP) offers a highly efficient nickel-based catalytic system to prepare difluoroalkylated arenes which have important applications in medicinal chemistry.
92 citations
TL;DR: An unprecedented {Gd18} nanowheel was solvothermally synthesized with a novel diacylhydrazone ligand that features a rare single-stranded skeleton just like a Reuleaux triangle with vertices buckled in, and represents the highest nuclearity and largest size in lanthanide wheels reported so far.
75 citations
TL;DR: The computational results demonstrate that the origin of TADF can be ascribed to 1,3(ILCT + XLCT+ MLCT) states in complexes 1 and 2 and 1,2,4,5-tetrakis(diphenylphosphine)benzene states mixed with minor contributions of MLCT and ILCT in complex 3.
Abstract: A series of highly emissive neutral dinuclear silver complexes [Ag(PPh3)(X)]2(tpbz) (tpbz = 1,2,4,5-tetrakis(diphenylphosphanyl)benzene; X = Cl (1), Br (2), I (3)) was synthesized and structurally characterized. In the complexes, the silver atoms with tetradedral geometry are bridged by the tpbz ligand, and the ends of the molecules are coordinated by a halogen anion and a terminal triphenylphosphine ligand for each silver atom. These complexes exhibit intense white-blue (λmax = 475 nm (1) and 471 nm (2)) and green (λmax = 495 nm (3)) photoluminescence in the solid state with quantum yields of up to 98% (1) and emissive decay rates of up to 3.3 × 105 s–1 (1) at 298 K. With temperature decreasing from 298 to 77 K, a red shift of the emission maximum by 9 nm for all these complexes is observed. The temperature dependence of the luminescence for complex 1 in solid state indicates that the emission originates from two thermally equilibrated charge transfer (CT) excited states and exhibits highly efficient the...
69 citations
TL;DR: The Pd-catalyzed enantioselective C–P cross-coupling between racemic, configurationally stable heterobiaryl triflates and trialkylsilyldiaryl(dialkyl)phosphines has been used for the synthesis of several families of enantiomerically enriched heterobiaries phosphines including QUINAP, PINAP, and QUINAZOLINAP analogues.
Abstract: The Pd-catalyzed enantioselective C–P cross-coupling between racemic, configurationally stable heterobiaryl triflates and trialkylsilyldiaryl(dialkyl)phosphines has been used for the synthesis of several families of enantiomerically enriched heterobiaryl phosphines including QUINAP, PINAP, and QUINAZOLINAP analogues, which can be performed with good yields and enantioselectivities using JOSIPHOS-type bidentate phosphines The strategy relies on two key assumptions: (I) The N atom of the heterocycle is a better ligand than triflate, and upon oxidative addition, it incorporates into the coordination sphere of the PdII center to form cationic cyclic intermediates (II) The geometry of the palladacycle results in a widening of the angles involved in the stabilization of the stereogenic axis, facilitating a fast interconversion of diastereomeric structures and, hence, a dynamic kinetic C–P cross-coupling reaction These starting hypotheses are supported by experimental and computational studies
68 citations
TL;DR: In this paper, a Cp*Ir complex with a bidentate pyridyl-imidazoline ligand achieved the evolution of 1.02 m3 of H2/CO2 gases by formic acid dehydrogenation without any additives or adjustments in the solution system.
TL;DR: The results indicate that these complexes can bind to DNA covalently and non-covalently, and only compounds that hydrolyze the monodentate ligand at a reasonable rate show moderate activity.
Abstract: In this study, two representatives of previously synthesized ruthenium(II) terpyridine complexes, i.e., [Ru(Cl-tpy)(en)Cl][Cl] (1) and [Ru(Cl-tpy)(dach)Cl][Cl] (2), were chosen and a detailed study of the kinetic parameters of their reactivity toward L-histidine (L-His), using the UV-Vis and 1H NMR techniques, was developed. The inner molecular rearrangement from N3-coordinated L-His to the N1 bound isomer, observable in the NMR data, was corroborated by DFT calculations favoring N1 coordination by nearly 4 kcal mol−1. These two ruthenium(II) terpyridine complexes were investigated for their interactions with DNA employing UV-Vis spectroscopy, DNA viscosity measurements and fluorescence quenching measurements. The high binding constants obtained in the DNA binding studies (Kb = 104–105 M−1) suggest a strong binding of the complexes to calf thymus (CT) DNA. Competitive studies with ethidium bromide (EB) showed that the complexes can displace DNA-bound EB, suggesting strong competition with EB (Ksv = 1.5–2.5 × 104 M−1). In fact, the results indicate that these complexes can bind to DNA covalently and non-covalently. In order to gain insight of the behavior of a neutral compound, besides the four previously synthesized cationic complexes [Ru(Cl-tpy)(en)Cl][Cl] (1), [Ru(Cl-tpy)(dach)Cl][Cl] (2), [Ru(Cl-tpy)(bpy)Cl][Cl] (3) and [Ru(tpy)Cl3] (P2), a new complex, [Ru(Cl-tpy)(pic)Cl] (4), was used in the biological studies. Their cytotoxicity was investigated against three different tumor cell lines, i.e., A549 (human lung carcinoma cell line), HCT116 (human colon carcinoma cell line), and CT26 (mouse colon carcinoma cell line), by the MTT assay. Complexes 1 and 2 showed higher activity than complexes 3, 4 and P2 against all the selected cell lines. The results on in vitro anticancer activity confirmed that only compounds that hydrolyze the monodentate ligand at a reasonable rate show moderate activity, provided that the chelate ligand is a hydrogen bond donor.
TL;DR: Each complex is formed as a single compound only: the strong trans influence of the metallated rings dictates the relative disposition of the ligands, whilst the use of symmetrically substituted tridentate ligands eliminates the possibility of Λ and Δ enantiomers that are obtained when bis-bidentate units are linked through bridging ligands.
Abstract: A new family of eight dinuclear iridium(III) complexes has been prepared, featuring 4,6-diarylpyrimidines Ly as bis-N^C-coordinating bridging ligands. The metal ions are also coordinated by a terminal N^C^N-cyclometallating ligand LX based on 1,3-di(2-pyridyl)benzene, and by a monodentate chloride or cyanide. The general formula of the compounds is {IrLXZ}2Ly (Z = Cl or CN). The family comprises examples with three different LX ligands and five different diarylpyrimidines Ly, of which four are diphenylpyrimidines and one is a dithienylpyrimidine. The requisite proligands have been synthesised via standard cross-coupling methodology. The synthesis of the complexes involves a two-step procedure, in which LXH is reacted with IrCl3·3H2O to form dinuclear complexes of the form [IrLXCl(μ-Cl)]2, followed by treatment with the diarylpyrimidine LyH2. Crucially, each complex is formed as a single compound only: the strong trans influence of the metallated rings dictates the relative disposition of the ligands, whilst the use of symmetrically substituted tridentate ligands eliminates the possibility of Λ and Δ enantiomers that are obtained when bis-bidentate units are linked through bridging ligands. The crystal structure of one member of the family has been obtained using a synchrotron X-ray source. All of the complexes are very brightly luminescent, with emission maxima in solution varying over the range 517–572 nm, according to the identity of the ligands. The highest-energy emitter is the cyanide derivative whilst the lowest is the complex with the dithienylpyrimidine. The trends in both the absorption and emission energies as a function of ligand substituent have been rationalised accurately with the aid of TD-DFT calculations. The lowest-excited singlet and triplet levels correlate with the trend in the HOMO–LUMO gap. All the complexes have quantum yields that are close to unity and phosphorescence lifetimes – of the order of 500 ns – that are unusually short for complexes of such brightness. These impressive properties stem from an unusually high rate of radiative decay, possibly due to spin–orbit coupling pathways being facilitated by the second metal ion, and to low non-radiative decay rates that may be related to the rigidity of the dinuclear scaffold.
TL;DR: The antiproliferative properties of the complexes were assessed in human ovarian cancer cells (A2780 and A2780cisR, the latter being resistant to cisplatin) and nontumorigenic human embryonic kidney (HEK-293) cells.
Abstract: Compounds that combine metal-based drugs with covalently linked targeted organic agents have been shown, in some instances, to exhibit superior anticancer properties compared to the individual counterparts. Within this framework, we prepared a series of organometallic ruthenium(II)- and osmium(II)-p-cymene complexes modified with the nonsteroidal anti-inflammatory drugs (NSAIDs) indomethacin and diclofenac. The NSAIDs are attached to the organometallic moieties via monodentate (pyridine/phosphine) or bidentate (bipyridine) ligands, affording piano-stool Ru(II) and Os(II) arene complexes of general formula [M(η6-p-cymene)Cl2(N)], where N is a pyridine-based ligand, {2-(2-(1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indol-3-yl)acetoxy)ethyl-3-(pyridin-3-yl)propanoate} or {2-(2-(2-((2,6-dichlorophenyl)amino)phenyl)acetoxy)ethyl-3-(pyridin-3-yl)propanoate}, [M(η6-p-cymene)Cl2(P)], where P is a phosphine ligand, {2-(2-(1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indol-3-yl)acetoxy)ethyl-4-(diphenylphosphanyl)benzo...
TL;DR: In this paper, the Ru(II) center has a pseudo-octahedral three legged piano stool geometry in which the arene ring occupies the apex of the stool and the ruthenium is coordinated to the N,N′-bidentate ligand and a chloride ligand at the base.
TL;DR: Bidentate coordination was favorable to the asymmetric splitting of AlCl3 with the same amide-AlCl3 molar ratio and under the influence of the steric and inductive effects of the methyl group, the ionic species percentages in these IL analogues ranked in the following order: N-methylacetamide > N,N-dimethylacetamide < acetamide.
Abstract: Several amide–AlCl3-based ionic liquid (IL) analogues were synthesized through a one-step method using three different structure amides as donor molecules. The effects of the steric and inductive effects of the methyl group substituted on the N atom on the asymmetric splitting of AlCl3 and the coordination site of the amide were investigated by 27Al NMR, Raman, in situ IR, and UV–vis spectra for these IL analogues. Bidentate coordination through both the O and N atoms was dominant in the N-methylacetamide–AlCl3- and N,N-dimethylacetamide–AlCl3-based IL analogues because of the inductive effect of the methyl group. By contrast, the acetamide–AlCl3-based IL analogue presented mainly in the form of monodentate coordination via the O atom. Compared with monodentate coordination, bidentate coordination was favorable to the asymmetric splitting of AlCl3 with the same amide–AlCl3 molar ratio. Under the influence of the steric and inductive effects of the methyl group, the ionic species percentages in these IL an...
TL;DR: Two new photopharmacological ruthenium prodrugs are described that can be activated by green light that are not a consequence of singlet oxygen generation, but of light-induced photosubstitution reactions.
Abstract: In this work, two new photopharmacological ruthenium prodrugs are described that can be activated by green light. They are based on the tetrapyridyl biqbpy ligand (6,6′-bis[N-(isoquinolyl)-1-amino]-2,2′-bipyridine), which coordinates to the basal plane of the metal centre and leaves two trans coordination sites for the binding of monodentate sulphur ligands. Due to the distortion of the coordination sphere these trans ligands are photosubstituted by water upon green light irradiation. In vitro cytotoxicity data on A431 and A549 cancer cell lines shows an up to 22-fold increase in cytotoxicity after green light irradiation (520 nm, 75 J cm−2), compared to the dark control. Optical microscopy cell imaging and flow cytometry indicate that the cancer cells die via apoptosis. Meanwhile, very low singlet oxygen quantum yields (∼1–2%) and cell-free DNA binding studies conclude that light-induced cell death is not caused by a photodynamic effect, but instead by the changes induced in the coordination sphere of the metal by light, which modifies how the metal complexes bind to biomolecules.
TL;DR: In this paper, metal-to-ligand stoichiometric formulae of 3-[(2-hydroxy-3-methoxybenzylidene)hydrazo]-1,3-dihydroindol-2-one (HL) were prepared, their compositions and physicochemical properties were characterized on the basis of elemental analysis, molar conductivity, 1 H NMR, UV-Vis, IR, mass spectroscopy, X-ray, magnetic measurements and thermogravimetric analysis (TGA).
TL;DR: Mechanistic investigations revealed that the difluoromethylation reaction proceeds by initial copper-mediated formation of diflorocarbene and subsequent concerted addition of d ifluorocarbene to the phenol to form a three-center transition state.
Abstract: This article describes the new economic decarboxylative trifluoromethylating reagent [Cu(phen)(O2 CCF3 )] (1; phen=1,10-phenanthroline) and the efficient difluorocarbene precursor [Cu(phen)2 ][O2 CCF2 Cl] (2). Treatment of copper tert-butoxide with phen and subsequent addition of trifluoroacetic acid or chlorodifluoroacetic acid afforded air-stable complexes 1 and 2, respectively, which were characterized by X-ray crystallography. The copper(I) ion in 1 is coordinated by a bidentate phen ligand, a monodentate trifluoroacetate group, and a molecule of CH3 CN in a distorted tetrahedral coordination geometry. The molecular structure of 2 adopts an ionic form that consists of a [Cu(phen)2 ]+ cation and a chlorodifluoroacetate anion. Complex 1 reacted with a variety of aryl and heteroaryl halides to form trifluoromethyl (hetero)arenes in good yields. The corresponding Hammett plot exhibited a linear relationship and a reaction parameter (ρ)=+0.56±0.02, which indicated that the trifluoromethylation reaction proceeded via a nucleophilic reactive species. Complex 2 reacts with phenols to produce aryl difluoromethyl ethers in modest-to-excellent yields. Mechanistic investigations revealed that the difluoromethylation reaction proceeds by initial copper-mediated formation of difluorocarbene and subsequent concerted addition of difluorocarbene to the phenol to form a three-center transition state.
TL;DR: In this paper, a review collects and discusses the hitherto known reactions involving this ligand transformation, also shedding light on the factors that make it possible, and a ringexpansion process transforms the original monodentate (κ1E) ligand into a bidentate one (κ2E,D).
Abstract: Intramolecularly stabilized heavier tetrylenes (HTs) are group 14 metalylenes featuring at least one intramolecular DE interaction between a two-electron-donor group (D) and the group 14 atom (E = Si, Ge, Sn or Pb). With regard to their coordination chemistry, they normally bind to transition metals as monodentate ligands through the lone electron pair of their E atom; however, the donor group D initially involved in their internal stabilization can sometimes migrate from the E atom to the transition metal. This ring-expansion process transforms the original monodentate (κ1E) ligand into a bidentate one (κ2E,D) and enhances the stability of the resulting complex. This review collects and discusses the hitherto known reactions involving this ligand transformation, also shedding light on the factors that make it possible.
TL;DR: The kinetics and mechanism of catalytic radical termination (CRT) of n-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally as mentioned in this paper.
Abstract: The kinetics and mechanism of catalytic radical termination (CRT) of n-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally. The tetradentate TPMA, TPMA*1, TPMA*2, TPMA*3, and the newly synthesized tridentate N-propyl-N,N-bis(4-methoxy-3,5-dimethylpyrid-2-ylmethyl)amine (BPMA*Pr) as well as tridentate BPMAMe were used as ligands. L/CuIIX2 (X = Cl or OTf) complexes were characterized by cyclic voltammetry (CV), UV–vis–NIR, and X-ray diffraction. Polymerization of BA initiated by azobis(isobutyronitrile) (AIBN) in MeCN in the presence of a L/CuI complex showed higher rates of CRT for more reducing L/CuI complexes. The ligand denticity (tri- vs tetradentate) had a minor effect on the relative polymerization kinetics but affected the molecular weights in a way specific for ligand denticity. Quantification of the apparent CRT rate coefficients, kCRTapp, showed larger values for more reducing L/CuI complexes, ...
TL;DR: In this paper, the authors used reticular chemistry for the design and construction of four novel Zn(II)/Cd(II) coordination polymers, which were successfully synthesized from bi-, tri-, and tetratopic phenylamine derivatives.
Abstract: Using reticular chemistry allowed the design and construction of four novel Zn(II)/Cd(II) coordination polymers, {[Zn(BTPA)(TPA)]·H2O}n (1), {[Zn(TTPA)(TPA)]·H2O}n (2), {[Cd2(TTPA)2(TPA)2(DMF)]·2H2O}n (3), and {[Cd(TTPBDA)(TPA)]0.5·DMF·H2O}n (4). They were successfully synthesized from bi-, tri-, and tetratopic phenylamine derivatives (BTPA = bis(4-(1H-1,2,4-triazol-1-yl)phenyl)amine, TTPA = tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine, TTPBDA = N4,N4,N4′,N4′-tetrakis(4-(1H-1,2,4-triazol-1-yl)phenyl)-(1,1′-biphenyl)-4,4′-diamine) incorporating a linear terephthalic acid (H2TPA) ligand and Zn(II)/Cd(II) nitrate salts. These transparent crystals present gradually increasing dimensionality and complexity upon extension of the denticity of the phenylamine organic building blocks, as clearly supported by single-crystal X-ray analysis, infrared spectroscopy, elemental analysis, powder X-ray diffraction, and thermogravimetric analysis. Complex 1 shows two-dimensional (2D) threefold-interpenetrating layers (2D + 2D...
TL;DR: In this article, a Schiff base ligand was synthesized by condensation of 2-(3,4-dimethoxyphenyl)ethanamine with 2-hydroxy benzaldehyde (L1H) and 2′-hydroxyphenone (L2H) respectively.
TL;DR: HyHybrid bidentate phosphine-phosphorodiamidite ligands based on a chiral Betti base backbone and diphenylphosphinoaniline derivatives have been prepared (BettiPhos) as mentioned in this paper.
Abstract: Hybrid bidentate phosphine-phosphorodiamidite ligands based on a chiral Betti base backbone and diphenylphosphinoaniline derivatives have been prepared (BettiPhos). The ligands possess a stereogenic P atom at the phosphorodiamidite moiety, whose configuration can be largely controlled by the synthetic route and the choice of base and solvent. The new ligands were applied in the rhodium-catalyzed asymmetric hydroformylation (AHF) of vinyl esters and vinyl amides. Very high enantioselectivities of up to 97% ee accompanied by excellent regioselectivities (up to b/l > 1000) were obtained using the BettiPhos ligand (SC,SC,RP,SC)-4b bearing an additional chiral group at the aniline nitrogen. The catalyst resting state [RhH(CO)2{(SC,SC,RP,SC)-4b}] was investigated by high pressure-NMR studies, revealing an equatorial–apical coordination of the bidentate ligand where the two phosphorus donors rapidly exchange their positions through an intermediate with the ligand bound via the phosphine group only.
TL;DR: Three new organometallic trimethylplatinum(IV) iodide complexes of 2,2′:6′,2″-terpyridines have been synthesized and characterized by 1H NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray diffraction analysis.
Abstract: Three new organometallic trimethylplatinum(IV) iodide complexes of 2,2′:6′,2″-terpyridines have been synthesized and characterized by 1H NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray diffraction analysis. The X-ray crystal structures of PtMe3I(L) complexes 1–3 {L for 1 = 4′-chloro-2,2′:6′,2″-terpyridine, 2 = 4′-(4-cyanophenyl)-2,2′:6′,2″-terpyridine, and 3 = 4′-(4-tolyl)-2,2′:6′,2″-terpyridine} reveal distorted octahedral coordination geometry of the platinum(IV) metal centers with bidentate coordination of the terpyridine ligands. Complexation of 1–3 with iodopentafluorobenzene (IPFB) afforded single-crystal structures of halogen bond (XB) complexes 1a–3a, in which the Pt-complexes act as bifunctional XB bond acceptor wherein the pendant pyridine nitrogen atom and the platinum bound iodine atom act as XB acceptors toward the polarized iodine of IPFB. In addition, complexation of 1 with 1,4-diiodotetrafluobenzene (DITFB) afforded single-crystal structure of dimeric XB c...
TL;DR: In this article, an energy measure of the quantitative dative character of a bond is derived by extension of Haaland's definition of dative bonding with respect to pure (shared) covalency.
TL;DR: The computational analysis was found to be consistent with the rates of reductive elimination of benzene from a series of isoelectronic Ir(III) phenyl hydride complexes, measured experimentally in this work and previously reported.
Abstract: A study of electronic factors governing the thermodynamics of C–H and N–H bond addition to Ir(I) complexes was conducted. DFT calculations were performed on an extensive series of trans-(PH3)2IrXL complexes (L = NH3 and CO; X = various monodentate ligands) to parametrize the relative σ- and π-donating/withdrawing properties of the various ligands, X. Computed energies of oxidative addition of methane to a series of three- and four-coordinate Ir(I) complexes bearing an ancillary ligand, X, were correlated with the resulting (σX, πX) parameter set. Regression analysis indicates that the thermodynamics of addition of methane to trans-(PH3)2IrX are generally strongly disfavored by increased σ-donation from the ligand X, in contradiction to widely held views on oxidative addition. The trend for oxidative addition of methane to four-coordinate Ir(I) was closely related to that observed for the three-coordinate complexes, albeit slightly more complicated. The computational analysis was found to be consistent wit...
TL;DR: The results show that DAF and 6,6'-Me2bpy destabilize the corresponding ground-state Pd(N~N)(OAc)2 complexes, while stabilizing the rate-limiting transition state for alkene insertion into a Pd-N bond.
Abstract: 2,2'-Bipyridine (bpy), 1,10-phenanthroline (phen) and related bidentate ligands often inhibit homogeneous Pd-catalyzed aerobic oxidation reactions; however, certain derivatives, such as 4,5-diazafluoren-9-one (DAF), can promote catalysis. In order to gain insight into this divergent ligand behavior, eight different bpy- and phen-derived chelating ligands have been evaluated in Pd(OAc)2-catalyzed oxidative cyclization of (E)-4-hexenyltosylamide. Two of the ligands, DAF and 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me2bpy), support efficient catalytic turnover, while the others strongly inhibit the reaction. DAF is especially effective and is the only ligand that exhibits "ligand-accelerated catalysis". Evidence suggests that the utility of DAF and 6,6'-Me2bpy originates from the ability of these ligands to access κ1-coordination modes via dissociation of one of the pyridyl rings. This hemilabile character is directly observed by NMR spectroscopy upon adding one equivalent of pyridine to solutions of 1:1 L/Pd(OAc)2 (L = DAF and 6,6'-Me2bpy), and is further supported by an X-ray crystal structure of Pd(py)(κ1-DAF)OAc2. DFT computational studies illuminate the influence of three different chelating ligands [DAF, 6,6'-Me2bpy, and 2,9-dimethyl-1,10-phenanthroline (2,9-Me2phen)] on the energetics of the aza-Wacker reaction pathway. The results show that DAF and 6,6'-Me2bpy destabilize the corresponding ground-state Pd(N~N)(OAc)2 complexes, while stabilizing the rate-limiting transition state for alkene insertion into a Pd-N bond. Interconversion between κ2- and κ1-coordination modes facilitate access to open coordination sites at the PdII center. The insights from these studies introduce new ligand concepts that could promote numerous other classes of Pd-catalyzed aerobic oxidation reaction.
TL;DR: A series of organotin(IV) complexes have been synthesized by reacting potassium o-isobutyl carbonodithioate with di- and triorganotin halides in methanol under stirring conditions.
TL;DR: In this article, a new azo dye ligand was synthesized by diazotization of m-phenylene diamine and coupled with coupling compound, p-methoxy benzaldehyde.
Abstract: As a part of systematic investigation of biologically active compound, m-phenylene diamine, new azo dye ligand was synthesized by diazotization of m-phenylene diamine and coupled with coupling compound, p-methoxy benzaldehyde. A new series of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes derived from this azo dye ligand (L) were synthesized. The structures of the ligand and metal complexes were confirmed by elemental analysis, spectroscopic studies (IR, UV–Vis, 1H NMR, mass spectrometry, electronic spectra, magnetic susceptibility and ESR), conductivity measurements, thermogravimetric analyses (TG-DTG) and X-ray powder diffraction. The molar conductance measurements of the complexes in DMF determine electrolytic nature of the complexes. On the basis of elemental and thermal analyses, magnetic moment, electronic and ESR spectral studies, an octahedral geometry was assigned for metal complexes. XRD data reflect that azo dye ligand and its Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes are amorphous while Cd(II) complex is crystalline. Also, the newly synthesized azo dye ligand, in comparison with metal complexes, is screened for its antimicrobial and anticancer activity against breast cancer cell line (MCF7). The results showed that Mn(II), Ni(II) and Zn(II) metal complexes have higher anti-breast cancer activity than free ligand.