Thioether Ligands Research Articles

Hydrogen bond networks in five- and eight-membered palladium and platinum complexes derived from bis(2-aminophenyl)ether and bis(2-aminophenyl)thioether ligands

The reaction of [MII(MeCN)2Cl2] (M=Pd, Pt) with the diamino ligands either bis(2-aminophenyl)ether or bis(2-aminophenyl)thioether {(NH2-C6H4)2D} [D=O (L1); D=S (L2)] yielded neutral coordination complexes of general formulae [M(Ln)Cl2] [M=Pd, n=1 (1); Pt, n=1 (2); Pd, n=2 (3); Pd, n=2 (4); Pt, n=2 (5). The reaction of L2 with K2[PtCl6] promoted the mono-deprotonation of the diamino ligand to yield the neutral complex [PtIV{(NH2-C6H4)S(NH-C6H4)}Cl3] (6); when the H2[PtCl6] acid was used an ionic complex [PtIV(L2)Cl3]Cl (7) was obtained. All complexes were characterized by NMR in solution, vibrational spectroscopy, and by X-ray diffraction studies. The molecular structures of the complexes revealed different coordination patterns of the diamino ligands; L1 just displayed a κ2N mode meanwhile L2 exhibited a wide variety of patterns (κ2N, κNκS, and κ2NκS) forming chelate rings of five- or eight-members. The presence of N–H functions in the ligand moieties enhanced the formation of extended hydrogen-bond networks; these supramolecular arrangements were mainly discussed at unitary and binary levels and sorted according to the molecular coordination patterns observed.

Crystal structures and biological activities of a symmetrical quinoline thioether ligand and its transition metal complexes

The ligand 2,6-bis (8-quinolinylthiomethyl) pyridine and its four transition metal complexes have been synthesized and characterized by elemental analysis (EA), infrared spectra (IR) and single-crystal diffraction. It was revealed that compounds 1–3 were comprised of discrete mononuclear units and double nuclear structure in compound 4. The antibacterial activities and pesticide activities of the ligand and complexes 1–4 were tested. The results showed that some compounds had absolute specificity for certain bacteria, and could have good application prospect in pharmaceutical and agricultural use.

Tungsten carbonyl σ-complexes with charge-compensated nido-carboranyl thioether ligands.

Charge-compensated nido-carboranyl thioether ligands [7-MeS-10-Me2S-7,8-C2B9H10] and [7,8-(MeS)2-10-Me2S-7,8-C2B9H9] were prepared and fully characterized. They readily react with labile tungsten carbonyls to give σ-complexes - mono-substituted (CO)5W[7-MeS-10-Me2S-7,8-C2B9H10-κ(1)-S(1)] and (CO)5W[7,8-(MeS)2-10-Me2S-7,8-C2B9H9-κ(1)-S(1)] and chelate (CO)4W[7,8-(MeS)2-10-Me2S-7,8-C2B9H9-κ(2)-S(1),S(2)]. The synthesized metallocomplexes were characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. The donor ability of the 7-methylsulfide-nido-carborane ligand is not sensitive to introduction of the charge-compensating dimethylsulfonium group.

Atroposelective synthesis of axially chiral P,S-ligands based on arynes

An unprecedented atropo-diastereoselective aryl–aryl coupling via arynes allows for the modular synthesis of enantiopure P,S-ligands.

Bis(ether-functionalized NHC) Nickel(II) Complexes, Trans to Cis Isomerization Triggered by Water Coordination, and Catalytic Ethylene Oligomerization

The new nickel(II) complexes containing NHC ligands N-substituted by a CH2CH2OR ether group (R = Me or Ph) [NiCl2{ImMes(C2OMe)}2] (6), [NiCl2{Imn-Bu(C2OMe)}2] (7), [NiBr2{ImDiPP(C2OMe)}2] (8), [NiBr2{ImMes(C2OMe)}2] (9), [NiBr2{Imn-Bu(C2OMe)}2] (10), NiBr2{ImMes(C2OPh)}2] (18), [NiI2{ImDiPP(C2OMe)}2] (21), [NiI2{ImMes(C2OMe)}2] (22), and [NiI2{Imn-Bu(C2OMe)}2] (23) were synthesized in good yields and fully characterized by NMR spectroscopy and X-ray diffraction analysis. The reaction conditions were optimized and further applied to thioether or nonfunctionalized NHC ligands, affording [NiBr2{ImDiPP(C2SPh)}2] (19) and [NiBr2{ImDiPP(n-Bu)}2] (20), respectively. Equilibria involving syn/anti isomers were unveiled for complexes [NiCl2{ImDiPP(C2OMe)}2] (5), 6–10, and 18–23. Reactions of 6 and 20 with a halide abstractor afforded the dicationic aquo complexes cis-[Ni{ImMes(C2OMe)}2(H2O)2][PF6]2 (27) and cis-[Ni{ImDiPP(n-Bu)}2(H2O)2][PF6]2 (28), in which a cis arrangement of the carbene ligands is evidenced, which contrasts with that in their precursors. These molecules represent rare examples of nickel aquo NHC complexes and of complexes with two cis monodentate NHC ligands. The new complexes reported in this work (15 crystal structures) displayed moderate activities as precatalysts for ethylene oligomerization and favored dimerization.

Influence of crown thioether ligands in the structures and of perhalophenyl groups in the optical properties of complexes with argentoaurophilic interactions.

Reaction of [{Au(C6X5)2}Ag]n (X = Cl, F) with the crown thioethers 1,4,7-trithiacyclononane ([9]aneS3), 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4), or 1,4,7,10,13,16,19,22-octathiacyclotetracosane ([24]aneS8) affords a series of heteronuclear Au(I)/Ag(I) compounds of stoichiometry [{Au(C6X5)2}Ag(L)x] (L = [9]aneS3, x = 2 (1, 4); L = [14]aneS4, x = 1 (2, 5); L = [24]aneS8, x = 0.5 (3, 6)) formed via Ag-S bonds and Au···Ag contacts. X-ray diffraction studies of some of these complexes reveal different structural arrangements and nuclearity depending on the nature of the crown thioether ligand and on the presence or absence of aurophilic interactions. All the complexes are luminescent in the solid state but not in solution. Density functional theory calculations on representative model systems of complexes 2-4 and 6 were carried out to determine the origin of the electronic transitions responsible for their optical properties, which strongly depend on the nature of the perhalophenyl groups bonded to gold.

A multi-state, allosterically-regulated molecular receptor with switchable selectivity.

A biomimetic, ion-regulated molecular receptor was synthesized via the Weak-Link Approach (WLA). This structure features both a calix[4]arene moiety which serves as a molecular recognition unit and an activity regulator composed of hemilabile phosphine alkyl thioether ligands (P,S) chelated to a Pt(II) center. The host-guest properties of the ion-regulated receptor were found to be highly dependent upon the coordination of the Pt(II) center, which is controlled through the reversible coordination of small molecule effectors. The environment at the regulatory site dictates the charge and the structural conformation of the entire assembly resulting in three accessible binding configurations: one closed, inactive state and two open, active states. One of the active states, the semiopen state, recognizes a neutral guest molecule, while the other, the fully open state, recognizes a cationic guest molecule. Job plots and (1)H NMR spectroscopy titrations were used to study the formation of these inclusion complexes, the receptor binding modes, and the receptor binding affinities (Ka) in solution. Single crystal X-ray diffraction studies provided insight into the solid-state structures of the receptor when complexed with each guest molecule. The dipole moments and electrostatic potential maps of the structures were generated via DFT calculations at the B97D/LANL2DZ level of theory. Finally, we describe the reversible capture and release of guests by switching the receptor between the closed and semiopen configurations via elemental anion and small molecule effectors.

Half-sandwich η6-arene ruthenium and Cp∗ rhodium/iridium compounds comprising with thioether ligands: Synthesis, spectral and molecular studies

The reaction of [(η6-arene)Ru(μ-Cl)Cl]2 and [Cp∗M(μ-Cl)Cl]2 (M=Rh, Ir) with tetradentate N,N′-donor chelating ligand viz 3,6-bis(2-thiopyridyl)pyridazine(L1) leads to the formation of mononuclear compounds as general formula [(arene)MCl(L1)]+ {M=Ru, arene=C6H6 (1); p-iPrC6H4Me (2); C6Me6 (3); Cp∗, M=Rh (4); Cp∗, M=Ir (5)} where as 4,6-bis(2′-thiopyridyl)pyrimidine(L2) and 2,3-bis(2-thiopyridyl)pyrazine(L3) leads to the formation of dinuclear compounds as general formula [{(arene)MCl}2(L)]2+ {M=Ru, L=L2, arene=C6H6 (6); p-iPrC6H4Me (7); C6Me6 (8); Cp∗, M=Rh, (9); Cp∗, M=Ir, (10) and L=L3 C6H6 (11); p-iPrC6H4Me (12); C6Me6 (13), Cp∗, M=Rh, (14) Cp∗, M=Ir (15)}, respectively. The cationic complexes have been isolated as their PF6/SbF6 salts and characterized by FT-IR, UV–Vis, 1H NMR, Mass spectroscopic methods. X-ray crystallographic studies of some representative compounds revealed that typical piano-stool geometry around the metal center with a six-membered metallocycles in which thioether ligand acts as a N,N′-chelating ligand. Variation of bridging motifs of thioether ligands is revealed that formation of mono/dinuclear complexes. The L1 ligand yielded predominantly mononuclear compounds where as L2 and L3 yielded dinuclear compounds with trans and cis isomers, respectively.

High-pressure studies of palladium and platinum thioether macrocyclic dihalide complexes.

The mononuclear macrocyclic Pd(II) complex cis-[PdCl2([9]aneS3)] ([9]aneS3 = 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur-metal interaction and an intermolecular equatorial sulfur-metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl2([9]aneS3)], [PdBr2([9]aneS3)], [PtBr2([9]aneS3)], [PdI2([9]aneS3)] and [PtI2([9]aneS3)] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl2([9]aneS3)] undergoes a phase change. Pressure-induced I...I interactions were observed for [PdI2([9]aneS3)] and [PtI2([9]aneS3)] at 19 kbar, but the corresponding Br...Br interactions in [PdBr2([9]aneS3)] and [PtBr2([9]aneS3)] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur-metal interactions.

Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism.

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface.

Solvent effect on heavy metal coordination with thioether ligands: A thermodynamic and theoretical study

The thermodynamic parameters for the complexation between the monodentate diethylsulfide (Et2S), the macrocyclic thioethers 1,4,7-trithiacyclononane ([9]aneS3) 1,4,7,10-tetrathiacyclododecane ([12]aneS4) and 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) have been determined in dimethylsulfoxide (DMSO) with d10 metal ions such as Hg2+, Ag+, Cd2+and Zn2+.Mononuclear MLj (j=1, 2) complexes are formed by all ligands with Hg2+ and Ag+ with associated negative enthalpy and entropy changes. Differently from what previously found in acetonitrile (AN), no reaction occurs with Zn2+ and Cd2+.The stabilities are lower in DMSO and the selectivity, much higher for Hg2+ than Ag+ in AN, is leveled in DMSO, being higher only when [9]aneS3 is concerned (ΔlogK1,Hg→Ag=8.9 and 0.9 for [9]aneS3 in AN and DMSO, respectively). Density Functional Theory (DFT) calculations are used to interpret at molecular level the subtle interplay between the intrinsic affinity of a given metal ion for a thioether and solvation in different media. The reliability of this approach is demonstrated by the good correlation obtained for the calculated and theoretical solvation energy of the metal ions. Theoretical results clearly indicate that: (i) the medium (solvent) strongly modulates the relative selectivity of thioethers towards different cations, i.e. Hg2+ and Ag+; (ii) Zn2+ complexes are not formed in DMSO mostly because of the strong solvation of the ion; (iii) for Cd2+ the less favorable pure interaction with the ligands is most detrimental to complex formation.

ChemInform Abstract: Thioether‐Promoted Direct Olefination of Polyfluoroarenes Catalyzed by Palladium.

A methyl(phenyl)sulfane-promoted direct olefination of polyfluoroarenes catalyzed by palladium has been reported. With use of this new thioether ligand, a high reaction efficiency and excellent E/Z ratio of desired olefinated polyfluoroarenes were obtained. This represents a first example of thioether promoted oxidative Heck reaction.

Thioether-ligated iron(II) and iron(III)-hydroperoxo/alkylperoxo complexes with an H-bond donor in the second coordination sphere.

The non-heme iron complexes, [Fe(II)(N3PySR)(CH3CN)](BF4)2 () and [Fe(II)(N3Py(amide)SR)](BF4)2 (), afford rare examples of metastable Fe(iii)-OOH and Fe(iii)-OOtBu complexes containing equatorial thioether ligands and a single H-bond donor in the second coordination sphere. These peroxo complexes were characterized by a range of spectroscopic methods and density functional theory studies. The influence of a thioether ligand and of one H-bond donor on the stability and spectroscopic properties of these complexes was investigated.

Palladium–phosphorus/sulfur nanoparticles (NPs) decorated on graphene oxide: synthesis using the same precursor for NPs and catalytic applications in Suzuki–Miyaura coupling

PdP2 and Pd4S nanoparticles (NPs) (size: ∼2-6 and 9-15 nm respectively) have been prepared for the first time from a single source precursor complex [Pd(L)Cl2] (1) by its one pot thermolysis at 200 °C in TOP and OA/ODE (1 : 1) respectively. These NPs were stirred with graphene oxide (GO) at room temperature to prepare NP composites, GO-PdP2 and GO-Pd4S. The GO-PdP2 NPs have been synthesized for the first time. The thioether ligand L prepared by reaction of 1,3-dibromo-2-propanol with the in situ generated PhSNa reacts with [PdCl2(CH3CN)2] in CH3CN at 70 °C resulting in 1. The L and 1 have been characterized by (1)H and (13)C{(1)H} NMR and HR-MS. The single crystal structure of 1 determined by X-ray diffraction reveals nearly square planar geometry around the Pd metal centre. The catalytic activities of two palladium nano-phases having phosphorus and sulphur respectively as a co-constituent for Suzuki-Miyaura coupling have been found to be exceptionally different, as PdP2 nanoparticles (NPs) grafted on graphene oxide (GO-PdP2) are significantly more efficient than Pd4S NPs grafted on GO. Without grafting PdP2 and Pd4S both have low efficiency. This is the first report comparing the influence of P and S on the catalytic activity of Pd NPs. TEM, SEM-EDX and powder-XRD have been used to authenticate all NPs. The GO-PdP2 NPs have been found to be efficient catalysts for Suzuki-Miyaura coupling reactions (yield up to 96% in 30 min) at room temperature to 80 °C. Their recyclability has been found up to 6 cycles. In contrast, GO-Pd4S NPs are little active in comparison with GO-PdP2 NPs. The size of NPs and their distribution on GO appear to be key factors affecting the catalytic efficiency of the composite NPs. Leaching of Pd from GO-PdP2 NPs contributes significantly to the catalysis as evidenced by the three phase test, hot-filtration and recycling experiments. The catalysis is almost homogeneous.

ChemInform Abstract: A Survey of Sulfide Ligands for Allylic C—H Oxidations of Terminal Olefins.

AbstractScreening a 37‐membered library of thioether ligands has shown that tetrahydrothiophene is a highly reactive and selective ligand for Pd‐catalyzed allylic C—H oxidation reactions.

Cu(II) complexes of a new tetradentate N2SO donor: synthesis, structure, electrochemistry, and DFT computation

Cu(II) complexes having distorted square pyramidal geometry with N2SO donor azo–thioether ligand, [Cu(L)X] (X = Cl (1) and Br (2)), have been synthesized and characterized. The geometries of the complexes are confirmed by single crystal X-ray analysis. The complexes form supramolecular 1D chains by intermolecular H-bonding and π–π interaction between the pyridines. Spectral and electrochemical properties have been studied. Electronic structure and spectral properties are explained by DFT and TDDFT analysis.

Synthesis and Characterization of Nickel Compounds with Tetradentate Thiolate–Thioether Ligands as Precursors for [NiFe]–Hydrogenase Models

AbstractSynthesis and X‐ray structural analyses of three NiS4 compounds with aliphatic tetradentate thiolato/thioether ligands―[Ni(xch)], [Ni(pdtch)], and [Ni(pdtdm)], in which H2xch, H2pdtch, and H2pdtdm are α,α′‐bis(trans‐2‐mercapto‐1‐thiacyclohexyl)‐o‐xylene, 1,3‐bis(trans‐2‐mercapto‐1‐thiacyclohexyl)propane, and 1,9‐dimercapto‐3,7‐dithia‐2,2,8,8‐tetramethylnonane―are reported and further investigated by NMR spectroscopy, electronic absorption spectroscopy, and cyclic voltammetry. The molecular and electronic structures of these nickel complexes are described. All complexes are square planar and show only a small tetrahedral distortion, consistent with a low‐spin nickel(II) center (S = 0). Cyclic voltammetry data reveal that for all compounds both one‐electron oxidation and reduction are irreversible, which is explained by means of DFT calculations. The presented complexes are discussed with regard to their suitability as precursors for dinuclear [NiFe]–hydrogenase model compounds.

Ru(II) thioether complexes with dangling pyridine ligands

Through two different methods, new Ru(II) polypyridyl complexes were prepared in an attempt to replicate previously reported heptacoordinate Ru(II) syntheses. The tetradentate thioethers, 1,8-bis(2′-pyridyl)-3,7-dithianonane (Pdto), 1,9-bis(2′-pyridyl)-3,7-dithianonane (Pdtn), and 1,10-bis(2′-pyridyl)-3,8-dithiadecane (Pdtd), were used to form dinuclear ruthenium(II) complexes of the type [{Ru(L1)}2(μ-Cl)2]2+via reaction with RuCl3·xH2O. Upon reaction of the dinuclear complexes with the triimine ligand 2,6-bis(N′-methyl-benzimidazolyl)pyridine (Me2Bzimpy), facile symmetrical bridge cleavage occurs, producing mononuclear complexes of the form [Ru(L1)(L2)]2+, where L1 is one of the three tetradentate thioether ligands and L2 is the tridentate triimine. A second method of producing the mononuclear [Ru(L1)(L2)]2+ complexes involves the reaction of Ru(L2)Cl3 with L1 under ethanolic conditions. In such mononuclear complexes, one of the pyridine arms of the tetradentate thioether is forced to be uncoordinated, due to the firmly hexacoordinate nature of Ru(II). A similar experiment was conducted using the pentadentate thioether 1,11-bis(2′-pyridyl)-3,6-9-dithianonane (Pttu) and the diimine Phen, forming the stable hexacoordinate [Ru(Pttu)(Phen)]2+ complex. The mononuclear complexes exhibit single-electron Ru(II)→Ru(III) oxidative response, in the range of +825 to +845mV versus APE, involving the removal from an electron from the t2g orbital set.

Thioether-Promoted Direct Olefination of Polyfluoroarenes Catalyzed by Palladium

A methyl(phenyl)sulfane-promoted direct olefination of polyfluoroarenes catalyzed by palladium has been reported. With use of this new thioether ligand, a high reaction efficiency and excellent E/Z ratio of desired olefinated polyfluoroarenes were obtained. This represents a first example of thioether promoted oxidative Heck reaction.

Dinuclear niobium(III) and tantalum(III) complexes with thioether and selenoether ligands [{MIIIX2(L)}2(μ-X)2(μ-L)] (M = Nb, Ta; X = Cl, Br; L = R2S, R2Se): Syntheses, structures, and the optimal conditions and the mechanism of the catalysis for regioselective cyclotrimerization of alkynes

A series of dinuclear niobium(III) and tantalum(III) halide complexes with chalcogen donors [{MIIIX2(L)}2(μ-X)2(μ-L)] (M = Nb; X = Cl, Br; L = R2S, R2Se) (M = Ta; X = Cl, Br; L = R2S) have been prepared by the reaction of dimetal(V) decahalide (M2X10) with magnesium and L. The structures of five of those new complexes were determined by X-ray crystallography to have a M–M double bond. It is evidenced that the solvent and the temperature play important roles in achieving high yield and regioselectivity for cyclotrimerization of alkynes. The reaction of the niobium(III) chloride complexes (L = dimethyl sulfide (Me2S), tetrahydrothiophene (C4H8S, THT, thiolane)) with phenylacetylene at room temperature in toluene gave both head-to-tail cycloadded trimers of alkyne, 1,3,5-(Ph)3-2,4,6-(H)3-benzene and head-to-head cycloadded 1,2,4-(Ph)3-3,5,6-(H)3-benzene, in high yields. The smaller the thioether ligands, the higher the catalytic activity. The niobium(III) chloride complexes with selenoether (L = dimethyl selenide (Me2Se), tetrahydroselenophene (C4H8Se, THSe, selenolane) have higher rates for the reaction with alkynes, but low activity for the cyclotrimerization. Tantalum(III) chloride complexes (L = Me2S, THT, tetrahydrothiopyran (C5H10S, THTP, thiane)) have lower catalytic activities than the niobium(III) ones, because the Ta–S(μ-L) bond lengths are shorter than those of niobium analogs. The stability of the precursor complexes toward the first oxidative addition depends on the M–S(μ-L) bond strength, and controls the concentration of catalytic active species. The niobium(III) bromide complexes (L = Me2S, THT) and the tantalum(III) bromide one (L = Me2S) react with alkynes to give head-to-tail compounds regioselectively, but are less catalytically active than those of chloride complexes.