Aminothiolate Ligands Research Articles

Indium complexes with aminothiolate ligands as single precursors for indium chalcogenides

Indium complexes with aminothiolate ligands, In(dmampS)2Cl (1) and In(dmampS)3 (2), were synthesized by the metathesis reaction of InCl3 with 2 equiv. and 3 equiv. of Li(dmampS), respectively. The reaction of 1 with 1 equiv. of KSeCN resulted in the formation of In(dmampS)2(NCSe) (3). The three complexes have been characterized by IR, NMR, Mass spectroscopy, and microanalysis. Single-crystal X-ray diffraction studies revealed that complexes 1 and 3 have distorted trigonal bipyramidal geometry at the indium center. Thermogravimetric analyses indicated that the residual materials of the complexes 1, 2, and 3 could be presumably In2S3, In2S3, and In2Se2S, respectively. Thermal decomposition of 1–3 formed In2S3 (for 1 and 2) and In2Se2S (for 3). This was confirmed using EDS and ICP-AES.

Synthesis of Gold(III) Complexes with Bidentate Amino-Thiolate Ligands as Precursors of Novel Bifunctional Acyclic Diaminocarbenes.

Two neutral bis(pentafluorophenyl)thiolate gold(III) complexes with the unsymmetrical S^N ligands 2-aminothiophenol or cysteamine have been synthesized and their reactivity has been studied. Homo- and heterodinuclear compounds were obtained by their coordination to gold(I) or silver(I) derivatives through the sulfur atom. Interestingly, a tetranuclear derivative bearing short gold(I)···gold(I) and the more unusual gold(I)···gold(III) interactions has been prepared. These amino-thiolate derivatives can be used as precursors for the synthesis of novel gold(III) acyclic diaminocarbene complexes by reaction with isocyanides CNR. The nucleophilic attack of the amino group to isocyanide molecules affords the synthesis of unprecedented bidentate C^S acyclic diaminocarbene ligands. All of the complexes are air- and moisture-stable at room temperature and have been spectroscopically and structurally characterized.

Germanium Compounds Containing Ge═E Double Bonds (E = S, Se, Te) as Single-Source Precursors for Germanium Chalcogenide Materials.

New germanium chalcogenide precursors, S═Ge(dmamp)2 (3), S═Ge(dmampS)2 (4), Se═Ge(dmamp)2 (5), Se═Ge(dmampS)2 (6), Te═Ge(dmamp)2 (7), and Te═Ge(dmampS)2 (8), were synthesized from Ge(dmamp)2 (1) and Ge(dmampS)2 (2) using sulfur, selenium, and tellurium powders (dmamp = 1-dimethylamino-2-methyl-2-propanolate, dmampS = 1-dimethylamino-2-methylpropane-2-thiolate). Complexes 1 and 2 were synthesized from metathesis reactions of GeCl2·dioxane with 2 equiv of aminoalkoxide or aminothiolate ligands. Thermogravimetric analysis of complex 1 displayed good thermal stability and volatility. The molecular structures of complexes 2-8 from X-ray single crystallography showed distorted trigonal bipyramidal geometry at the germanium centers. Germanium chalcogenide materials (GeSe and GeTe) were obtained from the thermal decomposition of complexes 5, 6, and 8 in hexadecane. X-ray diffraction patterns exhibited that GeSe and GeTe had orthorhombic and rhombohedral phases, respectively. This study affords a facile method to easily prepare germanium chalcogenide materials using well-designed and stable complexes by thermal decomposition of single-source precursors in solution.

Synthesis of a Free-Standing Monolayer of Covalently Bonded Gold Nanoparticles

We present synthesis of a free-standing monolayer film of gold nanoparticles (AuNPs) which are linked by covalent bonds. In the method developed, the free-standing film is obtained by chemical cross-linking of the AuNPs of the core diameter of 5.6 nm that form a dense monolayer at the oil–liquid interface. As the cross-linking agent, naphthalene dianhydride derivative, which forms amide bonds with the ligand molecules, is used. The AuNPs are coated with aminothiolate ligands that can change their character from a hydrophilic to a hydrophobic one via the reversible protonation/deprotonation mechanism. When adsorbed at the oil–water interface, such functionalized AuNPs display amphiphilic (Janus-like) structure and self-assemble into a highly stable monolayer. To bring the AuNPs at the oil–water interface, an excitation of the system that leads to the formation of the oil-in-water emulsion is required. After the excitation, the AuNPs are transported onto the oil–water interface on the surface of the oil dro...

A 1 : 1 intercluster compound consisting of +6 and −6 charged RhIII4ZnII4 octanuclear cations and anions with aminothiolate ligands

The first example of a 1 : 1 metal–organic intercluster compound with +6 charged cations and −6 charged anions was synthesized from [Zn4O{Rh(aet)3}4]6+ (aet = 2-aminoethanethiolate) and [Zn4O{Rh(L-cys)3}4]6− (L-cys = L-cysteinate). Its structure was determined by single-crystal X-ray crystallography, which revealed the formation of a diamondoid (dia) hydrogen-bonding network of the cluster anions, accommodating the cluster cations in its cavities.

ChemInform Abstract: Concepts for Ligand Design in Asymmetric Catalysis: A Study of Chiral Amino Thiol Ligands.

Abstract A series of new chiral sulfur–nitrogen chelate ligands, derived from amino acids, has been synthesised rationally. Fruitless experiments into catalytic asymmetric conjugate additions and desymmetrisation of meso-epoxides led us to analyse our ligands in the catalytic asymmetric addition of diethylzinc to aromatic aldehydes. These latter experiments were successful with chiral benzylic alcohols being obtained in up to 82% enantiomeric excess.

Amino thiols versus amino alcohols in the asymmetric alkynylzinc addition to aldehydes

A series of modular amino thiol and amino alcohol ligands have been synthesized in enantiopure form from common enantiopure precursors. Their structures have been optimized for performance in the asymmetric alkynylzinc addition to aldehydes, and a direct comparison of the effect of the S and O coordinating atoms on the catalytic outcome of these ligands has been performed. Amino thiols have shown to be superior as ligands for this type of chemistry.

(η6-Arene)RuII/Chiral SN Ligand: A Novel Bifunctional Catalyst System for Asymmetric Transfer Hydrogenation of Aromatic Ketones

A binary catalyst system of [RuCl 2 (η 6 -arene)] 2 and a protic aminothiol (SN) ligand has been found to promote hydrogen transfer between alcohols and carbonyl compounds. The chiral catalyst system with the pipecolinol-derived chiral SN ligand displays excellent stereoselectivity in the asymmetric transfer hydrogenation of aromatic ketones using HCO 2 H―Et 3 N. Novel unsymmetrical bis(thiolate)-bridged binuclear complex, which is relevant to the generation of catalytically active species, has been synthesized and structurally characterized.

Linear-Type S-Bridged Triruthenium Complexes with Aliphatic Aminothiolate Ligands: Synthesis, Characterization, and Properties

Treatment of [RuCl(2)(DMSO)(4)] with 2-aminoethanethiol (Haet) in ethanol gave a dicationic triruthenium complex, [Ru[Ru(aet)(3)](2)]Cl(2) ([1]Cl(2)). Complex [1]Cl(2) was also obtained by treatment of RuCl(3).nH(2)O with excess Haet in water. When [1](2+) was chromatographed on a cation-exchange column of SP-Sephadex C-25, meso (DeltaLambda) and racemic (DeltaDelta/LambdaLambda) isomers of the corresponding tricationic complex, [Ru[Ru(aet)(3)](2)](3+) ([2](3+)), were eluted with aqueous NaNO(3). The racemic isomer of [2](3+) was optically resolved into DeltaDelta and LambdaLambda isomers by using [Sb(2)(R,R-tartrato)(2)](2-) as a resolving agent. The molecular structures of DeltaLambda- and DeltaDelta/LambdaLambda-[2](NO(3))(3) were determined by X-ray crystallography. In these complexes, the central Ru atom is coordinated by six thiolato groups from two terminal fac-(S)-[Ru(aet)(3)] units in an octahedral geometry, forming a linear-type S-bridged triruthenium structure. The spectroelectrochemical studies on the electronic absorption and CD spectra, together with the electrochemical studies, demonstrated that [1](2+) and [2](3+) are interconvertible with each other through a one-electron redox process, retaining the chirality of the triruthenium structure. Their electronic structures were investigated on the basis of EPR and magnetic susceptibility measurements, which indicated that [1](2+) and [2](3+) have spin ground states of S(t) = 0 and S(t) = 1/2, respectively. The corresponding L-cysteinato complex, [Ru[Ru(L-cys-N,S)(3)](2)](3-), which was formed from RuCl(3).nH(2)O and excess L-cysteine (L-H(2)cys) in water followed by air oxidation, is also presented.

On the role of chiral catalysts in the alkenyl zirconocene/zinc addition to aldehydes: a study of ligand loading and asymmetric amplification.

Unusual nonlinear asymmetric amplification and chiral ligand loading effects were discovered for the use of catalytic quantities of chiral aminoalcohols in the in situ hydrozirconation-transmetalation-aldehyde addition processes. While the stereochemically most efficient aminothiol ligands demonstrated mechanistically conventional reaction parameters in excellent agreement with Kagan's ML(2) system, the asymmetric induction in the presence of a chiral aminoalcohol was found to vary greatly with loading and %ee of the ligand. Aminothiols remain the ligands of choice for the highly enantioselective formation of allylic alcohols and provide experimentally more predictable reaction variables. However, new, optimized conditions lead to a synthetically useful product %ee using the readily available and scalable aminoalcohol 2a.

Ultrasonic extraction of iron from non-aqueous liquids

A novel procedure for the extraction of iron from predominately organic solvents has been described. An ultrasonic probe was used to create a microemulsion with a small quantity of nitric acid such that labile iron could be released into the aqueous vesicles and subsequently quantified after phase separation. The analytical and operational viability of using a simple colorimetric assay based on the coordination of aminothiol ligands (principally homocysteine) was evaluated in terms of signal sensitivity, selectivity and stability. The use of homocysteine provided a linear range for iron(III) from 9 microM to 50 microM with a corresponding limit of detection of 2 microM (based on 3s(b)). The effectiveness of the approach was assessed through the recovery of 0.3 ppm iron from a sample of commercial kerosene and the results compared with those obtained through attempting to quantify the iron under passive (ultrasonically silent) conditions.

6-Mercaptomethylpyridine-3-carboxylic acid (MEMNIC): a new reagent for peptide labeling with Tc-99m

As part of our ongoing research into the development of peptide based radiopharmaceuticals, we have explored 2-mercaptopyridines and 2-mercapto-pyrimidines (2MPs) as coligands to control the radiochemical speciation of 99mTc-labeled hydrazinonicotinamide (HYNIC) derivatized chemotactic peptides. In an attempt to develop an aminothiol ligand with greater stability, we synthesized 6-mercaptomethylpyridine–3-carboxylic acid (MEMNIC), assuming a five-member chelate ring complex would be more stable than the four-membered ring possible with 2MPs. Initial experiments suggested that 99mTc–MEMNIC was stable in vivo and led to our investigation of it as a bifunctional chelator for 99mTc labeling of peptides. The utility of MEMNIC was tested in a rabbit model of infection. The N-epsilon MEMNIC derivative of For–MLFK was prepared using the N-hydroxysuccinimidyl ester of MEMNIC. For–MLFK–MEMNIC was labeled via 99mTc–mannitol and its imaging and biodistribution properties compared to Tc–For–MLFK–HYNIC and Tc–For–MLFCys (labeled via the free thiol of cysteine). Sites of infection were produced in New Zealand white rabbits ( n=6/peptide) by injection of a suspension of Escherichia coli in a posterior thigh. Twenty-four hours after infection, the rabbits were injected intravenously with 0.5 mCi of HPLC purified 99mTc-peptide and imaged at 2.5 and 18 h p.i. The animals were sacrificed at 18 h and tissue activity determined. At 2.5 and 18 h, the organ distribution of Tc–For–MLFK–HYNIC and Tc–For–MLFK–MEMNIC were qualitatively similar with the exception of higher renal accumulation of the latter, whereas Tc–For–MLFKCys showed rapid and prolonged accumulation in bowel. ROI analysis gave target/background ratios of 3.91±0.32 and 11.89±2.21 for Tc–For–MLFK–HYNIC, 5.09±0.66 and 9.88±1.12 for Tc–For–MLFK–MEMNIC and 2.59±0.16 and 1.70±0.37 for Tc–For–MLFCys, at 2.5 and 18 h. Tissue radioactivity measurements (18 h) demonstrated that compared to Tc–For–MLFK–HYNIC, the accumulation of Tc–For–MLFK–MEMNIC was less in all organs except in kidney which was greater. Direct labeling of the thiol group of cysteine led to lower accumulation in all organs compared to Tc–For–MLFK–MEMNIC, except in GI tract which was fivefold higher. While, Tc–For–MLFK–MEMNIC had half the accumulation of Tc–For–MLFK–HYNIC in infected muscle and pus, the lower accumulation in most organs and normal muscle resulted in good infection localization. These results indicate that MEMNIC can be successfully used to label peptides with 99mTc while exhibiting good in vivo stability. The chemistry of MEMNIC with the {M(V)O} 3+ core characteristic of technetiun and its Group V congener rhenium was modeled by investigating the reactions of 2-mercaptomethylpyridine with appropriate Re(V)-oxo precursors in the presence of a variety of coligands. With diolate type tridentate donors of the class {X(CH 2CH 2O) 2} 2− (X=–NR, O, S), the ‘3+2’ compounds [ReO{η 3-(OCH 2CH 2) 2S}{η 2-SCH 2C 5H 4N}] ( 2) and [ReO{η 3-(OCH 2CH 2) 2NCH 3}{η 2-SCH 2C 5H 4N] ( 3) were isolated. In contrast, with the more sterically demanding dirmercapto class of tridentate ligands {S(CH 2CH 2S) 2} 2−, the ‘3+1’ species [ReO{η 3-(SCH 2CH 2) 2S}{η 1-(SCH 2C 5H 4N)}] ( 1) was isolated.

Novel oxorhenium and oxotechnetium complexes from an aminothiol[NS]/thiol[S] mixed-ligand system.

The simultaneous action of a bidentate aminothiol ligand, LnH, (n = 1: (CH3CH2)2NCH2CH2SH and n = 2: C5H10NCH2CH2SH) and a monodentate thiol ligand, LH (LH: p-methoxythiophenol) on a suitable MO (M = Re, 99gTc) precursor results in the formation of complexes of the general formula [MO(Ln)(L)3] (1, 2 for Re and 5. 6 for 99gTc). In solution these complexes gradually transform to [MO(Ln)(L)2] complexes (3, 4 for Re and 7, 8 for 99gTc). The transformation is much faster for oxotechnetium than for oxorhenium complexes. Complexes 1-4, 7, and 8 have been isolated and fully characterized by elemental analysis and spectroscopic methods. Detailed NMR assignments were made for complexes 3, 4, 7, and 8. X-ray studies have demonstrated that the coordination geometry around rhenium in complex 1 is square pyramidal (tau = 0.06), with four sulfur atoms (one from the L1H ligand and three from three molecules of p-methoxythiophenol) in the basal plane and the oxo group in the apical position. The L1H ligand acts as a monodentate ligand with the nitrogen atom being protonated and hydrogen bonded to the oxo group. The four thiols are deprotonated during complexation resulting in a complex with an overall charge of zero. The coordination geometry around rhenium in complex 4 is trigonally distorted square pyramidal (tau = 0.41), while in the oxotechnetium complex 7 it is square pyramidal (tau = 0.16). In both complexes LnH acts as a bidentate ligand. The NS donor atom set of the bidentate ligand and the two sulfur atoms of the two monodentate thiols define the basal plane, while the oxygen atom occupies the apical position. At the technetium tracer level (99mTc), both types of complexes, [99mTcO(Ln)(L)3] and [99mTcO(Ln)(L)2], are formed as indicated by HPLC. At high ligand concentrations the major complex is [99mTcO(Ln)(L)3], while at low concentrations the predominant complex is [99mTcO(Ln)(L)2]. The complexes [99mTcO(Ln)(L)3] transform to the stable complexes [99mTcO(Ln)(L)2]. This transformation is much faster in the absence of ligands. The complexes [99mTcO(Ln)(L)2] are stable, neutral, and also the predominant product of the reaction when low concentrations of ligands are used, a fact that is very important from the radiopharmaceutical point of view.

Schiff bases derived from mercury(II)–aminothiolate complexes as metalloligands for transition metals

Mercury(II) complexes of aromatic aminothiolate ligands of formula [Hg( n-SC 6H 4NH 2) 2], n=3 ( 1) or 4 ( 2) and [RHg( n-SC 6H 4NH 2)], R=Me, n=3 ( 3) or 4 ( 4); R=Ph, n=3 ( 5) or 4 ( 6) have been obtained and characterized by infrared and 1H, 13C and 199Hg-NMR spectroscopies. The latter indicates that, in solution, complexes 1– 6 have an essentially linear coordination about Hg(II). Unprecedented Schiff bases containing the Hg–S(thiolate) bond have been synthesized from 3– 6 and salicylaldehyde yielding complexes of formula [RHg( n-SC 6H 4NCHC 6H 4OH)], R=Me, n=3 ( 7) or 4 ( 8); R=Ph, n=3 ( 9) or 4 ( 10). The template reaction of 3 and 4 with M(CH 3COO) 2, M=Zn(II), Cd(II), and salicylaldehyde has afforded trimetallic complexes of formula [M II{MeHg( n-SC 6H 4NCHC 6H 4O)} 2], M=Zn, n=3 ( 11) or 4 ( 12); M=Cd, n=3 ( 13) or 4 ( 14). Complexes 7– 14 have also been explored by use of infrared and NMR spectroscopies. The crystal structure determination of 2, 3, 5, 7 and 8 by X-ray diffraction shows that Hg(II) has an essentially linear coordination. The presence of additional secondary Hg⋯S interactions in all these complexes leads to an increase in the coordination number of Hg to 4 or 5. In 2, the interaction of each S–Hg–S unit with three neighbouring units gives rise to a polymeric chain, which can be considered as being formed by pairs of fused incomplete cubanes. In 3, 5, 7 and 8, secondary Hg⋯S bonds between pairs of C–Hg–S fragments yield Hg 2S 2 dimers. In 3, these dimers afford two-dimensional sheets by means of additional Hg⋯N secondary interactions. The crystal packing of the Hg 2S 2 dimers in 5, 7 and 8 is very similar and gives rise to one-dimensional chains by means of additional Hg⋯S bonds. The resulting polymeric zig-zag ladders can be described as formed by Hg 4S 4 pseudo-cubanes sharing opposite faces.

ChemInform Abstract: Trends in NMR Chemical Shifts and Ligand Mobility of TcO(V) and ReO(V) Complexes with Aminothiols

Detailed 1H and 13C NMR studies have been conducted in a series of oxotechnetium and oxorhenium complexes with aminothiol ligands ([SNS][S], [SNN][S], [SNNS]) designed as potential radiopharmaceuticals. The results of these studies in combination with others in the literature show that the oxometal core creates an anisotropic environment and affects the chemical shifts of the coordinated ligandbackbone in a consistent way. Protons oriented towards the oxygen appear deshielded relative to their geminals oriented away from the oxygen. In addition, the direction of a side chain (towards or away from the oxometal core) on the ligand backbone is shown to have a major effect on chemical shifts. The fluxional mobility of the ligand in complexes of the [SNS][S] type was also studied by NMR and the free energy of activation delta G(C)double dagger for the conformational inversion of the ligand was calculated from the temperature dependence of the carbon chemical shifts. delta G(C)double dagger was found to depend on the orientation of the side chain present on the coordinated nitrogen. The energy barrier for the inversion is larger for the oxorhenium complexes than for the analogous oxotechnetium complexes.

Trends in NMR chemical shifts and ligand mobility of TcO(V) and ReO(V) complexes with aminothiols

Detailed 1H and 13C NMR studies have been conducted in a series of oxotechnetium and oxorhenium complexes with aminothiol ligands ([SNS][S], [SNN][S], [SNNS]) designed as potential radiopharmaceuticals. The results of these studies in combination with others in the literature show that the oxometal core creates an anisotropic environment and affects the chemical shifts of the coordinated ligand backbone in a consistent way. Protons oriented towards the oxygen appear deshielded relative to their geminals oriented away from the oxygen. In addition, the direction of a side chain (towards or away from the oxometal core) on the ligand backbone is shown to have a major effect on chemical shifts. The fluxional mobility of the ligand in complexes of the [SNS][S] type was also studied by NMR and the free energy of activation Δ G C ≠ for the conformational inversion of the ligand was calculated from the temperature dependence of the carbon chemical shifts. Δ G C ≠ was found to depend on the orientation of the side chain present on the coordinated nitrogen. The energy barrier for the inversion is larger for the oxorhenium complexes than for the analogous oxotechnetium complexes.

Conceptualisation of diagnostic agents: from empirical in vivo screening to rational in vitro predictive parameters.

A new rational conceptualisation protocol in new isotopic diagnostic agents has been designed to avoid systematic empirical in vivo screening. This protocol is based on multiple regression analysis, in order to determine the pharmacokinetic model capable of explaining in the best possible way the in vivo behaviour of molecules injected into an organism. Nine technetium complexes (99mTc-L) were synthesised from aminothiol ligand vectors. These complexes were characterised in terms of their physical, chemical and biological in vitro properties, i.e. lipophilicity (P), free fraction unbound to plasmatic proteins (Fup), the fraction unbound to blood cells (FuCb), and membrane adsorption fraction (Fad), an original factor assessed in vitro. Thus, two pharmacokinetic models were tested. The first takes into account the parameters classically used in pharmacokinetics (P, Fup, FuCb), and the second, in parallel with the first, includes the membrane adsorption rate (polar/apolar/polar membrane model). According to the phenomenon of tissular distribution, the explanatory power of the second model, including the Fad, is radically greater than that of the classical model. The comparative adjusted coefficient of determination (R2) of the model, including the Fad versus R2 of the first model, are heart (91%/6%), liver (89%/47%), spleen (64%/44%), lung (78%/26%), kidney (70%/33%) and brain (73%/8%), respectively. In addition, as for the myocardium, the membrane adsorption factor seems to be the only predictive factor of the affinity between the myocardium and neutral or cationic molecules. This refutes the generally held view that only cationic molecules could have an affinity with the heart.

Concepts for ligand design in asymmetric catalysis: a study of chiral amino thiol ligands

A series of new chiral sulfur–nitrogen chelate ligands, derived from amino acids, has been synthesised rationally. Fruitless experiments into catalytic asymmetric conjugate additions and desymmetrisation of meso-epoxides led us to analyse our ligands in the catalytic asymmetric addition of diethylzinc to aromatic aldehydes. These latter experiments were successful with chiral benzylic alcohols being obtained in up to 82% enantiomeric excess.

ChemInform Abstract: The Importance of Nitrogen Substituents in Chiral Amino Thiol Ligands for the Asymmetric Addition of Diethylzinc to Aromatic Aldehydes.

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Unprecedented Polycrystal Structure of a New Cadmium Thiolate Containing an Unusually Highly Charged [ClCd8{SCH(CH2CH2)2N(H)Me}16]15+ Core

A new cadmium thiolate with overall composition [ClCd8{SCH(CH2CH2)2N(H)Me}16](ClO4)15·16[SCH(CH2CH2)2N(H)Me]·32H2O has been obtained in a high ionic strength aqueous medium. The solid is a polycrystal consisting of equally oriented microcrystals of formula [ClCd8{SCH(CH2CH2)2N(H)Me}16](ClO4)15·16H2O held together by uncoordinated aminothiolate ligands and water molecules occupying the intercrystal spaces. The composition and structure of the microcrystals is shown by X-ray, XPS, and 113Cd NMR data. The uncoordinated aminothiolate ligands in zwitterionic form and water molecules are essential for the initial formation but not for the continued stability of the microcrystals as their chemical extraction leads to a new microcrystalline powder with essentially the same powder X-ray diffraction pattern. The existence of intercrystal spaces is confirmed by electron and atomic force microscopy techniques, SEM and AFM. The [ClCd8{SCH(CH2CH2)2N(H)Me}16]15+ cage can be described in terms of metal and ligand concent...