Pyrazole complexes as anion receptors

The behavior of the receptors [Re(CO)3(Hdmpz)3]BAr'4 (Hdmpz = 3,5-dimethylpyrazole) (1) and [Re(CO)3(HtBupz)3]BAr'4 (HtBupz = 3(5)-tert-butylpyrazole) (2; Ar' = 3,5-bis(trifluoromethyl)phenyl) toward the anions fluoride, chloride, bromide, iodide, hydrogensulfate, dihydrogenphosphate, nitrate, and perrhenate was studied in CD3CN solution. In most cases, the receptors were stable. Anion exchange was fast, and binding constants were calculated from the NMR titration profiles. The structure of the adduct [Re(CO)3(HtBupz)3] x NO3 (3) was determined by X-ray diffraction. Two pyrazole moieties are hydrogen-bonded to one nitrate oxygen atom, and the third pyrazole moiety is hydrogen-bonded to an oxygen atom of an adjacent nitrate, leading to infinite chains. The structure of the adduct [Re(CO)3(Hdmpz)3]BAr'4acetone (4), also determined by X-ray diffraction, showed a similar interaction of two pyrazole N-H groups with the acetone oxygen atom. F- and H2PO4(-) deprotonate the receptors, and HSO4(-) decomposed 1. The structure of one of the decomposition products (5), determined by X-ray diffraction, is consistent with pyrazole protonation and substitution by sulfate.     

Cationic fac-tris(pyrazole) complexes as anion receptors

New receptors fac-[Re(CO)3(pz)3]BAr'4 (pz = 3,5-dimethylpyrazole or 3(5)-tert-butylpyrazole, Ar' = 3,5-(CF3)2C6H3), synthesized from [Re(OTf)(CO)5] and the pyrazoles, have been found to show a high affinity for chloride.     

Ruthenium complexes as protein kinase inhibitors

[reaction: see text] Replacing complex natural products with simple metal complexes could lead to a new class of metallopharmaceuticals in which the metal center plays mainly a structural role. A strategy is introduced for the creation of ruthenium complex-based protein kinase inhibitors 1 (X = CO or CH(2)), morphed out of the class of indolocarbazole inhibitors with the alkaloid staurosporine as its most prominent member.     

BF(2) complexes of alpha-alkyl-substituted dipyrrolyldiketones as acyclic anion receptors

alpha-Alkyl-substituted dipyrrolyldiketones have exhibited anion binding behaviours with pyrrole rotations, whose rates depend on the alkyl chain lengths.     

Organometallic complexes as anion hosts

New anion hosts have been accessed using cationic organometallic fragments with sufficient kinetic stability as geometry-organizing cores, simple ditopic ligands featuring hydrogen bond donor groups, and the inert, low interacting, lipophilic BAr'(4) anion.     

Ruthenium dihydride complexes as enyne metathesis catalysts

Ruthenium–catalyzed enyne metathesis is a reliable and efficient method for the formation of 1,3-dienes, a common structural motif in synthetic organic chemistry. The development of new transition-metal complexes competent to catalyze enyne metathesis reactions remains an important research area. This report describes the use of ruthenium (IV) dihydride complexes with the general structure RuH₂Cl₂(PR₃)₂ as new catalysts for enyne metathesis. These ruthenium (IV) dihydrides have been largely unexplored as catalysts in metathesis-based transformations. The reactivity of these complexes with 1,6 and 1,7-enynes was investigated. The observed reaction products are consistent with the metathesis activity occurring through a ruthenium vinylidene intermediate.     

Diol-substituted boron complexes of dipyrrolyl diketones as anion receptors and covalently linked 'pivotal' dimers

Diol-substitution at a boron unit results in the formation of anion receptors consisting of dipyrrolyl diketones and covalently linked dimers, which exhibit selective binding for dianions with appropriate lengths.     

Pyridyl thioureas as switchable anion receptors

The binding selectivity of simple pyridyl thioureas in acetonitrile can be completely switched by protonation; hence the neutral thiourea binds acetate, but not chloride or bromide, whereas the protonated thiourea binds strongly to chloride or bromide, but is deprotonated by acetate.     

Polyaza metacyclophanes as ditopic anion receptors

Five macrocyclic polyaza metacyclophanes L1-L5 prepared by dipode coupling of the tosylated precursors have been studied. The basicity of the ligands has been measured potentiometrically and their ability to complex halides and perchlorate has been studied in the solid state by X-ray crystallography. The results reveal that the ligands generally act as ditopic halide receptors with even the largest, L5, being too small to envelop the anion. The ligand's basicity behaviour parallels that observed for related para-analogues. Despite the ready crystallisation of fluoride, HF2-, chloride, bromide, iodide and triiodide salts in the solid state, there appears to be little affinity for halides in aqueous solution in the pH range accessible via potentiometry. The results do give a detailed insight into the role of the aryl ring in restricting the conformational flexibility of the ligands and, hence, the ability to chelate perching anions.     

Phenanthroline complexes bearing fused dipyrrolylquinoxaline anion recognition sites: efficient fluoride anion receptors

Novel anion recognition host molecules, tris-1,10-phenanthroline cobalt(III) and bis-2,2'-bipyridine mono-1,10-phenanthroline ruthenium(II) complexes bearing fused dipyrrolylquinoxaline moieties have been synthesized. As determined by UV-vis spectroscopic and electrochemical studies, these metal complexes bind fluoride with high affinity in polar media both in absolute terms and relative to the metal-free phenanthroline dipyrrolylquinozaline precursor from which they are derived (fluoride is bound to the tris-1,10-phenanthroline cobalt(III) dipyrrolylquinoxaline system with a 1:1 binding constant of 54 000 M-1 in DMSO). The large observed binding constants are ascribed to two factors, (i) the presence of a phenanthroline-coordinated cationic charge that decreases the electron density on the pyrrole NH protons and (ii) pure electrostatic effects.     

Steroids as organising elements in anion receptors

The steroid nucleus has proved useful in various areas of supramolecular chemistry, acting as a building-block for extended, well-defined molecular architectures, and a scaffold for preorganised arrays of functionality. This article discusses its applications in the area of anion recognition, where cholic acid (2) has been especially valuable. The three secondary hydroxyl groups on 2 are nicely arranged for H-bond donation to a single anion, and may be converted into stronger neutral or positively-charged H-bond donors. Macrocyclic and acyclic receptors derived from 2 have been used to bind inorganic anions, carboxylates and nucleic acids.     

Ruthenium amino carboxylate complexes as asymmetric hydrogen transfer catalysts

The synthesis and characterization of optically active amino carboxylate complexes of formula [(η(6)-arene)Ru(Aa)Cl] (arene = C(6)H(6), C(6)Me(6), Aa = amino carboxylate) as well as those of the related trimers [{(η(6)-arene)Ru(Aa)}(3)][BF(4)](3) are reported. Trimerization takes place with chiral self-recognition: only diastereomers equally configured at the metal, R(Ru)R(Ru)R(Ru) or S(Ru)S(Ru)S(Ru), are detected. The crystal structures of the complexes [(η(6)-C(6)H(6))Ru(Pip)Cl] and [{(η(6)-C(6)Me(6))Ru(Pro)}(3)][BF(4)](3) have been determined by X-ray diffraction methods. Both types of complexes catalyse the hydrogen transfer reaction from 2-propanol to ketones with moderate enantioselectivity (up to 68% ee). The enantiodifferentiation achieved can be accounted for by assuming that Noyori's bifunctional mechanism is operating.     

Ruthenium sorption as heterometallic complexes with phosphoryl-containing impregnated sorbents

It is shown that the main features of ruthenium extractive recovery with neutral organophosphorus compounds (L) as [RuNO(NO₂)₄ML _n ] (M = Zn, Cu, Co, Ni; n = 2–3) heterometallic complexes are retained on the sorption recovery with sorbents impregnated with L. The sorbent based on mixed trialkylphosphine oxide can be used for the chromatographic recovery of ruthenium, the extent of total ruthenium recovery at sorption-desorption stages (90–94%) retains after seven cycles.     

Ruthenium complexes with heteropoly anion PW11O39 7− and their redox properties

A new heteropoly complex PW₁₁Ru^IV and complexes of Ru^II, Ru^III and Ru^V based thereon have been obtained. Using specrophotometry the states of Ru^III and Ru^IV complexes in solution, the pH range of their stability, and the interaction of PW₁₁Ru^IV with ClO₄ ^–,SO₄ ^2–, Cl^– ions have been studied. A conclusion has been thus made that the ruthenium ion in such a complex is not incorporated in the heteropolyanion lattice, but is attached only to its external oxygen atoms. Kinetics of oxidation of PW₁₁Ru^IV and PW₁₁Ru^III with potassium chlorate have been studied. The activation energy and pre-exponential factor have been found for the reaction. The possibility that ClO₄ ^– and ClO₃ ^– in aqueous solutions can be activated by PW₁₁Ru^II with the former and by PW₁₁Ru^III and PW₁₁Ru^IV with the latter has been demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1363–1369, August, 1993.The authors wish to thank I. L. Krayevskaya and V. M. Novopashina for X-ray fluorescence and ionic chromatographic analyses, respectively.     

BF2 complexes of beta-tetraethyl-substituted dipyrrolyldiketones as anion receptors: potential building subunits for oligomeric systems

Synthesis and anion binding properties of BF2 complexes of beta-tetraethyl-substituted dipyrrolyldiketones, with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole alpha-positions, are reported. The substituents at pyrrole rings of these acyclic anion receptors are found to play a key role to control not only the polarization of binding sites (NH and CH) but also the relative stabilities of the preorganized conformations and the degrees of sterical repulsion, both of which notably affect the affinities for anions.     

Thiourea isosteres as anion receptors and transmembrane transporters

Compounds containing cyanoguanidine and 3-amino-1,2,4-benzothiadiazine-1,1-dioxide have been studied as anion receptors and transporters. Significant affinity for oxo-anions was observed in organic solution and the receptors were found to function as transmembrane chloride/nitrate antiporters with transport rates enhanced in the presence of valinomycin-K(+) complex.     

Tetraphosphinitoresorcinarene complexes: cationic silver(I) and copper(I) halide complexes as mercurate(II) anion receptors

The reactions of mercury(II) halides with the tetraphosphinitoresorcinarene complexes [P4M5X5], where M=Cu or Ag, X=Cl, Br, or I, and P4=(PhCH2CH2CHC6H2)4(O2CR)4(OPPh2)4 with R=C6H11, 4-C6H4Me, C4H3S, OCH2CCH, or OCH2Ph, have been studied. The reactions of the complexes with HgX2 when M=Ag and X=Cl or Br occur with elimination of silver(I) halide and formation of [P4Ag2X(HgX3)], but when M=Ag and X=I, the complexes [P4Ag4I5(HgI)] are formed. When M=Cu and X=I, the products were the remarkable capsule complexes [(P4Cu2I)2(Hg2X6)]. When M=Ag and X=I, the reaction with both CuI and HgI2 gave the complexes [P4Cu2I(Hg2I5)]. Many of these complexes are structurally characterized as containing mercurate anions weakly bonded to cationic tetraphosphinitoresorcinarene complexes of copper(I) or silver(I) in an unusual form of host-guest interaction. In contrast, the complex [P4Ag4I5(HgI)] is considered to be derived from an anionic silver cluster with an iodomercury(II) cation. Fluxionality of the complexes in solution is interpreted in terms of easy, reversible making and breaking of secondary bonds between the copper(I) or silver(I) cations and the mercurate anions.     

Ruthenium complexes of phosphine-aminophosphine ligands

Ruthenium complexes of phosphinoferrocenylaminophosphine ligands (BoPhoz™ ligands) have been prepared by combining the ligands with tris(triphenylphosphine)ruthenium dichloride and precipitating the complexes. The optimal species exhibit high enantioselectivities for the asymmetric hydrogenation of functionalized ketones, particularly β-ketoesters.     

Metal-assembled anion receptors

This review describes the self-assembly of anion receptors from organic ligands and transition metal ions. These metal-assembled anion receptors can be synthesised from a number of different species; bidentate ligands with metals that prefer octahedral coordination geometries and monodentate ligands with metals that prefer square planar geometries are common. Anion binding transition metal helicates and systems where the coordination of metal ions results in the formation of an anion receptor by conformational locking are also reported. The effect of anion binding on the different properties of these complexes is discussed.     

Ruthenium(II) polypyridyl complexes as carriers for DNA delivery

Two novel water soluble ruthenium(II) complexes [Ru(bpy)(2)(bqbg)](2+) and [Ru(phen)(2)(bqbg)](2+) have been structurally characterized and their DNA condensation activity, cytotoxicity, and cellular uptake studies of DNA condensates as potential non-viral DNA carriers were evaluated.