Tropolonato Ligands Research Articles

Chiroptical switching behavior of heteroleptic ruthenium complexes bearing acetylacetonato and tropolonato ligands.

Four types of tris-chelate ruthenium complexes bearing acetylacetonato (acac) and tropolonato (trop) ligands were synthesized and optically resolved into Δ and Λ isomers: [Ru(acac)3] (Ru-0), [Ru(acac)2(trop)] (Ru-1), [Ru(acac)(trop)2] (Ru-2), and [Ru(trop)3] (Ru-3). Chiral HPLC chromatograms, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) of the four ruthenium complexes were systematically investigated. As a result, the absolute configurations of the newly prepared enantiomeric complexes Ru-2 and Ru-3 were determined. For the case of Ru-2, its absolute configuration was also confirmed by single crystal X-ray diffraction analysis. The ECD changes upon chemical oxidation were further investigated for the four complexes. An ECD change in enantiomeric Ru-1 was observed upon oxidation, but the oxidized species soon returned to the neutral state within a few minutes. Enantiomers of Ru-3 also showed explicit ECD changes upon oxidation. Further, the lifetime of the oxidized state was the longest among the four investigated complexes, whereas they racemized in solution at room temperature. In contrast, the enantiomers of heteroleptic complexes (Ru-1 and Ru-2) concurrently exhibited ECD changes, relatively long lifetime of the oxidized state, and nil or quite slow racemization behavior. The coexistence of acac and trop ligands was key to making the competing factors compatible in the resultant ruthenium complexes.

A New Dirhodium Catalyst with Hemilabile Tropolonato Ligands for CH Bond Functionalization

Don't hold on too tightly! In a new dirhodium catalyst for C-H functionalization reactions, two tropolonato ligands are introduced as hemilabile chelating ligands (see scheme). Only two bridges hold the Rh-Rh core together. The tropolonato ligands can liberate a binding site in the equatorial coordination sphere of the catalyst. This opens a doorway to new mechanistic channels in C-H functionalization.

Influence of pH and Counteranion on the Structure of Tropolonato−Lead(II) Complexes: Structural and Infrared Characterization of Formed Lead Compounds

Reactions of tropolone with lead(II) trifluoromethanesulfonate, perchlorate, and nitrate in water/methanol mixtures at pH below 1.0 lead to the formation of three different polymeric lead(II) complexes, [Pb(trop)(CF3SO3)(H2O)]n (1), [Pb3(trop)4(ClO4)2]n (2), and [Pb2(trop)2(NO3)2(CH3OH)]n (3), respectively. On the other hand, if the reactions are performed at pH above 2.0, the dimeric compound [Pb(trop)2]2 (4) is obtained independently of the lead(II) salt used, as long as lead(II) does not form any strong complexes with the counterion. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction. The structure of solid tetrakis(tropolonato)lead(IV), Pb(trop)4 (5), has been studied by means of the EXAFS technique because it was not possible to obtain sufficiently large single crystals. In the polymeric structures, the counterions are coordinated to the lead(II) ions and act as bridges. The tropolonato ligand behaves as a chelating agent and a tri- or tetraconnective bridge. The total coordination number of the lead(II) ion is five in compound 4, seven in 1 and 3, and eight in 2, and the lead(IV) ion in 5 is eight-coordinated. The 6s2 lone electron pair on the lead(II) ion seems to be stereochemically active in all lead(II) complexes studied. All compounds have been characterized by IR spectroscopy as well.

Synthesis of molybdenocene(IV) and tungstenocene(IV) tropolonato complexes: Its derivative containing calix[4]arene moiety

The cationic di-μ-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp 2M(μ-OH) 2MCp 2] + (Cp = η-C 5H 5; M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp 2M(trop)] + (trop = C 7H 5O 2). The products were investigated by IR, 1H NMR, and 13C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the upper rim with two tropolonato-molybdenocene centers.

Antiferromagnetic coupling between rare earth ions and semiquinones in a series of 1:1 complexes.

We use the strategy of diamagnetic substitution for obtaining information on the crystal field effects in paramagnetic rare earth ions using the homologous series of compounds with the diamagnetic tropolonato ligand, Ln(Trp)(HBPz(3))(2), and the paramagnetic semiquinone ligand, Ln(DTBSQ)(HBPz(3))(2), (DTBSQ = 3,5-di-tert-butylsemiquinonato, Trp = tropolonate, HBPz(3)= hydrotrispyrazolylborate) for Ln = Sm(iii), Eu(iii), Gd(iii), Tb(iii), Dy(iii), Ho(iii), Er(iii) or Yb(iii). The X-ray crystal structure of a new form of tropolonate derivative is presented, which shows, as expected, a marked similarity with the structure of the semiquinonate derivative. The Ln(Trp)(HBPz(3))(2) derivatives were then used as a reference for the qualitative determination of crystal field effects in the exchange coupled semiquinone derivatives. Through magnetisation and susceptibility measurements this empirical diamagnetic substitution method evidenced for Er(iii), Tb(iii), Dy(iii) and Yb(iii) derivatives a dominating antiferromagnetic coupling. The increased antiferromagnetic contribution compared to other radical-rare earth metal complexes formed by nitronyl nitroxide ligands may be related to the increased donor strength of the semiquinone ligand.

Gallium-Gallium Single Bonds Terminally Coordinated by Tropolonato Ligands

Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1) reacted with tropolone (2-hydroxi-2,4,6-cycloheptatrien-1-one) by replacement of two bis(trimethylsilyl)methyl groups and retention of its Ga-Ga single bond. Each gallium atom of the centrosymmetric product (2) is chelated by a tropolonato ligand. The Ga-Ga bond length (244.9 pm) is in the characteristic range of unsupported Ga-Ga bonds.

Structure of (tropolonato)4M-Type Compounds (M = Si, Ge, Sn)

T4M (M = Si, Ge, Sn; T = tropolonato)-type compounds were synthesized by reactions of tropolone with tetramethoxysilane, tetramethoxygermane, and tetrachlorostannane, respectively. X-ray and NMR analyses have shown that, both in the solid state and in solution, T4Si exists as an ion pair of a hexacoordinate silicocation (T3Si+) with an associated tropolone anion (T-), while T4Sn has an octacoordinate structure. The geometry around the tin atom is best described as a bicapped trigonal prism distorted toward a dodecahedron, in which the eight oxygen atoms of four tropolonato ligands are coordinated to a tin atom with an average Sn−O bond distance of 2.168 Å. Features of NMR and UV−vis spectra of T4Ge are similar to those of T4Si, indicating ion pairing between T3Ge+ and T- in solution; the black color of the solid of T4Ge is suggestive of the ion pairing in the solid-state as well, whereas single crystals suitable for X-ray analysis have not been obtained.

Synthesis and Reactions of Neutral Hypercoordinate Allylsilicon Compounds Having a Tropolonato Ligand

A novel intramolecular allylic migration from silicon to carbon was observed during the reaction of allylmethyldichlorosilane with tropolone in the presence of triethylamine to give an isomeric mix...

Synthesis and Structure of Hexacoordinate Organosilicon Compounds Having Tropolonato Ligands

Abstract R2SiT2 type of compounds (R = alkyl, aryl, OMe; T = tropolonato) have been found to hold rather exceptionally hexacoordinate dialkyl- and diarylsilicon geometry with two bidentate tropolonato ligands both in the solid state and in solution. A facile intramolecular stereoisomerization of these neutral hexacoordinate silicon compounds was observed by temperature dependent NMR spectroscopy in solution.

Structural characterization of two lipophilic tris(tropolonato) gallium(III) and indium(III) complexes of radiopharmaceutical interest

Tris(tropolonato)gallium(III), GaT 3, and tris(tropolonato)indium(III), InT 3, have been prepared in water from tropolone and the corresponding metal(III) nitrate salt and structurally characterized. GaT 3 ( 1) crystallizes in the monoclinic space group C2/ c with a=10.899(1), b=10.282(1), c=16.970(2) Å, β=103.721(8)° and Z=4. InT 3 ( 2) crystallizes in the rhombohedral space group R 3 c with a=10.5349(5), b=10.5349(5), c=32.738(2) Å and Z=6. The structures have been refined to an R factor of 0.027 for 1, based on 2171 observed reflections, and to an R factor of 0.030 for 2, based on 507 observed reflections. The octahedral coordination of the metal(III) ions leads to an OMO' bond angle of 81.1(1)° (mean value) in 1 and 75.3(1)° in 2 and to an MO bond length of 1.967(1) Å (mean value) in 1 and 2.134(3) Å in 2. Structural parameters are compared to AlT 3 and FeT 3 analogues and show the inflexibility of the tropolonato anion. The structural variations observed in the parameters external to the ring are consistent with the variation of the ionic radius in this series. The five signals observed on the 13C NMR spectra are consistent with the C 2 v symmetry of the tropolonato ligand. A downfield shift for each carbon atom is observed upon complexation.

The crystal structure of tetrakis(tropolonato) aquothorium(IV)

Tetrakis(tropolonato)aquothorium(IV) crystallizes in the triclinic system having a = 17·838, b = 11·951, c = 13·883 A ̊ , α = 81·85, ß = 93·02, γ = 93·02 , space group C 1 . The coordination number of the metal atom is nine and the coordination polyhedron is one of the nine possible isomers that use the mono-capped square antiprism. One tropolonato ligand occupies a slant position on the pyramidal cap while the water molecule occupies another vertex on the pyramidal cap yielding trivial C 1 symmetry.