Packing of complexes and intermolecular interactions in the crystals of volatile palladium(II) β-diketonates. crystal structure of palladium(II) benzoyltrifluoroacetonate

This paper reports on the synthesis and crystal structure analysis of palladium(II) bis-(trans-benzoyltrifluoroacetonate). Crystal data for PdO₄C₂₀F₆H₁₂:a= 4.748, b = 22.237, c = 9.410 Å, P = 105.44° Z = 2, space group P2₁/c, d_calc. = 1.86 g/cm . CAD-4 diffmctometer(MoKa), heavy atom method, R = 0.041 for 986 reflections. The structure is molecular; the planar molecules are stacked. The Pd atom is surrounded by a square of four O atoms (Pd?O = 1.97 Å, chelate angle 94.4°); Pd is involved in additional intemctions with the C_γ atoms of two neighboring molecules (Pd...C_γ= 3.44 Å). The molecular structure of palladium β-diketonate complexes, molecular packing in crystal, and intermolecular intemctions are considered. The van der Waals energies of the crystal lattice are calculated. The results are compared with the experimental values. In the structures of palladium( 11) β-diketonates, three groups of crystals are isolated: one group with 2 nearest-neighbor interactions (stacks), the second with 4 nearest-neighbor interactions (two-dimensional nets), and the third with 1 nearest-neighbor interaction (dimers). The latter are characteristic of the cis-complexes. The intemctions with 10–12 nearest neighbor molecules determine the energetics of the whole crystal. The high volatility of Pd(hfa)₂ is explained by the weaker intermolecular contacts between stacks in crystal.     

Enantioselective synthesis of β-lactams via the IndaBox-Cu(II)-catalyzed Kinugasa reaction

The enantioselective Kinugasa reaction of nitrones with terminal alkynes in the presence of 20 mol % of IndaBox-Cu(OTf)₂ and di-sec-butylamine (1.5 equiv) produced β-lactams with the highest level of enantiomeric excesses among the catalytic enantioselective Kinugasa reactions reported so far.     

Liquid crystals 100 years later. What are the new concepts used in the design of molecular,macromolecular and supramolecular liquid crystals?

A brief discussion of selected synthetic strategies pursued in the field of molecular, macromolecular and supramolecular liquid crystals is made by reviewing some tandem historical events of the past 100 years of activity in this field. This survey will try to suggest the rational for the discovery, evolution and investigation of some of these new concepts. Also a brief and speculative forecast of the future of this field will be presented.     

Design criteria for molecular mimics of fragments of the β-turn. 1. Cα atom analysis

Peptides represent an extensive class of biologically active molecules. They may be used as leads in the development of novel therapeutic agents provided the pharmacophoric information present within them can be translated into non-peptide analogs that lack the peptide backbone and are stable to proteolysis. This is the rationale for peptidomimetic drug design. Frequently, the -turn has been implicated as a conformation important for biological recognition of peptides. Empirical evidence from known peptidomimetics, coupled with a theoretical model of peptide binding and the observation that glycine and proline residues are common within the -turn, has suggested the design of molecules to mimic placement of between two and four of the side-chains. The moderate number of different -turn conformations, combined with the combinatoric nature of side-chain selection complicates the procedure. In this paper, cluster analysis has been used to classify the arrangement of C_{_} atoms about the various fragments of the -turn. Recombination of the observed patterns provides a general model for the -turn which may be used as an effective screen for potential peptidomimetic scaffolds in chemical databases.     

Immobilization of Pd(II) Catalysts for Cyclopropanation in Ionic Liquid

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The kinetics of reduction of palladium (II) complexes with β-alanine at dropping mercury electrode and the complexes’ stability constants

By using dc and ac polarography, the kinetics of electroreduction of the palladium (II) complexes with β-alanine at a dropping mercury electrode was studied in solutions with the palladium (II) concentration from 2 × 10^?5 to 2 × 10^?4 M and variable β-alanine and sodium perchlorate concentrations (pH 6–12). One polarographic wave was observed in solutions with pH 9 and 10 at the β-alanine overall concentration of c _βala = 1 × 10^?3 to 5 × 10^?2 M; two waves, at lower pH or higher c _βala. It was concluded on the formation of different forms of palladium (II) complexes in the studied solutions; the complexes contained two to four β-alanine coordinated anions. Using the limiting diffusion currents for the two waves at pH 9–11 and c _βala = 0.1 and 0.5 M, the stepwise stability constant for the Pd(βala) ₄ ^2? complex was calculated. Using two ac peaks observed at pH 7–8 and c _βala = 1 × 10^?2 to 0.1 M, the stepwise stability constant for the Pd(βala) ₃ ^? . was calculated. The perchlorate ions adsorbed at the dropping mercury electrode, as well as βala^? anions at their higher concentrations, hamper the electroreduction of the palladium (II) complexes with β-alanine.     

The adsorption of mercury(II) on the surface of silica modified with β-cyclodextrin

Multistage chemical modification of the surface of silica with β-cyclodextrin was performed. IR spectroscopy and quantitative analysis of surface compounds were used to prove the structure of modified silica. The adsorption of Hg(II) from dilute solutions was studied. The adsorption affinity of silica for mercury ions increased because of the formation of supramolecular structures with chemically immobilized β-cyclodextrin.     

Reaction of nickel(II) β-diketonates with hydroxylamine. Synthesis of nickel(II) complexes of mono-oximes of β-diketones (β-ketooximes)

Nickel(II) acetylacetonate or benzoylacetonate on treatment with hydroxylamine at O°C give adducts of the type Ni(β-diket)₂(NH₂OH) ₂ which on heating in refluxing ethanol afford β-ketooximato complexes of the type Ni(β-ketox)₂(H₂O)₂.     

Synthesis of volatile copper(II) β-diketonates, β-ketiminates, and β-diiminates. The problem of synthesis of copper(II) Bis(2,2,6,6-tetramethyl-3-methylaminoheptane-5-onate)

The methods of synthesis of the copper(II) β-diketonates, β-ketiminates, and β-diiminates containing in the composition CH₃, CF₃, C(CH₃)₃, and Ph substituents were summarized. At the formation of metallocycles with 2,2,6,6-tetramethyl-3-methylaminoheptane-5-one ligand the intraligand repulsion of tret-butyl group and the methyl group at the nitrogen atom is noted, impeding the complexation.     

Structure of the hexanuclear Cu(II) β-diketonate complex

The structure of the hexanuclear copper(II) β-diketonate complex with gfa (hexafluoroacetylacetone) and dpm (dipivalylmethanate) ligands was studied by low-temperature (T = 100 K) X-ray diffraction. Crystal data for Cu₆(gfa)₄(dpm)₄(OH)₄ [C₆₄H₈₄Cu₆F₂₄O₂₀]: a = 28.2364(7) Å, b = 12.8072(3) Å, c = 24.7199(7) Å, β= 115.900(1)°, V = 8041.5(4) ų, space group C2/m, Z = 4, d _calc 1.661 g/cm³. The coordination polyhedra of the copper atoms — squares and octahedra — are formed by the oxygen atoms of the gfa and dpm ligands and groups. In all cases, the Cu-O distances vary from 1.89 Å to 2.13 Å. The complexes follow the sites of the rhombohedral sublattice with the parameters a _c ≈ 14.4 Å and a _c ≈ 61.5°.     

Complexes of copper(II) with the β-blocker atenolol

Mono- and binuclear copper(II) complexes with atenolol (HAt) can be obtained, depending on the reaction conditions. The mononuclear violet complex cation has the general formula Cu(HAt)₄ ²⁺ with an elongated octahedral geometry. The two ligands in the equatorial plane are bound in a bidentate fashion through the hydroxyl oxygen and amino nitrogen, while the other two atenolol molecules in axial position are coordinated in a monodentate way. The binuclear green complex Cu₂At₂Cl₂, is neutral, where atenolol acts as a bidentate (O^–, NH) bridging ligand. The bridge between the two Cu atoms is realized by the deprotonated oxygen of the alcohol group.     

The inclusion of rhodium(II)α-methyl-cinnamate in β-cyclodextrin

The preparation and characterization of the 1:1 inclusion compound of rhodium(II) -methyl cinnamate in -cyclodextrin is reported. Evidence of inclusion was obtained from X-ray powder diffraction results, Raman, IR and UV-Vis spectroscopic studies and thermal analysis. Given the potential antitumor activity of the rhodium(II) carboxylate and its virtual insolubility in water, its inclusion in -cyclodextrin opens the possibility for its transference to the aqueous phase.     

α-Metallated vinyl carbanionoids: II. Preparation and stability of vinyllithiums containing triorganostannyl groups on the α-carbon atom

The influence of intramolecular coordination and solvent effects on the formation and stability of α-stannylvinyllithium reagents RR′CC(Li)SnMe₃ (R′ = H, alkyl, aryl) has been investigated; intramolecular coordination via a 5-membered ring is particularly effective. Mechanisms for the isomerisation and thermal decomposition of RR′CC(Li)SnMe₃ are discussed, and multinuclear NMR data (¹¹⁹Sn, ¹³C and ¹H) for these species are presented.     

The role of the βAsp residue in copper(II) binding by modified peptides

The synthesis and binding abilities of peptides containing β-amino acids towards Cu(II) ions are presented. The peptides studied were: Ala-βAsp-Ser-Gly and Arg-Lys-βAsp-Val-Tyr. Potentiometric titrations were carried out to establish the stoichiometry of the resulting metal-ligand complexes. The copper(II) coordination mode of the complexes was investigated by performing detailed spectroscopic analyses (UV–Vis, CD) in strict correlation with potentiometric measurements. The results obtained on the β-peptides studied allowed the characterization of the influence of this structural modification on the coordination abilities of the peptides. Moreover, the role of the α-Asp position in the peptide chain was also described.     

The mass spectral fragmentation of copper(II) complexes of cyclic β-diketones

Summary Electron impact mass spectra of several bis(2-trifluoroacetylcycloalkanonato) copper(II) and bis(2-acetylcycloalkanonato) copper(II) chelates, in which the cyclic -diketonate moiety comprises five-, six-, seven-, and eight-membered ring systems, have been recorded. Compared with other copper(II) chelates of acyclic -diketonates, the present series of copper(II) cyclic -diketonates exhibited more pronounced intramolecular reduction reactions accompanied by a remarkably facile hydrogen migration resulting in the formation of the [LCu^(I)-H]⁺ ion as the base peak in all complexes investigated. The proposed fragmentation pathways leading to the formation of a number of important copper-containing daughter ions have been confirmed by metastable scanning of the corresponding parent ion spectra using the defocusing technique.

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Massenspektroskopische Fragmentierung von Kupfer(II)-Komplexen cyclischer -Diketone

Zusammenfassung Es wurden die EI-Massenspektren einiger Bis(2-trifluoracetylcycloalkanato)kupfer(II)-und Bis(2-acetylcycloalkanato)kupfer(II)-Chelate mit fünf-, sechs-, sieben- und achtgliedrigen cyclischen -Diketonat-Liganden gemessen. Im Vergleich zu anderen Kupfer(II)-Chelaten mit offenkettigen -Diketonaten zeigen die cyclischen Komplexe eine ausgeprägte Neigung zu intramolekularen Reduktionsreaktionen, die von einer bemerkenswert leicht erfolgenden Wasserstoffwanderung begleitet sind; dies führt zur Bildung von [LCu^(I)-H]⁺ als Basispeak für alle untersuchten Komplexe. Die vorgeschlagenen Fragmentierungswege, die zur Bildung einer Reihe wichtiger kupferhaltiger Tochterionen führen, wurden durch Untersuchung der entsprechenden metastabilen Mutterionen mittels der Defokussierungsmethode überprüft.

     

The salt effect for the solubilities of metal β-diketonates—II: Beryllium benzoylacetonate

In order to confirm extensively a generalized interpretation for the salt effect in solvent extraction of metal chelates, the solubilities of bis(1-phenyl-1,3-butanedionato) Be(II) (Be(bzac)₂) in aqueous solutions of LiCl, NaClO₄, NaNO₃, KBr, NaBr, KCl, NaCl and Na₂SO₄ were determined at 25°C. The salting coefficients of these salts for Be(bzac)₂ were obtained from the above data, and were found to accord with McDevit-Long equation except for LiCl. The salting-in effect of LiCl is discussed from the aspect of the strong hydration of small Li⁺ ion. The salting coefficients for Be(bzac)₂ are compared with those for the corresponding copper chelate (Cu(bzac)₂) and an influence of the stereochemical configurations of the metal chelates on the salt effect is also discussed.     

Study of the Possibility of Using Salt Metathesis Reactions for the Synthesis of the Neodymium and Samarium β-Diketiminate Chalcogenide Complexes. Unexpected Reduction of Sm(III) to Sm(II)

Russian Journal of Coordination Chemistry - The possibilities of the ion exchange reactions between the neodymium(III) and samarium(III) diiodo-β-diketiminate complexes...     

Halogenation of Fluoro-Substituted Zinc(II) Tetraphenylporphyrins at the β-Position

Russian Journal of Organic Chemistry - [2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrinato]zinc(II) was synthesized by reaction of...     

Reduction of sterically hindered β-diketiminato europium(III) complexes by the β-diketiminato anion: a convenient route for the synthesis of β-diketiminato europium(II) complexes

The metathesis reaction of anhydrous EuCl(3) with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me(3)C(6)H(2))C(Me)](2)CH(-), L(2, 4, 6-Me3); [N(2,6-(i)Pr(2)C(6)H(3))C(Me)](2)CH(-), L(2, 6-ipr2) and [(2, 6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(C(6)H(5))](-), L(2, 6-ipr2)(Ph)) in THF at 60 °C afforded the corresponding Eu(II) complexes: Eu(II)(L(2, 4, 6-Me3))(2)(THF) (1), Eu(II)(L(2, 6-ipr2))(2) (2) and Eu(II)(L(2, 6-ipr2)(Ph))(2) (5) with the formations of dimers (L(2, 4, 6-Me3))(2) (3) and (L(2, 6-ipr2))(2) (4) for the former two reactions and proligand L(2, 6-ipr2)(Ph)H (6) for the latter one. Compounds 1-6 were confirmed by an X-ray crystal structure analysis. The central metal Eu(II) in 1 is coordinated by two monoanionic L(2, 4, 6-Me3) ligands and one THF molecule in a trigonal bipyramid. The Eu(II) in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L(2, 4, 6-Me3))(2) and L(2, 6-ipr2))(2) and proligand L(2, 6-ipr2)(Ph)H demonstrates that the reducing agent in the present reduction of a Eu(III) ion to a Eu(II) ion might be the (L(2, 4, 6-Me3))(-), (L(2, 6-ipr2))(-) and (L(2, 6-ipr2)(Ph))(-), respectively. The possible mechanism for the reduction pathway is presented.     

Preparation of α-alkyl-β-amino acids via β-alanine Ni(II) complex

A new β-amino acrylic acid Ni(II) complex has been developed and used for the synthesis of α-alkyl-β-amino acids via alkylation with alkyl halides under operationally convenient conditions. The pivotal α-alkylated intermediate can be converted into the corresponding α-alkyl-β-amino acids via two steps with a wide range of substituents.