Synthesis and properties of group 9 metal complexes bearing a β-ketophosphenato ligand

A novel β-ketophosphenato ligand bearing a bulky substituent, Tbt(2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), on the phosphorus atom was newly designed and synthesized as a heavier congener of a β-ketoiminato ligand. Rhodium and iridium complexes bearing this new β-ketophosphenato ligand have been synthesized and fully characterized by spectroscopic and elemental analyses together with X-ray crystallographic analyses. The results of NMR spectroscopic studies and the X-ray structural analyses suggested that the β-ketophosphenato ligand has unique electronic features due to the low-coordinated phosphorus atom. Comparison of properties between rhodium β-ketophosphenates 2a,b and rhodium β-ketoiminate 7 revealed the character of the β-ketophosphenato ligand, where the trans influence of the phosphorus atom should be stronger than the nitrogen atom of the β-ketoiminato ligand.     

Synthesis and fluorescence properties of novel pyrazine-boron complexes bearing a β-iminoketone ligand

A novel fluorescence dye based on pyrazine-boron complexes bearing a β-iminoketone ligand has been synthesized by using a simple two-step reaction. Synthesized complexes exhibited fluorescence in solution (F(max): 472-604 nm) and in the solid state (F(max): 496-624 nm). These complexes showed a larger Stokes shift (3690-4900 cm(-1)) than well-known boron dipyrromethene dyes (400-600 cm(-1), in most cases).     

Chemistry of nitrosyliron complexes supported by a β-diketiminate ligand

Several nitrosyl complexes of Fe and Co have been prepared using the sterically hindered Ar-nacnac ligand (Ar-nacnac = anion of [(2,6-diisopropylphenyl)NC(Me)](2)CH). The dinitrosyliron complexes [Fe(NO)(2)(Ar-nacnac)] (1) and (Bu(4)N)[Fe(NO)(2)(Ar-nacnac)] (2) react with [Fe(III)(TPP)Cl] (TPP = tetraphenylporphine dianion) to generate [Fe(II)(NO)(TPP)] and the corresponding mononitrosyliron complexes. The factors governing NO transfer with dinitrosyliron complexes (DNICs) 1 and 2 are evaluated, together with the chemistry of the related mononitrosyliron complex, [Fe(NO)Br(Ar-nacnac)] (4). The synthesis and properties of the related cobalt dinitrosyl [Co(NO)(2)(Ar-nacnac)] (3) is also discussed for comparison to DNICs 1 and 2. The solid-state structures of several of these compounds as determined by X-ray crystallography are reported.     

Synthesis and X-ray structure of cationic β-diimine palladium complexes containing π-methallyl ligand

High yield of cationic palladium β-diimine complexes [(CH₂(MeCNAr)₂)Pd(η³-C₄H₇)][Y] (Ar = C₆H₅, Y = PF₆ (8); 2-Me-C₆H₄, Y = PF₆ (9); 2,6-Me₂-C₆H₃, Y = PF₆ (10); 2,6-iPr₂-C₆H₃, Y = PF₆ (11), Y = B(3,5-(CF₃)₂-C₆H₃)₄ (12)) have been obtained by an oxidative addition of the methallyloxyphosphonium salts (5, 6) to a preformed complex Pd(dba)₂ (7) in the presence of the β-iminoamine ligands (1-4).These complexes are thermally stable and have been characterized by ¹H and ¹³C{¹H} NMR as well as IR spectroscopy. The structure of the cationic allyl palladium complex (12) has been solved by X-ray crystallography.     

Electronic and resonance Raman spectra of iron(II)—tetraazamacrocyclic complexes containing N-heterocyclic ligands

The adducts of the meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,4,8,11-tetraene iron(II) complex with N-heterocyclic ligands exhibit three characteristic absorption bands in the ranges 690-640, 505-470 and 435-340 nm. Using excitation wavelengths coinciding with the low energy band, a selective enhancement of the Raman vibrational modes of the macrocyclic ligand is observed, supporting the assignment of a metal-to-diimine charge-transfer transition. The high energy band is strongly dependent on the nature and pK_a, of the axial ligands. Excitation at this band leads to the enhancement of the N-heterocyclic vibrational modes in the Raman spectra, indicating a metal-to-(N-heterocycle) charge-transfer transition. The intermediate band exhibits weak resonance Raman activity. Its intensity depends on the proximity of the high energy band and is consistent with the occurrence of an intensity stealing mechanism.     

Synthesis and characterization of sterically encumbered β-ketoiminate complexes of iron(II) and zinc(II)

The synthesis, structure, and spectroscopic signatures of a series of four-coordinate iron(II) complexes of β-ketoiminates and their zinc(II) analogues are presented. An unusual five-coordinate iron(II) triflate with three oxygen bound protonated β-ketoimines is also synthesized and structurally characterized. Single-crystal X-ray crystallographic analysis reveals that the deprotonated bis(chelate)metal complexes are four-coordinate with various degrees of distortion depending on the degree of steric bulk and the electronics of the metal center. Each of the high-spin iron(II) centers exhibits multiple electronic transitions including ligand π to π*, metal-to-ligand charge transfer, and spin-forbidden d-d bands. The (1)H NMR spectra of the paramagnetic high-spin iron(II) centers are assigned on the basis of chemical shifts, longitudinal relaxation times (T(1)), relative integrations, and substitution of the ligands. The electrochemical studies support variations in the ligand strength. Parallel mode EPR measurements for the isopropyl substituted ligand complex of iron(II) show low-field resonances (g > 9.5) indicative of complex aggregation or crystallite formation. No suitable solvent system or glassing mixture was found to remedy this phenomenon. However, the bulkier diisopropylphenyl substituted ligand exhibits an integer spin signal consistent with an isolated iron(ii) center [S = 2; D = -7.1 ± 0.8 cm(-1); E/D = 0.1]. A tentative molecular orbital diagram is assembled.     

Mixed ligand complexes of β-diketonates: synthesis,characterization, and FAB mass spectral analysis

Complexes of the type MLL′ · nB (where M = Ni(II) and Cu(II); LH and L′H = 2,4-pentanedione (acacH), 1-phenyl-1,3-butanedione (bacH), and 1,3-diphenyl-1,3-propanedione (dbmH); n = 0 to 2 and B = water or pyridine) have been synthesized and characterized. IR spectra are consistent with uninegative bidentate ligands. Magnetic moments and electronic spectral studies reveal high-spin octahedral geometry for nickel(II) complexes and distorted octahedral stereochemistry for copper(II) complexes. Frozen chloroform solution ESR spectra of the copper(II) complexes display significant Jahn–Teller distortion and dimeric behavior of the complexes in solution. FAB mass spectra of the copper(II) complexes also exhibit peaks corresponding to dimers. Molecular, pseudo-molecular, dimeric pseudo-molecular, and fragment ion peaks in unit resolution mass spectra have been identified with the help of their isotope distribution pattern expected due to natural abundances of the ⁶³Cu and ⁶⁵Cu isotopes. All the FAB mass spectral peaks from the fragment ions containing copper have been interpreted on the basis of isotope distribution pattern.     

Modeling and conformation analysis of β-cyclodextrin complexes

Summary A series of -cyclodextrin complexes containing various guest molecules was studied using computer-aided molecular modeling and conformation analysis techniques. The geometry of each complex was studied using crystallographic data. The positions of the glycosidic O4 atoms indicate that the -cyclodextrin molecules are elliptically distorted. This distortion can be related to the van der Waals volume of the guest molecules. This correlation is different for aromatic and non-aromatic guest compounds. Rigid body docking experiments demonstrated that in crystal structures the guest molecule occupies a position in the cavity of nearly minimum interaction energy when there are no other molecules having interactions with the guest molecule. From the crystallographic data several rules could be deduced which seem to determine the conformation of -cyclodextrin molecules in complexes. A procedure was developed to construct -cyclodextrin molecules that are able to encompass guest molecules having a given van der Waals volume.     

Conformational and Electronic Interaction Studies of Some β-Ketosulfoxides

ABSTRACT.

The analysis of the carbonyl I.R. band and the U.V. phoelectron spectroscopic data along with the ab-initio calculations and X-ray diffraction of α-(methylsulfinyl)- and α-(phenylsulfinyl)-acetophenones indicated the predominance of the cis rotamers over the qauche ones.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Preparation and evaluation of inclusion complexes of diacerein with β-cyclodextrin and hydroxypropyl β-cyclodextrin

The objective of this research was to improve the aqueous solubility, dissolution rate and, consequently, bioavailability of diacerein, along with avoiding its side effect of diarrhea, by complexation with β-cyclodextrin (β-CD) and HP-β-cyclodextrin (HP-β-CD). Phase solubility curve was classified as an A_N type for both the CDs, which indicated formation of complex of diacerein with β-CD and HP-β-CD in 1:1 stoichiometry and demonstrating that both CDs are proportionally less effective at higher concentrations. The complexes were prepared by kneading method and were evaluated to study the effect of complexation on aqueous solubility and rate of dissolution in phosphate buffer (pH 6.8). Based on the dissolution profile HP-β-CD was selected for preparing fast disintegrating tablet of diacerein which was compared with marketed formulation (MF-J). The HP-β-CD complex was probed for Fourier transform infrared spectroscopy, differential scanning calorimetry, and powder X-ray diffraction studies which evidenced stable complex formation and increase in amorphousness of diacerein in complex. In brief, the characterization studies confirmed the inclusion of diacerein within the non-polar cavity of HP-β-CD. HP-β-CD complex showed improved in vitro drug release profile compared to pure drug and similar to that of marketed formulation respectively.     

Synthesis and structure of mono- and dinuclear cyclopentadienyl–indenyl complexes of iron(II) and further reactions to mixed tri- and tetranuclear iron–cobalt complexes

The reaction of a mixture of sodium cyclopentadienide and the monolithium salt or dilithium salt of 2,2-bis(indenyl)propane with FeCl₂ leads to the mononuclear complex [(η⁵-C₅H₅)Fe(η⁵-ind-C(CH₃)₂-ind)] (ind = 1-indenyl) (1) and the dinuclear complex [{(η⁵-C₅H₅)Fe(η⁵-ind)}₂C(CH₃)₂] (2), respectively. [(η⁵-Me₅C₅)Fe(tmeda)Cl] reacts with dilithium 1,1′-biindenyl under formation of [{(η⁵-Me₅C₅)Fe}₂(μ-η⁵:η⁵-1,1′-biind)] (4). Due to the annelated arene rings of the η⁵-indenyl ligands, 2 and 4 may act as 4-electron donor ligands, as exemplified by the reaction with the triple-decker complex [{(η⁵-Me₅C₅)Co}₂(μ-η⁶:η⁶-toluene)], which afforded the tetranuclear dimer of triple-decker complexes [{(η⁵-C₅H₅)Fe(η⁵-Me₅C₅)Co(μ-η⁵:η⁴-1-ind)}₂C(CH₃)₂] (3) and the trinuclear complex [{(η⁵-Me₅C₅)Fe}₂(η⁵-Me₅C₅)Co(μ₃-η⁵:η⁴:η⁵-1,1′-biind)] · Et₂O (5 · Et₂O) by replacement of the central toluene deck, respectively. The [(η⁵-Me₅C₅)Co] fragments of 3 and 5 are bonded via the six-membered rings of the indenyl ligands in a η⁴-fashion. Caused by the coordination to the Co atoms the six-membered rings lose their planarity and adopt a butterfly structure. The coordination geometry of the Fe atoms is similar in all five complexes. Each Fe atom is coordinated by the C atoms of one of the five-membered rings of the indenyl ligands in a slightly distorted η⁵ manner (η³ + η²-coordination) and by a cyclopentadienyl ligand in a regular η⁵-fashion. The structures of 3 and 5 represent the first examples of slipped triple-decker complexes which comprise indenyl ligands in a μ-η⁵:η⁴ coordination mode.     

Volatility and thermal stability of vanadyl β-diketonate complexes

Thermal behavior and thermodynamic characteristics of vanadyl β-diketonates—acetylacetonate VO(acac)₂, dipivaloylmethanate VO(thd)₂, and tris-hexafluoroacetylacetonate VO(hfa)₂ (Hacac, 2,4-pentanedione; Hthd, 2,2,6,6-tetramethyl-3,5-heptanedione; Hhfa, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione)—have been studied by thermal analysis and the Knudsen effusion mass spectrometry study of gas phase composition. The compounds have been shown to undergo congruent sublimation. Saturated vapor over the complexes has been shown to comprise monomeric VOL₂ molecules. Absolute values of partial pressures and sublimation enthalpies of these compounds have been determined.     

Mixed ligand complexes of trivalent lanthanide ions with β-diketones and heterocyclic amines and their use as possible shift reagents

Sixty new complexes of the trivalent lanthanides (except Pm and Lu) and Yttrium of the general formulae, Ln(TFAA)₃o-phen, Ln(TFAA)₃dipy·2H₂O, Ln(dpm)₃im, Ln(dpm)₃pz, and Ln(fod)₃o-phen where TFAA = trifluoroacetyl-acetone-H, dpm = 2,2,6,6-tetramethyl 3,5-heptane dione-H, fod = 1,1,1,2,2,3,3-heptafluoro, 7,7-dimethyl 4,6-octane dione-H, o-phen = 1,10-phenathroline, dipy = 2,2′dipyridyl, im = imidazole and pz = pyrazole, have been synthesised and characterised by elemental analyses, melting points, molar conductance, magnetic susceptibility, thermogravimetric analysis, and IR spectral studies. The trivalent lanthanide ions have a coordination number of ten in the series Ln(TFAA)₃dipy·2H₂O. Their avidity to enhance their coordination number is so great that een in the presence of three such bulky ligands as heptafluorooctane dione the Ln(fod)₃ still coordinates with o-phen. Hexacoordinated trivalent lanthanides act as LIS reagents but it has been observed that even the eight coordinated and very bulky Pr(fod)₃o-phen produces dipolar shifts in the proton resonances of organic moities.     

Enantioselective chlorination of β-keto esters and amides catalyzed by chiral copper（Ⅱ） complexes of squaramide-linked bisoxazoline ligand

Enantioselective chlorination of b-keto esters and amides catalyzed by squaramide-linked bisoxazoline ligand–Cu（OAc）2complexes was investigated. The corresponding chlorinated products were obtained in excellent yields with moderate enantioselectivities. The effect of solvent, temperature, Lewis acid, and ligand structure on the reaction is discussed. This was the first investigation of catalytic asymmetric achlorination of b-keto amides. This study has highlighted that a simple chiral squaramide–oxazoline with cheap Cu（OAc）2 H2 O complexes can catalyze this chlorination.     

Electronic and geometric structure of the protonated forms of nickel β-diketonates

The effect of protonation on the electronic and spatial structure of nickel malonodialdehynate Ni(Mal)₂ and acetylacetonate Ni(Acac)₂ were studied by quantum chemical density functional theory (DFT) method. The metal ring geometry, the energies and the composition of molecular orbitals (MO), the effective charges on atoms, and the total overlap populations were determined, and the possible proton location sites were identified. The variation of the MO energy depending on the electron density distribution on the protonated and non-protonated ligands was considered. Proton addition to one of the oxygen atoms was shown to be most likely.     

Magnesium complexes containing β-ketiminate and β-diketiminate ligands with dimethylamino substituents on the ligand core nitrogen atoms

Treatment of dibutylmagnesium with two equivalents of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (L¹H) in diethyl ether afforded Mg(L¹)₂ (76%), which contains η²-L¹ ligands with tetrahedral coordination at the magnesium ion. Similar treatment of dibutylmagnesium with 4-(2,2-dimethylhydrazino)-3-penten-2-one (L²H) or 5-(2,2-dimethylhydrazino)-2,6-dimethyl-4-hepten-3-one (L³H) and 4-tert-butylpyridine (4-tBupy) in diethyl ether afforded the octahedral complexes Mg(L²)₂(4-tBupy)₂ (85%) and Mg(L³)₂(4-tBupy)₂ (79%). Treatment of dibutylmagnesium with two equivalents of L²H or L³H in the absence of 4-tBupy afforded [Mg(L²)₂]₂ and Mg(L³)₂, however, these complexes were difficult to isolate due to the sticky nature of the crude products. A better synthetic approach entailed sublimation of Mg(L²)₂(4-tBupy)₂ or Mg(L³)₂(4-tBupy)₂ at 95-100 °C/0.05 Torr, which afforded [Mg(L²)₂]₂ (94%) and Mg(L³)₂ (80%) as colorless crystalline solids that were easily isolated. Treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents each of 4-tBupy and L¹H afforded MgCp(L¹)(4-tBupy) (65%). Similar treatment of [MgCp(CH₃)(OEt₂)]₂ with two equivalents of L²H or L³H afforded the dimeric complexes [MgCp(L²)]₂ (81%) and [MgCp(L³)]₂ (84%), respectively. [MgCp(L²)]₂ and [MgCp(L³)]₂ decompose upon attempted sublimation at 125-130 °C/0.05 Torr to afford Cp₂Mg (47-53%) and [Mg(L²)₂]₂ (67%) or Mg(L³)₂ (74%). The X-ray crystal structures of Mg(L¹)₂, Mg(L³)₂(4-tBupy)₂, [Mg(L²)₂]₂, Mg(L³)₂, MgCp(L¹)(4-tBupy), [MgCp(L²)]₂, and [MgCp(L³)]₂ are described. The thermal stability and volatility of the complexes were determined through preparative sublimation experiments. Many of the complexes sublime without decomposition at moderate temperatures and low pressures, and thus represent new potential precursors for thin film growth using chemical vapor deposition and related techniques.     

A new approach to the synthesis of N-monosubstituted aniline and its derivatives via β-cyclodextrin host-guest complexes

A novel method for the synthesis of N-monosubstituted aniline and its derivatives β-cyclodextrin(CD)host-guest complexes has been presented.The mild reaction gives the title compounds with high selectivity in good yields of 90-98%.