Asymmetric Β-diketones Research Articles

Terbium complexes of an asymmetric β-diketone: Preparation, photophysical and thermal investigation

Chromophoric 1,3-diketone ligand has been utilized to prepare novel ternary complexes of terbium with differently substituted 2,2′-bipyridines as auxiliary ligands. These prepared complexes were thoroughly investigated with the help of numerous spectroscopic techniques. Infrared spectral analysis has suggested the coordination of diketone and ancillary ligand to the Tb(III) ion through oxygen and nitrogen atom respectively. Photoluminescence emission spectra of complexes have displayed only characteristic peaks of Tb3+ ion suggesting the efficient sensitization of metal ion by chromophoric ligands. Emission spectra of all complexes have displayed the ligand sensitized green emission due to the 5D4→7F5 transition situated at around 548 nm. Colorimetric investigation and color purity of complexes reveal the green luminous character of synthesized complexes. Thermogravimetric measurements have revealed the thermal stability of the complexes. Optical and electronic band gaps are found to be in good agreement with each other that shows their importance as semiconductor material. These trivalent complexes of terbium could be utilized as the green component in displays and light emissive materials.

Tautomeric Equilibrium of an Asymmetric β-Diketone in Halogen-Bonded Cocrystals with Perfluorinated Iodobenzenes

In order to study the effect of halogen bond on tautomerism in β-diketones in the solid-state, we have prepared a series of cocrystals derived from an asymmetric β-diketone, benzoyl-4-pyridoylmethane (b4pm), as halogen bond acceptor and perfluorinated iodobenzenes: iodopentaflourobenzene (ipfb), 1,2-, 1,3- and 1,4-diiodotetraflorobenzene (12tfib, 13tfib and 14tfib) and 1,3,5-triiodo-2,4,6-trifluorobenzene (135titfb). All five cocrystals are assembled by I···N halogen bonds involving pyridyl nitrogen and iodoperfluorobenzene iodine resulting in 1:1 (four compounds) or 1:2 (one compound) cocrystal stoichiometry. Tautomer of b4pm in which hydrogen atom is adjacent to the pyridyl fragment was found to be more stable in vacuo than tautomer with a benzoyl hydroxyl group. This tautomer is also found to be dominant in the majority of crystal structures, somewhat more abundantly in crystal structures of cocrystals in which additional I···O halogen bond with the benzoyl oxygen has been established. Attempts have also been made to prepare an equivalent series of cocrystals using a closely related asymmetric β-diketone, benzoyl-3-pyridoylmethane (b3pm); however, all attempts were unsuccessful, which is attributed to more effective crystal packing of b3pm isomer compared to b4pm, which reduced the probability of cocrystal formation.

The abnormal solvatochromism, high-contrast mechanochromism and internal mechanism of two AIEE-active β-diketones

Tradition β-diketones are rarely used as fluorescent emitters and mechanochromic materials. Here, TPED2F and TPED2T with tiny structural differences (Furan unit and thiophene unit) and the same asymmetric β-diketone skeleton were designed and synthesized. Both of them show abnormal solvatochromism, water-sensitive fluorescence emission, marked aggregation-induced enhanced emission (AIEE) activity and high-contrast mechanochromism. Furthermore, crystal TPED2T displays inferior quantum efficiency (0.08) and hypsochromic-shift fluorescence emission (493 nm) in contrast with crystal TPED2F presenting 0.20 quantum efficiency and 516 nm emission maxima. However, ground and cured TPED2T exhibit deeper bathochromic-shift (54 nm and 59 nm in turn) than ground (37 nm) and cured (1 nm) TPED2F. In addition, ground TPED2F show reversible mechanochromism by heating, but mechanochromism of ground TPED2T is irreversible whether heating or solvent fuming. Based on 1H NMR, 13C NMR, UV–vis absorption spectra, emission spectra, XRD, DSC, single crystal analysis and theoretical calculation, the abnormal solvatochromism and water-sensitive fluorescence emission are attributed to enol-keto tautomerism and solvent polarity induced conformation changes of excited states, while heavy atom effect and wide band gap respectively lead to inferior quantum efficiency and hypsochromic-shift emission for crystal TPED2T compared with TPED2F. Moreover, excellent crystallization ability and close melting point before/after grinding endow TPED2F with thermal reversible mechanochromism. The amorphous state provided grinding and melting may contain distinct local energy traps, resulting in different fluorescence emission. Finally, existence forms of TPED2F and TPED2T depend on intramolecular hydrogen bonds, conjugate structure and small relative energy.

Structure and thermal properties of (1,1,1-trifluoro-4-methyliminopentanoato-2) (cyclooctadiene-1,5)iridium(I)

A mixed-ligand iridium(I) complex with the imino-derivative of asymmetric β-diketone [Ir(cod)(Meitfac)] (cod = C8H12, cyclooctadiene-1,5; Mei-tfac = CF3C(O)CHC(NMe)CH3, 1,1,1-trifluoro-4-methyliminopentanoato-2) is synthesized for the first time. The compound is obtained by the interaction of [Ir(cod)Cl]2 with sodium β-iminoketonate in diethyl ether in the inert atmosphere and is characterized by elemental analysis, IR and NMR spectroscopy. According to the single crystal X-ray diffraction analysis, the compound is a monomeric molecular complex. The coordination environment of iridium is a distorted square; the Ir–O and Ir–N bond lengths are 2.031(1) A and 2.086(2) A respectively; the average distance Ir–C′ = 1.994(8) A (C′ is the center of the С=С bond of the cod ligand); the NIrO chelate angle is 91.30(6)°, and the C′IrC′ angle is 87.63°. The crystal packing contains dimers formed by weak F…H–C hydrogen interactions. The thermal properties of the complex are studied by thermogravimetry. The compound passes into the gas phase in the temperature range 150-260 °C (mass loss 93.5%) and is characterized by a lower volatility as compared with its β-diketonate analog [Ir(cod)(tfac)] (tfac = CF3C(O)CHC(O)CH3, 1,1,1-trifluoropentadionato-2,4).

Fluorine atom influence on intramolecular hydrogen bonding, isomerization and methyl group rotation in fluorinated acetylacetones

1-Fluoro-pentane-2,4-dione (monofluoroacetylacetone, MFAA) is an asymmetric β-diketone with a strong intramolecular hydrogen bond similar to acetylacetone (AA) and its fluorinated analogs 1,1,1-trifluoro-(TFAA), and 1,1,1,5,5,5-hexafluoroacetylacetone (HFAA). The presence of a fluorine atom in MFAA has the potential to open an HF elimination channel in its gas-phase photochemistry motivating this study of MFAA hydrogen bonding by computer modeling using Density Functional Theory (DFT). As a context, we also report DFT modeling of AA and selected fluorinated acetylacetones: 1,1-difluoro-pentane-2,4-dione (difluoroacetylacetone, DFAA), TFAA, and HFAA. The most stable molecular structure for all three asymmetric β-diketones (MFAA, DFAA and TFAA) is the isomer with the fluoromethyl group proximal to the carbonyl carbon; in comparison to the proton transfer isomer, which has the fluoromethyl group proximal to the hydroxyl carbon, the carbonyl isomer is lower in energy by 5.1–5.5kJmol−1 (B3LYP/cc-pVTZ) and 2.1–3.7kJmol−1 (MP2/Aug-cc-pVTZ). We also report hydrogen bond strengths, barriers to proton transfer interconversion and barriers to rotation of the methyl/fluoromethyl groups. Our study, the first to report molecular structure information on MFAA and DFAA, indicates that the most stable chelated isomer of MFAA is not the structure with the strongest hydrogen bond as conventionally determined. Our modeling also reveals a coupling between proton transfer isomerization and methyl group rotation, and an unexpected double-minimum potential for the rotation of the fluoromethyl group of MFAA.

Novel valuable fluorine free copper(I) precursors for copper chemical vapor deposition

Novel fluorine free (β-diketonate)Cu (I)BTMSA precursors (where BTMSA is bis(trimethylsilyl) acetylene) were prepared in good yield (63–80%) by a simple acid–base reaction. The starting β-diketone structure was modified for tailoring physico-chemical properties of synthesized precursors. High volatile, relative thermally stable and low-melting precursors were prepared when asymmetric β-diketones were used. By using the (1-(cyclobutyl)-1,3-butandionate)Cu (I)BTMSA precursor, highly pure, compact and smooth copper films were deposited on Ta/TaN substrates at deposition temperatures as low as 150 °C.

Theoretical studies of the equilibria between two enolic forms of asymmetric β‐diketones

17O NMR chemical shifts of two frozen enols in hydrogen tautomerizations for asymmetric β-diketones were calculated at the Hartree–Fock and density functional B3LYP levels of theory using various basis sets. From the theoretical 17O chemical shifts of frozen enols, the equilibrium constants for the enol–enol equilibria were estimated and used for comparison with previous experimental results based on model shifts for the pure enol forms. The results show that our theoretical method can complement some inadequacies in the experimental NMR techniques in evaluating equilibrium constants of systems undergoing rapid dynamic equilibrium. Copyright © 2001 John Wiley & Sons, Ltd.

Regioselective pyrrole synthesis from asymmetric β-diketone and conversion to sterically hindered porphyrin

The condensation of asymmetric β-diketones with α-oximinoacetoacetate esters affords pyrroles regioselectively. The mechanism of the regioselectivity is studied using 13C-NMR spectroscopy. Pyrrole having a neopentyl group at the 4-position is synthesized by the method, and further converted to a steric hindered porphyrin in good yield.

Interaction of fluoroalkyl-containing ?-diketones with amines

The composition of products of the interaction of asymmetric fluoroalkyl-containing β-diketones with amines was studied. Mixtures of regioisomeric β-aminovinylketones and products of cleavage and secondary condensation are formed, depending on the temperature, the solvent, the nature of the fluorinated and nonfluorinated substituents in the β-diketone, and the basicity of the amine. The major product is a β-aminovinylketone in which the NH2 group is removed from the fluoroalkyl substituent. No β-aminovinylimines, products of condensation involving two electrophilic centers, were observed.

The preferential direction of enolization of some asymmetric 1,3-dicarbonyl compounds in solution: a study by multinuclear NMR spectroscopy

Previously described methods for determining the relative concentrations of the two cis-enol tautomers of asymmetric β-diketones using 13C and 17O NMR were compared and applied to a wider range of compounds. From the chemical shifts of the enol peaks and model shifts for the pure enol forms, the equilibrium constant for the enol—enol equilibrium was obtained. The small but significant effects of the β-substituents on the direction of enolization are in the following order of stabilization of the enol form at the adjacent carbonyl carbon: COOC 2H 5 > CF 3 > C 6H 5 > C(CH 3) 3 > CH 3. This relative order does not totally coincide with the preferred location of the regioselective attack of those compounds to form monodithioacetals. This indicates that, besides electronic effects, steric effects may also be quite important in determining regioselectivity in this type of compound.

Infrared and NMR, 1H, 19F, 31P studies of Rh(I) complexes of the formula: [Rh(β-diketone)(CO)X(P)Y] (x = 0, 1, 2; y = 0, 1, 2; × + y = 2; P = PPh3 or P(OP)3)

Abstract Products of substitution reactions of CO by PPH3 and P(OP)3 in Rh(β-diketone)(CO)2 complexes (where β-diketone: acetylacetone, thenoyltifluoroacetone, trifluoracetone, benzoyltrifluoroacetone, naphthoyltrifluoroacetone) were examined by IR and NMR. Reactions with PPh3 produced the compounds containing one CO group, i.e. Rh(β-diketone(CO)(PPh3). In the case of asymmetric β-diketones, two isomers were observed in solution. The presence of free phosphine caused labilization of the coordination sphere of complexes followed by fast exchange between the free and the coordinated phosphine. Reactions with P(OPh)3 produced Rh(β-diketone)-[P(OPh)3]2 or Rh(β-diketone)[P(OPh)3] complexes, depending on the amount of P(OPh)3 used. The NMR results indicate considerable delocalization of the electron density in these compounds.

Biosynthesis of β-diketones and hydrocarbons in barley spike epicuticular wax

Aided by the analysis of induced, single gene mutants in barley, independent elongation systems were inferred for the synthesis of β-diketones (98% hentriacontan-14,16-dione) and hydrocarbons (primarily hentriacontane). This proposal has been substantiated by comparing the effects of preincubations of inhibitors on the ability of whole spikes to incorporate [2- 14C]acetate into the various epicuticular wax lipids. Dithiothreitol and mercaptoethanol inhibited the incorporation of label into hydrocarbons, but not into β-diketones. Cyanide blocked the synthesis of β-diketones, while stimulating hydrocarbon formation more than twofold. β-diketone synthesis was far more sensitive to arsenite than was synthesis of hydrocarbons. Degradation of the asymmetric β-diketone molecules by base hydrolysis and determination of the amount of label in the resulting fragments revealed a specific inhibition by arsenite of label incorporation into the C-31 end, i.e., the end from which previous studies have shown elongation to proceed. Tissue slices prepared from spikes minus awns were able to incorporate into β-diketones 1abel from [1- 14C]palmitate and shorter evenchained fatty acids, but not from [1- 14C]stearate. However, all fatty acids tested served equally well as hydrocarbon precursors. The elongation systems leading to the β-diketones and hydrocarbons are thought to diverge when the chain has 16 carbons. Thus, when a C 16 chain is elongated by the addition of a C 2 unit to form a C 18 β-keto acyl chain, the β-keto group is not reduced as in normal fatty acid synthesis, but both carbonyl groups are protected and retained during further elongation. After reaching a C 32 chain length, decarboxylation and release of the protected carbonyl groups yield the β-diketone.

Studies on Pyrido [2, 3-d] pyrimidine 3-Oxide

The reaction of pyrido [2, 3-d] pyrimidine (I) with several nucleophilic reagent was carried out. In the reaction of I with hydrazine reagent added across the 3, 4-positions in I to result in the formation of 3-hydroxy-4-hydrazino-3, 4-dihydropyrido [2, 3-d] pyrimidine (V). In the case of the reaction with acetic anhydride ring fission between the 2- and 3-positions took place and resulted in the formation of 2-aminonicotinonitrile (VI). The similar ring fission also occurred in the use merely alkali hydroxide for I at ordinary temperature to form 2-(formylamino) nicotinoaldehyde oxime (VII). In the case of the reactions with ethyl cyanoacetate, malononitrile and ethyl acetoacetate without base catalyst the transformation of I into 1, 8-naphthyridine derivatives proceeded to result in the formation of ethyl 2-amino-1, 8-naphthyridine-3-carboxylate (X), 2-amino-1, 8-naphthyridine-3-carbonitrile (XI) and ethyl 2-methyl-1, 8-naphthyridine-3-carboxylate (XII), respectively. In the case of the reaction with symmetric β-diketone without base catalyst 2-substituted-pyrido [2, 3-d] pyrimidine was formed. Thus the reactions with 2, 4-pentanedione and with 1, 3-diphenyl-1, 3-propanedione gave 1-(2-pyrido [2, 3-d] pyrimidinyl)-2-propanone (XX) and 2-(2-pyrido [2, 3-d] pyrimidinyl) acetophenone (XXI), respectively. But in the case of the reaction with asymmetric β-diketone such as 1-phenyl-1, 3-butanedione it proceeded in a defferent way from the reaction with symmetric β-diketone and resulted in the transformation of I into 2-phenyl-1, 8-naphthyridine (XXVIII). The possible reaction processes for the reactions described above were also proposed and discussed.

13C Nuclear Magnetic Resonance of Some Alkyl-Substituted β-Diketones

13C-NMR spectra have been examined to obtain the structural informations on a series of alkyl-substituted β-diketones and we found correlation between chemical shift and substituent.Structual formulas of β-diketones employed in our experiment are listed in Table 1 and 13C chemical shifts are given in Table 2.Since most of those β-diketones are enolised at equilibrium state, satisfactory spectrum of the keto form could not be obtained except three compounds. Therefore, chemical shifts of enol carbons are discussed mainly here.(1)The existence. of two forms of enol([1-A]and[1-B])is supposed to B-diketone, but we cannot observe their spectra. This fact suggests the rapid evchange between these two forms.(2) the shifts of the enol carbons (C-2, C-3) decrease monotonously with the increased inductive (-I) effect of alkyl substituents. That is, the enol carbons of a molecule with two methyl groups resonate at the highest field, and those with two butyl groups, resonate at low field. The similar effect which appears in the mono ketone has been reported by several workers.(3) The signal of the enolic methine carbon (C-1) appears in 90-lO2 ppM region. lt lies in -extraordinary high field compared with those of mono olefinic or aromatic carbons. ln chelate ring of enol form, lone-pair electrons on the oxygen atom could take part in rr-conjugation. This effect causes the increase of π-electron density of methine carbon to make them more shielded.(4) Furthermore, an additivity is found in the observed 13C shifts of m.ethine carbon for each alkyl substituent. Chemical shifts of asymmetric β-diketones calculated from the value of symmetric β-diketone are in good agreement with the experiinental values as shown in Table 3.