Acac Complexes Research Articles

Palladium(II) Agostic Complex: Exchange of Aryl–Pd and Alkyl–Pd Bonds

Cyclopalladation of 2-tbutyl-6-(4-fluorophenyl)pyridine with palladium acetate cleanly gives cyclometalated complex 3 with an aryl–Pd bond. Replacement of the acetates by chloride gives the monomeric species 4 with a crystal structure confirming the presence of an agostic interaction from the alkyl group. Reaction of 3 with Na(acac) initially gives the monomeric acac complex 5 which maintains the aryl–Pd bond. Complex 5 shows fluxional behavior of the acac group, and this provides a pathway for its isomerization to complex 6 which has an alkyl–Pd bond; complex 6 was characterized crystallographically. Reaction of agostic 4 with triphenylphosphine gives an initial complex that maintains the aryl–Pd bond, but this complex isomerizes to crystallographically characterized 8 which has an alkyl–Pd bond.

Synthesis and Opto‐electronic Properties of a Red‐Emitting Heteroleptic Platinum Complex Using Pyrazol‐based Diketone Derivative as Ancillary Ligand

AbstractA red‐emitting heteroleptic cyclometalated platinum(II) complex containing an ancillary ligand of pyrazol‐based diketone derivative was synthesized. Its optophysical and electroluminescent properties were studied. Compared to the reported (piq)Pt(acac) complex, this platinum(II) complex exhibited a blue‐shifted UV absorption band at 300–450 nm, a low LUMO energy level and improved electroluminescent property. Using this platinum(II) complex as a single doping emitter and a blend of ploy(9,9‐dioctylfluorene) and 2‐tert‐butylphenyl‐5‐phenyl‐1,3,4‐oxadiazole as a host matrix, the fabricated polymer light‐emitting devices displayed saturated red emission with a peak at 648 nm and a shoulder at 601 nm. Furthermore, the emission quenching of the platinum(II) complex was significantly suppressed in these devices at high current density due to an introduction of the non‐planar pyrazol group into the ancillary ligand.

Synthesis and photophysics of a new deep red soluble phosphorescent iridium(III) complex based on chlorine-methyl-substituted 2,4 diphenyl quinoline

A new iridium complex with a chlorine-methyl-substituted 2,4 diphenyl quinoline, (Cl-MDPQ) ligand has been synthesized. The synthesized iridium metal complex, Ir(Cl-MDPQ) 2(acac) where Cl-MDPQ=chlorine-methyl substituted, 2,4 diphenyl quinoline, acac=acetyl acetone is characterized by employing different techniques such as mass spectrometry, 1H NMR, DTA/TGA, XRD, and FTIR. The molecular structures of Cl-MDPQ and Ir(Cl-MDPQ) 2(acac) complexes are confirmed by the FTIR spectra. Strong singlet metal-to-ligand charge-transfer ( 1MLCT) and triplet metal-to-ligand charge-transfer ( 3MLCT) absorption peaks at 353 and 437 nm in tetrahydrofuran (THF) are reported in the synthesized complex, respectively. A deep red emitting Ir(Cl-MDPQ) 2(acac) complex at 662 nm is promising for flexible organic devices.

Synthesis, Structure, and C–C Cross‐Coupling Activity of (Amine)bis(phenolato)iron(acac) Complexes

AbstractA series of (amine)bis(phenolato)iron(III)acac complexes has been prepared and characterized. Reaction of Fe(acac)3 with the diprotonated linear tetradentate proligand N,N′‐bis(4,6‐di‐tert‐butyl‐2‐methylphenol)‐N,N′‐dimethyl‐1,2‐diaminoethane, H2[L1], and tripodal tetradentate ligand precursors dimethylaminoethylamino‐N,N‐bis(2‐methylene‐4,6‐di‐tert‐butylphenol), H2[L2], dimethylaminoethylamino‐N,N‐bis(2‐methylene‐4‐methyl‐6‐tert‐butylphenol), H2[L3], 2‐methoxyethylamino‐N,N‐bis(2‐methylene‐4,6‐di‐tert‐butylphenol), H2[L4], 2‐methoxyethylamino‐N,N‐bis(2‐methylene‐4‐methyl‐6‐tert‐butylphenol), H2[L5], and 2‐methoxyethylamino‐N,N‐bis(2‐methylene‐4,6‐dimethylphenol), H2[L6], produces the distorted octahedral FeIII complexes [L1]Fe(acac) (1), [L2]Fe(acac) (2), [L3]Fe(acac) (3), [L4]Fe(acac) (4), [L5]Fe(acac) (5), and [L6]Fe(acac) (6). In all of these complexes, the phenolato oxygen atoms are cis‐oriented. The paramagnetic FeIII complexes 1–6 were also characterized by UV/Vis and IR spectroscopy, mass spectrometry, cyclic voltammetry, and magnetic measurements. Single crystal X‐ray molecular structures have been determined for complexes 1, 2, 3, 5, and the proligand H2[L6]. Preliminary investigations of complexes 1–6 for catalytic cross‐coupling reactions of aryl Grignard reagents with cyclic and acyclic secondary alkyl halides and benzyl halides were performed. While the activity for cyclohexyl chlorides and bromides was high, cross‐coupling of benzyl halides was moderate and 2‐bromo‐ and 2‐chlorobutane gave poor yields of cross‐coupled product.

Synthesis and characterization of UV‐curable phosphorus containing hybrid materials prepared by sol–gel technique

AbstractIn this study, a series of ultraviolet (UV)‐curable organic–inorganic hybrid coating materials containing phosphorus were prepared by sol–gel approach from acrylate end‐capped urethane resin, acrylated phenyl phosphine oxide oligomer (APPO), and inorganic precursors. TEOS and MAPTMS were used to obtain the silica network and Ti:acac complex was employed for the formation of the titania network in the hybrid coating systems. Coating performance of the hybrid coating materials applied on aluminum substrates was determined by the analysis techniques, such as hardness, gloss, impact strength, cross‐cut adhesion, taber abrasion resistance, which were accepted by international organization. Also, stress–strain test of the hybrids was carried out on the free films. These measurements showed that all the properties of the hybrids were enhanced effectively by gradual increase in sol–gel precursors and APPO oligomer content. The thermal behavior of the hybrid coatings was investigated by thermogravimetric analysis (TGA) analysis. The flame retardancy of the hybrid materials was examined by the limiting oxygen index (LOI); the LOI values of pure organic coating (BF) increased from 31 to 44 for the hybrid materials containing phosphorus (BF‐P:40/Si:10). The data from thermal analysis and LOI showed that the hybrid coating materials containing phosphorus have higher thermal stability and flame resistance properties than the organic polymer. Besides that, it was found that the double bond conversion values for the hybrid mixtures were adequate in order to form an organic matrix. The polycondensation reactions of TEOS and MAPTMS compounds were also investigated by 29Si‐NMR spectroscopy. SEM studies of the hybrid coatings showed that silica/titania particles were homogenously dispersed through the organic matrix. In addition, it was determined that the hybrid material containing phosphorus and silica showed fibrillar structure. Copyright © 2009 John Wiley & Sons, Ltd.

Osmium(II) bipyridine (bpy) complexes containing O,O-donor ligands and X-ray crystal structure of the acetylacetonato(acac) complex [Os(bpy) 2(acac)](PF 6)

The new complexes [Os 11(bpy) 2L](PF 6) [bpy = 2,2′-bipyridine; HL = acetylacetone (Hacac), trifluoroacetylacetone (Htfacac), hexafluoroacetylacetone, dibenzoylmethane or tropolone] have been prepared and the chemical oxidation of the [Os II(bpy) 2L] + species (L = acac or tfacac) by aqueous S 2 O 8 2 - solution in the presence of (NH 4)PF 6 gave the reddish brown complexes [Os III(bpy) 2L](PF 6) 2. These complexes were characterized by spectroscopic measurements and also investigated by cyclic voltammetry. The X-ray crystal structure of [Os(bpy) 2(acac)](PF 6) ( 1) has been determined and showed that the complex has a distorted octahedral geometry in an environment of N 4O 2 donors. The reactivity toward oxidation of benzyl alcohol by complex ( 1) using H 2O 2 or other co-oxidants has been studied and compared with that of the related ruthenium(II) complexes.

Emissive Metallomesogens Based on 2-Phenylpyridine Complexes of Iridium(III)

Preparation of Ir(III) complexes using anisotropic 2,5-di(4-alkoxyphenyl)pyridine ligands leads to emissive, liquid-crystalline complexes containing bound Cl and dimethyl sulfoxide. Using analogous poly(alkoxy) ligands allows the preparation of bis(2-phenylpyridine)iridium(III) acac complexes, which are also mesomorphic. The observation of liquid crystallinity in octahedral complexes of this type is without precedent.

Halogen bonding or close packing? Examining the structural landscape in a series of Cu(ii)-acac complexes

A series of four bifunctional ligands based on β-diketonate moieties bearing methyl (2), chloro (3), bromo (4) and iodo (5) substituents and their corresponding Cu(II) complexes have been synthesized and crystallographically characterized in order to explore the possibility of using halogen bonds for the directed assembly of predictable architectures in coordination chemistry. The four ligands have characteristic O-H···O intramolecular hydrogen bonds and the structure of ligand 2 is close packed whereas, ligands 3, 4 and 5 contain extended 1-D architectures based on C=O···X halogen bonds. In each case, the halogen-bond donor seeks out the most powerful halogen-bond acceptor (based on electrostatic considerations). In the corresponding Cu(II) complexes the coordination chemistry remains a constant throughout the series, the four-coordinate metal ion sits in a slightly distorted square-planar arrangement, and there are no unexpected appearances of coordinated or non-coordinated solvent molecules. Furthermore, the most powerful halogen-bond acceptors have been almost depleted of charge as a result of metal chelation and none of the potential halogen-bond interactions are capable of competing with the head-to-head close packing that is observed in the methyl, chloro, and bromo, substituted Cu(II) complexes. The enhanced polarizability of the iodine atom, produces a more electropositive surface which means that this structure cannot accommodate a linear head-to-head arrangement due to electrostatic repulsion, and thus [Cu(5)(2)] adopts a unique close-packed structure very different from the other three iso-structural complexes, [Cu(2)(2)]-[Cu(4)(2)].

Ratiometric luminescent molecular oxygen sensors based on uni-luminophores of C⁁N Pt(ii)(acac) complexes that show intense visible-light absorption and balanced fluorescence/phosphorescence dual emission

Uni-luminophores of C^N cyclometalated Pt(II) complexes with balanced room temperature fluorescence/phosphorescence dual emission were prepared for ratiometric oxygen sensing in both intensity mode and lifetime mode.

Enhancing Phosphorescence and Electrophosphorescence Efficiency of Cyclometalated Pt(II) Compounds with Triarylboron

AbstractA synthetic strategy for the preparation of cyclometalated platinum(II) acetylacetonate (acac) complexes functionalized with triarylboron is achieved. This method is used to synthesize a series of triarylboron‐functionalized phosphorescent Pt(acac) compounds, which are characterized by NMR spectroscopy, X‐ray crystallography, and theoretical calculations. These complexes exhibit a range of bright phosphorescent colors spanning the green to red region of the visible spectrum (λmax = ∼520–650 nm) in solution and the solid state. Functionalization with a triarylboron group leads to significant enhancement in quantum yield for several of these complexes relative to the non‐borylated Pt(II) parent chromophores, which may be attributed to the increased mixing of 1MLCT and 3LC states. The phosphorescent enhancement, electron transport capabilities, and steric bulkiness offered by the triarylboron group can be used to significantly enhance the performance of electrophosphorescent devices based on Pt(II) emitters. A high efficiency green electrophosphorescent device is fabricated with a maximum external quantum efficiency of 8.9%, luminance efficiency of 34.5 cd A−1, and power efficiency of 29.8 lm W−1, giving significantly improved performance over control devices in which the Pt(II) emitter lacks the boron functionality.

Enhancing Phosphorescence and Electrophosphorescence Efficiency of Cyclometalated Pt(II) Compounds with Triarylboron

AbstractA synthetic strategy for the preparation of cyclometalated platinum(II) acetylacetonate (acac) complexes functionalized with triarylboron is achieved. This method is used to synthesize a series of triarylboron‐functionalized phosphorescent Pt(acac) compounds, which are characterized by NMR spectroscopy, X‐ray crystallography, and theoretical calculations. These complexes exhibit a range of bright phosphorescent colors spanning the green to red region of the visible spectrum (λmax = ∼520–650 nm) in solution and the solid state. Functionalization with a triarylboron group leads to significant enhancement in quantum yield for several of these complexes relative to the non‐borylated Pt(II) parent chromophores, which may be attributed to the increased mixing of 1MLCT and 3LC states. The phosphorescent enhancement, electron transport capabilities, and steric bulkiness offered by the triarylboron group can be used to significantly enhance the performance of electrophosphorescent devices based on Pt(II) emitters. A high efficiency green electrophosphorescent device is fabricated with a maximum external quantum efficiency of 8.9%, luminance efficiency of 34.5 cd A−1, and power efficiency of 29.8 lm W−1, giving significantly improved performance over control devices in which the Pt(II) emitter lacks the boron functionality.

Modulation of iridium(iii) phosphorescence via photochromic ligands: a density functional theory study

The photochromic iridium(iii) complex (Py-BTE)(2)Ir(acac) synthesized by Tan et al. [W. Tan et al., Org. Lett. 2009, 11, 161-164] has shown distinct photo-reactivity and photo-controllable phosphorescence. We here present a density functional theory study on the (Py-BTE)(2)Ir(acac) complex to explore the mechanism at the molecular level and to help further design of photochromic iridium(iii) complexes with the desirable properties. The hybrid functional PBE0, with 25% Hartree-Fock exchange, is found to give an optimal structure compared with X-ray crystallographic data. The absorption bands are well reproduced by using time-dependent density functional theory calculations, lending the possibility to assign the metal-to-ligand and intra-ligand charge transfer transitions. The radiative and nonradiative deactivation rate constants, k(r) and k(nr), are rationalized for both the open-ring and closed-ring forms of the complex. The very large k(nr) and small k(r) make the closed-ring form of the complex non-emissive. The triplet reactivity of the Py-BTE ligand is also studied by performing density functional theory calculations on the potential energy surfaces of the ground state and the lowest triplet state.

Highly efficient catalysts‐acetylacetonato complexes of transition metals in the 4th period for ring‐opening polymerization of 1,3‐benzoxazine

AbstractAcetylacetonato (acac) complexes of transition metals in the 4th period were examined as catalysts for the ring‐opening polymerization of benzoxazine. This examination revealed that acac complexes of manganese, iron, and cobalt exhibited the highest activity, which was comparable or slightly higher than that exhibited by p‐toluenesulfonic acid. By replacing acac ligand by hexafluoroacetylacetonato (F6‐acac) ligand, the activity of manganese and iron complexes was remarkably enhanced. These metal F6‐acac complexes were tolerant to moisture to allow their use under air without special caution. Another advantage was their negligible effect to promote unfavorable weight loss during the polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 479–484, 2010

Heterogenized Fe(III) phthalocyanine: Synthesis, characterization and application in liquid-phase oxidation of phenol

Tetra- tert-butyl substituted FePc(acac) complexes were supported upon mesoporous molecular sieves MCM-41 and SBA-15 via adsorption and coordination bondings as well as by covalent grafting. Prepared materials were characterized by UV–vis, MALDI, N 2-BET, SEM, TEM, FTIR, 13C, 29Si NMR and DSC–TG techniques. Supported FePcs exhibited high activity in liquid-phase oxidation of phenol with H 2O 2. The most resistant towards oxidative degradation were shown to be the covalently grafted FePc species.

Chiral Catalysts Dually Functionalized with Amino Acid and Zn2+ Complex Components for Enantioselective Direct Aldol Reactions Inspired by Natural Aldolases: Design, Synthesis, Complexation Properties, Catalytic Activities, and Mechanistic Study

Aldolases are enzymes that catalyze stereospecific aldol reactions in a reversible manner. Naturally occurring aldolases include class I aldolases, which catalyze aldol reactions via enamine intermediates, and class II aldolases, in which Zn(2+) enolates of substrates react with acceptor aldehydes. In this work, Zn(2+) complexes of L-prolyl-pendant[15]aneN(5) (ZnL(3)), L-prolyl-pendant[12]aneN(4) (ZnL(4)), and L-valyl-pendant[12]aneN(4) (ZnL(5)) were designed and synthesized for use as chiral catalysts for enantioselective aldol reactions. The complexation constants for L(3) to L(5) with Zn(2+) [logK(s)(ZnL)] were determined to be 14.1 (for ZnL(3)), 7.6 (for ZnL(4)), and 9.6 (for ZnL(5)), indicating that ZnL(3) is more stable than ZnL(4) and ZnL(5). The deprotonation constants of Zn(2+)-bound water [pK(a)(ZnL) values] for ZnL(3), ZnL(4), and ZnL(5) were calculated to be 9.2 (for ZnL(3)), 8.2 (for ZnL(4)), and 8.6 (for ZnL(5)), suggesting that the Zn(2+) ions in ZnL(3) is a less acidic Lewis acid than in ZnL(4) and ZnL(5). These values also indicated that the amino groups on the side chains weakly coordinate to Zn(2+). We carried out aldol reactions between acetone and 2-chlorobenzaldehyde and other aldehydes in the presence of catalytic amounts of the chiral Zn(2+) complexes in acetone/H(2)O at 25 and 37 degrees C. Whereas ZnL(3) yielded the aldol product in 43% yield and 1% ee (R), ZnL(4) and ZnL(5) afforded good chemical yields and high enantioselectivities of up to 89% ee (R). UV titrations of proline and ZnL(4) with acetylacetone (acac) in DMSO/H(2)O (1:2) indicate that ZnL(4) facilitates the formation of the ZnL(4)(acac)(-) complex (K(app)=2.1x10(2) M(-1)), whereas L-proline forms a Schiff base with acac with a very small equilibrium constant. These results suggest that the amino acid components and the Zn(2+) ions in ZnL(4) and ZnL(5) function in a cooperative manner to generate the Zn(2+)-enolate of acetone, thus permitting efficient enantioselective C-C bond formation with aldehydes.

Modeling excitation properties of iridium complexes

AbstractFive iridium Ir(III) complexes have been studied using B3P86, B3LYP, M05, M06, M05‐2X, and M06‐2X functionals within configuration interaction singles (CIS) and time dependent density functional theory (TDDFT) formalisms with the aim of finding theory level that would allow for reliable prediction of emission properties. Knowledge of these properties prior to synthesis may significantly facilitate rational design of organic light‐emitting diodes (OLEDs). Our results indicate that the M05‐2X functional gives excellent results in this respect for the class of complexes studied here with the exception of the (bsn)2Ir(acac) complex. We have shown that the discrepancy between the theoretical and experimental values for this complex is due to the presence of the sulfur atom. Copyright © 2009 John Wiley & Sons, Ltd.

Determination of the enthalpies of sublimation and evaporation from thermogravimetric data: Application to metalorganic complexes of Al and Cr

A series of bimetallic acetylacetonate (acac) complexes, Al x Cr 1− x (acac) 3, 0 ≤ x ≤ 1, have been synthesized for application as precursors for the CVD of substituted oxides, such as (Al x Cr 1− x ) 2O 3. Detailed thermal analysis has been carried out on these complexes, which are solids that begin subliming at low temperatures, followed by melting, and evaporation from the melt. By applying the Langmuir equation to differential thermogravimetry data, the vapour pressure of these complexes is estimated. From these vapour pressure data, the distinctly different enthalpies of sublimation and evaporation are calculated, using the Clausius–Clapeyron equation. Such a determination of both the enthalpies of sublimation and evaporation of complexes, which sublime and melt congruently, does not appear to have been reported in the literature to date.

Ligand reduction in variously substituted cerium (IV) tetrakis acetylacetone complexes by electrochemistry technique

In this work, substantial evidence was obtained for ligand reduction in cerium tetrakis acac complexes. Also, this ligand reduction of a negatively charged ligand proved to depend far less on the nature central metal than neutral ligands does. It is supposed that in Mz(acac)z complexes the charge is distributed evenly over the whole molecule. In this work these complexes were prepared and characterized by IR and CHN analysis to indicate the purities of these complexes. The electrochemistry techniques were shown as obtained for ligand reduction. This research was carried out at School of Chemistry and Molecular Science, Sussex University, U.K.

Ligand reduction in variously substituted cerium (IV) tetrakis acetylacetone complexes by electrochemistry technique

In this work, substantial evidence was obtained for ligand reduction in cerium tetrakis acac complexes. Also, this ligand reduction of a negatively charged ligand proved to depend far less on the nature central metal than neutral ligands does. It is supposed that in Mz(acac)z complexes the charge is distributed evenly over the whole molecule. In this work these complexes were prepared and characterized by IR and CHN analysis to indicate the purities of these complexes. The electrochemistry techniques were shown as obtained for ligand reduction. This research was carried out at School of Chemistry and Molecular Science, Sussex University, U.K.

Synthesis, X-ray structures, and magnetic properties of heterometal dinuclear Cr(III)–M(II) complexes

New 3,5-bis(2-pyridyl)pyrazolato (bpypz) bridged heterometal dinuclear complexes [(nta)Cr(μ-bpypz)M II(picen)] + (M = Mn(II), Ni(II)) and [(acac) 2Cr(μ-bpypz)Ni II(picen)] 2+ (nta = nitrilotriacetate, picen = N, N′-bis(2-pyridylmethyl)ethylenediamine, acac = acetylacetate) were synthesized and characterized by the X-ray analysis, ESI-MS and the magnetic measurements, and/or 2H NMR spectra. The molecular structures were compared from a viewpoint of the conformation of the picen depending on M II ionic radii or different modes of hydrogen bonds. The picen in [(nta)Cr(μ-bpypz)Mn II(picen)]BF 4 takes an abnormal conformation with intramolecular bifurcated three-center hydrogen bonds between two carboxylate oxygens of nta and an amine proton of the picen as found for the previously reported corresponding Fe(II) complex [K. Ni-iya, A. Fuyuhiro, T. Yagi, S. Nasu, K. Kuzushita, S. Morimoto, S. Kaizaki, Bull. Chem. Soc. Jpn. 74 (2001) 1891]. On the other hand, for both Ni(II)-nta and Ni(II)-acac complexes, the picen takes a normal conformation with only a two-center hydrogen bond between non-bridging ligands. The magneto-structural relation is discussed for the Cr(III)–Ni(II) complexes in connection with the orthogonality or orbital overlap arising from the difference in distortion around Cr(III) moiety.