Acetylacetonato Complexes Research Articles

Co(II) complexes of curcumin and a ferrocene-based curcuminoid: a study on photo-induced antitumor activity.

Co(II) complexes having a ferrocene-based curcuminoid (Fc-curH) ligand viz. [Co(L)2(Fc-cur)]ClO4 (1, 2), where L is phenanthroline base, namely, 1,10-phenanthroline (phen in 1) and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 2) have been synthesized, characterized and evaluated as photochemotherapeutic agents in vitro. The corresponding Co(II) complexes of the naturally occurring polyphenol curcumin (curH), namely, [Co(L)2(cur)]ClO4 (3, 4), where L is phen (in 3) and dppz (in 4) were synthesized and their photo-induced anticancer activities compared with their ferrocene containing counterparts 1 and 2. The Co(II) acetylacetonato complex viz. [Co(phen)2(acac)]ClO4 (5) was structurally characterized through X-ray crystallography and used as control for cellular experiments. The Co(II) complexes having ferrocene-based curcuminoid are remarkably stable at physiological condition with higher lipophilicity compared to their curcumin analogues. The complexes display significant binding propensity to calf thymus (ct) DNA and human serum albumin (HSA). The complexes 1-4 display remarkable visible light induced cytotoxicity with the ferrocenyl analogues showing more phototoxic index (PI). The Co(II) curcumin complexes localize in the nucleus and mitochondria of A549 cells. The primary cell death mechanism is believed to be apoptotic in nature induced by light assisted generation of reactive oxygen species (ROS).Graphic abstract.

The kinetic substitution reactions and structural analysis of manganese(I) acetylacetonato complexes

The methanol substitution reactions in the manganese acetylacetonato complex, fac-[Mn(CO)3(acac)(CH3OH)], was kinetically investigated with a range of entering ligands including pyridine (Py), imidazole (Im) and 4-dimethylaminopyridine (DMAP). All the complexes were characterized by NMR, UV–vis and IR spectroscopy. Moreover, crystal structures of fac-[Mn(CO)3(acac)(CH3OH)] (1), fac-[Mn(CO)3(acac)(Py)] (2) and fac-[Mn(CO)3(acac)(DMAP)] (3) are reported. The substitution of methanol in fac-[Mn(CO)3(acac)(CH3OH)] (1) by DMAP is approximately 2 times faster than Py, and 1.7 times faster when compared to Im. The results correlate well with the pKa of the entering nucleophile where pyridine (Py) < imidazole (Im) < 4-dimethylaminopyridine (DMAP). The activation parameters for complex (1) were determined as ΔH≠=73.9 ± 0.6 kJ mol−1 and the entropy of activation ΔS≠=−28 ± 2 JK−1 indicating an interchange associative mechanism.

Ni(II) curcumin complexes for cellular imaging and photo-triggered in vitro anticancer activity

Nickel(II) complexes [Ni(cur)(L)2](OAc) (1-3) where L is N,N-donor heterocyclic bases namely 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2), dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3) and Hcur is curcumin were prepared, fully characterized and light-induced in vitro anticancer activity studied. Three nickel(II) complexes containing acetylacetonato (Hacac) ligand, viz.[Ni(acac)(L)2](OAc) (4-6) where L is phen (in 4), dpq (in 5), dppz (in 6) were prepared and used as controls. Complex 4 was structurally characterized by single crystal X-ray diffraction technique, which revealed an octahedral NiN4O2 geometry around the metal centre. Complexes 1-3 showed an intense curcumin-based band at ∼440 nm in DMSO-Tris-HCl buffer (pH = 7.2) (1:4 v/v) which masks the nickel based d-d band. The curcumin comlexes (1-3) were redox inactive at the nickel centre, whereas the acetylacetonato complexes (4-6) displayed an irreversible voltammetric response at ∼1.00 V vs. Ag/AgCl reference electrode in DMF. The complexes bind to calf thymus DNA (ct-DNA) with considerable affinity and interacted with human serum albumin (HSA) with moderate affinity. The Ni(II) curcumin complexes display significant in vitro light-induced cytotoxicity in HeLa (human cervical carcinoma) and A549 (lung cancer cells) involving reactive oxygen species (ROS), with very low dark toxicity. The complexes were found to be much less toxic to immortalized lung epithelial normal cells (HPL1D). Confocal microscopic images using complex 2 and 3 showed that they primarily localize in the cytosol of A549 cells. The mechanism of cell death is mainly apoptosis in nature showing arrest of sub-G1 phase of cell cycle progression in A549 cells under visible light exposure and involves significant loss of mitochondrial membrane potential as observed from JC-1 assay.

Heteroleptic cobalt(iii) acetylacetonato complexes with N-heterocyclic carbine-donating scorpionate ligands: synthesis, structural characterization and catalysis.

Exposure of O2 to a reaction mixture containing bis(acac)cobalt(ii), a facially capping tris(N-heterocyclic carbene)borate ligand and 1-methylimidazole yields a heteroleptic cobalt(iii) complex with acac, 1-methylimidazole and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this heteroleptic complex to catalytically oxidize cyclohexane at ambient temperature.

A comparative DFT study of stacking interactions between adjacent metal atoms in linear chains of Ir and Rh acetylacetonato complexes

A computational chemistry study using DFT explains why the electrical conductivity along the metal axis in adjacent [Rh(acetylacetonato)(CO)2] molecules was found to be four to five orders of magnitude smaller than along the metal axis of adjacent [Ir(acetylacetonato)(CO)2] molecules. Computational chemistry results, obtained by a variety of different techniques, showed that strong interaction exists between iridium atoms in neighbouring [Ir(acetylacetonato)(CO)2] molecules. Bonds between the neighbouring iridium atoms were identified by quantum theory of atoms in molecules (QTAIM) calculations. A natural bond orbital (NBO) analysis showed that LP(Ir) donor – LP*(Ir) acceptor interactions between the two adjacent iridium centres in [Ir(acetylacetonato)(CO)2]2, are more than twice the value of the LP(Rh) donor – LP*(Rh) acceptor interactions obtained for adjacent rhodium centres in [Rh(acetylacetonato)(CO)2]2. The stacking of [Ir(acetylacetonato)(CO)2] molecules in the solid state is further stabilised by additional four weak BD(COcarbonyl) donor – BD*(CHmethyl) acceptor interactions, as well as four weak BD(COcarbonyl) donor – BD*(COacac) acceptor interactions between adjacent [Ir(acetylacetonato)(CO)2] molecules, which were not obtained by the NBO analysis of [Rh(acetylacetonato)(CO)2]2. A fragment analysis of the frontier molecular orbitals of [Ir(acetylacetonato)(CO)2]2 showed that the intermolecular iridium-iridium bonding energy in dimolecular [Ir(acetylacetonato)(CO)2]2 is about six times higher than the intermolecular rhodium-rhodium bonding energy in [Rh(acetylacetonato)(CO)2]2.

Cobalt complexes as internal standards for capillary zone electrophoresis-mass spectrometry studies in biological inorganic chemistry.

Run-by-run variations are very common in capillary electrophoretic (CE) separations and cause imprecision in both the migration times and the peak areas. This makes peak and kinetic trend identification difficult and error prone. With the aim to identify suitable standards for CE separations which are compatible with the common detectors UV, ESI-MS, and ICP-MS, the CoIII complexes [Co(en)3]Cl3, [Co(acac)3] and K[Co(EDTA)] were evaluated as internal standards in the reaction of the anticancer drug cisplatin and guanosine 5'-monophosphate as an example of a classical biological inorganic chemistry experiment. These CoIII chelate complexes were considered for their stability, accessibility, and the low detection limit for Co in ICP-MS. Furthermore, the CoIII complexes are positively and negatively charged as well as neutral, allowing the detection in different areas of the electropherograms. The background electrolytes were chosen to cover a wide pH range. The compatibility to the separation conditions was dependent on the ligands attached to the CoIII centers, with only the acetylacetonato (acac) complex being applicable in the pH range 2.8-9.0. Furthermore, because of being charge neutral, this compound could be used as an electroosmotic flow (EOF) marker. In general, employing Co complexes resulted in improved data sets, particularly with regard to the migration times and peak areas, which resulted, for example, in higher linear ranges for the quantification of cisplatin.

4,5-Substituted C^C* cyclometalated thiazol-2-ylidene platinum(ii) complexes - synthesis and photophysical properties.

We report the synthesis of seven novel backbone functionalized N-phenyl-1,3-thiazol-2-ylidene platinum(ii) complexes and their photophysical properties. Electronically diverse N-phenyl-1,3-thiazol-2-thiones were prepared by a reaction of aniline with carbon disulfide and different α-haloketone compounds. Oxidative desulfuration and salt metathesis yielded the desired NHC-precursors with hexafluorophosphate counterions. In addition, a new route for the synthesis of N-phenyl-1,3-benzo[d]thiazole tetrafluoroborate via N-arylation using hypervalent iodine species is presented. All complexes were prepared from the corresponding NHC precursor in a one-pot process using silver(i)oxide, transmetalation to platinum and reaction with the β-diketone acetylacetone under basic conditions. These complexes exhibit strong phosphorescence with quantum yields up to 72% in 2 wt% PMMA films with decay lifetimes of 8.8-12.3 μs. The influence of methyl- and phenyl-groups, and an ester-substituent at the 4- and/or 5-position of the 1,3-thiazole moiety, as well as the N-phenyl-1,3-benzo[d]thiazole-derived motif is discussed. The 4,5-unsubstituted-N-phenyl-1,3-thiazol-2-ylidene platinum(ii) acetylacetonato complex served as a reference in this study to evaluate the electronic effects originating from the backbone substitution. All complexes emit in a narrow range of the bluish-green spectrum of the visible light (510 ± 10 nm).

Dysprosium Acetylacetonato Single-Molecule Magnet Encapsulated in Carbon Nanotubes.

Dy single-molecule magnets (SMMs), which have several potential uses in a variety of applications, such as quantum computing, were encapsulated in multi-walled carbon nanotubes (MWCNTs) by using a capillary method. Encapsulation was confirmed by using transmission electron microscopy (TEM). In alternating current magnetic measurements, the magnetic susceptibilities of the Dy acetylacetonato complexes showed clear frequency dependence even inside the MWCNTs, meaning that this hybrid can be used as magnetic materials in devices.

Palladium(ii)-Acetylacetonato Complexes with Mesoionic Carbenes: Synthesis, Structures and Their Application in the Suzuki-Miyaura Cross Coupling Reaction.

A series of novel palladium(ii) acetylacetonato complexes bearing mesoionic carbenes (MICs) have been synthesized and characterized. The synthesis of the complexes of type (MIC)Pd(acac)I (MIC = 1-mesityl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (1), 1,4-(2,4,6-methyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (2), 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (3); acac = acetylacetonato) via direct metalation starting from the corresponding triazolium iodides and palladium(ii) acetylacetonate is described herein. All complexes were characterized by 1H- and 13C-NMR spectroscopy and high resolution mass spectrometry. Additionally, two of the complexes were characterized by single crystal X-ray crystallography confirming a square-planar coordination geometry of the palladium(ii) center. A delocalized bonding situation was observed within the triazolylidene rings as well as for the acac ligand respectively. Complex 2 was found to be an efficient pre-catalyst for the Suzuki-Miyaura cross coupling reaction between aryl-bromides or -chlorides with phenylboronic acid.

Orientation of trimethylolethane cyclic phosphite in rhodium complexes: Structure of [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)

Density functional theory calculations showed that rotation of the (P(OCH2)3CCH3) group in the rhodium–acetylacetonato complex [Rh(acac)(CO)(P(OCH2)3CCH3)] has a negligible influence on the energy of the complex. Density functional theory calculations further showed that the minimum energy orientation of the cyclic (P(OCH2)3CCH3) group in square planar rhodium–(P(OCH2)3CCH3)–(CO) complexes containing a bidentate ligand that is larger than the acetylacetonato ligand, is with one of the PO bonds near parallel (within 10°) to the plane defined by the four atoms coordinated to Rh. The three PO bonds of the rigid (P(OCH2)3CCH3) group adopt a C3-symmetrical conformation around the RhP axis. The lowest energy geometry of [Rh(BID)(CO)(P(OCH2)3CCH3)] (BID=bidentate ligand with two O donor atoms and charge −1) complexes is where one PO bond is aligned near parallel to the RhOBIDtransto CO bond, while the geometry with a PO bond orientated near parallel to the RhCCO bond, is slightly higher in energy, but still possible experimentally. The highest energy orientation of the (P(OCH2)3CCH3) group in square planar [Rh(BID)(CO)(P(OCH2)3CCH3)] complexes, is with one of the PO bonds near perpendicular to the plane described by the four atoms coordinated to Rh. The orientation of the cyclic (P(OCH2)3CCH3) group in available experimental structures of square planar [Rh(BID)(CO)(P(OCH2)3CCH3)] complexes, confirms this finding.

Photoluminescence of a New Material: Cyclometalated C∧C* Thiazole-2-ylidene Platinum(II) Complexes

A new class of platinum(II) compounds, the 4,5-dimethyl-3-aryl-thiazole-2-ylidene platinum(II) acetylacetonato complexes, are described. Their efficient phosphorescent emission at room temperature makes them suitable for potential applications in organic light-emitting diodes. A new synthetic pathway that allows the preparation of a broad range of different N-arylthiazole-2-thiones and their subsequent conversion into the corresponding N-arylthiazolium perchlorate and hexafluorophosphate salts has been developed. Not only electron-rich (4-OMe, 4-Me, 3-Me) N-arylthiazoles but also electron-deficient ligands with a cyano or an ester group could be synthesized. From commercially available anilines N-arylthiazolium perchlorate and hexafluorophosphate salts were synthesized via ring-closure of in situ generated N-aryldithiocarbamate salts followed by a sulfur-oxidation/-substitution protocol to the air-stable carbene precursors. All reactions were performed in multigram scale in good yields. The synthesis of t...

Preparation of novel cationic acetylacetonate complexes of palladium with diimine ligands

Catalytic systems based on palladium and nickel complexes with α-diimine ligands are known as the Brookhart catalysts [1, 2]; they are well known in modern practice of laboratory and industrial homogeneous catalysis of oligoand polymerization of lower alkenes. The strong point of such catalysts is their stability towards polar functional groups of the monomer, allowing preparation of hyperbranched polyolefines. Significant part of palladium complexes with α-diimine ligands described in the literature are neutral (halogenide or alkyl) complexes of palladium that generally require activation with organoaluminum compounds to initiate the active cationic sites [2]. A common feature of preparations of the known cationic palladium complexes is that they are multi-stage processes. On top of that, expensive starting materials are normally used (salts of silver and thallium) as well as magnesiumortincontaining chemicals [1]. There have been no examples of preparation of cationic acetylacetonato complexes of palladium with αdiimine ligands.

A Ditopic Catechol Phosphane as Building Block for Selective Construction of Heterometallic Complexes with Early and Late Transition Metal Centers

Base-assisted reaction of catechol phosphane 2 (H2L) with [M′Cl2(cod)] (cod = 1, 5-cyclooctadiene, M′ = Pd, Pt) yielded chelate complexes [M′(HL)2] (7a, b). Spectroscopic and single-crystal X-ray diffraction studies revealed that both complexes feature cis-configuration of the P- and O-donor atoms in solution and in the solid state. Reaction of 7a, b with acetylacetonato or alkoxide complexes [MO2(acac)2] (M = Mo, W), [VO(acac)2], [{Ti(μ-O)(acac)2}2], or Ti(OiPr)4 gave good to excellent yields of early-late heterometallic complexes [MOn(μ-L)2M′] (MOn = MoO2, WO2, VO; 8a, b–10a, b) or [Ti(RO-1κO)2(μ-L-1κ2O, O'-2κ2P, O)2Pd] (R = Me, iPr; 11a, b), which were inaccessible via other synthetic routes. Spectroscopic and single-crystal X-ray diffraction studies revealed that the early metal centres in 8a, b, 9b and in 11b feature distorted octahedral coordination spheres with rigid transoid alignment of the catechol ring planes. Vanadium complexes 10a, b exhibit a square-pyramidal coordination sphere with cisoid alignment of the catechol ring planes and evidence for intermolecular pairing via weak VO···Pd contacts in the solid state; complexes 8, 9 do not undergo conformational inversion on the NMR time-scale. The molecular structure of Ti complex 11a is characterized by a different orientation of the catechol moieties, which can be envisaged to picture an intermediate state during a configuration inversion process, and a strong hydrogen bridge between a terminally coordinated catecholato-oxygen atom and a solvent molecule (MeOH). Solution NMR studies indicate that the (MeO)2Ti(μ-L)2M' framework is in this case conformationally labile and that the MeO ligands undergo intermolecular dynamic exchange with the solvent.

Zn and Mn Acetylacetonato Complexes as Precursors for Hexadecylamine-Capped ZnO and MnO Nanoparticles and their Water Solubility

Zn and Mn Acetylacetonato Complexes as Precursors for Hexadecylamine-Capped ZnO and MnO Nanoparticles and their Water Solubility

Labile Rhodium(I)–N-Heterocyclic Carbene Complexes

The neutral square-planar complexes Rh(acac)(IPr)(η2-olefin) have been prepared from [Rh(μ-Cl)(IPr)(η2-olefin)]2 (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene; olefin = cyclooctene, ethylene) and sodium acetylacetonate (acac). Protonation of the acetylacetonato complexes with triflic acid opens the way to the formation of the putative bare [Rh-IPr]+ fragment that has been stabilized at low temperature by labile ligands such as triflate, cyclooctene, and acetonitrile to generate Rh(OTf)(IPr)(η2-coe), [Rh(IPr)(η2-coe)(NCCH3)2]OTf, and [Rh(IPr)(NCCH3)3]OTf complexes. The derivative [Rh(IPr)(η2-coe)(NCCH3)2]OTf was further characterized by an X-ray diffraction analysis.

Preparation of Highly Active Noble Metal Phosphide Catalysts: Effect of Precursors on the Formation of the Active Phase and Hydrodesulfurization Activity

Abstract The effect of precursors on the active phase formation and hydrodesulfurization activities of noble metal phosphide catalysts was examined. The maximum activities of Pd–P and Rh–P catalysts prepared from acetylacetonato (acac) complex were observed at lower reduction temperatures than those for catalysts prepared from chlorides (Cl). The Pd–P catalyst prepared from acac also showed higher activity than that obtained from Cl. However, this trend was not observed in the Rh–P catalyst. The characterization results revealed that the higher activity of the Pd–P catalyst prepared from the acac is due to the highly dispersed Pd4.8P.

Theoretical Investigation of Paramagnetic NMR Shifts in Transition Metal Acetylacetonato Complexes: Analysis of Signs, Magnitudes, and the Role of the Covalency of Ligand–Metal Bonding

Ligand chemical shifts are calculated and analyzed for three paramagnetic transition metal tris-acetylacetonato (acac) complexes, namely high-spin Fe(III) and Cr(III), and low-spin Ru(III), using scalar relativistic density functional theory (DFT). The signs and magnitudes of the paramagnetic NMR ligand chemical shifts are directly related to the extent of covalent acac oxygen-to-metal σ donation involving unoccupied metal valence d(σ) acceptor orbitals. The role of delocalization of metal-centered spin density over the ligand atoms plays a minor secondary role. Of particular interest is the origin of the sign and magnitude of the methyl carbon chemical shift in the acac ligands, and the role played by the DFT delocalization error when calculating such shifts. It is found that the α versus β spin balance of oxygen σ donation to metal valence d acceptor orbitals is responsible for the sign and the magnitude of the ligand methyl carbon chemical shift. A problematic case is the methyl carbon shift of Fe(acac)(3). Most functionals produce shifts in excess of 1400 ppm, whereas the experimental shift is approximately 279 ppm. Range-separated hybrid functionals that are optimally tuned for Fe(acac)(3) based on DFT energetic criteria predict a lower limit of about 2000 ppm for the methyl carbon shift of the high-spin electronic configuration. Since the experimental value is based on a very strongly broadened signal it is possibly unreliable.

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.

Potentiometric studies of Nickel (II) and copper (II) acetyl acetonato complexes

The dissociation constant pKa of acetylacetone has been determined potentiometrically. The pKa value obtained is 9.40, indicating a weak acid. The stability constants of the complex compounds formed from the reaction of nickel (II) and copper (II) with acetylacetone determined using potentiometer are 6.32x1015 and 2.82x1014, respectively. Similarly, the number of acetylacetonato ligands coordinated to each metal ion determined potentiometrically is 3. Key words: Potentiometry, Acetylacetone, Dissociation and Stability Constants.

Methyl iodide oxidative addition to [Rh(acac)(CO)(PPh3)]: an experimental and theoretical study of the stereochemistry of the products and the reaction mechanism

Density functional theory was used to investigate the oxidative addition and subsequent carbonyl insertion and deinsertion steps of the reaction of methyl iodide to a rhodium(I) acetylacetonato complex of the formula [Rh(acac)(CO)(PPh(3))] (Hacac = acetylacetone). This process has been studied experimentally for many rhodium β-diketonato complexes, but, to the best of our knowledge, this is the first systematic computational study of the complete reaction sequence. Experimental (1)H techniques complement the theoretical results on the stereochemistry of the reaction intermediates and products. (1)H NMR also revealed the existence of a second rhodium(III)-acyl product, which has not been previously observed in this reaction. The calculated Gibbs free energy of activation of the oxidative addition reaction is 71 kJ mol(-1), which is in agreement with the experimental value of 82(1) kJ mol(-1). The DFT-calculated oxidative addition corresponds to an associative S(N)2 nucleophilic attack by the rhodium metal centre on the methyl iodide, which is in agreement with calculated and experimental (in brackets) activation parameters of the reaction, 27 (38.8) kJ mol(-1) for ΔH((≠)) and -147 (-146) J K(-1) mol(-1) for ΔS((≠)).