Free Β-diketone Research Articles

Synthesis Comparative Electrochemistry and Spectroelectrochemistry of Metallocenyl β-Diketonato Dicarbonyl Complexes of Rhodium(I)—Cytotoxicity of [Rh(FcCOCHCOCF3)(CO)2

The metallocenyl-containing β-diketonato rhodium(I) dicarbonyl complexes of [Rh(FcCOCHCOR)(CO)2] where R = CF3, 10; Fc = ferrocenyl = FeII(C5H5)(C5H4), 11; Rc = ruthenocenyl = RuII(C5H5)(C5H4), 12; and Oc = osmocenyl = OsII(C5H5)(C5H4), 13 were synthesized. Complexes 10–13 were then subjected to an electrochemical study utilizing cyclic voltammetry (CV), square wave voltammetry (SWV), and linear sweep voltammetry (LSV) in the non-coordinating solvent/supporting electrolyte medium CH2Cl2/0.1 mol dm−3 [N(nBu)4][B(C6F5)4]. The formal reduction potential for the electrochemical reversible Fc0/+ couples in 10–13 was identified in the range 0.156 ≤ Eo′ ≤ 0.328 V while the electrochemically irreversible osmocenyl and ruthenocenyl oxidations were observed at peak anodic potentials of Epa = 0.640 V and Epa = 0.751 V, respectively. Resolution between the closely overlapping CV-determined Fc0/+ and RhI/II couples was too poor for unambiguous measurement of the RhI/II redox potential, but square wave voltammetry allowed estimates of Eo′ (RhI/II) in the range 0.156 ≤ Eo′ ≤ 0.398 V. FT-IR spectroelectrochemistry confirmed the one-electron oxidation of RhI by the appearance of CO vibrational bands at stretching frequencies, which are associated with rhodium(II) and not rhodium(III). Cytotoxicity tests on 10 (IC50 = 19.2 µM) showed it to be substantially less cytotoxic than the free β-diketone, FcCOCH2COCF3, and [Rh(FcCOCHCOCF3)(cod)].

Unexpected XPS Binding Energy Observations Further Highlighted by DFT Calculations of Ruthenocene-Containing [IrIII(ppy)2(RCOCHCORc)] Complexes: Cytotoxicity and Crystal Structure of [Ir(ppy)2(FcCOCHCORc)

The series of iridium(III) complexes, [Ir(ppy)2(RCOCHCOR')], with R = CH3 and R' = CH3 (1), Rc (2), and Fc (3), as well as R = Rc and R' = Rc (4) or Fc (5), and R = R' = Fc (6), ppy = 2-phenylpyridinyl, Fc = FeII(η5-C5H4)(η5-C5H5), and Rc = RuII(η5-C5H4)(η5-C5H5), has been investigated by single-crystal X-ray crystallography and X-ray photoelectron spectroscopy (XPS) supplemented by DFT calculations. Here, in the range of 3.74 ≤ ΣχR ≤ 4.68, for Ir 4f, Ru 3d and 3p and N 1s orbitals, binding energies unexpectedly decreased with increasing ΣχR (ΣχR = the sum of Gordy group electronegativities of the R groups on β-diketonato ligands = a measure of electron density on atoms), while in Fe 2p orbitals, XPS binding energy, as expected, increased with increasing ΣχR. Which trend direction prevails is a function of main quantum level, n = 1, 2, 3…, sub-quantum level (s, p, d, and f), initial state energies, and final state relaxation energies, and it may differ from compound series to compound series. Relations between DFT-calculated orbital energies and ΣχR followed opposite trend directions than binding energy/ΣχR trends. X-ray-induced decomposition of compounds was observed. The results confirmed good communication between molecular fragments. Lower binding energies of both the Ir 4f7/2 and N 1s photoelectron lines are associated with shorter Ir-N bond lengths. Cytotoxic tests showed that 1 (IC50 = 25.1 μM) and 3 (IC50 = 37.8 μM) are less cytotoxic against HeLa cells than cisplatin (IC50 = 1.1 μM), but more cytotoxic than the free β-diketone FcCOCH2COCH3 (IC50 = 66.6 μM).

The investigation of modification in structural flexibility and coordination modes in a solvent free β-diketone Cu(II) complex by crystal structure and DFT studies

Coordination-driven self-assembly in inorganic complexes is a viable methodology to construct supramolecular coordination complexes. Crystal engineering of β-diketone Cu(II) coordination complexes can be achieved via the host–guest complexation method. The effect of metal–ligand interactions (coordination polyhedra) on the supramolecular framework has been analysed by crystal structure and computational studies. A new crystal form of a Cu(II) complex with 4,4,4-trifluoro-naphthyl butanedione has been identified and characterized using various spectroscopic techniques. X-ray diffraction studies unveiled that complex 1, [Cu(TFNB)2], crystallized in the monoclinic (P21/n) space group and its solvent-induced crystal forms, complex 2, [Cu(TFNB)2DMSO] (Database Identifier: IVAKIC), and complex 3, [Cu(TFNB)2DMF] (Database Identifier: ZOCHOR), which were reported earlier, are in the triclinic (P1¯) crystal system. The previously reported crystal forms (complexes 2 and 3) are examples of a single crystal coordinated solvent exchange (SCCSE) transformation. In complex 1, the β-diketone molecules are attached to the metal ion in an equatorial form with a perfect square planar geometry, whilst complexes 2 and 3 feature a slightly distorted square pyramidal geometry with chelated donor oxygen atoms of the β-diketone ligands in equatorial sites and the crystallizing DMSO and DMF solvents are apically coordinated to the metal centre, respectively. Interestingly, the oxygen donors of the β-diketone ligands in complex 1 are inclined in a trans configuration, whereas in the solvent-induced pseudopolymorphic forms of complexes 2 and 3, a cis configuration is observed. The variation in the supramolecular framework with the coordination geometry in different crystal forms is analysed using the crystal structures and compared with quantum computational (Hirshfeld surface, enrichment ratio, energy framework, NCI index model and DFT) results. Molecular docking analysis was performed for all the complexes against the SARS-CoV2 main protease to explore the structure–property relationship.

The Investigation of Modification in Structural Flexibility and Coordination Modes in Solvent Free Β-Diketone Cu(Ii) Complex by Crystal Structure and Dft Studies

The Investigation of Modification in Structural Flexibility and Coordination Modes in Solvent Free Β-Diketone Cu(Ii) Complex by Crystal Structure and Dft Studies

Redox behaviour of bis(β-diketonato)copper(II) complexes

In this study for the first time, a comprehensive report was compiled on the electrochemical behavior of a series of eight square planar bis(β-diketonato)copper(II) complexes, with a variety of substituents R1 and R2 on the β-diketonato ligand (R1COCHCOR2)−. The character of the observed redox features was determined by computational chemistry calculations of the frontier molecular orbitals involved. The experimentally obtained electrochemically irreversible CuII/CuI reduction potentials, Epc(CuII/CuI), were related to various electronic descriptors (such as electronegativities, Hammett constants and Lever electronic parameters), which describe the electron withdrawing power of the β-diketonato ligands attached to the copper metal. Linear relationships have also been obtained between Epc(CuII/CuI) and computational chemistry calculated energies of the eight bis(β-diketonato)copper(II) complexes. These linear relationships confirmed good communication between the copper metal and the eight different β-diketonato ligands attached to it. Furthermore, the experimentally observed electrochemically irreversible CuII/CuI reduction potentials of those [CuII(β-diketonato)2] complexes which are metal based, were also linearly related to the reduction potentials of the uncoordinated free β-diketones which are ligand based. Furthermore, the DFT calculated LUMO energies reproduce the experimental absolute reduction potential.

Electrochemical behaviour of Tris(β-diketonato)iron(III) complexes: A DFT and experimental study

Abstract A combined experimental and theoretical study on the electrochemical behaviour of a series of tris(β-diketonato) iron(III) complexes is reported. The experimental cyclic voltammetric data showed the reversible reduction and reoxidation of FeIII/FeII. A diffusion coefficient of 5.6 × 10-6 cm2 s-1 was obtained for tris(acetonato) iron(III) in acetonitrile. Linear relationships and trends obtained between the formal reduction potential of FeIII/FeII in tris(β-diketonato) iron(III) complexes and those electronic parameters describing the electron donating ability of the β-diketonato ligand, such as the Gordy scale group electronegativities, and the Hammett meta substituent constants of the side groups R1 and R2 on the β-diketonato ligand (R1COCHCOR2)−, the Lever electronic parameters and the pKa of the free β-diketone ligand, are presented. The experimental formal reduction potential relates linearly to the density functional theory calculated electron affinity, as well as to the energy of the lowest unoccupied molecular orbital of the tris(β-diketonato) iron(III) complexes.

Electrochemical study of carbonyl phosphine β-diketonato rhodium(I) complexes

Cyclic voltammetry of [Rh(RCOCHCOR′)(CO)(PPh 3 )] complexes. The electrochemical oxidation of a series of [Rh(RCOCHCOR′)(CO)(PPh 3 )] complexes studied in acetonitrile, containing 0.100 mol dm −3 tetra- n -butylammonium hexafluorophosphate as supporting electrolyte, shows that Rh(I) is being oxidized in an electrochemically irreversible two-electron transfer process, at peak anodic potentials ranging from E pa (Rh) = 0.29–0.57 V vs. Fc/Fc + . R and R′ groups on the β-diketonato ligand (RCOCHCOR′) which are more electron withdrawing, reduce electron density on the rhodium atom to a larger extent than electron donating groups do. This leads to a higher, more positive, electrochemical oxidation potential, E pa (Rh). Relationships were established between the electrochemical quantity, E pa (Rh), and chemical oxidation, in terms of the second order kinetic oxidative addition rate constant, k 2 , as well as other parameters related to the electronic effect of the R and R′ groups through conjugation on rhodium in [Rh(RCOCHCOR′)(CO)(PPh 3 )]; such as the sum of the group electronegativities (Gordy Scale) of the R and R′ groups ( χ R + χ R′ ), the Hammett meta σ values ( σ R + σ R′ ) and the p K a of the free β-diketone R′COCH 2 COR. E pa can also be predicted by the density functional theory calculated HOMO energy and the two-electron adiabatic ionization potential, IP 2e− , of these [Rh(RCOCHCOR′)(CO)(PPh 3 )] complexes.

A DFT study of the reactivity of β-diketonato-1,5-cyclo-octadieneiridium(I) complexes

Good linear relationships exist between density functional theory (DFT) calculated orbital energies and charges of [Ir(β-diketonato)(cod)] complexes and the experimental second order substitution rate constant of the [Ir(R′COCHCOR)(cod)]+phen→[Ir(R′COCHCOR)(cod)(phen)] reaction. Both calculated and experimental values relate to the electron-donating and -withdrawing properties of the side groups R and R′ on the β-diketonato ligand (RCOCHCOR′)− as described by the Gordy scale group electronegativities, Hammett meta substituent constants, Lever electronic parameters and the pKa of the free β-diketone.

Reactivity of [Rh(β-diketonato)(cod)] complexes: A DFT approach

The density functional theory calculated energies of the highest molecular orbital of [Rh(R′COCHCOR)(cod)] relate to the electrochemical oxidation potential of rhodium(I) to rhodium(III) in [Rh(R′COCHCOR)(cod)] complexes. They also relate to the experimental second order substitution rate constant of the [Rh(R′COCHCOR)(cod)] + phen → [Rh(phen)(cod)]+ + (R′COCHCOR)− reaction. The results are in close agreement with the electron-donating and -withdrawing properties of the side groups R and R′ on the β-diketonato ligand (RCOCHCOR′)− as described by the Gordy scale group electronegativities, Hammett meta substituent constants, Lever electronic parameters and the pKa of the free β-diketone.

Prediction of chemical and electrochemical oxidation potentials of β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A DFT study

The density functional theory calculated energies of the highest molecular orbital of the [Rh(β-diketonato)(P(OX)3)2] complexes (X=H, CH3, Ph) and calculated activation energies of the oxidative addition reaction [Rh(β-diketonato)(P(OH)3)2]+CH3I relate to the electrochemical oxidation potential of rhodium(I) to rhodium(III) in [Rh(β-diketonato)(P(OPh)3)2]. They also relate to the experimental second order oxidative addition rate constant of the reaction [Rh(β-diketonato)(P(OPh)3)2]+CH3I. The results are in close agreement with the electron-donating and -withdrawing properties of the side groups R and R′ on the β-diketonato ligand (RCOCHCOR′)− as described by the Gordy scale group electronegativities, Hammett meta substituent constants, Lever electronic parameters and the pKa of the free β-diketone.

Exploring photophysical properties of new boron and palladium(ii) complexes with β-diketone pyridine type ligands: from liquid crystals to metal fluorescence probes

Pyridine-functionalized β-diketone ligands of the type 1-(2-pyridyl)-3-(4-n-alkyloxyphenyl)propane-1,3-dione [HLR(n)py] (R = C6H4OCnH2n + 1, n = 12 (1), 14 (2)) were carried to react with the BF2 fragment giving rise to the corresponding adducts [BF2(LR(n)py)] (n = 12 (5), 14 (6)) which were characterized and their luminescent and thermal behaviour studied. All the ligands and boron derivatives are photoluminescent both in the solid state and in solution. The related compounds 2-[3-(4-n-alkyloxyphenyl)propane-1,3-dion-1-yl]pyridinium chloride [HLR(n)pyH]Cl (n = 12 (3), 14 (4)) were also proved to have luminescent properties. On the other hand the organometallic compounds [Pd(η3-C3H5)(HLR(14)py)][PF6] (7) and [Pd(η3-C3H5)(LR(14)pyH)][PF6] (8), based on the coordination of the [Pd(η3-C3H5)]+ fragment to the above neutral 2 or ionic 4β-diketone derivatives, respectively, were also established to be luminescent materials, compound 8 exhibiting liquid crystalline properties. The luminescent behaviour of all compounds was also investigated as a function of the metal addition of Zn2+ and Cu2+ ions. As a result it is proven that the free β-diketone pyridine ligands [HLR(n)py], the related chloride salts [HLR(n)pyH]Cl and their palladium(II) complexes behave as fluorescence chemosensors for Zn2+ and Cu2+. The luminescent behaviour of the allyl-palladium complex 8, which exhibits enantiotropic liquid crystalline properties, was also studied as a function of the temperature. As a consequence it is established that the liquid crystal state does not quench the fluorescence emission.

Electrochemical and density functional theory study of bis(cyclopentadienyl) mono(β-diketonato) titanium(IV) cationic complexes

The electrochemical behaviour of fluorinated bis(cyclopentadienyl) mono(β-diketonato) titanium(IV) complexes, of general formula [Cp 2Ti(R′COCHCOR)] +ClO 4 − with Cp = cyclopentadienyl and R′, R = CF 3, C 4H 3S; CF 3, C 4H 3O; CF 3, Ph (C 6H 5); CF 3, CH 3; CH 3, CH 3; Ph, Ph and Ph, CH 3 is described. Both metal and ligand based redox processes are observed. The chemically and electrochemically reversible Ti IV/Ti III couple is followed by an irreversible ligand reduction at a considerably more negative (cathodic) potential. A comparison of the ligand reduction in its free and chelated state indicates that the β-diketonato ligand (R′COCHCOR) − in [Cp 2Ti(R′COCHCOR)] +ClO 4 − is electroactive at more negative potentials. A theoretical density functional theory (DFT) study shows that a highly localized metal centred frontier orbital dominates the Ti IV/Ti III redox chemistry resulting in a non-linear relationship between the formal redox potential ( E°′) and the sum of the group electronegativities of the R and R′ groups, χ R + χ R′, of the ligand. Linear relationships, however, are obtained between the DFT calculated electron affinity (EA) of the complexes and χ R + χ R′, the p K a of the free β-diketones R′COCH 2COR and the carbonyl stretching frequency, v CO, of the complexes. The DFT calculated electronic structure of the second reduced species [Cp 2Ti(β-diketonato)] − shows that it is best described as Ti(III) coupled to a β-diketonato radical.

Synthetic, electrochemical and structural aspects of a series of ferrocene-containing dicarbonyl β-diketonato rhodium(I) complexes

Treatment of [Rh(β-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO) 2] than by treating [Rh(Cl)(CO) 2] 2 with FcCOCH 2COR, R = CF 3 (Hfctfa), CH 3 (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc = ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C 16H 10F 3FeO 4Rh], monoclinic, C 2/c(15), a = 13.266(3) Å, b = 19.553(3) Å, c = 13.278(3) Å, β = 100.92(2)°, Z = 8 showed both rotational and translational displacement disorders for the CF 3 group. An electrochemical study revealed that the formal reduction potential, E 0′, for the electrochemically reversible one electron oxidation of the ferrocenyl group varied between 0.304 (for the fctfa complex) and 0.172 V (for the dfcm complex) versus Fc/Fc + in a manner that could be directly traced to the group electronegativities, χ R, of the R groups on the β-diketonato ligands, as well as to the p K a ′ values of the free β-diketones. Anodic peak potentials, E pa,Rh, for the dominant cyclic voltammetry peak associated with rhodium(I) oxidation were between 0.718 (bfcm complex) and 1.022 V (dfcm complex) versus Fc/Fc +. Coulometric experiments implicated a second, much less pronounced anodic wave for the apparent two-electron Rh I oxidation that overlaps with the ferrocenyl anodic wave and that the redox processes associated with these two Rh I oxidation waves are in slow equilibrium with each other.

Synthesis and characterisation of ferrocene-containing β-diketonato complexes of rhodium(I) and rhodium(III)

The synthesis of new β-diketonato rhodium(I) complexes of the type [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] with Fc=ferrocenyl and R=Fc, C6H5, CH3 and CF3 are described. 1H, 13C and 31P NMR data showed that for each of the non-symmetric β-diketonato mono-carbonyl rhodium(I) complexes, two isomers exist in solution. The equilibrium constant, Kc, which relates these two isomers in an equilibrium reaction, are concentration independent but temperature and solvent dependent. ΔrG, ΔrH and ΔrS values for this equilibrium have been determined and a linear relationship between solvent polarity on the Dimroth scale and Kc exists. The relationship between Rh-P bond lengths, d(Rh-P), and 31P NMR peak positions as well as coupling constants 1J(31P-103Rh) has been quantified to allow calculation of approximate d(Rh-P) values. Variations in d(Rh-P) for [Rh(RCOCHCOR′)(CO)(PPh3)] complexes have also been related to the group electronegativities (Gordy scale) of the terminal β-diketonato R groups trans to PPh3. A measure of the electron density on the rhodium centre of [Rh(RCOCHCOR′)(CO)(PPh3)] may be expressed in terms of the IR carbonyl stretching wave number, ν(CO), the sum of the group electronegativities of the R and R′ groups, (χR+χR′), or the observed pKa′ values of the free β-diketones RCOCH2COR′. An empirical relationship between ν(CO) and either pKa′ or (χR+χR′) has also been quantified.

Electrochemical oxidation of Rh(I) to Rh(III) in rhodium(I) β-diketonato carbonyl phosphine complexes

Cyclic voltammetric (CV) studies revealed a direct relationship between the irreversible oxidation potentials of Rh(I) to Rh(III) in complexes of the type [Rh(I)(β-diketonato)(CO)(PPh 3)] and the p K a-values of the free β-diketones dibenzoylmethane (Hdbm), benzoylacetone (Hba), benzoyltrifluoroacetone (Hbtfa) and trifluoroacetone (Htfaa). More electronegative β-diketone ligands remove electron density from the rhodium metal, making the complex a stronger Lewis acid and less reactive towards oxidative addition. The effect of different solvents on the reduction potential of these complexes proved solvent co-ordination during the electrochemical oxidation of square planar Rh(I) to the octahedral Rh(III). A direct relationship was obtained between the irreversible reduction potential and the solvent donicity of the solvent acetonitrile, methanol, dimethylformamide and pyridine.

Reactions of trans- and cis-Dichlorobis(benzonitrile)platinum(II) with Acetylacetonate and Benzoylacetonate Carbanions. Formation of N-Acetyl β-Ketoamine Complexes by the Acetyl Group Migration

Abstract trans-Dichlorobis(benzonitrile) platinum(II) reacted with twice the molar amount of thallium(I) acetylacetonate and benzoylacetonate in dichloromethane at room temperature to afford mainly N-acetyl β-ketoamine chelates, trans-[Pt{N(COMe)=C(Ph)CH=COMe(and Ph)}2] (1a and 3a). This N,O-chelate structure of 1a was determined by X-ray analysis. Reactions of cis-[PtCl2(PhCN)2] gave C-acetyl and C-benzoyl β-ketoamine chelates, cis-[Pt{NH=C(Ph)C(COMe(and Ph))=COMe}2], together with other minor products. Formation of these β-ketoamine chelates is explained by the nucleophilic reactions of the β-diketonate carbanions at the coordinated cyanide carbon atom, followed by migration of the acetyl group or the methine proton of the nucleophiles onto the imino nitrogen atom formed during these reactions. In the presence of free β-diketones, migration of the acyl group was generally suppressed; this led to high yields of C-acyl complexes especially in reactions of cis-[PtCl2(PhCN)2]. In each case, the reaction proceeded with retention of the geometrical configuration around the central metal atom. The structures of other products, including a compound obtained by acid hydrolysis of 1a, were explored and discussed, based on IR and 2H NMR data.

Kinetics of ligand exchange between a uranium(IV) β-diketonate and free β-diketone

The intermolecular ligand exchange kinetics between a uranium(IV) β-diketonate and free β-diketone were studied by 1H nmr as a function of temperature and concentration. The reaction was found to be of first order in both chelate and free ligand. The results suggest that the exchange mechanism involves a ninth coordination site in the uranium(IV) chelate.

The Kinetics of the Ligand Exchange between Zirconium, Hafnium, and Thorium Chelates and Free β-Diketones Measured by Nuclear Magnetic Resonance

The Kinetics of the Ligand Exchange between Zirconium, Hafnium, and Thorium Chelates and Free β-Diketones Measured by Nuclear Magnetic Resonance