Synthesis,characterization and molecular structure of Re(III) complexes containing 2-benzoylpyridine

The paper presents a combined experimental and computational study of Re(III) complexes containing 2-benzoylpyridine (bopy). Two novel complexes [ReX₃(bopy)(PPh₃)] (X = Cl, Br) have been obtained in the reactions of [ReX₃(MeCN)(PPh₃)₂] with 2-benzoylpyridine in dichloromethane and have been studied by IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure of [ReCl₃(bopy)(PPh₃)] has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of [ReCl₃(bopy)(PPh₃)] have been calculated with the time-dependent DFT method and the UV–Vis spectrum has been discussed on this basis.     

The first example of half-sandwich cobalt(III) complex with hydrotris(pyrazolyl)borate ligand

This paper presents the synthesis, crystal structure and spectroscopic properties of a novel half-sandwich mononuclear cobalt(III) complex with hydrotris(3,5-dimethylpyrazolyl)borate ligand and thiocyanate [Tp^*Co(Hpz^*)(NCS)₂]·H₂O·CH₃OH (Tp^*: hydrotris(3,5-dimethyl- pyrazolyl)borate, Hpz^*: 3,5-dimethylpyrazole). The structure was determined by X-ray diffraction. The complex crystallizes in the monoclinic system, space group C_c, a=18.591(6) Å, b=10.536(3) Å, c=17.568(5) Å, β=11.284(5)°, Z=4, R₁=0.0501, wR₂=0.1179. The cobalt(III) ion in the complex is six-coordinated with nitrogen atoms, three from Tp^*, two from pyrazole and two from two thiocyanates, to form octahedral environment. The hydrogen atoms of O(2) of water molecule are connected by hydrogen bonds with S atoms of two adjacent complex molecules to form 1-D chains. The hydrogen atom of N(8) of complex molecule is connected by hydrogen bond with methanol. The spectroscopic results are consistent with the crystallographic study.     

Cyclometallated iridium(III) complexes with dicyanamide or tricyanomethanide

Reaction of cyclometallated iridium(III) complex Ir(ppy)₂(PPh₃)Cl (2, ppy = 2-phenylpyridine) with dicyanamide or tricyanomethanide gave neutral mononuclear complexes Ir(ppy)₂(PPh₃)N(CN)₂ (3a) or Ir(ppy)₂(PPh₃)C(CN)₃ (3b), and dicyanamide/tricyanomethanide-linked binuclear iridium(III) complexes [{Ir(ppy)₂(PPh₃)}₂N(CN)₂]⁺ (4a) or [{Ir(ppy)₂(PPh₃)}₂C(CN)₃]⁺ (4b). Substitution of coordinated chloride in the precursor 2 with dicyanamide or tricyanomethanide improved significantly the luminescence properties of 3a–4b. Compared with that in the precursor 2 (1.6%), 2.2 to 9.3-fold enhancement of emission quantum yields was detected in 3a–4b.     

2-Mercapto-orotic acid as a bridging chelate in a Re(III)Re(IV) dimer with a metal-metal bond

The reaction of [ReCl₃(MeCN)(PPh₃)₂] with 2-mercapto-orotic acid (H₂moa) in ethanol led to the isolation of the multiply-bridged dimer (μ-Cl)(μ-O)(μ-moa)₂[Re^IIIRe^IV(PPh₃)]₂ (1). The compound has a ReRe bond distance of 2.5425(7) Å with a formal bond order of 2.5. The dianionic bridging ligands moa^2 − coordinate bidentately via a neutral pyrimidine nitrogen and carboxylate oxygen to one Re ion, and monodentately through a thiolate sulfur to the second metal ion. Complex 1 was characterized by FTIR, electronic spectroscopy, cyclic voltammetry, microanalysis and single crystal X-ray diffraction.     

Decarboxylation of 5-amino-orotic acid and a Schiff base derivative by rhenium(V)

The reaction of 5-amino-orotic acid (H₂aor) with trans-[ReOBr₃(PPh₃)₂] in 2-propanol produced the complex [Re^V(apd)Br(aor)(PPh₃)₂] (1, apd^2 − = 5-imidopyrimidine-2,4-dione). The ligand apd^2 − was formed by the decarboxylation of H₂aor, and it is coordinated via the dinegative imido nitrogen only. The Schiff base derivative of H₂aor, salicylimine-orotic acid {5-(2-hydroxy-benzylideneamino)-1,2,3,6-tetrahydro-2,6-dioxopyrimidine-4-carboxylic acid; H₂sor}, was also decarboxylated in the reaction with trans-[ReOI₂(OEt)(PPh₃)₂] in ethanol to form [Re^III(cor)I(PPh₃)₂]I (2, Hcor = 5-(2-hydroxybenzylideneamino)-pyrimidine-2,4(1H,3H)-dione). Decarboxylation of H₂sor was not observed in its reaction with trans-[ReOCl₃(PPh₃)₂], which led to the isolation of [ReOCl(sor)(PPh₃)] (3), in which sor^2 − is coordinated as a tridentate ligand as expected. Spectroscopic results and the X-ray crystal structures of compounds 1–3 are also presented.     

Study of Gold Species in Iron-Oxide-Supported Gold Catalysts Derived from Gold-Phosphine Complex Au(PPh3)(NO3) and As-Precipitated Wet Fe(OH)3*

Iron-oxide-supported gold catalysts were prepared by supporting a Au phosphine complex Au(PPh₃)(NO₃) on as-precipitated wet iron hydroxide Fe(OH)₃^*, followed by temperature-programmed calcination. The Au/Fe(OH)₃^*catalysts calcined at the temperatures 573–773 K showed extremely high catalytic performance for CO oxidation at temperatures as low as 203–253 K. Interaction of the Au(PPh₃)(NO₃) gold precursor with the Fe(OH)₃^*upon supporting, transformation of the precursor during the heat treatments, and state of the gold in the catalysts were studied by FT-IR, XRD, TEM, XPS, and EXAFS. The gold precursor dissociated on the Fe(OH)₃^*surface to produce [Au(PPh₃)]⁺species which partially decomposed at 473 K and was transformed to small gold metallic particles with coordination numbers of 7.4–8.0 for Au-Au bond at calcination temperatures ≥573 K. In contrast, decomposition of the gold complex over crystalline Fe₂O₃^*resulted in large gold particles. The Au/Fe₂O₃^*sample was inactive at 203–253 K and exhibited very low activity for CO oxidation at room temperature. The efficiency of the as-precipitated wet Fe(OH)₃^*as a support is explained in terms of a higher stability of [Au(PPh₃)]⁺on the Fe(OH)₃^*as compared to the Fe₂O₃^*due to more effective interaction of the Au species with OH groups and defects of the amorphous Fe(OH)₃^*surface. The results demonstrate the importance of support–metal precursor interactions, both upon supporting and during calcination, in the formation of highly active catalysts with small Au particles for low-temperature CO oxidation.     

First example of pyrrole-2-carbaldehyde thiosemicarbazone as tridentate dianion in [Pd(η3-N4,N3,S-ptsc)(PPh3)] complex

Reaction of pyrrole-2-carbaldehyde thiosemicarbazone (H₂ptsc) with PdCl₂(PPh₃)₂ in 1:1 mol ratio in presence of Et₃N leads to complete dechlorination to generate square planar complex, [Pd(η³-N⁴,N³,S-ptsc)(PPh₃)] (1), existing as three independent molecules in the same unit cell, and H₂ptsc behaves in an unusual dinegative tridentate mode. Salicylaldehyde thiosemicarbazone (H₂stsc) formed similar compound, [Pd(η³-O,N³,S-stsc)(PPh₃)] (3).     

NBu4[{Au(C6F5)3}2(μ-PPh2)]: a gold(III) phosphide with a single atom bridging the metallic centers

Reaction of [Au(C₆F₅)₃(PPh₂H)] with [Au(C₆F₅)₃(tht)] and NBu₄(acac) (acac=acetylacetonate) leads to the synthesis of NBu₄[{Au(C₆F₅)₃}₂(μ-PPh₂)] (1), an unprecedented complex with two gold(III) centers bonded to a unique bridging atom without any other stabilizing effect. The novel di-bridged gold(III) phosphide [Au₂(C₆F₅)₄(μ-PPh₂)₂] (2) is obtained by treatment of diphenylphosphine with [Au₂(C₆F₅)₄(μ-Cl)₂]. The crystal structures of both derivatives have been determined by X-ray diffraction.     

Absorption and emission spectrum of bis-(triphenylphosphine)-dicarbonylnickel(0)

The complex Ni⁰(PPh₃)₂(CO)₂ shows a red photoluminescence (λ_max=650 nm) at r.t. It is suggested that this emission originates from a Ni⁰→PPh₃ metal-to-ligand charge transfer triplet.     

Photoluminescence and photochemistry of Pt(II)(PPh3)2(C6O6) induced by rhodizonate IL excitation

The complex Pt(II)(PPh₃)₂(C₆O₆) was prepared by the reaction of Ag₂C₆O₆ with cis-Pt(PPh₃)₂Cl₂ in acetonitrile. Pt(PPh₃)₂(C₆O₆) is characterized by a lowest-energy IL (rhodizonate) excited state. The complex shows an IL fluorescence, but is also photoactive. The photolysis leads to the conversion of rhodizonate to croconate in the coordinated state: Pt(II)(PPh₃)₂(C₆O₆) → Pt(II)(PPh₃)₂(C₅O₅) + CO.     

Luminescent palladium(0) complexes bearing N-heterocyclic carbene and phosphine ligands

Palladium(0) complexes bearing a monodentate phosphine ligand and an N-heterocyclic carbene ligand have been prepared. In these complexes, photophysical properties of the complexes, [Pd(IPr)(PPh₃)] and [Pd(IPr)(P(o-tol)₃)] have been studied (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The emissive excited states have been tentatively assigned to ³MLCT. In addition to the results of the luminescent complexes, the synthesis of the related complexes, [Pd(O₂)(IPr)(P(m-tol)₃)] and [PdCl(CH₂Cl)(IPr)(P(MeOPh)₃)] (P(MeOPh)_3 = tris(pmethoxyphenyl)phosphine) have been studied and the structures were characterized by X-ray.     

Synthesis,characterization, and catalytic applications of Ru(III) complexes containing N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives and triphenylphosphine/triphenylarsine

Six coordinated ruthenium(III) complexes of the type [RuX₂(L)(PPh₃)₂] or [RuX₂(L)(AsPh₃)₂] {where L = N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives, X = Cl or Br} have been prepared by the reaction between [RuX₃(PPh₃)₃] or [RuX₃(AsPh₃)₃] (where X = Cl or Br) and N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives in toluene and characterized by elemental analysis, spectral data (electronic, IR and EPR) and magnetic moment studies. The complexes act as efficient catalysts for the oxidation of alcohols in presence of N-methylmorpholine-N-oxide as oxidant at room temperature.     

Iridium(III) complexes based on 5-nitro-2-(2′,4′-difluorophenyl)pyridyl: Syntheses,structures and photoluminescence properties

A series of cyclometalated Ir(III) complexes [Ir(dFNppy)₂(PPh₃)L] (PPh₃ = triphenylphosphine, L = Cl⁻, 1; NCS⁻, 2; NCO⁻, 3; N₃⁻, 4) in which 5-nitro-2-(2′,4′-difluorophenyl)pyridyl (dFNppy) is used as the main ligand are synthesized and characterized. The crystal structures of 3 and 4 are determined by X-ray diffraction analyses. Photoluminescence spectra of 1–4 in CH₂Cl₂ solutions at room temperature show the maximum emission wavelengths (λ_max) in the range from 586 to 627 nm, corresponding to red-orange luminescence. HOMO–LUMO energy levels of 1–4 are estimated by cyclic voltammetry measurements. Compared with corresponding 2-phenylpyridyl (ppy)-containing Ir(III) complexes having same ancillary ligands, 1–4 have obviously smaller HOMO–LUMO energy gaps (E_g). Simultaneously, 1–4 show relatively bigger E_g compared with 2-phenyl-5-nitropyridyl (5-NO₂-ppy)-containing Ir(III) complexes possessing same ancillary ligands. Methods of E_g adjustment are also discussed.     

Neutral Pd(II) and Ni(II) Acetylide Initiators for Polymerization of (Dimethylamino)ethyl Methacrylate

A series of air-stable, late transition, metal-based initiators with the structures ML₂(CCR)₂ (M=Pd and Ni; L=PPh₃ and Pn-Bu₃; R=Ph and CH₂OH) for the polymerization of (dimethylamino)ethyl methylate (DMAEMA) were developed. Transition metal, phosphine, alkynyl, as well as solvents exhibited significant influence on the polymerization. Among them, Pd(CCPh)₂(PPh₃)₂ (PPP) shows the highest activity in CHCl₃ for DMAEMA polymerization. The PDMAEMA obtained is a syndiotactic polymer with high number-average molecular weight (M_n) of 20.2 × 10⁴. A free radical polymerization mechanism with some ATRP characteristics was proposed for the present polymerization.     

NMR STUDY OF LANTHANIDE(III) NITRATE-CMPO EXTRACTION SYSTEM (II)MOLECULAR MOVEMENT OF CMPO AND La(III)(NO3) 3-CMPO COMPLEX AND LIGAND-EXCHANGE REACTION FOR Eu(III)-CMPO AND Gd(III)-CMPO SYSTEMS

ABSTRACT

NMR( Nuclear Magnetic Resonance ) measurements were car ried out to study the molecular movement of CMPO and La(III)(NO₃) _3? CMPO complex and the ligand-exchange reaction for Eu(III) and Gd(III)-CMPO systems. From the ¹³C relaxation time measurement of La(NO₃) ₃ 3CMPO it was found that the T₁ value for the isobutyl CH and CH₂ carbons and the carbonyl carbon became considerably shorter on complexation, indicating that the carbonyl group participates in the bonding between CMPO and La³⁺ ion as well as the phosphoryl group. The numbers of CMPO molecules coordinated to Eu³⁺ and Gd³⁺ ions in CDCl₃ solution were estimated to be 3 and 2, respectively, in the presence of excess CMPO. The activation parameters for the ligand-exchange reaction were evaluated to be ΔH^* = 37.8±1.9[kJ/mol],ΔS^* = -59.9±6.5[J/molk? K] and ΔH^* = 41.3±1.6[kJ/mol], ΔS^* = -44.1±5.3[J/mol-K] for Eu(III)-CMPO and Gd(III)-CMPO systems, respectively. The independence of the exchange rate constants on the concentration of CMPO indicates that these ligand-exchange reactions seem to proceed through either a dissociative ( D ) mechanism or an interchange dissociative ( Id ) mechanism characterized by a stability constant of outer-sphere complex( KQ ) ≥ 100.     

Lanthanide(III) 1,4-Phenylenediacetate Complexes: The Relation Between the Structure and Thermal Properties

The series of isostructural lanthanide coordination polymers with the empirical formula [Ln₂(PDA)₃(H₂O)]·2H₂O, where PDA = 1,4-phenylenediacetate anion = [C₈H₈(COO)₂]^2?; Ln = La-Lu(III), and Y(III) were produced in the reaction of LnCl₃·nH₂O with ammonium salt of 1,4-phenylenediacetic acid in water solution. The compounds were characterised structurally using powder X-ray diffraction, elemental and thermogravimetric analyses as well as FT-IR spectroscopy. Thermogravimetric analyses show that in the range 60–170 °C the dehydration process occurs. The thermal stability of dehydrated compounds, Ln₂(PDA)₃ increased from about 200–350 °C in the whole series of complexes. Single-crystal X-ray diffraction analysis for the Gd(III) complex revealed that the compound crystallizes in the monoclinic P2₁/c space group with a = 21.863(2) Å, b = 10.035(1) Å, c = 13.854(1) Å, β = 91.53(1)° and V = 3,038.5(4) ų. The complex contains one-dimensional gadolinium-carboxylato chains, which are connected with the –CH₂–C₆H₄–CH₂– spacers of PDA ligand to the three-dimensional metal–organic framework.     

Polymer/Trimer/Metal Complex Mixtures as Precursors of Gold Nanoparticles: Tuning the Morphology in the Solid-State

The pyrolysis of several physical mixtures of AuCl(PPh₃) with polymeric [NP(O₂C₁₂H₈)]_n or cyclic N₃P₃(O₂C₁₂H₈)₃ phosphazenes, formed as solid powders or films with different molar ratios, have been studied under air and at 800 °C. The characterization of the products has shown that the particle size and morphology are strongly dependent on the nature of the phosphazene, the phosphazene/AuCl(PPh₃) molar ratio and on the preparation methodology. Gold nanoparticles (NPs) with mean sizes as small as 3.5 nm were obtained from a [NP(O₂C₁₂H₈)]_n/AuCl(PPh₃) 1:1 film. The particle morphology was also strongly dependent on the experimentally conditions of the pyrolysis. Powdered materials exhibit a 3-D irregular morphology in the mixture [NP(O₂C₁₂H₈)]_n/AuCl(PPh₃) 3:1 film, and gold foams in the 1:1 ratio, both from the [NP(O₂C₁₂H₈)]_n/AuCl(PPh₃) as well as N₃P₃(O₂C₁₂H₈)₃/AuCl(PPh₃) mixtures. These results show for the first time the possibility of controlling morphology and size of gold particles obtained by solid-state reactions.     

Single‐Pot Ethane Carboxylation Catalyzed by New Oxorhenium(V) Complexes with N,O Ligands

The oxorhenium(V) chelates [ReOCl(N,O‐L)(PPh₃)] [N,O‐L=(OCH₂CH₂)N(CH₂CH₂OH)(CH₂COO) ( 2 ), (OCH₂CH₂)N(CH₂COO)(CH₂COOCH₃) ( 3 )] and [ReOCl₂(N,O‐L)(PPh₃)] [N,O‐L=C₅H₄N(COO‐2) ( 4 ) C₅H₃N(COOCH₃‐2)(COO‐6) ( 5 )] have been prepared by reaction of [ReOCl₃(PPh₃)₂] ( 1 ), in refluxing methanol, with N,N‐bis(2‐hydroxyethyl)glycine [bicine; N(CH₂CH₂OH)₂(CH₂COOH)], N‐(2‐hydroxyethyl)iminodiacetic acid [N(CH₂CH₂OH)(CH₂COOH)₂], picolinic acid [NC₅H₄(COOH‐2)] or 2,6‐pyridinedicarboxylic acid [NC₅H₃(COOH‐2,6)₂], respectively, with ligand esterification in the cases of 3 and 5 . All these complexes have been characterized by IR and multinuclear NMR spectroscopy, FAB⁺‐MS, elemental and X‐ray diffraction structural analyses. They act as catalysts, in a single‐pot process, for the carboxylation of ethane by CO, in the presence of potassium peroxodisulfate K₂S₂O₈, in trifluoroacetic acid (TFA), to give propionic and acetic acids, in a remarkable yield (up to ca. 30%) and under relatively mild conditions, with some advantages over the industrial processes. The picolinate complex 4 provides the most active catalyst and the carboxylation also occurs, although much less efficiently, by the TFA solvent in the absence of CO. The selectivity can be controlled by the ethane and CO pressures, propionic acid being the dominant product for pressures about ca. 7 and 4 atm, respectively (catalyst 4 ), whereas lower pressures lead mainly to acetic acid in lower yields. These reactions constitute an unprecedented use of Re complexes as catalysts in alkane functionalization.     

Hydrothermal synthesis and crystal structure of a new copper(II) molybdenum(VI) arsenate(III), (C5H5NH)2(H3O)2[(CuO6)Mo6O18(As3O3)2]

A new copper(II) molybdenum(VI) arsenate(III), (C₅H₅NH)₂(H₃O)₂[(CuO₆)Mo₆O₁₈(As₃O₃)₂], has been hydrothermally synthesized and characterized by single crystal X-ray diffraction and TG analysis. The compound crystallizes in the monoclinic space group P2₁/n with a=9.303(2), b=20.731(4), c=12.617(3) Å, β=104.17(3)°, V=2359.3(8) ų, Z=2 and R1(wR2)=0.0296(0.0683). The structure is composed of pyridinium cations, proton hydrates and [(CuO₆)Mo₆O₁₈(As₃O₃)₂]⁴⁻ polyanions. The polyanion framework derives from the Anderson type; the central octahedron is filled up by copper(II) and is capped on both sides by a cyclic As₃O₆ group.     

The redox pair {(μ4-TCNE)[Fe(CO)2(C5H5)]4}4+/3+: Surprisingly small metal–ligand interaction and the first resolved EPR hyperfine structure (13C, 14N, 57Fe) of a tetranuclear complex with TCNE−

Electrochemistry and absorption spectroscopy (UV/Vis, IR) of the complex {(μ₄-TCNE)[Fe(CO)₂(C₅H₅)]₄}(BF₄)₄ reveal only a small degree of metal-to-ligand π back donation, in contrast to previously characterized compounds [(TCNE)(ML_n)₄]. Accordingly, the one-electron reduced {(μ₄-TCNE)[Fe(CO)₂(C₅H₅)]₄}³⁺ exhibits a very well resolved EPR spectrum at g = 1.9965 with detectable coupling of 0.055 mT for ⁵⁷Fe in natural abundance from four coordinated [Fe(CO)₂(C₅H₅)]⁺ groups.