Structural studies and biological activity evaluation of Pd(II), Pt(II) and Ru(II) complexes containing N‐phenyl,N`‐(3‐triazolyl)thiourea

[MCl(H₂L)(OH₂)]·1.5H₂O (M = Pd(II) ( 1 ) and Pt(II) ( 2 )) and [Ru(H₂L)₂(OH₂)₂]·3H₂O ( 3 ) (H₃L: N‐phenyl, N`‐(3‐triazolyl)thiourea) were synthesized, characterized and tested for their antibacterial activities against Staphylococcus aureus and Escherichia coli bacteria. The thiourea derivative is coordinated to Mⁿ⁺ ions as a mono‐negatively N,S‐bidentate ligand via the enolization of C = S group and triazole N center. The density functional theory calculations reveal that presence of a water molecule in a trans position to triazole ring increased the stability of d⁸ metal ions complexes via the formation of strong Cl…NH intramolecular H‐bond. The cis‐Ru(II)‐isomer with two isoenergetically H₂L^? molecules are more stable than the trans‐analog. Coordination of H₃L to Ru(II) ion did not alter the toxicity of the free ligand, while the interaction with the d⁸ metal ions gave rise to inactive compounds.     

Copper Complexes with New Pyridylpyrazole Based Ligands

We report the synthesis, characterization, and crystal structures of new ligands of the pyridinylpyrazole type, i.e., 3,5‐bis(4‐butoxyphenyl)‐1‐(pyridin‐2‐yl)‐1H‐pyrazole ( L ¹ ) and 3,5‐bis(4‐phenoxyphenyl)‐1‐(pyridin‐2‐yl)‐1H‐pyrazole ( L ² ) (Scheme 1), and the study of their coordination behavior towards Cu^I and Cu^II. The versatility of this type of ligand, which can give access to different coordination spheres about the metal center, depending on the nature of the copper starting material used in the preparation of the complexes (Scheme 2), is illustrated. Thus, pseudo‐tetrahedral Cu^I as well as six‐coordinated tetragonal and distorted tetragonal pyramidal Cu^II derivatives were obtained for [Cu(L)₂]PF₆, [Cu(Cl)₂(L)₂] (L= L ¹ , L ² ), and [Cu(Cl)( L ¹ )₂]PF₆, respectively. We also present a crystallographic support of a distorted octahedral cis‐bis(tetrafluoroborato‐κF)copper(II) compound found for [Cu(BF₄)₂( L ¹ )₂] ( 3 ).     

New Rh(III) complexes of 5‐methyl‐5‐(pyridyl)‐2,4‐imidazolidenedione: Synthesis,X‐ray structure,electrochemical study and catalytic behaviour for hydrogenation of ketones

We describe the reaction of anion [RhCl₆]³⁻ with a series of hydantoin ligands (HL1, HL2 and HL3 = 5‐methyl‐5‐(2‐, 3‐ and 4‐pyridyl)‐2,4‐imidazolidenedione, respectively). Based on spectroscopic, cyclic voltammetric, elemental and MS analyses, the complexes have the general formula K[RhCl₂(L1)₂] ( 1 ), cis ‐ and trans ‐K[RhCl₄(HL2)₂] ( 2a and 2b ) and cis ‐ and trans ‐K[RhCl₄(HL3)₂] ( 3a and 3b ). Complexes 2a , 2b , 3a and 3b were characterized successfully using infrared, ¹H NMR and ¹³C NMR spectral analyses. Dissolution of complex 1 in dimethylsulfoxide (DMSO) led to elimination of one KL1 ligand and coordination of two DMSO molecules as ligands and transformation of this complex to cis ‐ and trans ‐[RhCl₂L1(DMSO)₂] ( 1a and 1b ). Recrystallization led to separation and isolation of crystals of 1a from the initial mixture. X‐ray analysis results showed that this complex was crystallized as solvated complex cis ‐[RhCl₂L1(DMSO)₂]DMSO. The catalytic activity of these complexes was then evaluated for the hydrogenation of various ketones.     

cis‐trans‐Isomerie bei (Me4Sb)2[Ph2Sb2I6]

cis‐trans‐Isomerism in (Me₄Sb)₂[Ph₂Sb₂I₆] Crystals of cis‐(Me₄Sb)₂[Ph₂Sb₂I₆] ( 1 a ) are formed by reaction of PhSbI₂ and Me₄SbI in ethanol/petroleum ether at –7 °C. In ethanol/acetone crystals of trans‐(Me₄Sb)₂[Ph₂Sb₂I₆] · acetone ( 1 b ) form. The X‐ray crystal structure analyses reveal that both isomers consist of tetrahedral cations and of dimeric anions with the geometry of two edge sharing tetragonal pyramids. The phenyl groups possess apical cis ( 1 a ) or trans ( 1 b ) positions relative to the I₂SbI₂SbI₂ plane. The acetone molecules in 1 b are non coordinating.     

Thiolato-technetium complexes. 4(1): Synthesis,characterization and electrochemical properties of bis(1,2-bis(dimethylphosphino)-ethane)technetium(III) complexes with arene-thiolato ligands

Summary The reaction of trans-[Tc^v(OH)(O)(DMPE)₂]²⁺ (DMPE = 1,2-bis(dimethylphosphino)ethane) with a series of arenethiols in base produces the novel complexes cis-[Tc^III-(SC₆H₄X-p)₂ (DMPE)₂]⁺ for X = H, Cl, Me, OMe, t-Bu. One of the complexes has been characterized by X-ray crystallography: cis-[Tc(SPh)₂(DMPE)₂]PF₆, chemical formula Tc₁S₂P₅F₆C₂₄H₄₂, crystallizes in the orthorhombic space group P2₁nb with Z = 4 and lattice parameters a = 9.311(1) Å, b=11.190(2) Å, c = 31.936(4) Å, Vol = 3327.3(8) ų. The final weighted R-value was 0.033. Averaged structural parameters are Tc—S = 2.29(2) Å, Tc—P (trans to P) = 2.42(1) Å, Tc—P (trans to S) = 2.49(3) Å, Tc—S—C = 118.5(5)°. The complexes have been characterized by FAB mass spectrometry and u.v.-vis. spectroscopy. The visible region charge transfer bands are diagnostic for cis geometry in the [Tc(SR)₂(DMPE)₂]⁺ complexes. Electrochemical and spectroelectrochemical measurements show reversible Tc^III/II redox couples in the range -0.19V to -0.38V versus Ag/AgCl (3 M NaCl). Irreversible couples are exhibited at ca. -1.1 V to -1.2 V for Tc^II/I and +0.7V to +0.9V for Tc^IV/III. Variation in redox potential is discussed in terms of sulphur nucleophilicity.On leave from the Department of Chemistry, The University of Tsukuba, Tsukuba, Ibaraki 305, Japan.On leave from Dipartimento di Chimica dell'Universita' di Sassari, Via Vienna, 2-Sassari, Italy.     

Synthesis,Structure and Characterization of Two Novel Mercury(II) Complexes with N‐(2‐aminoethyl)piperazine

Two novel mercury(II) complexes [Hg^II(μ₂‐LH)Cl₂]₂[Hg^II₂(μ₂‐Cl)₂Cl₄]·2H₂O ( 1 ) and [Hg^II₄(μ₂‐L)₂(μ₂‐Cl)₂Cl₆] ( 2 ) have been synthesized by the reaction of N‐(2‐aminoethyl)piperazine (L) with HgCl₂ under different pH conditions. 1 and 2 were characterized by single‐crystal X‐ray diffraction analysis. The results reveal that in 1 there exist discrete mononuclear [Hg^II(μ₂‐LH)Cl₂]⁺ units and binuclear [Hg^II₂(μ₂‐Cl)₂Cl₄]²⁺ unit while in 2 there exist the rarely reported discrete cylic tetranuclear [Hg^II₄(μ₃‐L)₂(μ₂‐Cl)₂Cl₆] cluster units, which are both assembled into 3D supramolecular structures via extensive hydrogen‐bonding interactions. 1 and 2 were also characterized by element analysis, FT‐IR and luminescence spectra.     

Four supramolecular isomers of dichloridobis(1,10‐phenanthroline)cobalt(II): synthesis,structure characterization and isomerization

Crystal engineering can be described as the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding to design new solids with desired physical and chemical properties. Free‐energy differences between supramolecular isomers are generally small and minor changes in the crystallization conditions may result in the occurrence of new isomers. The study of supramolecular isomerism will help us to understand the mechanism of crystallization, a very central concept of crystal engineering. Two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II), [CoCl₂(C₁₂H₈N₂)₂], i.e. (IA) (orthorhombic) and (IB) (monoclinic), and two supramolecular isomers of dichloridobis(1,10‐phenanthroline‐κ²N,N′)cobalt(II) N,N‐dimethylformamide monosolvate, [CoCl₂(C₁₂H₈N₂)₂]·C₃H₇NO, i.e. (IIA) (orthorhombic) and (IIB) (monoclinic), were synthesized in dimethylformamide (DMF) and structurally characterized. Of these, (IA) and (IIA) have been prepared and structurally characterized previously [Li et al. (2007). Acta Cryst. E 63 , m1880–m1880; Cai et al. (2008). Acta Cryst. E 64 , m1328–m1329]. We found that the heating rate is a key factor for the crystallization of (IA) or (IB), while the temperature difference is responsible for the crystallization of (IIA) or (IIB). Based on the crystallization conditions, isomerization behaviour, the KPI (Kitajgorodskij packing index) values and the density data, (IB) and (IIA) are assigned as the thermodynamic and stable kinetic isomers, respectively, while (IA) and (IIB) are assigned as the metastable kinetic products. The 1,10‐phenanthroline (phen) ligands interact with each other through offset face‐to‐face (OFF) π–π stacking in (IB) and (IIB), but by edge‐to‐face (EF) C—H...π interactions in (IA) and (IIA). Meanwhile, the DMF molecules in (IIB) connect to neighbouring [CoCl₂(phen)₂] units through two C—H...Cl hydrogen bonds, whereas there are no obvious interactions between DMF molecules and [CoCl₂(phen)₂] units in (IIA). Since OFF π–π stacking is generally stronger than EF C—H...π interactions for transition‐metal complexes with nitrogen‐containing aromatic ligands, (IIA) is among the uncommon examples that are stable and densely packed but that do not following Etter's intermolecular interaction hierarchy.     

Guest‐, Light‐ and Thermally‐Modulated Spin Crossover in [FeII2] Supramolecular Helicates

A new bis(pyrazolylpyridine) ligand (H₂L) has been prepared to form functional [Fe₂(H₂L)₃]⁴⁺ metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe₂(H₂L)₃]X(PF₆)₂?xCH₃OH ( 1 , x=5.7 and X=Cl; 2 , x=4 and X=Br), X@[Fe₂(H₂L)₃]X(PF₆)₂?yCH₃OH?H₂O ( 1 a , y=3 and X=Cl; 2 a , y=1 and X=Br) and X@[Fe₂(H₂L)₃](I₃)₂?3 Et₂O ( 1 b , X=Cl; 2 b , X=Br). Their structure and functional properties are described in detail by single‐crystal X‐ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2 , respectively, by a single‐crystal‐to‐single‐crystal mechanism. The three possible magnetic states, [LS–LS], [LS–HS], and [HS–HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe^II centers. The nature of the guest (Cl^? vs. Br^?) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS–HS] or [HS–HS] states are generated through irradiation. All helicates (X@[Fe₂(H₂L)₃])³⁺ persist in solution.     

Highly Active,Low‐Valence Molybdenum‐ and Tungsten‐Amide Catalysts for Bifunctional Imine‐Hydrogenation Reactions

The reactions of [M(NO)(CO)₄(ClAlCl₃)] (M=Mo, W) with (iPr₂PCH₂CH₂)₂NH, (PN^HP) at 90 °C afforded [M(NO)(CO)(PN^HP)Cl] complexes (M=Mo, 1a ; W, 1b ). The treatment of compound 1a with KOtBu as a base at room temperature yielded the alkoxide complex [Mo(NO)(CO)(PN^HP)(OtBu)] ( 2a ). In contrast, with the amide base Na[N(SiMe₃)₂], the PN^HP ligand moieties in compounds 1a and 1b could be deprotonated at room temperature, thereby inducing dehydrochlorination into amido complexes [M(NO)(CO)(PNP)] (M=Mo, 3a ; W, 3b ; PNP=(iPr₂PCH₂CH₂)₂N)). Compounds 3a and 3b have pseudo‐trigonal‐bipyramidal geometries, in which the amido nitrogen atom is in the equatorial plane. At room temperature, compounds 3a and 3b were capable of adding dihydrogen, with heterolytic splitting, thereby forming pairs of isomeric amine‐hydride complexes [Mo(NO)(CO)H(PN^HP)] ( 4a(cis) and 4a(trans) ) and [W(NO)(CO)H(PN^HP)] ( 4b(cis) and 4b(trans) ; cis and trans correspond to the position of the H and NO groups). H₂ approaches the Mo/W?N bond in compounds 3a , 3b from either the CO‐ligand side or from the NO‐ligand side. Compounds 4a(cis) and 4a(trans) were only found to be stable under a H₂ atmosphere and could not be isolated. At 140 °C and 60 bar H₂, compounds 3a and 3b catalyzed the hydrogenation of imines, thereby showing maximum turnover frequencies (TOFs) of 2912 and 1120 h^?1, respectively, for the hydrogenation of N‐(4 ‐ methoxybenzylidene)aniline. A Hammett plot for various para‐substituted imines revealed linear correlations with a negative slope of ?3.69 for para substitution on the benzylidene side and a positive slope of 0.68 for para substitution on the aniline side. Kinetics analysis revealed the initial rate of the hydrogenation reactions to be first order in c(cat.) and zeroth order in c(imine). Deuterium kinetic isotope effect (DKIE) experiments furnished a low k_H/k_D value (1.28), which supported a Noyori‐type metal–ligand bifunctional mechanism with H₂ addition as the rate‐limiting step.     

The Reaction of Cs2[Tc(NO)F5] with BF3 in Acetonitrile: Formation and Structure of [{Tc(NO)(CH3CN)4}2(μ‐F)](BF4)3

The deep blue, paramagnetic Cs₂[Tc^II(NO)F₅] is formed during reactions of pertechnetate, acetohydroxamic acid, and CsF in aqueous HF. A reaction of Cs₂[Tc(NO)F₅] with BF₃ · MeOH in acetonitrile gives yellow blocks of the fluorido‐bridged dimer [{Tc^I(NO)(CH₃CN)₄}₂F](BF₄)₃. The compound is stable as solid and in acetonitrile solutions. The complex cation contains a bent μ‐F^– ligand and two linear nitrosyl groups.     

Preparation and Characterization of Dinuclear Chromium(III) Complexes of a Hexadentate Tetraaza‐Dithiophenolate Ligand

The ability of the tetraaza‐dithiophenolate ligand H₂L² (H₂L² = N,N′‐Bis‐[2‐thio‐3‐aminomethyl‐5‐tert‐butyl‐benzyl]propane‐1,3‐diamine) to form dinuclear chromium(III) complexes has been examined. Reaction of Cr^IICl₂ with H₂L² in methanol in the presence of base followed by air‐oxidation afforded cis,cis‐[(L²)Cr^III₂(μ‐OH)(Cl)₂]⁺ ( 1a ) and trans,trans‐[(L²)Cr^III₂(μ‐OH)(Cl)₂]⁺ ( 1b ). Both compounds contain a confacial bioctahedral N₂ClCr^III(μ‐SR)₂(μ‐OH)Cr^IIIClN₂ core. The isomers differ in the mutual orientation of the coligands and the conformation of the supporting ligand. In 1a both Cl^? ligands are cis to the bridging OH function. In 1b they are in trans‐positions. Reaction of the hydroxo‐bridged complexes with HCl yielded the chloro‐bridged cations cis,cis‐[(L²)Cr^III₂(μ‐Cl)(Cl)₂]⁺ ( 2a ) and trans,trans‐[(L²)Cr^III₂(μ‐Cl)(Cl)₂]Cl ( 2b ), respectively. These bridge substitutions proceed with retention of the structures of the parent complexes 1a and 1b .     

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

The synthesis of the reactive PN(C^H) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine ( 1^H ) and its versatile coordination to a Rh^I center is described. Facile C?H activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [Rh^I(CO)(κ³‐P,N,C‐ 1 )] ( 3 ), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D₁]formic acid. The addition of HBF₄ to 3 leads to rapid net protonolysis of the Rh?C bond to produce [Rh^I(CO)(κ³‐P,N,(C?H)‐ 1 )] ( 4 ). This species features a rare aryl C?H agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [Rh^I(CO)(κ²‐P,N‐ 1^Me )] ( 5 ). Variable‐temperature NMR spectroscopy indicates the involvement of a Rh^III intermediate through formal oxidative addition to give trans‐[Rh^III(CH₃)(CO)(I)(κ³‐P,N,C‐ 1 )] prior to C?C reductive elimination. The Rh^III–trans‐diiodide complex [Rh^I(CO)(I)₂(κ³‐P,N,C‐ 1 )] ( 6 ) has been structurally characterized as a model compound for this elusive intermediate.     

Three Silver(I) Coordination Polymers Constructed from Flexible Bis(benzimidazole) and Carboxylates Ligands

Under hydrothermal conditions, three new Ag^I coordination polymers, [Ag(L1)(Hmip)]_n ( 1 ), [Ag(L2)_0.5(ndc)_0.5]_n ( 2 ), and {[Ag(L3)_0.5(Htbi)] · 0.25H₂O}_n ( 3 ) [H₂mip = 5‐methylisophthalic acid, L1 = 1,4‐bis(2‐methylbenzimidazol‐1‐ylmethyl)benzene, H₂ndc = 2,6‐naphthalenedicarboxylic acid, L2 = 1,3‐bis(2‐methylbenzimidazol‐1‐ylmethyl)benzene, H₂tbi = 5‐tert‐butyl isophthalic acid, L3 = 1,4‐bis(5,6‐dimethylbenzimidazole)butane] were synthesized by employing flexible bis(benzimidazole) and dicarboxylic acid ligands. Polymer 1 displays a 2D 4‐connected 4L2 underlying net topology with the point symbol of (6⁵.8) in standard representation. Compound 2 possesses a 2D uninodal 4‐connected Shubnikov tetragonal plane net (sql) based on a dinuclear Ag^I clusters with the point symbol (4⁴.6²), which is further extended into a 3D supramolecular framework by π–π interactions. Compound 3 possesses dinuclear molecular complex groups, which form chains by weak Ag–O (2.6 Å) coordination bonds, and further assembled into a 2D supramolecular layer by hydrogen bonds and π–π stacking interactions. These complexes exhibit intense fluorescent emissions in solid state. UV/Vis diffuse reflection spectra and the excellent catalytic activity for the degradation of the congo red azo dye in a Fenton‐like process are discussed.     

Gold(I) and Gold(III) Trifluoromethyl Derivatives

Trifluoromethylation of AuCl₃ by using the Me₃SiCF₃/CsF system in THF and in the presence of [PPh₄]Br proceeds with partial reduction, yielding a mixture of [PPh₄][Au^I(CF₃)₂] ( 1′ ) and [PPh₄][Au^III(CF₃)₄] ( 2′ ) that can be adequately separated. An efficient method for the high‐yield synthesis of 1′ is also described. The molecular geometries of the homoleptic anions [Au^I(CF₃)₂]^? and [Au^III(CF₃)₄]^? in their salts 1′ and [NBu₄][Au^III(CF₃)₄] ( 2 ) have been established by X‐ray diffraction methods. Compound 1′ oxidatively adds halogens, X₂, furnishing [PPh₄][Au^III(CF₃)₂X₂] (X=Cl ( 3 ), Br ( 4 ), I ( 5 )), which are assigned a trans stereochemistry. Attempts to activate C? F bonds in the gold(III) derivative 2′ by reaction with Lewis acids under different conditions either failed or only gave complex mixtures. On the other hand, treatment of the gold(I) derivative 1′ with BF₃?OEt₂ under mild conditions cleanly afforded the carbonyl derivative [Au^I(CF₃)(CO)] ( 6 ), which can be isolated as an extremely moisture‐sensitive light yellow crystalline solid. In the solid state, each linear F₃C‐Au‐CO molecule weakly interacts with three symmetry‐related neighbors yielding an extended 3D network of aurophilic interactions (Au???Au=345.9(1) pm). The high $\tilde \nu $ _CO value (2194 cm^?1 in the solid state and 2180 cm^?1 in CH₂Cl₂ solution) denotes that CO is acting as a mainly σ‐donor ligand and confirms the role of the CF₃ group as an electron‐withdrawing ligand in organometallic chemistry. Compound 6 can be considered as a convenient synthon of the “Au^I(CF₃)” fragment, as it reacts with a number of neutral ligands L, giving rise to the corresponding [Au^I(CF₃)(L)] compounds (L=CNtBu ( 7 ), NCMe ( 8 ), py ( 9 ), tht ( 10 )).     

Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO)3M(H2O)] (M = Mn, Tc, Re)

In this review ligand exchange and complex formation reactions on fac-[(CO)₃M(H₂O)₃]⁺ (M = Mn, Tc, Re) and on fac-[(CO)₂(NO)Re(H₂O)₃]²⁺ are presented. A variety of experimental NMR techniques are described and it is shown that sometimes combinations of techniques applied at variable temperature or variable pressure allowed to measure exchange rate constants and their activation parameters as well as thermodynamic parameters. Furthermore, the use of uncommon nuclei for NMR like ¹⁷O or ⁹⁹Tc extends considerably the range of applications especially in aqueous solutions when ¹H NMR is often not very useful.Tricarbonyl triaqua complexes of technetium(I) and rhenium(I) became important precursors for a variety of radiopharmaceuticals under development. It has been shown that the fac-[(CO)₃M]-unit is kinetically inert and that water molecules bound to it can be easily replaced. Reactivity of the Re^I complexes is one to two orders of magnitude slower than its Tc^I analogues. Furthermore, it shows a marked acidity dependence which has not been observed for Tc^I and Mn^I species.     

Electrochemical Investigations Give Some Insights into the Coordination Chemistry of New Stable Iridium(+1), Iridium(0), and Iridium(−1) Complexes

The redox chemistry of the stable tetracoordinated 16 valence electron d⁸‐[Ir^+I(tropp^Ph)₂]⁺(PF₆)^? and pentacoordinated 18 valence d⁸‐[Ir^+I(tropp^Ph)₂Cl] complexes was investigated by cyclic voltammetry (tropp^Ph=dibenzotropylidenyl phosphine). The experiments were performed using a platinum microelectrode varying scan rates (100 mV/s–10 V/s) and temperatures (? 40 to 20 °C) in tetrahydrofuran, THF, or acetonitrile, ACN, as solvents. In THF, the overall two‐electron reduction of the 16 valence electron d⁸‐[Ir^+I(tropp^Ph)₂]⁺(PF₆)^? proceeds in two well separated slow heterogeneous electron transfer steps according to: d⁸‐[Ir^+I (tropp^Ph)₂]⁺+e^?→d⁹‐[Ir⁰(tropp^Ph)₂]+e^?→d¹⁰‐[Ir^?I(tropp^Ph)₂]^?, [k^s₁=2.2×10^?3 cm/s for d⁸‐Ir^+I/d⁹‐Ir⁰ and k^s₂=2.0×10^?3 cm/s for d⁹‐Ir⁰/d¹⁰‐Ir^?I]. In ACN, the two redox waves merge into one “two‐electron” wave [k^s_1,2=7.76×10^?4 cm/s for d⁸‐Ir^+I/d⁹‐Ir⁰ and d⁹‐Ir⁰/d¹⁰‐Ir^?I] most likely because the neutral [Ir⁰(tropp^Ph)₂] complex is destabilized. At low temperatures (ca. ? 40 °C) and at high scan rates (ca. 10 V/s), the two‐electon redox process is kinetically resolved. In equilibrium with the tetracoordianted complex [Ir^+I(tropp^Ph)₂]⁺ are the pentacoordinated 18 valence [Ir^+I(tropp^Ph)₂L]⁺ complexes (L=THF, ACN, Cl^?) and their electrochemical behavior was also investigated. They are irreversibly reduced at rather high negative potentials (? 1.8 to ? 2.4 V) according to an ECE mechanism 1) [Ir^+I(tropp^Ph)₂(L)]+e^?→[Ir⁰(tropp^Ph)₂(L)]; 2) [Ir⁰(tropp^Ph)₂(L)]→[Ir(tropp^Ph)₂]+L, iii) [Ir⁰(tropp^Ph)₂]+e^?→[Ir^?I(tropp^Ph)₂]^?. Since all electroactive species were isolated and structurally characterized, our measurements allow for the first time a detailed insight into some fundamental aspects of the coordination chemistry of iridium complexes in unusually low formal oxidation states.     

Synthesis,spectroscopic, DFT,biological studies and molecular docking of oxovanadium (IV), copper (II) and iron (III) complexes of a new hydrazone derived from heterocyclic hydrazide

A new Schiff base hydrazone (Z)‐2‐(2‐aminothiazol‐4‐yl)‐N′‐(2‐hydroxy‐3‐methoxybenzylidene) acetohydrazide (H₂L) and its chelates [VO (HL)₂]·5H₂O, [Cu (HL)Cl(H₂O)]·2H₂O and [Fe(L)Cl(H₂O)₂]·3H₂O have been isolated and characterized using different physico‐chemical methods, for example infrared (IR), electron paramagnetic resonance (EPR), thermogravimetric analysis and DTG in the solid state, and ¹H‐NMR, ¹³C‐NMR and UV in solution. Magnetic and UV–visible measurements proposed that the coordination environments are square pyramidal, tetrahedral and octahedral geometries for oxovanadium (IV), Cu (II) and Fe (III), respectively. The ligand acts as mono‐negative NO towards oxovanadium (IV) and Cu (II) ions, and bi‐negative ONO for Fe (III) ion. The geometries of the ligand and its complexes were performed using Gaussian 9 program with density functional theory. The EPR spectral data of oxovanadium (IV) and Cu (II) chelates confirmed the mentioned geometries. The molecular modeling was done, and illustrated bond lengths, bond angles, molecular electrostatic potential, Mulliken atomic charges and chemical reactivity for the inspected compounds. Theoretical IR and ¹H‐NMR of the free ligand were calculated. Furthermore, thermodynamic and kinetic parameters for thermal decomposition steps were studied. Docking study of H₂L was applied against the proteins of both bacterial strains Staphylococcus aureus and Escherichia coli, as well as the protein of xanthine oxidase as antioxidant agent by Schrödinger suite program utilizing XP glide protocol. Furthermore, antimicrobial, antioxidant and DNA‐binding activities of the compounds have been carried out.     

Coordination Behavior of a D‐Penicillaminato Aurate(I) Metalloligand Toward Coblat(III) Centers

Treatment of (NH₄)[Au(D‐Hpen‐S)₂](D‐H₂pen = D‐penicillamine) with CoCl₂·6H₂O in an acetate buffer solution, followed by air oxidation, gave neutral Au^ICo^III and anionic Au^I₃Co^III₂ polynuclear complexes, [Au₃Co₃(D‐pen‐N,O,S)₆]([ 1 ]) and [Au₃Co₂(D‐pen‐N,S)₆]^3? ([ 2 ]^3?), which were separated by anion‐exchange column chromatography. Complexes [ 1 ] and [ 2 ]^3? each formed a single isomer, and their structures were determined by single‐crystal X‐ray crystallography. In [ 1 ], each of three [Au(D‐pen‐S)₂]^3?metalloligands coordinates to two Co^III ions in a bis‐tridentate‐N,O,S mode to form a cyclic Au^I₃Co^III₃ hexanuclear structure, in which three [Co(D‐pen‐N,O,S)₂]^? octahedral units and six bridging S atoms adopt trans(O) geometrical and R chiral configurations, respectively. In [ 2 ]^3?, each of three [Au(D‐pen‐S)₂]^3? metalloligands coordinates to two Co^III ions in a bis‐bidentate‐N,S mode to form a Au^I₃Co^III₂ pentanuclear structure, in which two [Co(D‐pen‐N,S)₃]^3? units and six bridging S atoms adopt ∧ and R chiral configurations, respectively.     

Reactivity of [M2(μ‐Cl)2(cod)2] (M=Ir,Rh) and [Ru(Cl)2(cod)(CH3CN)2] with Na[H2B(bt)2]: Formation of Agostic versus Borate Complexes

Treatment of [M₂(μ‐Cl)₂(cod)₂] (M=Ir and Rh) with Na[H₂B(bt)₂] (cod=1,5‐cyclooctadiene and bt=2‐mercaptobenzothiazolyl) at low temperature led to the formation of dimetallaheterocycles [(Mcod)₂(bt)₂], 1 and 2 ( 1 : M=Ir and 2 : M=Rh) and a borate complex [Rh(cod){κ²‐S,S′‐H₂B(bt)₂}], 3 . Compounds 1 and 2 are structurally characterized metal analogues of 1,5‐cyclooctadiene. Metal–metal bond distances of 3.6195(9) Å in 1 and 3.6749(9) Å in 2 are too long to consider as bonding. In an attempt to generate the Ru analogue of 1 and 2 , that is [(Rucod)₂(bt)₂], we have carried out the reaction of [Ru(Cl)₂(cod)(CH₃CN)₂] with Na[H₂B(bt)₂]. Interestingly, the reaction yielded agostic complexes [Ru(cod)L{κ³‐H,S,S′‐H₂B(bt)₂}], 4 and 5 ( 4 : L=Cl; 5 : L=C₇H₄NS₂). One of the key differences between 4 and 5 is the presence of different ancillary ligands at the metal center. The natural bond orbital (NBO) analysis of 1 and 2 shows that there is four lone pairs of electrons on each metal center with a significant amount of d character. Furthermore, the electronic structures and the bonding of these complexes have been established on the ground of quantum‐chemical calculations. All of the new compounds were characterized by IR, ¹H, ¹¹B, ¹³C NMR spectroscopy, and X‐ray crystallographic analysis.     

Facile Synthetic Access to Rhenium(II) Complexes: Activation of Carbon–Bromine Bonds by Single‐Electron Transfer

The five‐coordinated Re^I hydride complexes [Re(Br)(H)(NO)(PR₃)₂] (R=Cy 1 a , iPr 1 b ) were reacted with benzylbromide, thereby affording the 17‐electron mononuclear Re^II hydride complexes [Re(Br)₂(H)(NO)(PR₃)₂] (R=Cy 3 a , iPr 3 b ), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded Re^II hydrides 3 in addition to Re^I carbene hydrides [Re(?CHR¹)(Br)(H)(NO)(PR₃)₂] (R¹=H 4 , Br 5 ; R=Cy a , iPr b ) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re^I dibromide complexes [Re(Br)₂(NO)(PR₃)₂(η²‐H₂)] (R=Cy 2 a , iPr 2 b ) were reacted with allyl‐ or benzylbromide, thereby affording the monophosphine Re^II complex salts [R₃PCH₂R′][Re(Br)₄(NO)(PR₃)] (R′=? CH?CH₂ 6 , Ph 7 ). The reduction of Re^II complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h^?1) or allylbromide (TOF: 3 a 575, 3 b 562 h^?1). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re^I complexes [Re(Br)₂(NO)(MeCN)₂(PR₃)] (R=Cy 8 a , iPr 8 b ), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h^?1). Single‐electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a , 6 a , 6 b , 7 a , 7 b , and 8 a were established by single‐crystal X‐ray diffraction studies.