Silver(I) acetylides stabilized by η-alkynes: Synthesis, reaction chemistry and solid state structures

Individual synthetic routes to heterobimetallic Ti(IV)-Ag(I) acetylides of type {[Ti](μ-σ,π-CCR¹)₂}AgCCR² ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti: R¹ = SiMe₃: 6, R² = SiMe₃; 7, R² = Ph. R¹ = ^tBu: 8, R² = SiMe₃; 9, R² = Ph. [Ti] = (η⁵-C₅H₅)₂Ti): 10, R¹ = ^tBu, R² = SiMe₃) including (i) the reaction of {[Ti](μ-σ, π-CCR¹)₂}AgNO₃ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti): 1, R¹ = SiMe₃; 2, R¹ = ^tBu. [Ti] = (η⁵-C₅H₅)₂Ti: 3, R¹ = ^tBu) with LiCCR² (4, R² = SiMe₃; 5, R² = Ph) and (ii) treatment of [Ti](CCSiMe₃)₂ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) (11) with [AgCCR²] (12, R² = SiMe₃; 13, R² = Ph) are described. The reactions of 1-3 with 4 or 5 appeared to be sensitive towards stoichiometry because an excess of 4 or 5 resulted in the formation of [(Ag(CCR²)₂)Li(OEt₂)]_n (14) and [Ti](CCR¹)₂. Coordination polymer 14 is also accessible, when, for example, [AgCCSiMe₃] (12) is treated with 1 eq. of LiCCSiMe₃ (4) in diethyl ether.The titanium(IV)-silver(I) acetylides 6-10 are stable in the dark and at low temperature, while on exposure to light and on heating they decompose to give R²CC-CCR² together with [Ti](CCR¹)₂ and elemental silver.Complexes 6-10 contain a mono-nuclear AgCCR² entity stabilized by the chelate-bonded organometallic π-tweezer molecule [Ti](CCSiMe₃)₂, which was evinced by structure determination of 7 in the solid state. In 14 linear [Me₃SiCC-Ag-CCSiMe₃]⁻ units are connected by [Li(OEt₂)]⁺ building blocks forming a coordination polymer.     

Probing valence and spin situations in selective ruthenium-iminoquinonoid frameworks. An experimental and DFT analysis

The ruthenium-iminoquinone complexes, [Ru(tpm)(Cl)(Q)]⁺ [tpm = tris(1-pyrazolyl)methane, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl = C₆H₅, [1]⁺; m-(OCH₃)₂C₆H₃, [2]⁺; m-(Cl)₂C₆H₃, [3]⁺] have been synthesized. The sensitive bond distances of “Q” in [1](ClO₄) and [2](ClO₄), C-O: 1.294(8), 1.281(2) Å; C-N: 1.352(8), 1.335(2) Å; and C-C(meta): 1.366(10)/1.367(9) Å, 1.364(2)/1.353(2) Å, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [Ru^III(tpm)(Cl)(Q_Sq⁻)]⁺ for [1]⁺-[3]⁺. The paramagnetic [1]⁺-[3]⁺ show sharp ¹H NMR spectra with strikingly small J of 1.8-3.0 Hz. The DFT calculations on [1]⁺ predict that the triplet (S = 1) state exists above (1004 cm⁻¹) the singlet (S = 0) ground state. [1]⁺ exhibits μ = 2.2 BM at 300 K which diminishes to 0.3 BM near 2 K due to the steady decrease in the ratio of triplet to singlet population with the lowering of temperature. [1]⁺-[3]⁺ exhibit one oxidation and two successive reductions each in CH₃CN. Experimental and DFT analyses collectively establish the valence configurations at the non-innocent {Ru-Q} interface along the redox chain as [(tpm)(Cl)Ru^III(Q_Q^o)]²⁺ ([1]²⁺-[3]²⁺) → [(tpm)(Cl)Ru^III(Q_Sq⁻)]⁺ ([1]⁺-[3]⁺) → [(tpm)(Cl)Ru^II(Q_Sq⁻)] ↔ [(tpm)(Cl)Ru^III(Q_Cat)] (1-3) → [(tpm)(Cl)Ru^II(Q_Cat)]⁻ ([1]⁻-[3]⁻). The spectral features of [1]ⁿ-[3]ⁿ (n = +2, +1, 0) have been addressed based on the TD-DFT calculations on [1]ⁿ.     

Bis(acetylacetonato)ruthenium(II) complexes containing bulky tertiary phosphines. Formation and redox behaviour of Ru(acac)2 (PR3) (R = Pr, Cy) complexes with ethene, carbon monoxide, and bridging dinitrogen

Reaction of cis-[Ru(acac)₂(η²-C₈H₁₄)₂] (1) (acac = acetylacetonato) with two equivalents of PⁱPr₃ in THF at −25 °C gives trans-[Ru(acac)₂(PⁱPr₃)₂], trans-3, which rapidly isomerizes to cis-3 at room temperature. The poorly soluble complex [Ru(acac)₂(PCy₃)₂] (4), which is isolated similarly from cis-[Ru(acac)₂(η²-C₂H₄)₂] (2) and PCy₃, appears to exist in the cis-configuration in solution according to NMR data, although an X-ray diffraction study of a single crystal shows the presence of trans-4. In benzene or toluene 2 reacts with PⁱPr₃ or PCy₃ to give exclusively cis-[Ru(acac)₂(η²-C₂H₄)(L)] [L = PⁱPr₃ (5), PCy₃ (6)], whereas in THF species believed to be either square pyramidal [Ru(acac)₂L], with apical L, or the corresponding THF adducts, can be detected by ³¹P NMR spectroscopy. Complexes 3-6 react with CO (1 bar) giving trans-[Ru(acac)₂(CO)(L)] [L = PⁱPr₃ (trans-8), PCy₃ (trans-9)], which are converted irreversibly into the cis-isomers in refluxing benzene. Complex 5 scavenges traces of dinitrogen from industrial grade dihydrogen giving a bridging dinitrogen complex, cis-[{Ru(acac)₂(PⁱPr₃)} ₂(μ-N₂)] (10). The structures of cis-3, trans-4, 5, 6 and 10 · C₆H₁₄ have been determined by single-crystal X-ray diffraction. Complexes trans- and cis-3, 5, 6, cis-8, and trans- and cis-9 each show fully reversible one-electron oxidation by cyclic voltammetry in CH₂Cl₂ at −50 °C with E_1/2(Ru^3+/2+) values spanning −0.14 to +0.92 V (versus Ag/AgCl), whereas for the vinylidene complexes [Ru(acac)₂ (CCHR)(PⁱPr₃)] [R = SiMe₃ (11), Ph (12)] the process is irreversible at potentials of +0.75 and +0.62 V, respectively. The trend in potentials reflects the order of expected π-acceptor ability of the ligands: PⁱPr₃, PCy₃ <C ₂H₄ < CCHR < CO. The UV-Vis spectrum of the thermally unstable, electrogenerated Ru^III-ethene cation 6⁺ has been observed at −50 °C. Cyclic voltammetry of the μ-dinitrogen complex 10 shows two, fully reversible processes in CH₂Cl₂ at −50 °C at +0.30 and +0.90 V (versus Ag/AgCl) corresponding to the formation of 10⁺ (Ru^II,III) and 10²⁺ (Ru^III,III). The former, generated electrochemically at −50 °C, shows a band in the near IR at ca. 8900 cm⁻¹ (w_1/2 ca. 3700 cm⁻¹) consistent with the presence of a valence delocalized system. The comproportionation constant for the equilibrium 10 + 10²⁺ ? 2 10⁺ at 223 K is estimated as 10^13.6.     

Copper complexes of tripodal κN-donor ligands: A structural, EPR spectroscopic and electrochemical study

A new tris(pyridylhydrazonyl)methane ligand, HC[N(Me)NC(H)Py]₃ (L2) (Py = pyridyl), has been synthesized. The latter is accessible from triethyl orthoformate and 2-(2-methylhydrazono)methylpyridine in 63% isolated yield. We have investigated its coordination chemistry towards copper ions and compared the results with those obtained for the recently developed multifunctional ligand, (S)P[N(Me)NC(H)Py]₃ (L1). The copper(II) complexes [Cu(L1)](OTf)₂ (3) and [Cu(L2)](OTf)₂ (4) (OTf = triflate, (O₃SCF₃)⁻) are mononuclear with the cations coordinated by three imino and three pyridine nitrogen atoms. Almost axial symmetric EPR spectra have been obtained in frozen solutions at X-band. The spectra show resolved hyperfine couplings to the copper nuclei on one of the three g values. X-ray structural analyses revealed in each case a cis bond distortion and a trigonal twist due to Jahn-Teller effects. The Cu^II/Cu^I reduction potentials of 3 and 4 were shown to be remarkably low ( = −0.11 V for 3;  = −0.34 V for 4), especially for 3 consisting of the phosphorus supported ligand L1. The corresponding copper(I) complexes [Cu(L1)](OTf) (5) and [Cu(L2)](OTf) (6) are accessible by reduction using decamethyl ferrocene. Both copper(I) complexes have been characterized in detail including X-ray structure analyses.     

Electronic structures and reactivity aspects of ruthenium-nitrosyls

Nitrosyl complexes with {Ru-NO}⁶ (4(ClO₄)₃) and {Ru-NO}⁷ (4(ClO₄)₂) configurations have been isolated in the selective molecular framework of [Ru(tpm)(pap)(NO)]ⁿ⁺ (tpm = tris(1-pyrazolyl)methane and pap = 2-phenylazopyridine). The DFT optimized structures of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) and [Ru^II(tpm)(pap)(NO)]²⁺ (4²⁺) predict that the Ru-N-O groups in the complexes are in almost linear and bent geometries, respectively. In agreement with largely NO centered reduction a sizeable shift in ν(NO) frequency of 324 cm⁻¹ has been observed on moving from {Ru^II-NO⁺} state in 4³⁺ to {Ru^II-NO) state in 4²⁺. The DFT proposed NO centered spin in {Ru^II-NO) (4²⁺) (Mulliken spin-densities: 0.860 (NO) and 0.087 (Ru)) has been evidenced by its free radical EPR spectrum with g = 1.989. The strongly electrophilic {Ru^II-NO⁺} state in 4³⁺ (ν(NO): 1962 cm⁻¹) can be transformed to the corresponding complex (3⁺) in the presence of nucleophile, OH⁻ with k = 2.03 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN. On irradiation with light the acetonitrile solution of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) undergoes facile photorelease of NO (k_NO, s⁻¹ = 0.1 × 10⁻¹ and t_1/2, s = 69.3) with the concomitant formation of the solvate [Ru^II(tpm)(pap)(CH₃CN)]²⁺ (2²⁺). The photoreleased NO can be trapped as an Mb-NO adduct.     

Molecular and electronic structures of new iron complexes containing N,S-coordinated o-iminothionebenzosemiquinonate(1-) π radical ligands: An experimental and density functional theoretical study

Two new o-aminothiophenol type ligands have been synthesized, namely 1,3-propanediamine-N,N′-bis(benzenethiol), H₄(¹L), and 1,2-bis(2-mercapto-3,5-di-tert-butylaniline)ethane, H₄(²L). The reactions of these ligands with FeBr₂ in dry acetonitrile in the presence and absence of air (and other oxidants such as iodine) afforded seven new complexes which were characterized by single-crystal X-ray crystallography and Mössbauer spectroscopy (as well as EPR- and UV-Vis spectroscopies). Their magnetochemistry has been studied and their electronic structures have been established and verified by broken symmetry (BS) density functional theoretical (DFT) calculations using the B3LYP functional. The ligands are redox-active and the o-iminothiophenolate(2-)-o-iminothiobenzosemiquinonate(1-) oxidation levels are chemically readily accessible. The complexes characterized comprise the dimers [Fe^III(¹L)]₂ (S_T = 0) (1); [Fe^III(²L)]₂ (S_T = 0) (2), and the mononuclear, five coordinate species: [Fe^III(¹L)I] (S_T = ¹/₂) (3); [Fe^III(²L)I] (S_T = ¹/₂) (4); [Fe^II(¹L){P(CH₃)₃}] (S_T = 0) (5); [Fe^II(²L){P(C₆H₅)₃}] (S_T = 0) (6), and [Fe^III(²)(^tpy)] (S_T = 1) (7). (^tBupy) represents 4-tert-butylpyridine and (²)³⁻ is the π radical trianion of the one-electron reduced (²L_gma)²⁻ which in turn is the oxidized form of (²L)⁴⁻ (−4H⁺, −2e).     

Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.     

Activity of homobimetallic ruthenium alkylidene complexes on intermolecular [2+2+2] cyclotrimerisation reactions of terminal alkynes

The activity of homobimetallic ruthenium alkylidene complexes, [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(PCy₃)] [Ru-I] and [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(IPr)] [Ru-II], on intermolecular [2+2+2] cyclotrimerisation reactions of monoynes has been investigated for the first time. It was found that these complexes can catalyse the chemo and regioselective cyclotrimerisation reactions of alkynes at both 25 and 50 °C in polar, aprotic solvents. The catalytic activity of [Ru-I] and [Ru-II] was compared to other well-known ruthenium catalysts such as Grubbs first generation catalyst [RuCl₂(CHPh)(PCy₃)₂] [Ru-III], [RuCl(μ-Cl)(p-cymene)]₂ [Ru-IV] and [RuCl₂(p-cymene)PCy₃] [Ru-V] complexes. To examine the effect of the steric hinderance of substrates on the regioselectivity of the reaction, a series of sterically hindered silicon containing alkynes (1a, 1b, 1c) were used. It was shown that the isomeric product distribution of the reaction shifts from 1,2,4-trisubstituted arenes to 1,3,5-trisubstituted arenes as the steric hinderance on the substrates increases. These homobimetallic ruthenium alkylidene complexes also catalysed regio- and chemo-selective cross-cyclotrimerisation reactions between silicon-containing alkynes (1a, 1b, 1c) and aliphatic alkynes (1d-g).     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Synthesis and characterization of [H2NC(S)NP(S)(OiPr)2] complexes of Co(II), Ni(II), Zn(II) and Cd(II)

Reaction of the potassium salt of the N-thiophosphorylthiourea H₂NC(S)NHP(S)(OiPr)₂ (HL) with Co(II), Ni(II), Zn(II) and Cd(II) cations in aqueous EtOH leads to the chelate complexes [ML₂] all showing a 1,5-S,S′-coordination formed by the CS and PS sulfur atoms of two deprotonated ligands L⁻. The structures of the resulting compounds were studied by IR, UV-Vis, ¹H, ³¹P{¹H} NMR spectroscopy and microanalysis. The metal center is found in a tetrahedral environment in [CoL₂], [ZnL₂] and [CdL₂]. According to NMR and UV-Vis spectroscopy the metal cation of [NiL₂] exhibits square planar coordination geometry in CH₂Cl₂, CHCl₃ and C₆H₆, while tetrahedral geometry is observed in acetone, DMSO and DMF. Regardless of the solvent used for the crystallization of [NiL₂], the molecular structure in the solid is always square planar as was confirmed by XRD of single crystals and magnetic measurements of the polycrystalline material. The magnetic and photoluminescent properties of all complexes are also reported.     

Biotechnological application of homo- and heterotrinuclear iron(III) furoates for cultivation of iron-enriched Spirulina

New trinuclear iron(III) furoates with the general formula [Fe₃O(α-fur)₆(R-OH)₃]X, where α-fur C₄H₃OCOO, R = CH₃ (1), C₂H₅ (2), n-C₃H₇ (3), n-C₄H₉ (4), X = NO₃⁻ (1-4); [Fe₃O(α-Fur)₆(DMF)(CH₃OH)₂]NO₃ (5); [Fe₃O(α-Fur)₆(H₂O)(CH₃OH)₂]Cl (6); [Fe₂MO(α-Fur)₆(L)(H₂O)₂], where L = THF (7-9), DMF (10-12), M = Mn²⁺ (7, 10), Co²⁺ (8, 11), Ni²⁺ (9, 12) and [Fe₂MO(α-Fur)₆(3Cl-Py)₃], where M = Mn²⁺ (13), Co²⁺ (14), Ni²⁺ (15); have been prepared and investigated by Mössbauer and IR spectroscopy. The X-ray crystal structure for the 1·2CH₃OH complex indicates that it crystallizes in the monoclinic crystal system (P2₁/n) and has a structure typical of μ₃-O-bridged trinuclear iron(III) compounds. Coordination compounds 1, 4, 7, 8 can be used as regulators of the biochemical composition of cyanobacterium Spirulina platensis biomass. The supplementation of these compounds, in concentrations exceeding 5-10 mg/l, increases the content of iron, amino acids, peptides and carbohydrates in Spirulina.     

Cyclodiphosph(III)azane chemistry - Ylides from the reaction of [(RNH)P-N(t-Bu)]2 [R = t-Bu, i-Pr] with dimethyl maleate and chiral ansa-type derivatives from reaction of [ClP-N(t-Bu)]2 with a substituted BINOL

Use of a simple inorganic ring system with the cyclodiphosph(III)azane skeleton [e.g. [(RNH)P-N(t-Bu)]₂ [R = t-Bu (7), i-Pr (8)] to probe some of the intermediates proposed in phosphine mediated organic reactions is highlighted. Thus the reaction of 7-8 with the allenylphosphine oxide Ph₂P(O)C(Ph)CCH₂ (9) affords the phosphinimines [(RNH)P(μ-N-t-Bu)₂P(N-R)-C(CH₂)CH(Ph)-P(O)Ph₂] [R = t-Bu (10), i-Pr (11)], while a similar reaction of 7-8 with dimethyl maleate (or dimethyl fumarate) affords the ylides [(RNH)P(μ-N-t-Bu)₂P(NH-R)C(CO₂Me)-CH₂(CO₂Me) [R = t-Bu (18), i-Pr (19)]. The implication of such reactions on phosphine mediated organic transformations including Morita-Baylis-Hillman reaction is mentioned. In a rather rare type of situation, an unusually long phosphoryl (PO) bond [1.538 (5) Å] as revealed the X-ray structure of {(R)-6,6′-(t-Bu)₂-1,1′-(C₁₀H₅)₂-2,2′-O₂-}{P(O)(N-t-Bu)₂-P(Se)} (27) is rationalized by means of crystallographic disorder in packing after comparing the data with that in the literature and {1,1′-(C₁₀H₆)₂-2,2′-O₂}{P(Se)(N-t-Bu)₂-P(Se)} (29). X-ray structures of the new compounds 10-11, 18-19, 27 and 29 are discussed. Compound 10 crystallizes in the chiral space group Pca2(1) with (S)-chirality at the carbon center [-C(CH₂)CH(Ph)-P] suggesting a case of spontaneous resolution through crystallization.     

Co and Cu complexes of reduced Schiff bases: Generation of phenoxyl radical species

The three complexes [Co^IIIL¹Cl] (1), [Co^IIIL²]⁺·ClO₄⁻ (2⁺·ClO₄⁻), and [Cu^IIH₂L²]²⁺·2ClO₄⁻ (H₂3²⁺·2ClO₄⁻) [where H₂L¹ = N,N′-dimethyl-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H₂L² = N,N′-bis(2-pyridylmethyl)-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine] have been prepared. The bis-phenolate and bis-phenol complexes, 2⁺ and H₂3²⁺ respectively, have been characterized by X-ray diffraction, showing a metal ion within an elongated octahedral geometry. 1-2 exhibit in their cyclic voltammetry curves two anodic reversible waves attributed to the successive oxidation of the phenolates into phenoxyl radicals. The cobalt radical species (1)⁺, (2)²⁺, and (2)³⁺ have been characterized by combined UV-Vis and EPR spectroscopies. In the presence of one equivalent of base, one phenolic arm of H₂3²⁺ is deprotonated and coordinates the metal. The resulting complex (H3⁺) exhibits a single reversible redox wave at ca. 0.3 V. The electrochemically generated oxidized species is EPR silent and exhibits the typical features of a radical compound, with absorption bands at 411 and 650 nm. The fully deprotonated complex 3 is obtained by addition of two equivalents of nBu₄N⁺OH⁻ to H₂3²⁺. It exhibits a new redox wave at a lower potential (−0.16 V), in addition to the wave at ca. 0.3 V. We assigned the former to the one-electron oxidation of the uncoordinated phenolate into an unstable phenoxyl radical.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Copper(II)-mediated oxime-nitrile coupling in non-aqueous solutions: Synthetic, structural and magnetic studies of the copper(II)-salicylaldehyde oxime reaction system

The reactions of salicylaldehyde oxime (H₂salox) with Cu^II precursors yielded the known complexes [Cu(Hsalox)₂] (1) and [Cu(Hsalox)₂]_n (2), as well as complexes [Cu₃(salox)(L₁)(L₂)]·MeCN (3·MeCN), [CuCl(L₁)] (4) and [Cu₂Na(O₂CMe)₅(HO₂CMe)]_n (5), where L₁⁻ = o-O-C₆H₄-CHNO-C(CH₃)NH and L₂³⁻ = o-O-C₆H₄-CHNO-C(o-O-C₆H₄)N. L₁⁻ was formed in situ via the nucleophilic addition of the oximato O-atom of salox²⁻ to the unsaturated nitrile group of the MeCN reaction solvent. L₂³⁻ is also formed in situ probably through the nucleophilic attack of the oximato O-atom to the unsaturated nitrile group of salicylnitrile; the latter, although not directly added to the reaction mixture, can be produced via the dehydration of salox²⁻. Compounds 1 and 2 contain Hsalox⁻ bound to the metal center in two different coordination modes; they both contain the same mononuclear unit, however a 2D network is generated in 2 due to a relatively long Cu-O_oximato bond. Compound 3 contains three different ligands, i.e. salox²⁻, L₁⁻ and L₂³⁻, which act as μ₃-κ²O:κO′:κN, κO:κN:κN′ and μ₃-κ²O:κ²N:κO′:κN′, respectively, whereas 4 consists of a square planar Cu^II atom bound to a κO:κN:κN′ L₁⁻ and a chloride ion. Compound 5 consists of dinuclear [Cu₂(O₂CMe)₅(HO₂CMe)]⁻ units and Na⁺ ions assembled into an overall 3D network structure. Magnetic susceptibility measurements from polycrystalline samples of 2 and 5 gave best-fit parameters J = +0.36 cm⁻¹ (H = −J?_i?_j) and J = −360 cm⁻¹, zj = +20 cm⁻¹ (H = −J?_i?_j − zJ〈S_z〉?_z), respectively.     

Stepwise syntheses, structure and spectroscopic studies of ruthenium complexes of 2,6-bis(benzimidazol-2-yl)pyridine with o-iminoquinone ancillary ligand

The ruthenium complexes [Ru^II(bbp)(L)(Cl)] (1), [Ru^II(bbp)(L)(H₂O)] (2) and [Ru^II(bbp)(L)(DMSO)] (3) {bbp = 2,6-bis(benzimidazol-2-yl)pyridine, L = o-iminoquinone} have been synthesized in a stepwise manner starting from [Ru^III(bbp)Cl₃]. The single crystal X-ray structures, except for the complex 2, have been determined. All the complexes were characterized by UV-Vis, FT-IR, ¹H NMR, Mass spectroscopic techniques and cyclic voltammetry. The Ru^III/Ru^II couple for complexes 1, 2, and 3 appears at 0.63, 0.49, 0.55 V, respectively versus SCE. It is observed that complex 2, on refluxing in acetonitrile, results into [Ru^II(bbp)(L)(CH₃CN)], 4 which has been prepared earlier in a different method. The structural, spectral and electrochemical properties of complexes 1, 2 and 3 were compared to those of earlier reported complex 4, [Ru^II(bbp)(L)(CH₃CN)].     

{Ru-NO} and {Ru-NO} configurations in [Ru(trpy)(tmp)(NO)] (trpy = 2,2:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline): An experimental and theoretical investigation

The ruthenium-nitrosyl complexes [Ru^II(trpy)(tmp)(NO⁺)](ClO₄)₃ ([4](ClO₄)₃) and [Ru^II(trpy)(tmp)(NO)](ClO₄)₂ ([5](ClO₄)₂) with {Ru-NO}⁶ and {Ru-NO}⁷ configurations, respectively (trpy = 2,2′:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been isotaled. The nitrosyl complexes [4]³⁺ and [5]²⁺ have been generated by following a stepwise synthetic procedure: [Ru^II(trpy)(tmp)(X)]ⁿ, X/n = Cl/+ (1⁺) → CH₃CN/2+ (2²⁺) → NO₂/+ (3⁺) → NO⁺/3+ (4³⁺) → NO/2+ (5²⁺). The single-crystal X-ray structures of two precursor complexes [1]ClO₄ and [3]ClO₄ have been determined. The DFT optimized structures of 4³⁺ and 5²⁺ suggest that the Ru-N-O geometries in the complexes are linear (177.9°) and bent (141.4°), respectively. The nitrosyl complexes with linear (4³⁺) and bent (5²⁺) geometries exhibit ν(NO) frequencies at 1935 cm⁻¹ (DFT: 1993 cm⁻¹) and 1635 cm⁻¹ (DFT: 1684 cm⁻¹), respectively. Complex 4³⁺ undergoes two successive reductions at 0.25 V (reversible) and −0.48 V (irreversible) versus SCE involving the redox active NO function, Ru^II-NO⁺ ? Ru^II-NO and Ru^II-NO → Ru^II-NO⁻, respectively, besides the reductions of trpy and tmp at more negative potentials. The DFT calculations on the optimized 4³⁺ suggest that LUMO and LUMO+1 are dominated by NO⁺ based orbitals of around 65% contribution along with partial metal contribution of ∼25% due to (dπ)Ru^II → π∗(NO⁺) back-bonding. The lowest energy transitions in 4³⁺ and 5²⁺ at 360 nm and 467 nm in CH₃CN (TD-DFT: 364 and 459 nm) have been attributed to mixed MLLCT transitions of tmp(π) → NO⁺(π∗), Ru(dπ)/tmp(π) → NO⁺(π^∗) and Ru(dπ)/NO(π) → trpy(π^∗), respectively. The paramagnetic reduced species 5²⁺ exhibits an anisotropic EPR spectrum with g₁ = 2.018, g₂ = 1.994, g₃ = 1.880 (〈g〉 = 1.965 and Δg = 0.138) in CH₃CN, along with ¹⁴N (I = 1) hyperfine coupling constant, A2 = 35 G at 110 K due to partial metal contribution in the singly occupied molecular orbital (DFT:SOMO:Ru (34%) and NO (53%)). Consequently, Mulliken spin distributions in 5²⁺ are calculated as 0.115 for Ru and 0.855 for NO (N, 0.527; O, 0.328). The reaction of moderately electrophilic nitrosyl center in 4³⁺ with the nucleophile, OH⁻ yields the nitro precursor, 3⁺ with the second-order rate constant value of 1.7 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN-H₂O (10:1). On exposure to light (Xenon 350 W lamp) both the nitrosyl species, 4³⁺ ({Ru^II-NO⁺}) and 5²⁺ ({Ru^II-NO}) undergo photolytic Ru-NO bond cleavage process but with a widely varying k_NO, s⁻¹ (t_1/2, s) of 1.56 × 10⁻¹(4.4) and 0.011 × 10⁻¹(630), respectively.     

Sesquiterpene lactones from the endemic Cape Verdean Artemisia gorgonum

Leaves and flowers of Artemisia gorgonum (Asteraceae) collected in Fogo, Cape Verde islands, were phytochemically investigated and resulted in isolation and characterization of three guaianolides 1, 2, 5, and a secoguainolide 4, in addition to eight known guaianolides 6-11 and two known germacranolides 12, 13. Structures were elucidated by 1D and 2D NMR experiments. Careful examination of the ¹³C NMR spectrum led to revision of the structure of a previously described guaianolide from 2 to 3. Most compounds exhibited mild antiplasmodial activities, ridentin (13) being the most interesting with an IC₅₀ of 3.8 ± 0.7 μg ml⁻¹ against Plasmodium falciparum FcB1 and weak cytotoxicity in a vero cell line (IC₅₀ 71.0 ± 3.9 μg ml⁻¹).     

Sn-S and Ru-Ru bonds cleavage reactions between [Ph3SnS(CH2)3SSnPh3] and Ru3(CO)12: X-ray crystal structures of [Ph3SnS(CH2)3SSnPh3] and trans-[Ru(CO)4(SnPh3)2]

The organotin complex [Ph₃SnS(CH₂)₃SSnPh₃] (1) was synthesized by PdCl₂ catalyzed reaction between Ph₃SnCl and disodium-1,3-propanedithiolate which in turn was prepared from 1,2-propanedithiol and sodium in refluxing THF. Reaction of 1 with Ru₃(CO)₁₂ in refluxing THF affords the mononuclear complex trans-[Ru(CO)₄(SnPh₃)₂] (2) and the dinuclear complex [Ru₂(CO)₆(μ-κ²-SCH₂CH₂CH₂S)] (3) in 20 and 11% yields, respectively, formed by cleavage of Sn-S bond of the ligand and Ru-Ru bonds of the cluster. Treatment of pymSSnPPh₃ (pymS = pyrimidine-2-thiolate) with Ru₃(CO)₁₂ at 55-60 °C also gives 2 in 38% yield. Both 1 and 2 have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.