Syntheses, structures, and reactivity of new pentamethylcyclopentadienyl-rhodium(III) and -iridium(III) 4-acyl-5-pyrazolonate complexes

New [CpM(Q)Cl] complexes (M = Rh or Ir, Cp = pentamethylcyclopentadienyl, HQ = 1-phenyl-3-methyl-4R(C=O)-pyrazol-5-one in general, in detail HQ(Me), R = CH(3); HQ(Et), R = CH(2)CH(3); HQ(Piv), R = CH(2)-C(CH(3))(3); HQ(Bn), R = CH(2)-(C(6)H(5)); HQ(S), R = CH-(C(6)H(5))(2)) have been synthesized from the reaction of [CpMCl(2)](2) with the sodium salt, NaQ, of the appropriate HQ proligand. Crystal structure determinations for a representative selection of these [CpM(Q)Cl] compounds show a pseudo-octahedral metal environment with the Q ligand bonded in the O,O'-chelating form. In each case, two enantiomers (S(M)) and (R(M)) arise, differing only in the metal chirality. The reaction of [CpRh(Q(Bn))Cl] with MgCH(3)Br produces only halide exchange with the formation of [CpRh(Q(Bn))Br]. The [CpRh(Q)Cl] complexes react with PPh(3) in dichloromethane yielding the adducts CpRh(Q)Cl/PPh(3) (1:1) which exist in solution in two different isomeric forms. The interaction of [CpRh(Q(Me))Cl] with AgNO(3) in MeCN allows generation of [CpRh(Q(Me))(MeCN)]NO(3).3H(2)O, whereas the reaction of [CpRh(Q(Me))Cl] with AgClO(4) in the same solvent yields both [CpRh(Q(Me))(H(2)O)]ClO(4) and [CpRh(Cl)(H(2)O)(2)]ClO(4); the H(2)O molecules derive from the not-rigorously anhydrous solvents or silver salts.     

Li,Ti(III), and Ti(IV) trisamidotriazacyclononane complexes. Syntheses,reactivity, and structures

The preparations of 1,4,7-(NHPhSiMe(2))(3)-1,4,7-triazacyclononane (H(3)N(3)-tacn) and its lithium and sodium derivatives are described. The X-ray structure of the THF adduct of the lithium derivative, Li(3)N(3)-tacn(THF)(2), shows that one of the macrocycle pendant arms is bent to allow the coordination of the its lithium ion to two tacn amines. In solution, a fluxional process makes all the pending arms magnetically equivalent. The reactions of Li(3)N(3)-tacn or Na(3)N(3)-tacn with either TiCl(4) and TiCl(3)(THF)(3) led to the formation of [Ti(N(3)-tacn)], 5. The oxidation of 5 with various oxidizing reagents gave cationic complexes [Ti(N(3)-tacn)]X, 6 (X = I, Cl, SCN, PF(6), BPh(4)), that exist as a pair of enantiomers, lambda(lambdalambdalambda)/delta(deltadeltadelta), which interconvert in solution. The molecular structures of 5 and 6 (X = I, BPh(4)) show the coordination of the six nitrogen donor set to the titanium. Due to the short length of the tacn pendant arms, the hexadentate bonding mode of the ligand is mainly achieved through the sharpening of the N-Si-N angles. The reaction of [Ti(N(3)-tacn)]I, 6a, with W(CO)(6) led to the synthesis of [Ti(N(3)-tacn)][W(CO)(5)I], 7.     

Influence of carboxamido nitrogen donors on the redox potential of copper(III) complexes

The synthesis of a new copper(III) complex with aliphatic carboxamido-N and thiolato-S donors is reported. This complex was thoroughly characterized by ¹H NMR, UV–Vis spectroscopy, and cyclic voltammetry, as well as by single crystal X-ray crystallography. The copper(III) state in this complex is more stabilized than in the parent compound with aromatic carboxamido nitrogen donors.     

Syntheses, structures, and electrochemical properties of inclusion compounds of cucurbit[8]uril with cobalt(III) and nickel(II) complexes

Inclusion compounds of a macrocyclic cavitand cucurbit[8]uril (CB[8]) with cobalt(III) and nickel(II) complexes of 1,3-diaminopropane (tn) and 1,3-diamino-2-propanol (tmOH) { trans-[Co(tn) 2Cl 2]@CB[8]}Cl.14H 2O ( 1), { trans-[Co(tmOH)(tmO)]@CB[8]}Cl 2.22H 2O ( 2), and { trans-[Ni(tmOH) 2]@CB[8]}Cl 2.22H 2O ( 3) were synthesized and characterized by X-ray single crystal analysis, IR spectroscopy, ESI-MS, and by solid-state stripping voltammetry. The encapsulation of trans-[Co(tn) 2Cl 2] (+) within the cavity of CB[8] stabilizes the complex toward ligand substitution reactions in aqueous solution. The electrochemical study demonstrates that CB[8] prefers the oxidized species in trans-[Co(tn) 2Cl 2] (+)/ trans-[Co(tn) 2Cl 2] (0) and trans-[Co(tmO)(tmOH) 2] (2+)/ trans-[Co(tmO)(tmOH) 2] (+) redox couples, but stabilizes the reduced form trans-[Ni(tmOH) 2] (2+) against the oxidized species. The reversibility of voltammogram shapes evidence that for the inclusion compounds 1- 3 electron transfer reactions proceed within the cavity of the host.     

Syntheses,crystal structures,and antibacterial activities of two cobalt(III) complexes

Syntheses, structures, and antimicrobial activities of cobalt(III) complexes with two tetradentate Schiff-base ligands, (BA)₂en?=?bis(benzoylacetone)ethylenediimine dianion and (acac)₂en?=?bis(acetylacetone)ethylenediimine dianion, and two axial pyridines (py) have been investigated. These complexes were characterized by FT-IR, ¹H-NMR, UV-Vis spectroscopy, and elemental analysis. The crystal structures of the complexes were determined by X-ray crystallography. Single-crystal X-ray diffraction analyses revealed that both complexes have distorted octahedral environments, Schiff-base ligand coordinates cobalt in four equatorial positions, and the two axial positions are occupied by pyridines. The pyridines and Schiff-base ligands are involved in N–H···O hydrogen bonds with perchlorate. Biological activities of the ligands and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis by the well diffusion method. The activity data show the metal complexes to be more potent than the parent ligand against two bacterial species.     

Syntheses,structures, and spectroscopic properties of copper(II) and cobalt(III) complexes containing 1,4,7-tribenzyl-1,4,7-triazacyclononane ligand

Three new complexes [CuL(N₃)₂] (1), [CuL(SCN)₂] (2), and [CoL(SCN)₃] (3) (L?=?1,4,7-tribenzyl-1,4,7-triazacyclononane) have been synthesized and structurally characterized. Complex 1 crystallizes in monoclinic space group P2(1)/n with unit cell parameters a?=?14.105(7), b?=?8.999(5), c?=?21.603(11)?Å, β?=?100.470(7)°. While 2 crystallizes in triclinic space group P-1 with unit cell parameters a?=?9.6380(16), b?=?10.6993(18), c?=?15.798(3)?Å, α?=?106.636(3), γ?=?116.478(3)°. Complex 3 crystallizes in trigonal space group P–3c1 with unit cell parameters a?=?14.744(3), b?=?14.744(3), c?=?16.098(4)?Å, γ?=?120°. Elemental analysis, IR, UV-vis spectra of complexes 1–3 and ESR spectra of complexes 1–2 were also determined.     

Substituted cyclopentadienylchromium(III) complexes containing neutral donor ligands. Synthesis, crystal structures and reactivity in ethylene polymerization

Lithium derivatives of substituted cyclopentadiene ligands reacted with CrCl₃(THF)₃ in THF solution to afford homodinuclear complexes of the type [{(η⁵-RCp)CrCl(μ-Cl) }₂] [R=SiMe₃ (1), CH₂C(Me)CH₂ (2)]. Complex 1 reacts with pyrazole (C₃H₄N₂) to yield the mononuclear half-sandwich complex [(η⁵-Me₃SiCp)CrCl₂(pyrazole)] (3). The similar complex [Cp*CrCl₂(pyrazole)] (4) was synthesised by reaction of [{Cp*CrCl(μ-Cl)}₂] with pyrazole. Complex 2 reacts with bidentate ligands to give binuclear complexes of the type [{(η⁵-CH₂C(Me)CH₂Cp)CrCl₂ }₂(μ-L-L)] [L-L=Ph₂PCH₂CH₂PPh₂ (5), trans-Ph₂P(O)CHCHP(O)Ph₂ (6)]. All complexes were structurally characterised by X-ray diffraction. After reaction with methylaluminoxane these complexes are active in the polymerization of ethylene. At 25 °C and 4 bar of ethylene, complex 3 yields polyethylene with a bimodal molecular weight distribution centred at 155,000 and 2000 g/mol. Complex 4 shows similar activity, yielding only the low molecular weight fraction. On the other hand, the binuclear complexes 5 and 6 under the same conditions were three times more active than mononuclear complexes. The melting point of the polymers indicates the formation of linear polyethylene.     

Synthesis and structure of iron(III) complexes containing a quasi-crownether ring

A barium-iron(III) [BaFe(cr-salen)(py)₂](ClO₄)₃ (1) was prepared and an iron(III) complex [Fe(cr-salen)(py)₂]ClO₄ (2) complex was obtained by removing Ba²⁺ ion from the barium-iron(III) complexes with guanidinium sulfate. These complexes are in the high-spin state both in the solid state and in acetonitrile. Single crystals of [BaFe(cr-salen)(MeOH)₂]₂O(ClO₄)₄·2MeOH (3) were obtained by slow evaporation of a solution of (2) and Ba(ClO₄)₂, and the single crystal X-ray structure of (3) was determined: Crystal data for [BaFe(cr-salen)(MeOH)₂]₄O₂(ClO₄)₄·2MeOH: C₂₅H₃₆N₂O_17.5Cl₂BaFe, are: space group C2/c, Z=8, a=24.79(7) Å, b=16.11(6) Å, c=17.24(6) Å, V=6753(36) ų, R=0.133, R_w=0.154. The structure of the complex has a one order polymeric chain. An iron atom is located in a cavity of square pyramidal geometry and bridged by an oxygen atom of μ-oxo. A barium ion is sitted in a quasi-crownether ring and bridged by two perchlorate anions.     

EPR spectra and structures of spin-variable iron(III) complexes

The structures of the spin-variable iron(III) complexes Fe(4-OCH₃-SalEen)₂X and FeL′₂X (L′ is oxysalicylidene-N′-ethyl-N-ethylenediamine; X = PF₆, NO₃, and SCN) were examined from their EPR spectra. The coordination units (CUs) of these complexes are a high-symmetry octahedron with a slight tetrahedral distortion or a low-symmetry pseudooctahedron with considerable tetragonal and orthorhombic distortions. When the complex passes from the high-spin to low-spin state, its CU changes. The energy level splittings caused by various types of distortions were estimated from the EPR data. The distortion of the CU depends on the outer-sphere anion. The magnetic resonance parameters of the complexes were analyzed. The fine structure parameters of the EPR spectra of high-spin complexes (the ground-state term is $^6 A_{1_g }$ ) depend on the CU distortion and the covalent bonding. The spin-orbital coupling makes an appreciable second-order contribution to the expressions for the Zeeman coupling parameters of low-spin complexes (the ground-state term is $^2 T_{2_g }$ ).     

Syntheses,structures, and properties of two mononuclear cobalt(III) azido complexes containing a tetradentate N-donor Schiff base as end-capping ligand

Two hexacoordinated mononuclear Co(III) compounds of the type cis-[Co(L)(N₃)₂] X [1, X = ClO₄; 2, X = PF₆; L = N,N′-(bis(pyridine-2-yl)benzylidine)-1,4-butanediamine] have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structures of complexes 1 and 2 both have distorted octahedral geometry with two terminal azides in mutual cis orientations. In the crystalline state, two mononuclear units of 1 are associated by weak C–H…π interactions to produce a dimeric unit, which packs through C–H…O hydrogen bonds and π…π interactions leading to a 2-D continuum. The mononuclear units in 2 are engaged in weak cooperative intermolecular C–H…π interactions and multiple C–H…F hydrogen bonds giving rise to a 3-D network structure. These diamagnetic compounds are redox active and show luminescence in DMF solutions.     

Syntheses and magnetic properties of iron(III) complexes with imidazole groups

Iron(III) complexes with the general formula of [Fe (R-Himap)₂]X and [Fe(R-Himat)₂]X (Himap = shiff-base prepared from the condensation of 4-formylimidazole and 2-aminophenol, Himat = shiff base prepared from the condensation of 4-formylimidazole and 2-aminobenzenethiol, and R = H, Me, Ph; X = ClO₄, NO₃, BPh₄) have been synthesized. The complexes have an N₄O₂ donor set or an N₄S₂ donor set. These complexes have 5 and 5 member rings around an iron(III) atom per one chelate ring, that is, "5-5 member rings". The crystal structure, Mössbauer spectra, magnetic properties and absorption spectra of the complexes were examined. In addition, [Fe (Himsa)₂]ClO₄ having "5-6 member rings" of an N₄O₂ donor set and [Fe (Ph-Himap)(Ph-imap)] obtained by the deprotonation of [Fe (Ph-Himap)₂]ClO₄ have been also synthesized, and the Mössbauer spectra and magnetic properties of those complexes were examined. The X-ray structure of a single crystal of [Fe (Himap)₂]BPh₄ was determined: C₄₄H₃₆N₆BO₂Fe, triclinic, space group P(# 2), a = 12.452(2) Å, b = 12.748(2) Å, c = 11.996(2) Å, = 103.97(1)°, = 90.78(1)°, = 84.70(1)° and Z = 2. The moiety of an iron atom of [Fe(Himap)₂]BPh₄ was a pseudo octahedron with an FeN₄O₂ geometry. [Fe(R-Himap)₂]X was in high-spin state (about 5.9 B.M. at 80 K in solid state), and [Fe(R-Himat)₂]X was in low-spin state (about 2.0 B.M. at 293 K). The complex [Fe(Himsa)₂]ClO₄ with "5-6 member rings" and the deprotonated complex [Fe(Ph-Himap)(Ph-imap)] were in the high-spin state (6.0 B.M. at 80 K). It is concluded that the ligand field strength of an N₄S₂ donor set is stronger than that of an N₄O₂ donor set.     

Syntheses, crystal structures, reactivity, and photochemistry of gold(III) bromides bearing N-heterocyclic carbenes

Gold(I) complexes bearing N-heterocyclic carbenes (NHC) of the type (NHC)AuBr (3a/3b) [NHC = 1-methyl-3-benzylimidazol-2-ylidene (= MeBnIm), and 1,3-dibenzylimidazol-2-ylidene (= Bn(2)Im)] are prepared by transmetallation reactions of (tht)AuBr (tht = tetrahydrothiophene) and (NHC)AgBr (2a/2b). The homoleptic, ionic complexes [(NHC)(2)Au]Br (6a/6b) are synthesized by the reaction with free carbene. Successive oxidation of 3a/3b and 6a/6b with bromine gave the respective (NHC)AuBr(3) (4a/4b) and [(NHC)(2)AuBr(2)]Br (7a/7b) in good overall yields as yellow powders. All complexes were characterized by NMR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Reactions of the Au(III) complexes towards anionic ligands like carboxylates, phenolates and thiophenolates were investigated and result in a complete or partial reduction to a Au(I) complex. Irradiation of the Au(III) complexes with UV light yield the Au(I) congeners in a clean photo-reaction.     

Correlation of spin states and spin delocalization with the dioxygen reactivity of catecholatoiron(III) complexes

A series of catecholatoiron(III) complexes, [Fe(III)L(4Cl-cat)]BPh4 (L = (4-MeO)2TPA (1), TPA (2), (4-Cl)2TPA (3), (4-NO2)TPA (4), (4-NO2)2TPA (5); TPA = tris(pyridin-2-ylmethyl)amine; 4Cl-cat = 4-chlorocatecholate), have been characterized by magnetic susceptibility measurements and EPR, 1H NMR, and UV-vis-NIR spectroscopies to clarify the correlation of the spin delocalization on the catecholate ligand with the O2 reactivity as well as the spin-state dependence of the O2 reactivity. EPR spectra in frozen CH3CN at 123 K clearly showed that introduction of electron-withdrawing groups effectively shifts the spin equilibrium from a high-spin to a low-spin state. The effective magnetic moments determined by the Evans method in a CH3CN solution showed that 5 contains 36% of low-spin species at 243 K, while 1-4 are predominantly in a high-spin state. Evaluation of spin delocalization on the 4Cl-cat ligand by paramagnetic 1H NMR shifts revealed that the semiquinonatoiron(II) character is more significant in the low-spin species than in the high-spin species. The logarithm of the reaction rate constant is linearly correlated with the energy gap between the catecholatoiron(III) and semiquinonatoiron(II) states for the high-spin complexes 1-3, although complexes 4 and 5 deviate negatively from linearity. The lower reactivity of the low-spin complex, despite its higher spin density on the catecholate ligand compared with the high-spin analogues, suggests the involvement of the iron(III) center, rather than the catecholate ligand, in the reaction with O2.     

Syntheses,crystal structures,and electrochemical characterizations of two octahedral iron(III) complexes with Schiff base of pyridoxal and aminoguanidine

This article presents the synthesis, physico-chemical, in particular voltammetric, characteristics of two iron(III) complexes with pyridoxal aminoguanidine (PLAG), [Fe(PLAG)Cl₂(H₂O)]Cl (1) and [Fe(PLAG)₂](NO₃)₃ (2). As expected, the zwitterion of the chelate ligand is coordinated tridentate through oxygen of phenol and nitrogen atoms of azomethine and imino groups of the aminoguanidine fragment. In both complexes, Fe(III) is distorted octahedral. [Fe(PLAG)₂](NO₃)₃ (2) is the first bis(ligand) complex with this ligand. Cyclic voltammetric characteristics of the ligand and complexes were studied in DMF in the presence of TBAP or LiCl as supporting electrolytes. The complexes are unstable in this solvent, especially in the presence of an excess of chloride, thus forming several reducible species whose stabilities and behaviors were characterized.     

Synthesis and reactivity of water-soluble platinum(II) complexes containing nitrogen ligands

A series of water-soluble platinum(II) complexes containing bidentate imino pyridine ligands L of the general formula LPtX₂ (X=Cl or Me) have been prepared. The dichloro complexes are very stable in water or dimethyl sulfoxide (DMSO), even at elevated temperatures, whereas the dimethyl complexes are less stable in these strongly polar solvents. In DMSO, an equilibrium between the complex LPtMe₂ and (DMSO)₂PtMe₂ is observed, whereas in water decomposition is observed within 1 day at room temperature.     

Syntheses,crystal structures,and antibacterial activities of manganese(III), nickel(II), and copper(II) complexes containing a tetradentate Schiff base

Three new mononuclear Schiff-base complexes, namely [Mn(L)Cl] (1), [Ni(L)] (2), and [Cu(L)] (3), where L?=?anion of [N,N′-bis(2-hydroxybenzophenylidene)]propane-1,2-diamine, have been synthesized by reacting equimolar amounts of the respective metal chloride and the tetradentate Schiff base, H₂L, in methanol. The complexes have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction, and other physicochemical studies. Structural studies reveal that 1 adopts a distorted square-pyramidal geometry whereas 2 and 3 are isotypic with distorted square-planar geometries. The antibacterial activities of 1–3 along with their Schiff base have been tested against some Gram(+) and Gram(?) bacteria.     

Synthesis, crystal structures, and reactivity of osmium(II) and -(IV) complexes containing a dithioimidodiphosphinate ligand

Reduction of trans-[OsL2(O)2] (1) (L-=[N(i-Pr2PS)2]-) with hydrazine hydrate afforded a dinitrogen complex 2, possibly "[OsL2(N2)(solv)]" (solv=H2O or THF), which reacted with RCN, R'NC, and SO2 to give trans-[OsL2(RCN)2] (R=Ph (3), 4-tolyl (4), 4-t-BuC6H4 (5)), trans-[OsL2(R'NC)2] (R'=2,6-Me2C6H3 (xyl) (6), t-Bu (7)), and [Os(L)2(SO2)(H2O)] (8) complexes, respectively. Protonation of compounds 2, 3, and 6 with HBF4 led to formation of dicationic trans-[Os(LH)2(N2)(H2O)][BF4]2 (9), trans-[Os(LH)2(PhCN)2][BF4]2 (10), and trans-[Os(LH)2(xylNC)2][BF4]2 (11), respectively. Treatment of 1 with phenylhydrazine and SnCl2 afforded trans-[OsL2(N2Ph)2] (12) and trans-[OsL2Cl2] (13), respectively. Air oxidation of compound 2 in hexane/MeOH gave the dimethoxy complex trans-[OsL2(OMe)2] (14), which in CH2Cl2 solution was readily air oxidized to 1. Compound 1 is capable of catalyzing aerobic oxidation of PPh3, possibly via an Os(IV) intermediate. The formal potentials for the Os-L complexes have been determined by cyclic voltammetry. The solid-state structures of compounds 4, 6, cis-8, 13, and 14 have been established by X-ray crystallography.     

Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

The synthesis of the new complexes Cp*(dppe)FeCC2,5-C₄H₂SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a, R = CCH; 2b, R = CCSi(CH₃)₃; 2c, R = CCSi(CH(CH₃)₂)₃; 3a, R = CC2,5-C₄H₂SCCH; 3c, R = CC2,5-C₄H₂SCCSi(CH(CH₃)₂)₃) is described. The ¹³C NMR and FTIR spectroscopic data indicate that the π-back donation from the metal to the carbon rich ligand increases with the size of the organic π-electron systems. The new complexes were also analyzed by CV and the chemical oxidation of 2a and 3c was carried out using 1 equiv of [Cp₂Fe][PF₆]. The corresponding complexes 2a[PF₆] and 3c[PF₆] are thermally stable, but 2a[PF₆] was too reactive to be isolated as a pure compound. The spectroscopic data revealed that the coordination of large organic π-electron systems to the iron nucleus produces only a weak increase of the carbon character of the SOMO for these new organoiron(III) derivatives.     

Syntheses, structures, and physical properties of nickel bis(dithiolene) complexes containing tetrathiafulvalene (TTF) units

To contribute to the development of single-component molecular metals, several nickel complexes with cyclohexeno-condensed or ethylenedioxy-substituted TTF (tetrathiafulvalene) dithiolate ligands, (R(4)N)(n)[Ni(chdt)(2)] [R = Me, n = 2 (1); R = (n)Bu, n = 1 (2); n = 0 (3)] and (R(4)N)(n)[Ni(eodt)(2)] [R = Me, n = 2 (4); R = (n)Bu, n = 1 (5); n = 0 (6)], were prepared. X-ray structures were determined on the monoanionic species 2 and 5. The tetra-n-butylammonium complex of the monoanionic [Ni(chdt)(2)] (2) with a 1:1 composition revealed that its magnetic susceptibility gave a good agreement with the Bonner-Fisher model (J/k(B) = -28 K), which was derived from the one-dimensional chains of anions with a regular interval. On the other hand, the magnetic susceptibility of the tetra-n-butylammonium complex of the monoanionic [Ni(eodt)(2)] (5) showed the Curie-Weiss behavior (C = 0.376 K.emu.mol(-1) and Theta = -4.6 K). Both of the monoanionic species 2 and 5 indicate that they belong to the S = 1/2 magnetic system and have relatively large and anisotropic g-values, suggesting the contribution of the nickel 3d orbital. Electrical resistivity measurements were performed on the compressed pellets of the neutral species 3 and 6. Fairly large conductivities were obtained (sigma(rt) = 1-10 S.cm(-1)). In addition, despite the measurements on the compressed pellets of powder samples, the neutral species 6 showed metallic behavior down to ca. 120 K and retained high conductivity even at 0.6 K [sigma(0.6 K)/sigma(rt) approximately 1/30], suggesting the crystal to be essentially metallic down to very low temperature. The electrical behavior and Pauli paramagnetism of 6 indicate the system to be a new single-component metal.