Synthesis and conformation of cyclic hexapeptide cyclo(Pro-Sar-Sar)2

A cyclic hexapeptide, cyclo(Pro-Sar-Sar)₂, which consists of N-substituted amino acids only was synthesized, and its solution conformation was investigated by n.m.r. spectroscopy. Seven different C₂-symmetric conformations were detected, which were distinguishable from each other on the n.m.r. time scale. This is due to the cis/trans isomerization of N-substituted peptide bonds. Allowed C₂-symmetric conformations were computed on the basis of a hard-sphere model. Some conformations detected in n.m.r. spectra were not allowed in the calculation. This disagreement suggests that some asymmetric conformations with regard to the single bond rotation are averaged out due to a rapid rotation on the n.m.r. time scale. These points indicate that the molecule of cyclo (Pro-Sar-Sar)₂ is very flexible     

Supramolecular assemblies of new 2-D complexes: Syntheses, crystal structures, spectroscopic and magnetic properties of {[MnAu2(CN)4(NITpPy)2(H2O)2]}n and {[Co(N(CN)2)2(NITpPy)2(H2O)2]}n

Two new complexes, {[MnAu₂(CN)₄(NITpPy)₂(H₂O)₂]}_n (1) and {[Co(N(CN)₂)₂(NITpPy)₂(H₂O)₂]}_n (2), have been synthesized and characterized. The single-crystal X-ray analysis for the complexes 1 and 2 demonstrates that each M(II) (M = Mn or Co) ion assumes a distorted octahedral MN₄O₂ coordination polyhedron. Four nitrogen atoms come from the cyanide groups and the pyridyl rings in a common plane, and two oxygen atoms come from the H₂O molecules in trans-positions. The structures of complexes 1 and 2 illustrate that aurophilicity and/or hydrogen bonding interactions play important roles in increasing dimensionality. Magnetic investigations on complexes 1 and 2 show the presence of weak antiferromagnetic interactions.     

Synthesis, structure and properties of TTF-carboxylate bridged paddlewheel dirhodium complexes, Rh2(BuCO2)3(TTFCO2) and Rh2(BuCO2)2(TTFCO2)2

Reaction of tetrathiafulvalene carboxylic acid (TTFCO₂H) with paddlewheel dirhodium complex Rh₂(Bu^tCO₂)₄ yielded TTFCO₂-bridged complexes Rh₂(Bu^tCO₂)₃(TTFCO₂) (1) and cis- and trans-Rh₂(Bu^tCO₂)₂(TTFCO₂)₂ (cis- and trans-2). Their triethylamine adducts [1(NEt₃)₂] and cis-[2(NEt₃)₂] were purified and isolated with chromatographic separation, and characterized with single crystal X-ray analysis. Trans-[2(NEt₃)₂] is not completely separated from a mixture of cis- and trans-[2(NEt₃)₂], but its single crystals were obtained from a solution of the mixture. A three-step quasi-reversible oxidation process was observed for 1 in MeCN. The first two steps correspond to the oxidation of the TTFCO₂ moiety and the last one is the oxidation of the Rh₂ core. The oxidation of cis-2 is observed as a two-step process with very similar E_1/2 values to those of the first two processes for 1. Both 1⁺ and cis-2²⁺ in MeCN at room temperature show isotropic ESR spectra with a g value of 2.008 and a_H = 0.135 mT for two equivalent H atoms and a_H = 0.068 mT for one H atom. The redox and ESR data of cis-2 suggest that the intramolecular interaction between the TTF moieties is very small.     

Synthesis, spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(nia)2(H2O)2] and structural analysis of similar [Cu(RCOO)2(L-N)2(H2O)2] complexes

A new complex of composition [Cu(2-NO₂bz)₂(nia)₂(H₂O)₂] (1) (nia = nicotinamide, 2-NO₂bz = 2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8-300 K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitrobenzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal-bipyramidal coordination polyhedron about the copper atom. The complex 1 exhibits magnetic moment μ_eff = 1.86 B.M. at 300 K which decreases to μ_eff = 1.83 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie-Weiss law with Curie constant of 0.442 cm³ K mol⁻¹ and with Weiss constant of −1.0 K. EPR spectra at room temperature as well as at 77 K are of axial type with g_⊥ = 2.065 and g_∥ = 2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with A_II = 160 G, that is consistent with the determined molecular structure of 1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of 1 was extracted from CCD and analyzed. A significant correlation between the average Cu-O_ax bond length and tetragonality parameter τ which was found as a consequence of the Jahn-Teller effect.     

Catalytic and electrochemical properties of new manganese(III) compounds of 2-(2′-hydroxyphenyl)-oxazoline (Hphox or HClphox). Molecular structures of [Mn(Clphox)2(MeOH)2](ClO4) and [Mn(phox)2(MeOH)2][Mn(phox)2(ClO4)2](H2O)2

New manganese(III) complexes of Hphox (2-(2′-hydroxyphenyl)-oxazoline) and HClphox (2-(5′-chloro-2′-hydroxyphenyl)-oxazoline) have been synthesised. The X-ray structures of [Mn(phox)₂(MeOH)₂][Mn(phox)₂(ClO₄)₂](H₂O)₂ and [Mn(Clphox)₂(MeOH)₂](ClO₄) show the manganese(III) ions to be octahedrally coordinated with methanol or perchlorate at the axial coordination sites. The cyclic voltammograms of the complexes, with the exception of [Mn(phox)₂(acac)] (Hacac=2,4-pentanedione), show an irreversible reduction wave of manganese(III) to manganese(II). After addition of an excess of 1-methylimidazole (1-Meim), the reduction process shifts towards lower potentials and becomes (quasi-) reversible, indicating that the presence of 1-Meim affects the catalytic efficiency of the complexes. The complexes catalyse the epoxidation of styrene by dihydrogen peroxide. The cumulative turnover numbers towards styrene oxide obtained after 15 min. vary from 16 for [Mn(Clphox)₂(MeOH)₂](ClO₄) to 26 for [Mn(phox)₂(acac)]. Ligand degradation appears to be the limiting factor for obtaining higher turnover numbers.     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Comparative reactivity of triorganosilanes, HSi(OEt)3 and HSiEt3, with IrCl(CO)(PPh3)2. Formation of IrCl(H)2(CO)(PPh3)2 or Ir(H)2(SiEt3)(CO)(PPh3)2 depending on the substituents at Si

Reaction of HSi(OEt)₃ with IrCl(CO)(PPh₃)₂ (5:1 molar ratio) at room temperature for 1 h gives IrCl(H){Si(OEt)₃}(CO)(PPh₃)₂ (1), which is observed by the ¹H and ³¹P{¹H} NMR spectra of the reaction mixture. The same reaction, but in 20:1 molar ratio at 50 °C for 24 h produces IrCl(H)₂(CO)(PPh₃)₂ (2) rather than the expected product Ir(H)₂{Si(OEt)₃}(CO)(PPh₃)₂ (3) that was previously reported to be formed by this reaction. Accompanying formation of Si(OEt)₄, (EtO)₃SiOSi(OEt)₃, and (EtO)₂HSiOSi(OEt)₃ is observed. On the other hand, trialkylhydrosilane HSiEt₃ reacts with IrCl(CO)(PPh₃)₂ (10:1 molar ratio) at 80 °C for 84 h to give Ir(H)₂(SiEt₃)(CO)(PPh₃)₂ (4) in a high yield, accompanying with a release of ClSiEt₃.     

Syntheses and characterization of the W(II) and W(III) N2 complexes, [WCl2(PMe3)3]2N2 and [WCl3(PMe3)2]2N2

Refluxing WCl₄(PMe₃)₃ under a nitrogen atmosphere in the presence of two equivalents of sodium amalgam leads to a reduction to the W(II) complex [cis,mer-WCl₂(PMe₃)₃]₂N₂ (1), which can be converted to [mer,trans-WCl₃(PMe₃)₂]₂N₂ (2) via appropriate oxidation/chlorination. Structural data have been obtained for both complexes, and demonstrate significantly increased steric crowding in 1 due to PMe₃/PMe₃ interactions. The N-N bond distances in the two compounds are similar, at 1.279(4) and 1.243(18) Å, respectively.     

Synthesis and characterization of SrCu2(O2CR)3(bdmap)3 and Bi2(O2CCH3)4(bdmap)2(H2O) (R = CH3, CF3; bdmap = 1,3-bis(dimethylamino)-2-propanolato)

New mixed metal complexes SrCu₂(O₂CR)₃(bdmap)₃ (R = CF₃ (1a), CH₃ (1b)) and a new dinuclear bismuth complex Bi₂(O₂CCH₃)₄(bdmap)₂(H₂O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF₂ and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi₂O₃ at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2J = 34.0(8) cm⁻¹. Crystal data for 1a: C₂₇H₅₁N₆O₉F₉Cu₂Sr/THF, monoclinic space group P2₁/m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) ų, Z = 2; for 1b: C₂₇H₆₀N₆O₉Cu₂Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) ų, Z = 8; for 2: C₂₂H₄₈O₁₁N₄Bi₂, monoclinic space group P2₁/c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) ų, Z = 4.     

Crystal structures of MoCl2(O)(O2)(OPMePh2)2 and mixtures of MoCl2(O2)(OPPh3)2 and MoCl2(O)(O2)(OPPh3)2: allylic alcohol isomerization studies using MoCl2(O)(O2)(OPMePh2)2

Adding one equivalent of H₂O₂ to compounds of stoichiometry MoCl₂(O)₂(OPR₃)₂, OPR₃ = OPMePh₂ or OPPh₃, leads to the formation of oxo-peroxo compounds MoCl₂(O)(O₂)(OPR₃)₂. The compound MoCl₂(O)(O₂)(OPMePh₂)₂ crystallized with an unequal disorder, 63%:37%, between the oxo and peroxo ligands, as verified by single-crystal X-ray diffractometry, and can be isolated in reasonable yields. MoCl₂(O)(O₂)(OPPh₃)₂, was not isolated in pure form, co-crystallized with MoCl₂(O)₂(OPPh₃)₂ in two ratios, 18%:82% and 12%:88%, respectively, and did not contain any disorder in the arrangement of the oxo and peroxo groups. These complexes accomplish the isomerization of various allylic alcohols. A mechanism of this reaction has been constructed based on ¹⁸O isotopic studies and involves exchange between the alcohol and metal bonded O atoms.     

A novel ferromagnetic coupling one-dimensional complex {Cu(II)(NIT3Py)2[N(CN)2]2(H2O)2}

The novel ferromagnetic coupling one-dimensional complex {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} (NIT3Py=2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group C2/c. The Cu(II) ion is in a distorted octahedral environment. The units of {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} were connected as one-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show that there are intramolecular ferromagnetic interactions and intermolecular antiferromagnetic interactions within the chain.     

Dynamic properties of the fluxional Rh2H(μ-PPh2)2(PPh3)3 complex

The rhodium dimer [Rh₂H(PPh₂)₂(PPh₃)₃]⁻ was prepared from RhCl(PPh₃)₃ and K₄Sn₉ in the presence of 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-crypt)]⁺ salt was isolated and characterized via NMR and X-ray diffraction studies. The solid state structure reveals a binuclear, diphenylphosphido-bridged, 32 electron Rh(I)-Rh(I) complex with edge-shared tetrahedral and square planar Rh centers with overall C_s point symmetry. 1-D and 2-D ¹H, ³¹P, and ³¹P{¹H} NMR experiments were used to characterize the complex.     

Solvent influence in the formation of normal and abnormal carbene complexes in reactions of imidazolium salts with [Ir(H)2(PPh3)2(OCMe2)2]BF4

Abnormal and normal carbene complexes are formed in reactions of 2-pyridylmethylimidazolium salts with [Ir(H)₂(PPh₃)₂(OCMe₂)₂]BF₄ at room temperature in tetrahydrofuran (THF) or dichloromethane (CH₂Cl₂). Reactions in THF lead to the formation of abnormal carbene (C-5 bound), while reactions in CH₂Cl₂ lead to formation of normal carbene (C-2 bound).     

Reaction of Mo(CO)4(NCCH3)2 and 7-aza-2-Tosylnorbornadiene

Reaction of Mo(CO)₄(NCCH₃)₂ and 7-aza-2-tosylnorbornadiene (7-azaNBD) yielded five air-stable Mo complexes. One is Mo(CO)₄(η⁴-7-azaNBD), in which the molybdenum atom is chelated by the two π-bonds of 7-azaNBD. The other four are isomers of Mo(CO)₂(η²-7-azaNBD)₂, in which the molybdenum atoms are chelated by the nitrogen atom and one of the two double bonds of 7-azaNBD. In one pair of the isomers, the metal binds to C(2)C(3) of both 7-azaNBD ligands; whereas in the other pair of isomers the metal binds to C(2)C(3) of one 7-azaNBD ligand and C(5)C(6) of another ligand. All structures were fully characterized by NMR spectra. A single crystal of compound 4 was analyzed by X-ray diffraction analysis, which was found to be monoclinic with a = 8.4199, b = 23.984, c = 16.395 Å, and β = 99.99°.     

Mg-activated double-stranded DNA cleavage by [(bpy)2(OH2)Ru---O---Ru(H2O) (bpy)2]

The reaction of the title complex with DNA has been examined. Addition of [(bpy)₂(OH₂)RuORu(OH₂) (bpy)₂]⁴⁺ to DNA leads to the reduction of the complex to Ru(bpy)₂(OH₂)₂²⁺, as indicated by absorption spectroscopy and cyclic voltammetry. The reaction is accelerated by Mg²⁺. The combined evidence points to a mechanism where the oxo-bridged dimer is hydrolyzed to a monomeric Ru(III) complex that is capable of oxidizing DNA to effect strand scission. Gel electrophoresis demonstrates nicking of supercoiled /gfX174 DNA by [(bpy)₂(OH₂)RuORu(OH₂) (bpy)₂]⁴⁺, and double-stranded cleavage is observed in the presence of Mg²⁺. Linearization of the plasmid prior to treatment with the complex does not lead to further fragmentation, suggesting that supercoiling is required to realize double-stranded cleavage.     

Reactions of Zr(C5H5)(6,6-dmch)(PMe3)2 and Zr(6,6-dmch)2(PMe3)2 (dmch=dimethylcyclohexadienyl) with CO and alkynes

The reactions of Zr(C₅H₅)(6,6-dmch)(PMe₃)₂ and Zr(6,6-dmch)₂(PMe₃)₂ (dmch=dimethylcyclohexadienyl) with CO lead to the selective replacement of one PMe₃ ligand by CO. Both carbonyl complexes have been structurally characterized. Additionally, the reaction of the latter complex with PhC₂SiMe₃ leads to a similar replacement of one PMe₃ ligand, involving simple coordination of the alkyne, rather than any coupling to the dmch ligand.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)

Complexes of the types cis- and trans-Pt(amine)₂(NO₃)₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph-R-NH₂ (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In ¹⁹⁵Pt NMR spectroscopy, the dinitrato complexes of the amines Ph-R-NH₂ were observed around −1700 ppm for the cis isomers and at about −1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, −1528 ppm for cis-Pt(PhNH₂)(NO₃)₂ and around −1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine)₂(NO₃)₂ complexes and the pK_a of the protonated amines. The coupling constants ²J(¹⁹⁵Pt-¹HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)₂(R(COO)₂) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.     

Reduction of acetonitrile by neodymium diiodide: Molecular structure of [{(HNCMe)2MeCNH2}NdI(MeCN)5]I2 and [{(HNCMe)2MeCNH2}Nd(MeCN)6]I3

The reaction of neodymium diiodide NdI₂ (1) with acetonitrile is accompanied by C-C coupling and formation of bis(ethylimine)ethylamine/acetonitrile complexes {[(MeCNH)₂CMeNH₂]NdI(MeCN)₅}I₂ (2) and {[(MeCNH)₂CMeNH₂]Nd(MeCN)₆}I₃ (3). Yields of the products are 9% and 50%, respectively. Probable scheme of the complexes formation is discussed. Treatment of 3 with 2 equiv. of 1 in THF affords NdI₃(THF)₃, hydrogen and monoiodide complex containing presumably bis(imide)amine ligand, NdI[(MeCN)₂CMeNH₂]. The X-ray analysis revealed that in the molecule of 2 one I⁻ anion is directly bonded to Nd³⁺ cation while two other I⁻anions are not in contact to the metal centre. The molecule of 3 is isostructural to previously obtained Dy and Tm analogues. All three I⁻ anions in it are located away from Nd³⁺ cation.