Chemistry of re with N,N'-bis(2-pyridylmethyl)ethylenediamine (H2pmen): hydrolysis, dehydrogenation, and ternary complexes

A number of Re complexes with N,N'-bis(2-pyridylmethyl)ethylenediamine (H2pmen) have been made from [NH4][ReO4]. [ReOCl2(H2pmen)]Cl, [ReOCl(Hpmen)][ReO4], and [ReO2(H2pmen)][ReO4] are related by hydrolysis/HCl substitution. [ReOCl(Hpmen)][ReO4] was structurally characterized and found to contain a water-stable amido-Re bond. Dehydrogenation of the N-donor ligand from each amine to imine with concomitant two-electron reduction of the Re center occurs readily in these systems. With suitable 3-hydroxy-4-pyrones, ternary complexes such as [ReIIICl(ma)(C14H14N4)][ReO4].CH3OH, 5, were made from [NH4][ReO4], H2pmen.4HCl and pyrones in one-pot syntheses. 5, a seven-coordinate ReIII complex, was structurally characterized.     

The structural and spectroscopic characterisation of three actinyl complexes with coordinated and uncoordinated perrhenate: [UO2(ReO4)2(TPPO)3], [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2 and [NpO2(TPPO)4][ReO4

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO2(ReO4)2(TPPO)3] (1). In this [UO2]2+ complex two [ReO4]- anions and three TPPO (triphenylphosphine oxide) P=O donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective "shell" around a hydrophilic core of two UO2(ReO4)2 moieties. Solid state vibrational spectroscopy (infrared and Raman), 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and [ReO4]- groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [[(UO2)(TPPO)3]2(mu2-O2)][ReO4]2, 2, in which the coordinated [ReO4]- groups of 1 have been displaced by bridging O2(2-), derived from atmospheric O2. Finally, attempts to synthesise a [NpO2]+ analogue of have resulted only in the formation of [NpO2(TPPO)4][ReO4], 3, in which [ReO4]- acts solely as a counter anion. From these results it can be concluded that [ReO4]- will bond to [UO2]2+, but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, [NpO2]+, under the same reaction conditions.     

Rhenium(V) oxo complexes with N-heterocyclic carbenes

Air-stable rhenium(V) oxo complexes are formed when [ReOCl(3)(PPh(3))(2)] is treated with N-heterocyclic carbenes of the 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene type, L(R) (R = Me, Et, i-Pr). Complexes of the compositions [ReO(2)(L(R))(4)](+), [ReOCl(L(R))(4)](2+), or [ReO(OMe)(L(R))(4)](2+) can be isolated depending on the alkyl substituents at the nitrogen atoms of the ligands and the reaction conditions applied. Despite the steric overcrowding of the equatorial coordination spheres of the metal atoms by each of the four carbene ligands, stable complexes with six-coordinate rhenium atoms are obtained. Steric demands of the alkyl groups allow control of the stability of the mono-oxo intermediates. Air-stable cationic complexes of the compositions [ReOCl(L(Me))(4)](2+), [ReOCl(L(Et))(4)](2+), and [ReO(OMe)(L(Me))(4)](2+) have been isolated, whereas reactions of [ReOCl(3)(PPh(3))(2)] or other rhenium(V) precursors with the more bulky 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (L(i)(-)(Pr)) directly yield the dioxo complex [ReO(2)(L(i)(-)(Pr))(4)](+). X-ray structures of [ReO(2)(L(i)(-)(Pr))(4)][ReO(4)], [ReO(2)(L(i)(-)(Pr))(4)][PF(6)], [ReO(2)(L(Me))(4)][ReO(4)](0.45)[PF(6)](0.55), [ReO(MeOH)(L(Me))(4)][PF(6)](2), and [ReOCl(L(Et))(4)][PF(6)](2) show that the equatorial coordination spheres of the rhenium atoms are essentially planar irrespective of the steric demands of the individual carbene ligands.     

Synthesis, characterization, and stereochemistry of oxorhenium(V) complexes with 2-aminoethanethiolate

A series of oxorhenium(V) complexes with 2-aminoethanethiolate (aet), [ReO(aet-N,S)(D-pen-N,O,S)] (2), [[ReO(aet-N,S)(2)](2)O] (3), [ReO(Cl)(aet-N,S)(2)] (4), and [ReO(aet-N,S)(Haet-S)(2)]Cl(2) ([5]Cl(2)) was newly prepared starting from ReO(4)(-). The reaction of NH(4)ReO(4) with a 1:1 mixture of Haet.HCl and D-H(2)pen (D-penicillamine) in the presence of SnCl(2).2H(2)O in water gave 2, 3, and the known complex [ReO(D-Hpen-N,S)(D-pen-N,O,S)] (1). These complexes were fractionally precipitated by controlling the pH of the reaction solution. The complex 2 was also prepared in a higher yield by a similar reaction using methanol as a solvent. The crystal structure of 2 was determined by X-ray crystallography; 2 crystallizes in the tetragonal space group P4(3) with a = 9.621(1), c = 12.911(1) A, V = 1195.0(3) A(3), and Z = 4. The oxorhenium(V) core in 2 is coordinated by a bidentate-N,S aet ligand and a tridentate-N,O,S D-pen ligand, having a distorted octahedral geometry with a cis-N cis-S configuration in the equatorial plane perpendicular to the O-Re-O axis. The 1:2 reaction of NH(4)ReO(4) with Haet.HCl in the presence of SnCl(2).2H(2)O in methanol produced 4, which is interconvertible with 3, while the corresponding 1:3 reaction resulted in the isolation of [5]Cl(2). The complexes 4 and 5 were also structurally characterized; 4 crystallizes in the monoclinic space group P2(1)/c with a = 6.839(1), b = 10.0704(6), c = 14.1075(8) A, beta = 91.729(8) degrees, V = 971.2(2) A(3), and Z = 4, while [5]Cl(2) crystallizes in the triclinic space group P1 with a = 11.938(3), b = 12.366(3), c = 5.819(1) A, alpha = 102.71(2), beta = 101.28(2), gamma = 75.41(2) degrees, V = 802.0(3) A(3), and Z = 2. In 4, the oxorhenium(V) core is octahedrally coordinated by two bidentate-N,S aet ligands, which form a cis-N cis-S configurational equatorial plane with a Cl(-) ion trans to the oxo ligand. On the other hand, the oxorhenium(V) core in [5](2+) is coordinated by one bidenate-N,S aet and two monodentate-S Haet ligands, having a distorted trigonal-bipyramidal geometry with S and N donors at the apical positions.     

Synthesis and Characterization by (19)F and (125)Te NMR and Raman Spectroscopy of cis-ReO(2)(OTeF(5))(3) and cis-ReO(2)(OTeF(5))(4)(-), and X-ray Crystal Structure of [N(CH(3))(4)(+)][cis-ReO(2)(OTeF(5))(4)(-)

The pentafluorooxotellurate compound ReO(2)(OTeF(5))(3) has been synthesized from the reaction of ReO(2)F(3) with B(OTeF(5))(3) and structurally characterized in solution by (19)F and (125)Te NMR spectroscopy and in the solid state by Raman spectroscopy. The NMR and vibrational spectroscopic findings are consistent with a trigonal bipyramidal arrangement in which the oxygen atoms and an OTeF(5) group occupy the equatorial plane. The (19)F and (125)Te NMR spectra show that the axial and equatorial OTeF(5) groups of ReO(2)(OTeF(5))(3) are fluxional and are consistent with intramolecular exchange by means of a pseudorotation. The Lewis acid behavior of ReO(2)(OTeF(5))(3) is demonstrated by reaction with OTeF(5)(-). The resulting cis-ReO(2)(OTeF(5))(4)(-) anion was characterized as the tetramethylammonium salt in solution by (19)F and (125)Te NMR spectroscopy and in the solid state by Raman spectroscopy and X-ray crystallography. The compound crystallizes in the triclinic system, space group P&onemacr;, with a = 13.175(7) ?, b = 13.811(5) ?, c = 15.38(1) ?, alpha = 72.36(5)(o), beta = 68.17(5)(o), gamma = 84.05(4)(o), V = 2476(2) ?(3), D(calc) = 3.345 g cm(-)(3), Z = 4, R = 0.0547. The coordination sphere about Re(VII) in cis-ReO(2)(OTeF(5))(4)(-) is a pseudooctahedron in which the Re-O double bond oxygens are cis to one another.     

Nmr study of the solution structures of TcO(2)F(3) and ReO(2)F(3)

Both TcO(2)F(3) and ReO(2)F(3) are infinite chain, fluorine-bridged polymers in the solid state. Their solution structures have been studied by (19)F and (99)Tc NMR spectroscopy in SO(2)ClF solution and shown to exhibit cyclic (MO(2)F(3))(3) (M = Tc, Re) and (ReO(2)F(3))(4) structures that have been confirmed by simulation of the (19)F NMR spectra. The trimers dominate in both the technetium and rhenium systems, with both the tetramer and trimer existing in equilibrium in the rhenium system. A low concentration of a higher, possibly pentameric, cyclic rhenium polymorph is also present in equilibrium with the trimer and tetramer.     

Seven-coordinate [ReVON4X2]+ complexes (X = O and Cl)

The oxorhenium(V) complexes with ligands containing N4 (H2pmen) and N4O2 (H2bbpen, H2Clbbpen, and H2bped) donor atom sets have been synthesized. X-ray crystallographic analyses of the [ReO(H2pmen)Cl2]+, [ReO(bbpen)]+, and [ReO(bped)]+ complexes showed that all three cations share a rare seven-coordinate structure with a distorted pentagonal bipyramidal geometry, which represents a novel and potentially general structural motif in ReV = O complexes. 1H NMR spectroscopy shows that the structures of the complexes are retained in the solution.     

A selenium-bonded oxorhenium(V) complex: solvothermal synthesis,structural characterization,and electrochemical behavior

The solvothermal reaction of [ReOCl₃(PPh₃)₂] with 2,2′-seleno-bis(4,6-di-tert-butylphenol) (H₂L¹) in ethanol at 95 °C resulted in an oxorhenium(V) complex of formulation [ReO(L¹)(L²)] due to the in situ formation of 2-selenochloromethyl-4,6-di-tert-butylphenolate (L²) through the cleavage of one C–Se bond of H₂L¹. The mononuclear oxorhenium(V) complex was characterized by physicochemical and spectroscopic methods along with detailed structural analysis by single crystal X-ray crystallography. Electrochemical studies revealed a one-electron equivalent quasi-reversible voltammogram for the ReO(V)/ReO(VI) redox couple at 1.28 V (versus SCE) with no cathodic response for ReO(V) → ReO(IV) reduction.     

Heterobinuclear and Heterotrinuclear complexes of Oxorhenium(V) with Cu(II), Ni(II), Fe(III), UO2(VI) and Th(IV) in the solid state

New heteronuclear complexes containing oxorhenium(V), Cu(II), Ni(II), Fe(III), UO₂(VI) and Th(IV) ions were prepared by the reaction of the complex ligand, [ReO(H₄L)Cl]Cl₂, where H₄L = 8,17-dimethyl-6,15-dioxo-5,7,14,16-tetrahydrodibenzo[a,h][14]annulene-2,11-dicarboxylic acid, with the previous transition and actinide salts. Three heteronuclear Cu(II) complexes were isolated depending on the ratio of [ReO(H₄L)Cl]Cl₂?:?Cu(II) ion. When the ratios were 1?:?0.5, 1?:?1 and 1?:?2, the heteronuclear complexes {[ReO(H₃L)Cl]₂CuCl₂(OH₂)₂}SO₄ · H₂O (I), [ReO(H₃L)Cl₂Cu(OH₂)₂(SO₄)] (II) and {ReO(H₂L)Cl[Cu(OH₂)₃ SO₄]₂} (III) were obtained, respectively. Heteronuclear complexes of the other metal cations were obtained by mixing [ReO(H₄L)Cl]Cl₂ with the metal salt in the ratio 1?:?1 to obtain the heteronuclear complexes [ReO(H₃L)Cl₂Ni(OH₂)₂](NO₃)₂ (IV), [ReO(H₃L)Cl₃Fe(OH₂)₃](NO₃)₂ (V), [ReO(H₃L)ClUO₂(NO₃)₂ (OH₂)]Cl (VI) and [ReO(H₃L)Cl₃Th(NO₃)₂(OH₂)]NO₃ · 2H₂O (VII). The complex ligand coordinates with the heterometal ion via the carboxylate group, and the infrared bands ν_as COO and ν_s COO indicate that the carboxylate acts as a unidentate ligand to the heterometal cations. Cu(II) and Fe(III) cations in the heteronuclear complexes have octahedral geometry, while Ni(II) is square planar. Thermal studies explored the possibility of obtaining new heteronuclear complexes pyrolytically in the solid state from the corresponding mother complexes. The structures of the complexes were elucidated by conductance, IR and electronic spectra, magnetic moments, ¹H NMR and TG-DSC measurements as well as by mass spectroscopy.     

The synthesis, structural, and spectroscopic characterization of uranium(IV) perrhenate complexes

We report the synthesis, structural, and spectroscopic characterization of a series of uranium(IV)-perrhenato complexes. Three isostructural complexes with general formula [U(ReO4)4(L)4] (where L = tri-n-butylphosphine oxide/TBPO (2), triethyl phosphate/TEP (3), or tri-iso-butyl phosphate/TiBP (4)), have been synthesized, both through the photoreduction of ethanolic {UO2}2+ solutions and also via a novel U(IV) starting material, U(ReO4)4.5H2O (1). Compound 1 has also been used in the preparation of [U(ReO4)4(TPPO)3(CH3CN)].2CH3CN (5) and [U(ReO4)(DPPMO2)3(OH)][ReO4]2.2CH3CN (6), where TPPO represents triphenylphosphine oxide and DPPMO2 represents bis(diphenylphosphino)methane dioxide. All six complexes have been spectroscopically characterized using NMR, UV-vis-NIR, and IR techniques, with 2, 3, 5, and 6 also fully structurally characterized. The U atoms in compounds 2-6 all exhibit eight-coordinate geometry with up to four perrhenate groups in addition to three (DPPMO2 and TPPO) or four (TEP, TiBP, TBPO) coordinated organic ligands. In the case of compounds 5 and 6, the coordination of eight ligands to the U(IV) center is completed by the binding of a solvent molecule (CH3CN) and OH-, respectively. Solid-state physical analysis (elemental and thermogravimetric) and infrared spectroscopy are in agreement with the structural studies. The crystallographic data suggest that the strength of the U(IV)-O-donor ligand bonds decreases across the series R3PO > [ReO4]- > (RO)3PO. Solution-state IR and 31P NMR spectroscopy appear to be in agreement with these solid-state results.     

Discrete and monodimensional heteropolynuclear structures formed by tetracarboxylatodiruthenium(II,III) and perrhenato fragments

Reaction between cationic units of carboxylate-bridged diruthenium complexes [Ru(2)(mu-O(2)CR)(4)](+) (R = Me, CMePh(2), CMe(3), CH(2)CH(2)OMe, C(Me)=CHEt, C(6)H(4)-p-OMe, Ph) and tetrabutylammonium perrhenate gives complexes with different arrangements in the solid state. Thus, the compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)) [R = Me (1), CMePh(2) (2), CMe(3) (3), CH(2)CH(2)OMe (4), C(Me)=CHEt (5), C(6)H(4)-p-OMe (6), Ph (7)] have polymeric structures with the diruthenium units linked by perrhenate ligands in the axial positions. The structures of complexes 3.THF and 4 were established by single-crystal X-ray diffraction. The tetrahedral geometry of the ReO(4)(-) anion permits the formation of a chain close to the linearity. In contrast to the polymeric chains observed in complexes 1-7, the reaction of [Ru(2)(mu-O(2)CPh)(4)](+) with NBu(4)ReO(4) also affords the compounds Ru(2)(mu-O(2)CPh)(4)(ReO(4))(H(2)O) (8) and NBu(4)[Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)] (9) depending on the reaction conditions. The structure of 8 consists of cationic and anionic units, [Ru(2)(mu-O(2)CPh)(4)(H(2)O)(2)](+) and [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-), linked by hydrogen bonds, which give a three-dimensional net. The structure of complex 9.0.5H(2)O has an anionic unit similar to that of 8, whose counterion is NBu(4)(+). The Ru-Ru bond distances are slightly longer in [Ru(2)(mu-O(2)CPh)(4)(ReO(4))(2)](-) than in the polymeric compounds Ru(2)(mu-O(2)CR)(4)(ReO(4)). The magnetic behavior owes to the existence of zero-field splitting (ZFS) and a weak antiferromagnetic coupling. The experimental data are fitted with a model that considers the ZFS effect using the Hamiltonian (D) = SDS. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation.     

Development of a highly selective cell-permeable ratiometric fluorescent chemosensor for oxorhenium(V) ion

A novel 6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-c]quinazoline (HL) serves as a first-time highly selective and sensitive ratiometric fluorescent chemosensor probe for oxorhenium (ReO(V)) ion in acetonitrile : water = 9 : 1 (v/v) at 25 °C. The decrease in fluorescence at 410 nm and increase in fluorescence at 478 nm with an isoemissive point at 444 nm in the presence of ReO(V) ion is accounted for by the formation of mononuclear [ReOL(2)Cl] complex, characterized by physico-chemical and spectroscopic tools. The fluorescence quantum yield of the chemosensor (HL) was only 0.198 at 410 nm, and it increased more than 3-fold in the presence of 2 equiv. of the ReO(V) ion at 478 nm. Interestingly, the introduction of other metal ions and relevant anions caused the fluorescence intensity at 478 nm to be either unchanged or weakened. The fluorescence-response fits a Hill coefficient of 2.088 indicates the formation of a 1 : 2 stoichiometry for the L-ReO(V) complex. In the concentration range of 0-20 μM of oxorhenium(V) species calibration graph was linear with correlation coefficient (R) of 0.99994 and the calibration sensitivity was found to be 4.0 × 10(-7) M. The cellular image in the confocal microscope clearly indicated the presence of ReO(V) in Candida albicans cells using this chemosensor (HL).     

[ReO(MPMEP)(BMPBA)][ReO(MPMEP)(BMPBA)]的合成和结构

合成了未见文献报道的[ReO(MPMEP)(BMPBA)][ReO(MPMEP)(BMPBA)]配合物,其 中MPMEP = 1-（2-甲氧基苯基）-4-（2-巯基乙基）哌嗪,BMPBA = N,N-二（2-巯 基乙基）苄胺,并在适当的溶剂中培养出单晶,用X射线单晶衍射法测定了单晶结 构,晶体属三斜晶系,空间群P1,晶胞参数a = 0.93604(19) nm,b = 1.1044(2) nm,c = 1.3823(3) nm;α = 89.19(3)°,β = 74.50(3)°,γ = 75.04(3)° ;Z = 1,V = 1.3281(5) nm~3,μ = 4.836 mm~(-1),F(000) = 677,R = 0. 0403,wR = 0.0673。配合物的两个[ReO(MPMEP)(BMPBA)]部分均采取扭曲的三角双 锥几何结构,基底面由三齿配体的两个硫原子与氧原子构成,三齿配体的一个氮原 子和单齿配体的一个硫原子分别占取两个顶角位置,硫原子的离子化致使配合物呈 电中性。     

Binary and ternary oxorhenium(V) complexes: synthesis,characterization, and crystal structure

A series of anionic five-coordinate binary oxorhenium(V) complexes with dithiolato ligands, Bu₄N[ReO(L¹)₂] (1a), Bu₄N[ReO(L²)₂] (1b), and Bu₄N[ReO(L³)₂] (1c), and a series of neutral octahedral ternary oxorhenium(V) complexes of mixed dithiolato and bipyridine ligands, [ReO(L¹)(bpy)Cl] (2a), [ReO(L²)(bpy)Cl] (2b), and [ReO(L³)(bpy)Cl] (2c) (where L¹H₂ = ethane-1,2-dithiol, L²H₂ = propane-1,3-dithiol, L³H₂ = toluene-3,4-dithiol, and bpy = 2,2′-bipyridine), were isolated and characterized by physicochemical and spectroscopic methods. The solid state structure of 1c was established by X-ray crystallography. All the mononuclear oxorhenium(V) complexes are diamagnetic. The redox behavior of all the complexes has been studied voltammetrically.     

Oxygen-containing gas-phase diatomic trications and tetracations: ReO(z+), NbO(z+) and HfO(z+) (z=3, 4)

Three oxygen-containing gas-phase diatomic trications ReO(3+), NbO(3+) and HfO(3+) as well as the diatomic tetracation NbO(4+) have been observed by mass spectrometry at non-integer m/z values. These unusual triply charged molecular ion species, together with the corresponding diatomic dications ReO(2+), NbO(2+) and HfO(2+), were produced by energetic, high-current oxygen ((16)O(-)) ion beam sputtering of rhenium, niobium and hafnium metal samples, respectively, whose surfaces were dynamically oxidized by oxygen primary ion incorporation. In addition, NbO(z+) (z≤ 4) were generated by intense femtosecond laser excitation and photofragmentation (Coulomb explosion) of Nb(x)O(y) clusters and were detected through Time-of-Flight Mass Spectrometry (TOF). Our experimental results confirm previous reports on the detection of NbO(4+), NbO(3+), NbO(2+), HfO(3+) and HfO(2+) with Atom Probe mass spectrometry, whereas ReO(3+) and ReO(2+) apparently had not been observed before. In addition, these multiply charged molecular ions have been studied theoretically for the first time. Ab initio calculations of their electronic structures show that the diatomic trications ReO(3+), NbO(3+) and HfO(3+) are long-lived metastable gas-phase species, with bond lengths of 1.61 ?, 1.62 ? and 1.86 ?, respectively. They present large potential barriers with respect to dissociation of more than 2.7 eV. The corresponding diatomic dications are thermochemically stable molecules with very large dissociation energies (>3.5 eV). Our calculations predict the diatomic tetracation ReO(4+) to be a metastable ion species in the gas phase. We compute a potential barrier toward fragmentation of 0.6 eV; its formation requires a quadruple adiabatic ionization energy of 85.7 eV. Even though our calculations show that NbO(4+) is a weakly bound (dissociation barrier ～0.1 eV) metastable molecule, it is here identified via linear time-of-flight mass spectrometry.     

New oxorhenium(V) complexes from the widely used diaminedithiol (DADT) ligand system

Synthesis of the 2,9-dimethyl-4,7-diaza-4-alkyl-2,9-decanedithiol (1, alkyl = morpholinylethyl in a, and alkyl = pyrrolidinylethyl in b), following a widely used synthetic scheme for diaminedithiol (DADT) ligands, led to the isolation of 1-alkyl-2-(1'-methyl-1'-sulfanylethyl)-3-(2' '-methyl-2' '-sulfanylpropyl)diazolidine (3) as the major product. Both ligands 1 and 2 gave complexes with the oxorhenium ReO(V) core. Ligand 1 gave the expected ReO[SNNS] complex (2) with the side chain on nitrogen in the syn configuration. Ligand 3 gave, in the presence of a monodentate aromatic thiol, complexes of the ReO[SNN][S][S] (4) and ReO[SNN][S] type (5), respectively, in which the diazolidine ring has rearranged to a thiazolidine ring. Crystallographic analysis showed that in 4 the coordination geometry about the metal is distorted octahedral where the equatorial plane is defined by the sulfur and one of the nitrogen atoms of the ligand and the two sulfurs of the aromatic thiols, while the axial positions are occupied by the oxygen of the ReO core and the second nitrogen of the ligand. Specifically, complex 4a crystallizes in space group P2(1)/c, a = 15.63(1) A, b = 15.28(2) A, c = 16.07(1) A, beta = 113.78(2) degrees, V = 3512(5) A(3), Z = 4. Complex 4b crystallizes in space group P2(1)/n, a = 14.560(9) A, b = 14.804(9) A, c = 19.85(1) A, beta = 90.94(2) degrees, V = 4278(1) A(3), Z = 4. In 5b, the coordination geometry is distorted square pyramidal with the SNN donor atom of the ligand and the aromatic thiol defining the equatorial plane and the doubly bonded oxygen occupying the apex of the pyramid. Complex 5b crystallizes in space group P(-)1, a = 9.387(5) A, b = 11.306(5) A, c = 14.040(6) A, alpha = 84.51(1) degrees, beta = 84.45(2) degrees, gamma = 87.17(1) degrees, V = 1475(1) A(3), Z = 2. All isolated complexes are neutral and lipophilic. Complete assignments of (1)H and (13)C NMR resonances are reported.     

Olefin epoxidation with bis(trimethylsilyl) peroxide catalyzed by inorganic oxorhenium derivatives. Controlled release of hydrogen peroxide.

The replacement of organometallic rhenium species (e.g., CH(3)ReO(3)) by less expensive and more readily available inorganic rhenium oxides (e.g., Re(2)O(7), ReO(3)(OH), and ReO(3)) can be accomplished using bis(trimethylsilyl) peroxide (BTSP) as oxidant in place of aqueous H(2)O(2). Using a catalytic amount of a proton source, controlled release of hydrogen peroxide helps preserve sensitive peroxorhenium species and enables catalytic turnover to take place. Systematic investigation of the oxorhenium catalyst precursors, substrate scope, and effects of various additives on olefin epoxidation with BTSP are reported in this contribution.     

Calix[4]arene rhenium(V) complexes as potential radiopharmaceuticals

The calix[4]arene platform was used for the syntheses of novel rhenium(V) complexes, that may have potential applications as radiopharmaceuticals. The reaction of ReO(PPh3)2Cl3 with tetradentate N2O2-calix[4]arene ligand 8 in ethanol gave the novel mixed-ligand rhenium complex 9 with the structure ReO(N2O2-calix)OEt. The configuration was elucidated by using a number of 1H NMR techniques. In 9, the ethoxy ligand could be easily and quantitatively exchanged for another monodentate ligand to give complex 12. Tetradentate N2S2-calix[4]arene ligand 15 formed the rhenium complex 16 either via reaction with ReO(PPh3)2Cl3 in an organic solvent or by reaction with rhenium gluconate in an aqueous solution. Complex 16 showed good stability in phosphate-buffered saline solution (37 degrees C, 5 d). The crystal structures of a mono- and a bimetallic complex were determined. The bimetallic N2O2-calixarene complex dimer 11 crystallized in the monoclinic space group C2/c, with a = 38.963(5) A, b = 23.140(6) A, c = 27.382(6) A, beta = 128.456(10) degrees, V = 19,333(7) A3, Z = 8, and final R = 0.0519. The monometallic N2S2 model complex 17 crystallized in the monoclinic space group Cc, with a = 15.715(2) A, b = 12.045(2) A, c = 20.022(3) A, beta = 94.863(12) degrees, V = 3776.3(10) A3, Z = 4, and final R = 0.0342.     

Rhenium(V) oxocomplexes with novel pyrazolyl-based N4- and N3S-donor chelators

The novel pyrazolyl-based ligands 3,5-Me2pz(CH2)2NH(CH2)2NH(CH2)2NH2 and pz*(CH2)2NH-Gly-CH2STrit (pz*=pz, 3,5-Me2pz, 4-(EtOOC)CH(2)-3,5-Me2pz) were synthesized, and their suitability to stabilize Re(V) oxocomplexes was evaluated using different starting materials, namely (NBu4)[ReOCl4], [ReOCl3(PPh3)2] and trans-[ReO2(py)4]Cl. Compound reacts with trans-[ReO2(py)4]Cl yielding the cationic compound [ReO(OMe){3,5-Me2pz(CH2)2N(CH2)2NH(CH2)2NH2}](BPh4) in a low isolated yield. In contrast, the neutral complexes [ReO{pz*(CH2)2NH-Gly-CH2S}] (pz*=pz, 3,5-Me2pz, 4-(EtOOCCH2)-3,5-Me2pz) were synthesized almost quantitatively by reacting [ReOCl3(PPh3)2] or (NBu4)[ReOCl4] with the trityl-protected chelators. The X-ray diffraction analysis of and confirmed the tetradentate coordination mode of the respective ancillary ligands. In the monoanionic chelator coordinates to the metal through four nitrogen atoms, while in the chelator is trianionic, coordinating to the metal through three nitrogens and one sulfur atom. Solution NMR studies of , including two-dimensional NMR techniques (1H COSY and 1H/13C HSQC), confirmed that the N3S coordination mode of the chelators is retained in solution. Unlike , complexes may be considered relevant in the development of radiopharmaceuticals, as further corroborated by the synthesis of the congener [99mTcO{pz(CH2)2-NH-Gly-CH2S}]. This radioactive compound was obtained from 99mTcO4- in aqueous medium, in almost quantitative yield and with high specific activity and radiochemical purity.