Coordination of cyclo-octasulfur and cyclo-heptaselenium to dinuclear rhenium(I) systems

By substitution reactions of the coordinated THF ligands of Re(2)(mu-X)(2)(CO)(6)(THF)(2) by elemental chalcogens (S(8) and red selenium), the complexes Re(2)(mu-X)(2)(CO)(6)(S(8)) (X = Br, 1; I, 2), and Re(2)(mu-X)(2)(CO)(6)(Se(7)), (X = I, 3; Br, 4) have been prepared. Binuclear compound 3 was crystallographically established to be a coordination compound of cyclo-heptaselenium, two adjacent selenium atoms of the Se(7) ligand [Se-Se distance, 2.558(3) A] being bonded to rhenium(I), at an average Re-Se distance of 2.586(3) A, and the nonbonding Re.Re distance being 4.077(3) A. Spectroscopic evidence of the existence of these chalcogen complexes in solution is reported. The Re(2)(mu-X)(2)(CO)(6)(S(8)) complexes undergo S(8) displacement by THF, while the coordinated Se(7) moiety is less readily displaced from 3.     

Coordination polymers from silver(I) and bifunctional pyridyl ligands

Coordination polymers and a macrocycle formed from the reactions between flexible bis(2-pyridyl) ligands and AgCF(3)SO(3) are reported. The type of structure formed depends on the choice of ligand and the stoichiometry of the reaction. When 1 equiv of 1,4-bis(pyridin-2-ylmethoxy)benzene (L2), 4,4'-bis(pyridin-2-ylmethoxy)biphenyl (L4), or bis((4-pyridin-2-ylmethoxy)phenyl)methane (L5) is used, 1D chain coordination polymers held together via Ag-N bonds are generated. When a 2:1 ratio of L2 and silver ion is used, a 2D porous network is formed. The reaction between silver ions with a mixture of ligands (L1 and L2 in 1:1 ratio, L1 = 1,4-bis((pyridin-2-yl-methyl)thio)benzene) results in a novel 1D ABAB type coordination copolymer where L1 and L2 act as a bis-bidentate and a bis-monodentate ligand, respectively. The reaction of 1-(pyridin-2-ylmethoxy)-4-((pyridin-2-yl-methyl)thio)benzene (L3) with silver ions in a 1:1 ratio gives a bimetallic macrocycle rather than a polymeric species. Structural analyses of the polymeric compounds suggest that interactions between the aromatic rings play a significant role in stabilizing the polymeric structures.     

Tricarbonyl complexes of rhenium(I) and technetium(I) with thiourea derivatives

fac-[M(CO)₃X₃]²⁻ complexes (M=Re, X=Br; M=Tc, X=Cl) react with thiourea derivatives under formation of stable rhenium(I) and technetium(I) complexes. The composition of the products can be controlled by the steric requirements of the ligands and their ability to form chelates.The products of reactions with tetramethylthiourea, Me₄tu (I), N,N-diethylthiocarbamoylbenzamidine, H₂Et₂tcb (II), and morpholinylthiocarbamoylbenzamidine, H₂morphtcb (III), have been studied by X-ray crystallography showing that the products belong to three different structural types. A mononuclear complex of the composition fac-[Re(CO)₃Br(Me₄tu)₂] has been isolated with tetramethylthiourea, whereas the thiocarbamoylbenzamidines deprotonate and act as N,S-chelating ligands. This results in the formation of a dimeric [Tc(CO)₃(HEt₂tcb-N,S)]₂ complex with a central, almost square Tc₂S₂ unit and a monomeric compound of the composition [Tc(CO)₃(Hmorphtcb-N,S)(H₂morphtcb-S)]. The latter compound contains a neutral, S-bonded morpholinylthiocarbamoylbenzamidine in the unusual imine form in addition to a chelate-bonded Hmorphtcb⁻ ligand.     

Polyhydroxy complexes of rhenium(VII)

Perrhenate in concentrated alkali forms yellow complexes with a number of polyhydric compounds. With d-gluconolactone it was found that this color was due to a considerable broadening of the perrhenate band in the UV. The optical rotation of alkaline d-gluconate changes markedly on adding perrhenate, and increases almost linearly with increasing NaOH concentration from 2–16.8 M. A continuous variations analysis of this complex in 12M NaOH showed that it was a 1:1 compound of gluconate and perrhenate. Its formation constant was approximately 43 LM⁻¹. Ligands which produced a yellow color with perrhenate in 12 M NaOH, and whose optical rotation changed significantly included d-mannitol, d-glucitol (sorbitol), perseitol, arabinitol and sodium d-xylonate. Ligands which did not react with perrhenate were: ethylene glycol, glycerol, ribitol, ribonolactone and d-allonolactone. It was concluded that vicinal OH-bearing carbon atoms with opposing configurations (D-L) are required to form these complexes, and that the distance between the centers of adjacent oxygen atoms in the ligand is critical in determining whether the perrhenate will form a complex. It was further concluded that ligands of this type stabilize some sort of meso-perrhenate anion. Pertechnetate does not form these complexes under the same conditions.     

Coordination behaviour of acetylacetone-derived Schiff bases towards rhenium(I) and (V)

The oxo-bridged dinuclear rhenium(V) complex [(μ-O){ReOCl(amp)}₂] (1) was prepared by the reaction of trans-[ReOCl₃(PPh₃)₂] and 6-amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one (Hamp) in acetone. The characterization of 1 by elemental analysis, infrared and ¹H NMR spectroscopy and X-ray crystallography shows that amp is coordinated as a monoanionic NNO-donor chelate as an amino-amido ketone. However, the reaction of the similar ligand 7-amino-4,7-dimethyl-5-aza-3-octen-2-one (Hada) with [Re(CO)₅Br] produced fac-[Re(CO)₃Br(Hada)], with Hada coordinated as a neutral bidentate N,N-donor amino-imino-ketone.     

Synthesis and characterization of binuclear transition metal–rhenium(VII) complexes with bridging cyanide ligands

Reacting transition metal complexes in low oxidation states, containing one or two cyanide ligands, with methyltrioxorhenium(VII) leads to bridged mixed metal compounds in good yields. The Re(VII) core is then surrounded by five or six ligands, respectively. The strength of these CN bridges and thus the stability of the newly generated bimetallic compound strongly depends on the donor strength of the ligands surrounding of the Cr/Mo/W or Fe moiety. The stability of the mixed metal molecules is reflected in the temperature dependent behavior of their ¹⁷O-NMR spectra, in their IR (Re=O) stretching frequencies and force constants, as well as several other spectroscopic data. UV–vis absorption spectra show the appearance of charge transfer bands. In the case of the mixed Mo/Re complexes the ⁹⁵Mo-NMR spectroscopy is also a helpful tool to examine the donor capability of the Mo moiety. The described compounds also show photosensitivity.     

Photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand

Highly efficient photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand are reported. The ability to directly populate excited states localized on the bridging ligand is the key for the observed efficient photoisomerization.     

Separation studies of molybdenum(VI) and rhenium(VII) using TPPO as an extractant

A simple, rapid and reproducible method for the extractive separation of molybdenum(VI) and rhenium(VII) is proposed using triphenylphosphine oxide (TPPO) dissolved in toluene as an extractant. The extractions are carried out from the hydrochloric and hydrobromic acid medium. The extraction of molybdenum is quantitative from 2.54-3.10 M hydrochloric acid and from 3.76-3.98 M hydrobromic acid, and that of rhenium is from 6.78-7.91 M hydrochloric acid. The probable nature of the extractable species is established using log distribution ratio-log concentration plots. The method permits mutual separation of molybdenum(VI) and rhenium(VII) and is applicable for the analysis of alloys and pharmaceutical sample. The detection limits for molybdenum(VI) and rhenium(VII) are 0.8 ppm and 4 ppm respectively.     

Extraction of rhenium(VII) by phosphorylated podands

The interphase distribution of ReO ₄ ^- between aqueous H₂SO₄ solutions and solutions of phosphorylated podands in organic solvents is studied. The stoichiometry of extracted complexes is determined. The rhenium extraction efficiency is considered as a function of the structure of the extractant and the nature of the organic solvent.     

Coordination of a tridentate imido-amino-phenolate chelate to rhenium(V)

The complex cis-[Re(apa)Cl₂(PPh₃)] (1) (H₃apa?=?N-(2-aminophenyl)salicylideneamine) was prepared by reaction of trans-[ReOCl₃(PPh₃)₂] with H₃apa in ethanol. Apa acts as a tridentate chelate ligand via the doubly deprotonated amino nitrogen (which is coordinated as an imide), the amino nitrogen and the deprotonated phenolic oxygen atoms. The two chlorides lie cis to each other in a distorted octahedral geometry around the rhenium(V) centre.     

Protonation of N-heterocyclic carbene ligand coordinated to copper(I): Coordination mode of imidazolium cation as a function of counterion as determined by solid-state structures

Reactions of (IPr)Cu(X) (X = Cl or trifluoromethanesulfonate, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) complexes with the strong acids HOTf or HCl result in protonation of the C2 carbon of the IPr ligand to form imidazolium cations. Coordination of the imidazolium to the resulting Cu^I system depends upon the identity of the two counterions (chloride or triflate). The copper complexes [(IPrH)Cu(OTf)(μ-OTf)]₂ and [IPrH][CuCl₂] as well as the imidazolium salt [IPrH][OTf] have been characterized by NMR spectroscopy and single crystal X-ray diffraction studies.     

Radiochemical separation of rhenium(VII) from tungsten(VI)

The absorption of rhenium(VII) and tungsten(VI) ions on Al₂O₃ from HCl, HClO₄, HNO₃, H₂SO₄, H₃PO₄, NaOH, NH₄OH, NaCl, NaF, and Na-tartarate solutions by batch equilibration, as well as by passage through a chromatographic column, has been studied. The results show that rhenium(VII) can be effectively separated from tungsten(VI) using any of the acid or salt solutions investigated. The experimental data allowed to develop a simple procedure for the radiochemical separation of rhenium isotopes from an irradiated WO₃ sample.     

Mesomorphic complexes of rhenium(I) and manganese(I)

Abstract

Following our discovery of liquid crystals based on octahedral manganese(I), we have now extended these studies to the synthesis of what we believe to be unique examples of mesomorphic rhenium-based complexes. These complexes offer advantages over the related manganese(I) systems in that they are more thermally stable. Further, modification of the organic backbone has led to lower melting manganese materials.     

Synthesis and molecular structure of chlorotris(trimethylsilylmethyl)trimethylsilyl-methylidyne rhenium(VII)

The complex Re(CSiMe₃)(CH₂SiMe₃)₃Cl has been isolated as yellow crystals in low yield from the reaction of ReCl₄(THF)₂ with Me₃SiCH₂MgCl and characterised by X-ray crystallography. The molecule has a trigonal bipyramidal geometry with the alkylidyne and chlorine ligands axial.     

Synthesis and characterization of rhenium(VII) oxide complexes of phenothiazines

Summary Five complexes of rhenium(VII) oxide with N-alkylphenothiazines have been synthesized and characterized on the basis of elemental analyses, molar conductances, and u.v.-vis., i.r. and n.m.r. spectral data. The molecular formulas of the new ionic complexes are: [ReO₃(PTZ)₂(H₂O)][ReO₄], PTZ = chlorpromazine, promethazine or ethopropazine; [ReO₃(TF)(H₂O)][ReO₄], TF = trifluoperazine; and [ReO₃(TR)₃][ReO₄(H₂O)₂]·H₂O, TR = thioridazine. Tentative structures have been proposed.     

Metal chelates in adsorption polarography I: Mo(VI) and derivatives of oxine

The formation of complexes between Mo(VI) and 8-hydroxy-quinoline (oxine) and four oxine derivatives were investigated by multiwavelength molecular absorption spectrometry, potentiometry, and polarography. The following pK_OH- and pK_NH- values of the ligands and logK ₂₁₁-values of the complexes MoO₂(OH)₂L ^x– (x=1 or 2) were obtained at 25° C and an ionic strength of 1M(NaClO₄): 5,7-dinitro8-hydroxyquinoline 4.59, <0, 14.50; 7-nitro-8-hydroxyquinoline-5-sulfonic acid 5.34, 0.41, 15.70; 7-iodo-8-hydroxyquinoline-5-sulfonic acid 6.98, 2.62, 17.65; 8-hydroxyquinoline-5-sulfonic acid 8.33, 4.13, 18.71; and 8-hydroxyquinoline 9.62, 5.28, 19.69. A good linearity was found between logK ₂₁₁ and the sum of the pK-values of the OH- and NH⁺-groups. The dependence of the peak current of Mo(VI)-determinations by adsorption polarography of the 7-nitro-8-hydroxyquinoline-5-sulfonate complex of Mo(VI) MoO(OH)₃L^– can quantitatively be described at pH 0.8–2 using the corresponding pK-values and the log K₃₁₁ of 18.54±0.03, determined by polarography.     

Synthesis and structural characterization of acetatobis(triphenylphosphine)dicarbonylrhenium(I). new car☐ylato derivatives of rhenium(I)

Acetatobis(triphenylphosphine)dicarbonylrhenium (I), (PPh₃)₂(CO)₂Re(O₂CCH₃), has been prepared in a novel way by treating (PPh₃)₂(CO)₂Re(NHCOR) (R = C₆H₅, p-MeC₆H₄) with triethylamine and water in the presence of air. Oxidation of the ethyl group of the tertiary amine is presumably involved in the formation of the acetate ligand. Three-dimensional single-crystal X-ray diffraction analysis shows that the complex is octahedral with the phosphines in trans positions and the acetate ion acting as a chelating ligand. The complex crystallizes in theP2₁/c space group with cell dimensions a = 17.63(2), b = 9.72(1), c = 20.95(2)Å, β = 104°38'(6'), Z = 4. The mean values of bond lengths observed are Re-P 2.415, Re-O 2.21 and Re-(CO) 1.85Å. The same acetate derivative and a series of car?ylato complexes (PPh₃)₂(CO)₂Re(O₂CR') have been obtained from reactions of Re(CO)₂(PPh₃)₃H with car?ylic acids R'COOH (R' = H, CH₃, CH₂Cl, CH₂CH₃, C₆H₅). When trifluoroacetic acid is used, a product of formula (PPh₃)₂(CO)₃Re(OC(O)CF₃) is isolated. The action of neutral ligands L on some of these products gave rise to derivatives of formula (PPh₃)₂(CO)₂(L)Re(OC(O)R') (L = CO, R' = H, CH₃, C₆H₅; L = pMeC₆H₄NC, R' = CH₃), having monodentate car?ylato moieties.     

Coordination of a chiral tin(ii) cation bearing a bis(oxazoline) ligand with tetrahydrofuran derivatives

The reaction of SnCl(2) with the lithio derivative of a bis(oxazoline) ligand precursor afforded the enantiomeric chlorostannylene whose chloride ion can be substituted by several neutral or anionic Lewis donors. Abstraction of the chloride ion from the chlorostannylene with silver salts gave the corresponding tetrahydrofuran (THF) complexes of a chiral tin(ii) cation in 1,2-dimethoxyethane (DME) containing THF. That is, the reaction with silver hexafluoroantimonate (AgSbF(6)) afforded the THF complex without interaction with the counteranion. In contrast, reaction with silver triflate (AgOTf) gave the THF complex whose tin center had a pseudo-trigonal bipyramidal structure with two nitrogen atoms of a bidentate ligand and a lone pair at the equatorial positions and one of the oxygen atoms of triflate and an oxygen atom of THF at the apical positions in the solid state. Use of 3-methyltetrahydrofuran (3-MeTHF) instead of THF afforded the 3-MeTHF complexes, where the R-enantiomer of 3-MeTHF predominantly coordinates to the tin center. The previously reported germanium(ii) analogue of the tin(ii) cation indicated a similar enantioselectivity for the coordination of 3-MeTHF on the germanium center.     

Glucosamine conjugates of tricarbonylcyclopentadienyl rhenium(I) and technetium(I) cores

To obtain a 99mTc glucose conjugate for imaging, double-ligand transfer (DLT) and related reactions were examined for the preparation of CpM(CO)3 (Cp = cyclopentadienyl; M = Re, Tc) complexes with pendant carbohydrates at Cp. Tricarbonyl{N-(1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-beta-D-glucopyranose)cyclopentadienyl carboxamide}rhenium(I) (1a) and tricarbonyl{N-(2-amino-2-deoxy-beta-D-glucopyranose)cyclopentadienyl carboxamide}rhenium(I) (2a) were prepared. The compounds were fully characterized by mass spectrometry, elemental analysis, IR, and NMR spectroscopy. Full assignment of the NMR spectra verified the pendant nature of the glucosamine moieties in the solution state and that 2a exists as both anomers. The solid-state structure of 2a was determined by X-ray crystallography, again confirming the pendant nature of the glucosamine, but differing from the solution state in that the beta anomer crystallized preferentially (93%). Compound 2a was determined to be a high-affinity competitive inhibitor (Ki = 330 +/- 70 microM) of the glucose metabolism enzyme hexokinase, demonstrating that it retains certain biological activity. The 99mTc analogues 1b and 2b were prepared in moderate radiochemical yields by means of the single-ligand transfer (SLT) route, which is more pertinent to radiopharmaceutical synthesis.