Rhenium Derivatives Research Articles

σ-Hole Interactions Involving a Group 7 Metal: Close Contacts in Neutral and Anionic Rhenium Derivatives

Some cases of close contacts involving rhenium of perrhenate esters are presented and investigated computationally. The structures and calculated interaction energies confirm the attractiveness of these contacts, which display geometries typical of σ-hole interactions. The short Re···O contacts observed in three crystalline perrhenate salts confirm the general ability of rhenium compounds, both neutral and ionic, to form such interactions.

Biological Activity of fac-[Re(CO)3(phen)(aspirin)], fac-[Re(CO)3(phen)(indomethacin)] and Their Original Counterparts against Ishikawa and HEC-1A Endometrial Cancer Cells.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are inhibitors of cyclooxygenase enzyme (COX) and were found to have positive effects in reducing the risk of developing gynecological cancers. However, long-term administration of NSAIDs carries the risk of various side effects, including those in the digestive and circulatory systems. Therefore, there is a constant need to develop new NSAID derivatives. In this work, we investigated rhenium NSAIDs, comparing their effects on endometrial cancer cells with original NSAIDs, demonstrating the high activity of aspirin and indomethacin derivatives. The cytotoxic activity of rhenium derivatives against the Ishikawa and HEC-1A cancer cell lines was higher than that of the original NSAIDs. The IC50 after 24-h incubation of Ishikawa and HEC-1A were 188.06 µM and 394.06 µM for rhenium aspirin and 228.6 µM and 1459.3 µM for rhenium indomethacin, respectively. At the same time, IC50 of aspirin and indomethacin were 10,024.42 µM and 3295.3 µM for Ishikawa, and 27,255.8 µM and 5489.3 µM for HEC-1A, respectively. Moreover, these derivatives were found to inhibit the proliferation of both cell lines in a time- and state-dependent manner. The Ishikawa cell proliferation was strongly inhibited by rhenium aspirin and rhenium indomethacin after 72-h incubation (*** = p < 0.001), while the HEC-1A proliferation was inhibited by the same agents already after 24-h incubation (*** = p < 0.001). Furthermore, the ROS level in the mitochondria of the tested cells generated in the presence of rhenium derivatives was higher than the original NSAIDs. That was associated with rhenium indomethacin exclusively, which had a significant effect (*** = p < 0.001) on both Ishikawa and HEC-1A cancer cells. Rhenium aspirin had a significant effect (*** = p < 0.001) on the mitochondrial ROS level of Ishikawa cells only. Overall, the research revealed a high potential of the rhenium derivatives of aspirin and indomethacin against endometrial cancer cells compared with the original NSAIDs.

Rhenium(I) derivatives of aminoquinoline and imidazolopiperidine-based ligands: Synthesis, in vitro and in silico biological evaluation against Plasmodium falciparum

A small library of aminoquinoline and imidazolopiperidine (IMP)-based ligands, containing the 1,2,3-triazole moiety, and their corresponding tricarbonyl rhenium complexes were synthesised and their inhibitory activities evaluated against the chloroquine-sensitive (CQS) and multidrug-resistant (MDR) strains (NF54 and K1, respectively) of P. falciparum. The quinoline-based compounds (L1, L2, ReL1, and ReL2) were at least six-fold more potent than their IMP-based counterparts (L3, L4, ReL3, and ReL4) against both strains of P. falciparum, with the most promising compound (L1) displaying activity comparable to chloroquine diphosphate (CQDP) in the MDR strain. Additionally, all of the synthesised compounds have resistance indices less than CQDP. To gain insight into a possible mechanism of action, in silico hemozoin docking simulations were performed. These studies proposed that the tested compounds may act via hemozoin inhibition, as the new aminoquinoline-derivatives, with the exception of complex ReL2 (binding affinity: −12.62 kcal/mol), showed higher binding affinities than the reference drug chloroquine (CQ, −13.56 kcal/mol). Furthermore, the ligands exhibited superior binding affinity relative to their corresponding Re(I) complexes, which is reflected in their antiplasmodial activity.

Rhenium(I) Derivatives of Aminoquinoline and Imidazolopiperidine-Based Ligands: Synthesis, in Vitro and in Silico Biological Evaluation Against Plasmodium Falciparum

Rhenium(I) Derivatives of Aminoquinoline and Imidazolopiperidine-Based Ligands: Synthesis, in Vitro and in Silico Biological Evaluation Against Plasmodium Falciparum

Structure and Thermodynamic Stability of Rhenium and Ruthenium Oxoalkoxo Derivatives MxN4 – xO6(OMе)10 (M, N = Re, Ru; x = 4–0)

Quantum-chemical calculations of the structure and relative thermodynamic stability of tetranuclear clusters MxN4 – xO6(OMе)10 (M, N = Re, Ru; x = 4–0) including geometric isomers of bimetallic clusters are performed to establish the possibility of replacing Re atoms by Ru atoms while maintaining a cyclic tetranuclear structure. As the initial model, the structure of Re4O6(OPri)10 was chosen which is an almost regular rhombus. The values of the metal–metal and metal–oxygen interatomic distances are calculated, and features of their variation under the transition from mononuclear to heteronuclear clusters and from neutral clusters to anions are discussed. Differences between the relative thermodynamic stability of homometallic and heterometallic tetranuclear clusters, including the geometric isomers of the latter, are discussed.

Rhenium and technetium tricarbonyl, {M(CO)3} (+) (M = Tc, Re), binding to mammalian metallothioneins: new insights into chemical and radiopharmaceutical implications.

This paper deals with the binding of the four mammalian metallothioneins (MTs) to the organometallic metal fragment {fac-M(CO)3}(+) (M = (99)Tc, Re), which is highly promising for the preparation of second-generation radiopharmaceuticals. The study of the transmetallation reaction between zinc and rhenium in Zn7-MT1 by means of UV-vis and CD spectroscopy demonstrated the incorporation of the {fac-Re(CO)3}(+) fragment to the MTs. This reaction should be performed at 70 °C to accelerate the reaction rate, a result that is consistent with the reported reactivity of the rhenium fragment. ESI-TOF MS demonstrated the formation of mixed-metal species as Zn6,{Re(CO)3}-MT, Zn6,{Re(CO)3}2-MT, and Zn5,{Re(CO)3}3-MT, as well as the different reactivity of the four MT isoforms. Hence, Zn-MT3 showed the highest reactivity, in agreement with its high Cu-thionein character, whereas Zn-MT2 exhibited the lowest reactivity, in line with its high Zn-thionein character. The reactivity of the Zn-loaded forms of MT1 and MT4 is intermediate between those of MT3 and MT2. The study of the binding of the {fac-(99)Tc(CO)3}(+) fragment to MTs showed a significant and very interesting different reactivity in relation to rhenium. The transmetallation reaction is much more effective with technetium than with rhenium and significant amounts of mixed Zn x ,{(99)Tc(CO)3} y -MT species were formed with the four MT isoforms whereas only MT3 rendered similar amounts of rhenium derivatives. The results obtained in this study support the possible use of technetium for labelling mammalian metallothioneins and also for possible radiopharmaceutical applications.

Deoxydehydration of glycerol to allyl alcohol catalyzed by rhenium derivatives

Both ReO3 and methyltrioxorhenium combined with alcohol reductants are used for the efficient deoxydehydration of glycerol to allyl alcohol.

The prevalence of isocloso deltahedra in low-energy hypoelectronic metalladicarbaboranes with a single metal vertex: manganese and rhenium derivatives

Theoretical studies on the hypoelectronic metalladicarbaboranes CpMC(2)B(n-3)H(n-1) (M = Mn, Re; n = 9, 10, 11) having 2n skeletal electrons indicate that true isocloso MC(2)B(n-3) deltahedra are highly energetically favored in which the metal atom occupies the single degree 6 vertex. This contrasts with the previously studied isoelectronic diferradicarbaboranes Cp(2)Fe(2)C(2)B(n-3)H(n-1) for which the isocloso structure is clearly favored only for the 10-vertex system. For the 12-vertex hypoelectronic manganadicarbaborane CpMnC(2)B(9)H(11) with 2n (= 24) skeletal electrons the lowest energy structures have central MnC(2)B(9) icosahedra. However, for the corresponding rhenadicarbaborane CpReC(2)B(9)H(11) the lowest energy structures have central non-icosahedral ReC(2)B(9) deltahedra with two degree 6 vertices, one of which is occupied by the rhenium atom. The low-energy structures for the metalladicarbaboranes studied in this work relate to the preferences of transition metal atoms for degree 6 vertices but those of boron and carbon for degree 5 and 4 vertices, respectively.

99mTc- and Re-labeled 6-dialkylamino-2-naphthylethylidene derivatives as imaging probes for β-amyloid plaques

Based on the conjugate strategy, two neutral (99m)Tc labeled 2-(1-(6-(dialkylamino)naphthalen-2-yl)ethylidene)malononitrile (DDNP) and 1-(6-(dialkylamino)naphthalen-2-yl)ethanone (ENE) derivatives, and their corresponding rhenium complexes were synthesized. In vitro fluorescent staining indicated that the corresponding rhenium derivatives selectively stained the β-amyloid (Aβ) plaques in the brain sections of AD model mice with low background. Compared with FDDNP and FENE, the affinities of the corresponding rhenium derivatives to Aβ aggregates decreased about 10-14-fold. In vivo biodistribution experiments in normal mice showed that (99m)Tc-MAMA-ENE displayed medium initial brain uptake (0.65%ID/g at 2min) with a reasonable washout from the brain (0.19%ID/g at 2h) while (99m)Tc-MAMA-DDNP showed a low brain uptake (0.28%ID/g at 2 min). Further optimize these (99m)Tc-labeled tracers in order to improve their binding affinities to Aβ plaques and diffusion through the blood brain barrier may generate useful imaging agents for SPECT.

Fluorine and Rhenium Substituted Ghrelin Analogues as Potential Imaging Probes for the Growth Hormone Secretagogue Receptor

In our effort to create imaging probes targeting the growth hormone secretagogue receptor (GHSR), we now report on the design and synthesis of fluorine and rhenium containing ghrelin analogues through modification of the n-octanoyl Ser-3 side chain. Fluorine analogues were designed whereby the fluorine atom is situated at the terminus of an aliphatic chain using diaminopropionic acid (Dpr) as residue-3. Truncated ghrelin(1-5) and ghrelin(1-14) fluorine-bearing analogues were prepared, the best of which had a 28 nM IC(50) for GHSR. Ghrelin(1-14) analogues were also prepared containing rhenium, as a surrogate metal for technetium-99m, with a cyclopentadienylrhenium tricarbonyl being situated at the terminus of the residue-3 side chain, yielding compounds the best of which had a 35 nM IC(50). This represents a rare case of incorporating rhenium into a peptide structure where the metal complex is required for biological activity. These fluorine and rhenium derivatives demonstrate the ability to modify the Ser-3 side chain of ghrelin in order to create imaging probes for the GHSR.

Geometry and chemical bonding in polyhedral boranes, metallaboranes, and dimetallaboranes: From closo to isocloso to oblatocloso polyhedra

Abstract The geometry and chemical bonding in the closo metal-free boranes B n H n 2 - and the isoelectronic carboranes CB n - 1 H n - and C2Bn−2Hn with 2n + 2 skeletal electrons are based on the most spherical deltahedra with a preference for degree 5 vertices, particularly for the boron atoms. Such deltahedral boranes can be considered to be three-dimensional aromatic systems, as indicated by strongly diatropic nucleus independent chemical shift values for B n H n 2 - (n = 6, 8, 9, 12). Metallaborane structures, particularly those with 9–11 vertices and only 2n rather than 2n + 2 apparent skeletal electrons, are often based on isocloso deltahedra with the metal atom at a degree 6 vertex. Dimetallaborane structures, particularly the rhenium derivatives Cp2Re2Bn−2Hn−2 (8 ⩽ n ⩽ 12), are based on highly non-spherical and very oblate deltahedra with the metal atoms typically at degree 6 or 7 vertices, which are the lowest curvature sites of the deltahedra. A viable model for the skeletal bonding in such dimetallaboranes can be developed if each of the two metal vertices is assumed to contribute five internal orbitals to the skeletal bonding. This leads to 2n + 4 skeletal electrons, which are partitioned into n surface bonds and a formal metal–metal double bond inside the oblate deltahedron.

Deuterium Quadrupolar Coupling Constants of Deuteride Bridging Ligands: A Study on Rhenium Hydrido Carbonyl Clusters

Deuterium variable-temperature T1 measurements have been performed for a series of rhenium carbonyl clusters containing doubly and triply bridging deuterides, namely Re2(μ-D)2(CO)8 (1), Re3(μ-D)3(CO)12 (2), Re4(μ3-D)4(CO)12 (3), [NEt4][Re3(μ-D)4(CO)10] (4), [NEt4][Re3(μ-D)3(μ-Cl)(CO)10] (5), and [NEt4][Re3(μ-D)4(CO)9] (6). The deuterium quadrupolar coupling constants (DQCC) of the deuteride ligands have been evaluated for compounds 1−5, while the fluxionality of 6 hampered such a determination. The experimental DQCC of compound 3 (21.8 kHz) was, until now, the smallest found for organometallic compounds. Overall the DQCC values span a 4-fold range, and their fine-tuning depends on the bridging mode of the deuteride ligands (μ3 vs μ), the local unsaturation degree of the Re atoms bridged by the deuteride, and the presence of other bridging ligands. The experimental DQCC's of rhenium derivatives and those of bridging deuterides in Cr, W, and Os clusters linearly correlate with the respective metal−hydrogen ...

The [Re(CO)6]+ Cation as a Ligand-Transfer Reagent with Ferrocene Derivatives

The [Re(CO)6]+ cation is a stable compound, soluble in aqueous media. We show that it can be used as a reagent in the synthesis of tricarbonyl(cyclopentadienyl)rhenium complexes. [Re(CO)6]+ reacts with ferrocene derivatives, particularly acetylferrocene, in DMSO, DMF or a water/DMSO (1:1) mixture at 160 °C to give tricarbonyl(cyclopentadienyl)rhenium derivatives with high yields. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Luminescent metal complexes derived from carbene and related ligands: tuning excited-state properties with metal–carbon multiple bonds

This account begins with a report on the photophysical responses to pH exhibited by the luminescent chelating bis(carbene) platinum(II) complexes [(C10H21N4)Pt(CN)(CN t Bu)] (1) and [(C10H21N4)Pt(CN t Bu)2] (2), and concludes with an overview of recent work by our group regarding luminescent platinum and rhenium derivatives bearing metal‐carbon multiple bonds. © 2001 Elsevier Science B.V. All rights reserved.

Pyrazolato Metal Complexes: Synthesis, Characterization and X-ray Crystal Structures of Rhenium(I) Derivatives

Pyrazolato Metal Complexes: Synthesis, Characterization and X-ray Crystal Structures of Rhenium(I) Derivatives

A simple and efficient method for the preparation of pyridine- N-oxides II

Abstract Oxidation of pyridines with bis(trimethylsilyl)peroxide in the presence of catalytic amounts of inorganic rhenium derivatives gives high yields of their analytically pure N-oxides by simple work-ups, typically a filtration or a Kugelrohr distillation.

Resonance capture of electrons by cyclopentadienyltricarbonylmanganese and -rhenium derivatives

Negative ion mass spectra of cyclopentadienyltricarbonylmanganese and-rhenium derivatives RC5H4M(CO)3 (R=H, CN, COOH, COMe, COOMe, CH2OH, CHO; M=Mn, Re) were studied. The subsequent detachment of carbonyl groups is the main process of the fragmentation of these compounds under the conditions of the resonance capture of electrons. On going fron the rhenium complexes to manganese derivatives, the maxima of the yields of the ions [M-nCO]− (n=1–3) shift to the lower energy region indicating that the stability of the Re−CO bond is higher than that of Mn−CO. The average lifetimes of the molecular negative ions relative to the autodetachment of an electron (τa) and to dissociation (τd) were measured. It was found that electron-accepting substituents increase the τa value and decrease τd.

Formation of antiferromagnetic thiolate-bridged and sulfide-bridged complexes

Reactions of Cp2Cr2(SCMe3)2S (1) with rhenium complexes (CO)(NO)Re(PR3)2X2 [R=Et, X=Cl (7a); R=Et, X=O3SCF3 (7b); R=OMe, X=O3SCF3 (7c)] containing strongly bound phosphine ligands and with Pd(PPri3)2Cl2 (8) containing bulky P donors were studied. The reaction between compounds1 and7a does not occur in various solvents within a temperature range of 22–80 °C. Interaction of1 with triflat derivatives7b and7c yields the paramagnetic tetrahedral homonuclear cationic cluster Cp4Cr4S4+O3SCF3− (10) and the binuclear methylated complex Cp2Cr2(SCMe3)2(SMe)+O3SCF3− (11), respectively. The reaction of compound1 with8 affords the antiferromagnetic heteronuclear cluster Cp2Cr2(SCMe3)S2PdCl(PPri3) (12). The structure of the core of12 is analogous to the structures of the rhodium-containing complexes Cp2Cr2(μ-SCMe3)(μ3-S)2RhL2. Although compound8 reacts with Fe3S2(CO)9 (5), the major products are the homometallic trinuclear clusters Fe3S2(CO)8(PPri3) (14) (as a mixture of isomers) and Fe3S2(CO)7(PPri3)2 (15), whereas the heteronuclear complex (CO)6Fe2S2Pd(PPri3)2 (16) was found only in trace amounts. The reasons for the difference in the reactivities of the rhenium and palladium derivatives toward compounds1 and5 are discussed. The structures of complexes10 (two crystal modifications),11, 12, 15, and16 were established by X-ray structural analysis of the single crystals.

Chemie des η1‐Rhenium‐koordinierten Triphenylcyclopropenyl‐Liganden

Chemistry of the η1‐Rhenium‐Coordinated Triphenylcyclopropenyl LigandThe s̀‐coordinated pentacarbonyl[η1‐1,2,3‐triphenylcyclopropenyl)rhenium complex 1 is transformed into the green tetracarbonyl(η2‐1,2,3‐triphenylpropenetriyl)rhenium compound 2 with loss of CO by heating or irradiation. In addition, tetracarbonyl(η3‐4‐oxo‐1,2,3‐triphenylcyclobutenyl)rhenium (3a) and Tricarbonyl(η5‐1,2,3,4,5,6‐hexaphenylcyclohexadienyl)‐rhenium (4) were obtained from this reaction. Treatment of 1 with trimethylamine N‐oxide leads under oxygen transfer to tetracarbonyl(η2‐3‐oxo‐1,2,3‐triphenyl‐1‐propenyl)rhenium (5) and tricarbonyl(trimethylamine)(η2‐3‐oxo‐1,2,3‐triphenyl‐1‐propenyl)rhenium (6). The NMe3 ligand in 6 can be substituted either by CO or trimethyl phosphite to yield 5 or tricarbonyl‐(trimethyl phosphite)(η2‐oxo‐1,2,3‐triphenyl‐1‐propenyl)‐rhenium (7), respectively. Complex 1 reacts with trimethyl‐phosphane or trimethyl phosphite to give tetracarbonyl(phosphorus donor)(η1‐4‐oxo‐1,2,3‐triphenyl‐2‐cyclobuten‐1‐yl)rhenium 8b [L = PMe3] or 8c [L = P(OMe)3]. The derivatives Re(CO)3L2‐η1‐C3Ph3CO [L = CO, 8a; L = PMe3, 8d; L = P(O‐Me)3 8e] were obtained by treatment of 3a with CO or two equivalents of PMe3 or P(OMe)3. The formation of 8d and 8e proceeded via the tricarbonyl(phosphorus donor)(η3‐4‐oxo‐1,2,3‐triphenylcyclobutenyl)rhenium compounds 3b and 3c. The unusual η1‐coordination of the cyclobutenone system in 8 was established by an X‐ray structure analysis of 8c. Furthermore, 4 and 5 were characterized by single‐crystal X‐ray diffraction. Reactions of 2 with alkynes led to substituted tricarbonyl(cyclopentadienyl)rhenium derivatives Re(η5‐C5Ph3RR')(CO)3 9 (R = R' = Ph, 9a; R = R' = CO2Me, 9b; R = R' = CO2Et, 9c; R = Ph, R' = H, 9d).

Metallic carbonyl complexes containing heterocyclic nitrogen ligands—I. Rhenium derivatives

The preparation and spectroscopic properties of monometallic complexes of rhenium(I)tricarbonylbromide coordinated to 6,7-dihydrodipyrido-[2,3-b : 3′,2′-j]-1,10-phenanthroline (2-4N), 7,8-dihydro-6H-cyclohepta-[2,1-b : 3,4-b]-di-1,8-naphthyridine (3-4N), 2,2′-bi-(3-methyl)-1,8-naphthyridine (Me 2O-4N), 2,2′-bi-1,8-naphthyridine (O-4N) and 2,7-di(2′-pyridyl)-1,8-naphthyridine (bpnp) are described. The complexes show a low energy electronic absorption band which is solvent sensitive and has been assigned as a t 2 g → π* rhenium-to-ligand charge-transfer band. The CO stretching frequencies were in accord with facial geometry for the complexes. The NMR properties agreed with the IR results, showing the equivalence of the two naphthyridine fragments in the complexes. Electrochemically all the complexes display two reductions and two oxidations in the potential region from + 2.0 to - 1.6 V. The reduction potential, E red, for the Re I/Re 0 couple shows a good relationship with the lowest energy absorption band.