Binuclear Rhenium Research Articles

Rhenium(V) Tris(pyrazolyl)borate Thiolate Complex with the Disulfide Bridging Ligand: Synthesis and Structure

The reaction of TpReOCl(StBu) (Tp = tris(pyrazolyl)borate anion) with sodium disulfide in dimethoxyethane affords the new binuclear rhenium complex [TpReO(μ-StBu)]2(μ-S2) (I). Complex I can also be synthesized by the reaction of TpReO(StBu)2 with a suspension of manganese(II) bromide in toluene accompanied by the dealkylation of one of the ligands to form one more new complex [TpReO]2(μ-S2)(μ-S) (II) containing the bridging sulfide and disulfide ligands. The structures of two crystalline solvates of complex I with dichloromethane containing the molecules with different conformations of the Re2S2 fragment (Ia and Ib) and complex II are studied by X-ray diffraction (XRD) (CIF files ССDC nos. 2262677, 2262678, and 2267423 for Ia, Ib, and II, respectively).

Target-specific mononuclear and binuclear rhenium(i) tricarbonyl complexes as upcoming anticancer drugs.

Metal complexes have gradually been attracting interest from researchers worldwide as potential cancer therapeutics. Driven by the many side effects of the popular platinum-based anticancer drug cisplatin, the tireless endeavours of researchers have afforded strategies for the design of appropriate metal complexes with minimal side effects compared to cisplatin and its congeners to limit the unrestricted propagation of cancer. In this regard, transition metal complexes, especially rhenium-based complexes are being identified and highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body. This is attributed the amazing photophysical properties of rhenium complexes together with their ability to selectively attack different organelles in cancer cells. Therefore, this review presents the properties of different rhenium-based complexes to highlight their recent advances as anticancer agents based on their cytotoxicity results.

Synthesis, crystal structure and photoluminescence of a binuclear rhenium(I) carbonyl complex incorporated in a framework of a distorted salophen ligand

Abstract Re(CO)5Cl reacts with salophenH2 to yield Re(I)2(salophenH)(CO)6Cl. A crystal structure determination has shown that this binuclear complex contains two Re(CO)3 fragments which are bridged by a chloride and a heavily constrained salophenH– anion as ligands. Under ambient conditions in solution and in the solid state, the complex displays an orange emission which originates from the lowest-energy IL/MLCT triplet. In solution, this phosphorescence is completely quenched by oxygen.

Host-guest interaction studies of polycyclic aromatic hydrocarbons (PAHs) in alkoxy bridged binuclear rhenium (I) complexes.

The interaction of two neutral alkoxy bridged binuclear rhenium(I) complexes, 1 and 2 [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, R = C10H21; 1,4-NVP = 4-(1-naphthylvinyl)pyridine] with polycyclic aromatic hydrocarbons (PAH) is investigated. UV-vis absorption, emission, 1H NMR spectral titrations, TCSPC lifetime studies and DFT theoretical calculations were carried out to examine the binding responses of complexes 1 and 2 with various PAHs such as pyrene, naphthalene, anthracene and phenanthrene. The UV-Vis absorption spectra showed an increase in absorbance of the metal-to ligand charge-transfer (MLCT) and ligand centered (LC) bands upon addition of various PAH molecules to 1 and 2, whereas the emission behavior was found to show emission quenching, which might occur through energy transfer pathway. The binding constants (K) of complexes 1 and 2 for various PAHs are found to be in the order of 104 M-1 with a 1:1 binding mode, as determined from UV-vis absorption and emission spectral titration studies. 1H NMR spectral studies show that the chemical shifts of pyrene guest and the 1,4-NVP moiety of 2 are shifted up-field, whilst the alkoxy protons do not show any appreciable change in their chemical shifts. It is believed that the open cavities present in the Re(I) complexes may lead to the recognition of PAHs via CH···π interaction.

Mitochondria-Accumulating Rhenium(I) Tricarbonyl Complexes Induce Cell Death via Irreversible Oxidative Stress and Glutathione Metabolism Disturbance.

Mitochondria play a critical role in tumorigenesis. Targeting mitochondria and disturbing related events have been emerging as a promising way for chemotherapy. In this work, two binuclear rhenium(I) tricarbonyl complexes of the general formula [Re2(CO)6(dip)2L](PF6)2 (dip = 4,7-diphenyl-1,10-phenanthroline; L = 4,4'-azopyridine (ReN) or 4,4'-dithiodipyridine (ReS)) were synthesized and characterized. ReN and ReS can react with glutathione (GSH). They exhibit good in vitro anticancer activity against cancer cell lines screened. Besides, they can target mitochondria, cause oxidative stress, and disturb GSH metabolism. Both ReN and ReS can induce necroptosis and caspase-dependent apoptosis simultaneously. We also demonstrate that ReN and ReS can inhibit tumor growth in nude mice bearing carcinoma xenografts. Our study shows the potential of Re(I) complexes as chemotherapeutic agents to kill cancer cells via a mitochondria-to-cellular redox strategy.

Sensing of insulin fibrillation using alkoxy-bridged binuclear rhenium(I) complexes

For the first time we report the simple, cost-effective, sensitive detection of human insulin fibrils using an alkoxy-bridged binuclear rhenium(I) complexes by the enhancement in luminescence intensity, emission lifetime and the formation of fibrils. The Re(I) complexes are weakly emissive, when it is dissolved with native insulin in an incubation buffer, but it becomes highly luminescent after the formation of insulin fibrils. This binding of human insulin fibrils is attributed to the hydrophobic as well as π−π stacking interaction of naphthalene moiety present in rhenium(I) complexes.

Binuclear rhenium carbonyl nitrosyls related to dicobalt octacarbonyl and their decarbonylation products.

The geometries and thermochemistry of Re2(NO)4(CO) n (n = 4, 3, 2, 1, 0) structures isovalent with the binuclear cobalt carbonyls Co2(CO) n+4 have been examined using density functional theory. Eight low-energy Re2(NO)4(CO)4 structures, all with formal Re-Re single bonds, lie within 6kcalmol(-1) of the global minimum. These eight structures include unbridged structures as well as structures with two bridging NO groups but no structures with bridging CO groups. Similarly, five low-energy Re2(NO)4(CO)3 structures, all with formal Re=Re double bonds, lie within 6kcalmol(-1) of the global minimum. Again these five structures include unbridged structures as well as structures with one or two bridging NO groups but no structures with bridging CO groups. The Re2(NO)4(CO) n (n = 4, 3) appear to be fluxional systems similar to the well-known Co2(CO)8 for which doubly bridged and unbridged structures have approximately the same energies. The lowest energy Re2(NO)4(CO)2 structures have formal Re=Re double bonds including a structure with a five-electron donor bridging η(2)-μ-NO group. Isomeric Re2(NO)4(CO)2 structures with formal Re≡Re triple bonds lie approximately ∼10kcalmol(-1) above the global minimum. For the more highly unsaturated Re2(NO)4(CO) and Re2(NO)4 systems, the lowest energy structures have formal Re≡Re triple bonds of length ∼2.6Å. Higher energy Re2(NO)4(CO) structures have shorter Re-Re distances of length ∼2.5Å suggesting formal quadruple bonds. Graphical Abstract The geometries and thermochemistry of Re2(NO)4(CO) n (n = 4, 3, 2, 1, 0) structures isovalent with the binuclear cobalt carbonyls Co2(CO) n+4 have been examined using density functional theory. A number of energetically closely spaced Re2(NO)4(CO)4 and Re2(NO)4(CO)3 structures are found, including unbridged and NO-bridged structures but no CO-bridged structures. The Re2(NO)4(CO) n (n = 2, 1, 0) systems provide examples of Re-Re multiple bonds of orders ranging from 2 to 4.

High catalytic abilities of binuclear rhenium(i) complexes in the photochemical reduction of CO2 with a ruthenium(ii) photosensitiser.

Photocatalytic systems for CO2 reduction using a Ru(ii) tris-diimine complex (Ru) as a photosensitiser and dinuclear Re(i) diimine tricarbonyl complexes (Re(n)Re), in which diimine ligands are connected by alkyl chains of various lengths (-CnH2n-: n = 2, 3, 4, 6, 14), as catalysts were investigated. The photocatalytic systems using Re(n)Re exhibited improved durability compared with that using the corresponding mononuclear Re(i) complex (Re); moreover, among the Re(n)Re, shorter alkyl chains in the bridging ligands induced greater durability. We found that the durability of the photocatalytic system depended on the decomposition speed of Ru, which could be suppressed using Re(n)Re with shorter alkyl chains.

Modification of 1,2,4,5-tetrazine with cationic rhenium(I) polypyridine units to afford phosphorogenic bioorthogonal probes with enhanced reaction kinetics.

New phosphorogenic bioorthogonal probes derived from mononuclear and binuclear rhenium(I) polypyridine complexes containing a 1,2,4,5-tetrazine moiety were designed; these complexes displayed substantial dienophile-induced emission enhancement, and accelerated reaction kinetics and could target a protein conjugate in living cells.

Chemistry of vinylidene complexes. XXIII. Binuclear rhenium–palladium vinylidene bridged complexes, their reactions with diiron nonacarbonyl

The reaction of [Cp(CO)2ReCCHPh] (1) with [Pd(PPh3)4] followed by the treatment of resulting [Cp(CO)2RePd(μ-CCHPh)(PPh3)2] (2) with diphosphines (dppe, dppp) gave new complexes [Cp(CO)2RePd(μ-CCHPh)(dppe)] (3) and [Cp(CO)2RePd(μ-CCHPh)(dppp)] (4). Treatment of the synthesized complexes with [Fe2(CO)9] led to mixtures of [Cp(CO)2ReFe(μ-CCHPh)(CO)4] (5), [(dppe)PdFe2(CO)8] (6), [CpReFe2(μ3-CCHPh)(CO)8] (7), [CpReFePd(μ3-CCHPh)(CO)5(dppe)] (8) and of 5, [(dppp)PdFe2(CO)8] (9), [CpReFePd(μ3-CCHPh)(CO)5(dppp)] (10), respectively. The main products of both reactions were trinuclear μ3-vinylidene clusters 8 and 10. Reactions of the trinuclear μ3-vinylidene ReFePd clusters 8 and 10 with Fe2(CO)9 were also studied. New complexes were characterized by IR, 1H, 13C, 31P NMR spectroscopy and cyclic voltammetry. The structure of [CpReFe2(μ3-CCHPh)(CO)8] was determined by single-crystal X-ray diffraction.

Alkoxy bridged binuclear rhenium (I) complexes as a potential sensor for β-amyloid aggregation

Alkoxy bridged binuclear rhenium(I) complexes are used as a probe for the selective and sensitive detection of aggregation of β-amyloid fibrils that are consorted with Alzheimer׳s disease (AD). The strong binding of the complexes is affirmed by the fluorescence enhancement and calculated binding constant value in the order of 105M−1 is obtained from the Scatchard plots. The binding of β-amyloid can be attributed to π−π stacking interaction of naphthalene moiety present in rhenium(I) complexes, and it is supported by docking studies. The selectivity is quite high towards other proteins and the formation of fibrils can be observed in the range of 30–40nm through the AFM and TEM techniques.

Aggregation-Induced Emission Enhancement in Alkoxy-Bridged Binuclear Rhenium(I) Complexes: Application as Sensor for Explosives and Interaction with Microheterogeneous Media

The aggregation-induced emission enhancement (AIEE) characteristics of the two alkoxy-bridged binuclear Re(I) complexes [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, C10H21) bearing a long alkyl chain with 4-(1-naphthylvinyl)pyridine (1,4-NVP) ligand are illustrated. These complexes in CH2Cl2 (good solvent) are weakly luminescent, but their intensity increased enormously by almost 500 times by the addition of poor solvent (CH3CN) due to aggregation. By tracking this process via UV-vis absorption and emission spectral and TEM techniques, the enhanced emission is attributed to the formation of nanoaggregates. The nanoaggregate of complex 2 is used as a sensor for nitroaromatic compounds. Furthermore, the study of the photophysical properties of these binuclear Re(I) complexes in cationic, cetyltrimethylammonium bromide (CTAB), anionic, sodium dodecyl sulfate (SDS), and nonionic, p-tert-octylphenoxypolyoxyethanol (TritonX-100, TX-100), micelles as well as in CTAB-hexane-water and AOT-isooctane-water reverse micelles using steady-state and time-resolved spectroscopy and TEM analysis reveals that the nanoaggregates became small and compact size.

Binuclear rhenium(i) complexes for the photocatalytic reduction of CO2

Binuclear rhenium(I) complexes with 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-ethane and 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-dodecane as bridging ligands and their mononuclear analogues have been synthesized and characterized by their spectroscopic and electrochemical properties. First reduction potentials and luminescence properties as well as the reductive quenching of the emissive state with TEOA were not affected by the alkyl linker. By means of a detailed comparison of the photocatalytic CO(2) reductions of the monometallic and the bimetallic complexes a great beneficial effect on the activity depending on the proximity of the centres was found. In high dilution the overall kinetics in the CO(2) photoreduction of mononuclear complexes are clearly monometallic. If the proximity of the centres is adjusted according to the lifetime of the OER (one electron reduced species) the photocatalytic activity is greatly improved showing a clear bimetallic mechanism. In the binuclear rhenium complexes, both the facile generation of a free coordination site and binuclear interactions for effective two electron transfer can be realized.

Efficient electroluminescence based on a novel binuclear rhenium complex

A novel binuclear rhenium(I) (Re I) carbonyl complex with the formula [Re(DF)(CO) 3Br] 2, where DF represented 4,5-diazafluorene, was designed and synthesized for applications in organic light-emitting diodes (OLEDs). The OLEDs employing [Re(DF)(CO) 3Br] 2 as an emitter with the structure of ITO/m-MTDATA(10 nm)/NPB(20 nm)/CBP: Re-complex(x%, 30 nm)/Bphen(10 nm)/Alq 3(30 nm)/LiF(1 nm)/Al(100 nm) were fabricated. The OLEDs based on [Re(DF)(CO) 3Br] 2 exhibited green–yellow emissions with a peak current efficiency of 8.2 cd/A at 16 cd/m 2 and a maximum brightness of 2026 cd/m 2 at 17.5 V, respectively, which confirmed that the binuclear Re-complex could function as an efficient phosphor emitter.

The interplay between metal–metal bonds, four‐electron donor carbonyl groups, and five‐electron donor nitrosyl groups in highly unsaturated binuclear rhenium carbonyl nitrosyls

AbstractOptimization of structures for the highly unsaturated binuclear rhenium carbonyl nitrosyls Re2(NO)2(CO)n (n = 5, 4) using the MPW1PW91 and BP86 methods of density functional theory indicate complicated potential energy surfaces with eight singlet and three triplet energetically accessible structures for Re2(NO)2(CO)5 and 11 singlet and six triplet energetically accessible structures for Re2(NO)2(CO)4. The lowest energy structure for Re2(NO)2(CO)5 is a singlet predicted to have two bridging nitrosyl groups and a formal ReRe triple bond to give both rhenium atoms the favored 18‐electron configuration. However, other relatively low‐energy structures for Re2(NO)2(CO)5 are found with five‐electron donor bridging nitrosyl groups, four‐electron donor bridging carbonyl groups, and coordinatively unsaturated rheniumatoms. The lowest energy structures for Re2(NO)2(CO)4 are predicted to be unbridged structures having rhenium–rhenium distances short enough for formal triple or even quadruple bonds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Mononuclear and Binuclear Rhenium Carbonyl Nitrosyls: Comparison with Their Manganese Analogues

The structures and energetics of Re(NO)(CO)n (n = 5, 4, 3, 2) and Re2(NO)2(CO)n (n = 7, 6) have been investigated using density functional theory. For Re(NO)(CO)4 the preferred structure is an equatorially substituted trigonal bipyramid analogous to the known structure of the manganese analogue. The lowest energy structures for the unsaturated Re(NO)(CO)n (n = 3, 2) species can be derived from this structure by removal of carbonyl groups. A structure is found for Re(NO)(CO)5 in which the NO ligand has attached to one of the CO ligands by forming a C-N bond to give an unprecedented eta(2)-OCNO ligand. However, this structure is predicted to undergo exothermic CO loss to give Re(NO)(CO)4. The preferred structures for the binuclear derivatives Re2(NO)2(CO)n (n = 7, 6) are structures unprecedented for the manganese analogues and consist of a Re(CO)5 unit linked to a Re(NO)2(CO)(n-5) unit. However, only slightly higher in energy are structures of the type Re2(mu-NO)2(CO)n with two bridging nitrosyl groups, similar to the global minima for the manganese analogues. These results predict extensive areas of new rhenium carbonyl nitrosyl chemistry. Thus the synthesis of Re(NO)(CO)4 by methods related to the synthesis of the manganese analogue appears to be feasible. In addition, the existence of an extensive series of Re(NO)2(CO)2X derivatives, as well as a Re2(NO)4(CO)4 dimer, is predicted.

A novel rhenium-aqua structure: the synthesis and structural characterization of (PPh4)4[ReN(H2O)(CN)3-μ-CN-ReN(CN)4] · 5H2O

A novel cyano bridged rhenium nitrido complex, [ReN(H2O)(CN)4-μ-CN-ReN(CN)4]4− (I) was isolated during a kinetic study of the reaction of ReN(H2O)(CN)4]2− with pyridine-2,3-dicarboxylic acid. Yellow crystals of (I), suitable for X-ray structure determination were isolated and the structural data showed an unsymmetrical binuclear rhenium complex with a cyano ligand acting as a bridge between two metal atoms, Re(1) and Re(2). The nitrogen of the bridged cyano ligand coordinates trans to the nitrido ligand of Re(1). The rhenium-nitrido bond distances are 1.657(4) and 1.656(5) A for Re(1)–N(9) and Re(2)–N(10) respectively. Re(1) and Re(2) are displaced from the planes formed by the four carbon atoms of the cyano ligands towards the nitrido ligands by 0.348(2) and 0.3403(2) A, respectively.

Binuclear manganese and rhenium carbonyls M2(CO)n (n = 10, 9, 8, 7): comparison of first row and third row transition metal carbonyl structures

The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic binuclear rhenium carbonyls Re2(CO)n (n = 10, 9, 8, 7) were determined using the MPW1PW91 and BP86 methods from density functional theory (DFT) with the effective core potential basis sets LANL2DZ and SDD. In all cases triplet structures for Re2(CO)n were found to be unfavorable energetically relative to singlet structures, in contrast to corresponding Mn2(CO)n derivatives, apparently owing to the larger ligand field splitting of rhenium. For M2(CO)10 (M = Mn, Re) the unbridged structures (OC)5M-M(CO)5 are preferred energetically over structures with bridging CO groups. For M2(CO)9 (M = Mn, Re) the two low energy structures are (OC)4M(micro-CO)M(CO)4 with an M-M single bond and a four-electron donor bridging CO group and (OC)4M[double bond, length as m-dash]M(CO)5 with no bridging CO groups and an M[double bond, length as m-dash]M distance suggesting a double bond. The lowest energy structures for Re2(CO)8 have Re[triple bond, length as m-dash]Re distances in the range 2.6-2.7 A suggesting the triple bonds required to give the Re atoms the favored 18-electron configuration. Low energy structures for Re2(CO)7 are either of the type (OC)(4)M[triple bond, length as m-dash]M(CO)3 with short metal-metal distances suggesting triple bonds or have a single four-electron donor bridging CO group and longer M-M distances consistent with single or double bonds. The 18-electron rule thus appears to be violated in these highly unsaturated Re2(CO)7 structures.

Synthesis and characterization of binuclear rhenium(I) complexes containing bifunctional ligands

The ligand exchange reaction of the anionic binuclear rhenium complexes Re 2 ( CO ) 6 ( OR ) 3 - (R = H ( 1), or Me ( 2)) has been studied with the bifunctional ligands 2-aminophenol ( 3), 4-hydroxypyridine ( 4), 3-hydroxybenzoic acid ( 5), and 3-pyridylcarbinol ( 6). The reactivity the pendant pyridyl group of 6 was studied in reactions with the Lewis acids ZnCl 2 ( 7), and AgPF 6 ( 8). Crystal structure determinations for several of these derivatives have been carried out which reveal both discrete and polymeric complexes upon addition of the Lewis base.

Synthesis, characterization and X-ray structure of several aryloxide and alkoxide derivatives of [Et 4N][Re 2(CO) 6(OR) 3] (R = H or Me)

The ligand exchange reaction of the anionic binuclear rhenium complexes Re 2 ( CO ) 6 ( OR ) 3 - (R = H ( 1) or Me ( 2)) has been studied with the arylalcohols 4-aminophenol ( 3, 4), 3-dimethylaminophenol ( 5), 3-cyanophenol ( 6) and 4-cyanophenol ( 7, 8) and the diol ethylene glycol ( 9). Complete exchange of the three hydroxy or methoxy ligands by aryl alcohols can be attained by heating the reaction mixture or allowing the mixture to stir for several days. Incomplete exchange is achieved by stoichiometric control of the incoming ligand and is complete within twelve hours. For the alkyl alcohol ethylene glycol complete exchange can be obtained in 8 h. Crystal structure determinations for several of these derivatives have been carried out.