Rhenium Tricarbonyl Complexes Research Articles

Tricarbonyl rhenium complex of 2,6-bis(8′-quinolinyl)pyridine: Synthesis, spectroscopic characterization, X-ray structure and DFT calculations

2,6-Bis(8′-quinolinyl)pyridine (bqp) reacts with pentacarbonyl rhenium chloride in toluene to give fac,fac-[Re(bqp-κ3N)(CO)3](Cl). X-ray crystallographic data on fac,fac-[Re(bqp-κ3N)(CO)3](Cl) show that the bqp ligand and carbonyl ligands achieve a mutually facial arrangement. A mix of MLCT and π–π* ligand centered transitions is observed for the low energy UV–vis absorption bands. The complex is emissive in solution and appears to be dominated by a MLCT-based process. Electronic and structural characteristics are supported by DFT calculations.

The photochemistry of rhenium(i) tricarbonyl N-heterocyclic carbene complexes

The photophysical and photochemical properties of the new tricarbonyl rhenium(I) complexes bound to N-heterocyclic carbene ligands (NHC), fac-[Re(CO)3(N^C)X] (N^C = 1-phenyl-3-(2-pyridyl)imidazole or 1-quinolinyl-3-(2-pyridyl)imidazole; X = Cl or Br), are reported. The photophysics of these complexes highlight phosphorescent emission from triplet metal-to-ligand ((3)MLCT) excited states, typical of tricarbonyl rhenium(I) complexes, with the pyridyl-bound species displaying a ten-fold shorter excited state lifetime. On the other hand, these pyridyl-bound species display solvent-dependent photochemical CO dissociation following what appear to be two different mechanisms, with a key step being the formation of cationic tricarbonyl solvato-complexes, being themselves photochemically active. The photochemical mechanisms are illustrated with a combination of NMR, IR, UV-Vis, emission and X-ray structural characterization techniques, clearly demonstrating that the presence of the NHC ligand is responsible for the previously unobserved photochemical behavior in other photoactive tricarbonyl rhenium(I) species. The complexes bound to the quinolinyl-NHC ligand (which possess a lower-energy (3)MLCT) are photostable, suggesting that the photoreactive excited state is not any longer thermally accessible. The photochemistry of the pyridyl complexes was investigated in acetonitrile solutions and also in the presence of triethylphosphite, showing a competing and bifurcated photoreactivity promoted by the trans effect of both the NHC and phosphite ligands.

Tricarbonylrhenium complexes from 2-pyridyl-1,2,3-triazole ligands bearing a 4-substituted phenyl arm: a combined experimental and theoretical study

Three new pyridyltriazole ligands (named pyta) bearing a 4-substituted phenyl arm (nitro- (2a), chloro- (2b) or aminophenyl (2c) moiety) have been synthesized using a convenient click chemistry strategy. The corresponding tricarbonylrhenium complexes 3a, 3b and 3c were prepared and fully characterized by means of NMR, IR and mass spectrometry, as well as X-ray crystallography for two of them (3a and 3b). The direct connection of a 4-substituted phenyl arm at the N1 position of the triazolyl ring has a significant influence on the geometry of both, the ligands and their corresponding Re-complexes. The dominant structural feature of these complexes concerns the crystal cohesion. Slip-stacked π-π interactions between two molecules of the complex were observed for 3a and 3b probably resulting from the co-planarity of the organic framework. Furthermore, a combined experimental study and DFT calculations showed that the nature of the pendant arm (X = NO2, NH2 or Cl) could affect the electronic properties of the Re-complexes. If the chloro- or aminophenyl moieties unmodified the photo-physical properties of the complexes 3b and 3c, the presence of a nitrophenyl arm for the complex 3a quenched the luminescence, due to a high probability of non-radiative deactivation.

Visible light-absorbing rhenium(i) tricarbonyl complexes as triplet photosensitizers in photooxidation and triplet–triplet annihilation upconversion

We prepared N^N Re(I) tricarbonyl chloride complexes (Re-1 and Re-2) that give very strong absorption of visible light. To this end, it is for the first time that boron dipyrimethane (Bodipy) was used to prepare Re(I) tricarbonyl chloride complexes. The π-conjugation linker between the π-conjugation framework of the antenna Bodipy and the Re(I) coordination centre ensures efficient intersystem crossing (ISC). Re-0 without visible light-harvesting ligand was prepared as a model complex in the photophysical studies. Re-1 (with Bodipy) and Re-2 (with carbazole-ethynyl Bodipy) show unprecedented strong absorption of visible light at 536 nm (ε = 91700 M(−1) cm(−1)) and 574 nm (ε = 64,600 M(−1) cm(−1)), respectively. Interestingly, different from Re-0, Re-1 and Re-2 show fluorescence of the ligand, not the phosphorescence of the Re(I) coordination centre. However, long-lived triplet excited states were observed upon visible light excitation (τ(T) = 104.0 μs for Re-1; τ(T) = 127.2 μs for Re-2) vs. the short lifetime of Re-0 (τ(T) = 26 ns). With nanosecond time-resolved transient absorption spectroscopy and DFT calculations, we proved that the triplet excited states of Re-1 and Re-2 are localized on the Bodipy ligands. The complexes were used as triplet photosensitizers for two triplet–triplet-energy-transfer (TTET) processes, i.e.(1)O(2) mediated photooxidation and triplet–triplet annihilation (TTA) upconversion. With the strong visible light-harvesting ability, Re-1 proved to be a better (1)O(2) photosensitizer than the conventional triplet photosensitizer tetraphenylporphyrin (TPP). Significant upconversion was observed with Re-1 as the triplet photosensitizer. Our result is useful for preparation of Re(I) tricarbonyl chloride complexes that show strong absorption of visible light and long-lived triplet excited states and for the application of these complexes as triplet photosensitizers in photocatalysis, photodynamic therapy and TTA upconversion.

Rhenium(i) tricarbonyl complex of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-selenaporphyrin: first X-ray structural characterization of metal complex of 21-selenaporphyrin

Synthesis and first structural characterization of hexa coordinated rhenium(I) tricarbonyl complex of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-selenaporphyrin 3 are described. The Re(I) complex of 21-selenaporphyrin 3 was synthesized by treating free base 21-selenaporphyrin in 1,2-dichlorobenzene with Re(CO)5Cl at reflux for 7 h and analyzed using mass, NMR, FT-IR, UV-vis and electrochemical techniques. The first structure of metal complex of 21-selenaporphyrin was determined by X-ray single crystal analysis. The crystal structure revealed that the Re(CO)3 coordinates to two of the three inner nitrogens and one selenium to produce compound 3. The selenophene ring bent towards the Re(I) ion and the selenium is displaced by 0.41 Å from the mean plane of 24-atoms to coordinate with Re(I) ion in η(1)-fashion. The 21-selenaporphyrin is distorted in compound 3 compared to free base 21-selenaporphyrin. (1)H and (13)C NMR studies indicated that compound 3 exhibits fluxional behaviour in coordination mode of binding in solution. The compound 3 is highly stable and does not undergo decomplexation under acidic conditions. The absorption spectra showed three broad Q-bands and splitted Soret band and electrochemical studies indicated that compound 3 is stable under redox conditions.

Rhenium(i) phenanthrolines bearing electron withdrawing CF3 substituents: synthesis, characterization and biological evaluation

Rhenium(I) tricarbonyl complexes bearing a 2,4,7,9-tetraphenylphenanthroline ligand, where the 2,9-phenyl groups have either meta- or para-CF3 groups, have been screened against a selection of cell lines. The meta derivative shows anticancer activity against HeLa and A549 cell lines, whereas the para derivative causes proliferation of HL-60 cells, whilst showing toxicity towards A549 cells.

Tricarbonyltechnetium(i) and tricarbonylrhenium(i) complexes of amino acids: crystal and molecular structure of a novel cyclic dimeric Re(CO)3-amino acid complex comprised of the OON donor atom set of the tridentate ligand

Radiolabeled complexes of monoamino polycarboxylic, polyamino monocarboxylic and thiol containing amino acid ligands were prepared from a fac-[(99m)Tc(CO)3(H2O)3](+) precursor.The overall radiochemical yield was 94-98%. The complexes exhibited substantial in vitro and in vivo stability. The corresponding Re(I) complexes of the ligands DAPA, Asp and CysH were prepared and characterized by means of IR, NMR, and MS spectroscopic studies, as well as X-ray crystallography (for those containing D,L-DAPA and D,L-Asp). The rhenium complexes have been structurally correlated with the technetium complexes by means of HPLC studies. The reaction of Re(CO)5Cl with D,L-Asp in presence of triethylamine led to the formation of a new class of cyclic dimeric complexes formed by the OON donor atom set of the tridentate ligands. The amino carboxylate ligand system formed well defined complexes with a fac-[M(CO)3(H2O)3](+) core and shows good promise in (99m)Tc(CO)3 tracer development.

Re-Mediated C–C Coupling of Pyridines and Imidazoles

Rhenium tricarbonyl complexes with three N-heterocyclic ligands (N-alkylimidazoles or pyridines) undergo deprotonation with KN(SiMe(3))(2) and then oxidation with AgOTf to afford complexes with pyridylimidazole or bipyridine bidentate ligands resulting from deprotonation, C-C coupling and rearomatization.

Spectral Properties of the Optoelectronic Material Rhenium (I) Tricarbonyl Complexes with Bipyridine Ligand Containing Triphenylamine Moiety

The photophysical behavior of rhenium (I) complex having a bipyridine ligand with triphenylamidine moiety is investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The complex shows the maximum absorption band at 417.1 nm, with ligand-to-ligand charge transfer (LLCT) character. The lowest lying triplet excited state was localized on3LLCT/ILCT state

Electronic Structures and Spectral Properties of the Emitting Molecule Rhenium (I) Tricarbonyl Containing Naphthalimide Ring in Chemical Manufacturing System

Rhenium (I) tricarbonyl complexes comprise an important class of luminescent materials in chemical manufacturing system. A Re(I) complexes, Re(CO)3(phen-PIN)(Cl) (1), where PNI = 4-piperidinyl-1,8-naphthalimide, was investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The optimized ground structures show that the phen ring is not coplanar with the naphthalimide ring. The HOMO is π character, while the LUMO is π* orbitals of the phen ligands. The lowest lying absorption band of the complexes has the HOMO → LUMO+1 transition configurations resulting in the LLCT/ILCT characters.

Tricarbonyl rhenium(I) complex of benzothiazole – Synthesis, spectroscopic characterization, X-ray crystal structure and DFT calculations

The paper presents a combined experimental and computational study of a novel tricarbonyl rhenium(I) complex with benzothiazole ligand – [Re(CO)3(bt)2Cl]. The compound has been characterized by structural (single-crystal X-ray diffraction) and spectroscopic (IR, NMR, MS, UV–vis) methods. DFT and time-dependent DFT (TDDFT) calculations have been also carried out and the UV–vis spectrum of the complex has been discussed on this basis.

Rhenium(I) tricarbonyl complexes of salicylaldehyde semicarbazones: Synthesis, crystal structures and cytotoxicity

A series of N,N-disubstituted salicylaldehyde semicarbazones (SSCs), HOC6H4CHN-NHCONR2, and their rhenium(I) tricarbonyl complexes, [ReBr(CO)3(SSC)], have been synthesised and characterised by IR and 1H NMR spectroscopy. Crystallographic analysis of the complex [ReBr(CO)3(H2Bu2)] (H2Bu2=SSC where R=Bun) showed that the SSC acts as a bidentate ligand via its imino nitrogen and carbonyl oxygen atoms. The [ReBr(CO)3(SSC)] complexes exhibit moderate to high cytotoxicities towards MOLT-4 cells (IC50=1–24μM, cf. 18μM for cisplatin), and the majority of them are virtually non-toxic against non-cancerous human fibroblasts. Apoptotic assays of [ReBr(CO)3(H2Bnz2)] (Bnz=benzyl) revealed that it mediates cytotoxicity in MOLT-4 cells via apoptosis. The complex [ReBr(CO)3(H2Bnz2)] reacts with guanosine by proton transfer from the phenolic OH group to N(7) of guanosine. In (CD3)2SO, [ReBr(CO)3(H2Bnz2)] undergoes facile conversion to the dimeric complex, [Re(CO)3(HBnz2)]2, via bromide dissociation.

Synthesis and Characterization of Tricarbonyl-Re/Tc(I) Chelate Probes Targeting the G Protein-Coupled Estrogen Receptor GPER/GPR30

The discovery of the G protein-coupled estrogen receptor GPER (also GPR30) and the resulting development of selective chemical probes have revealed new aspects of estrogen receptor biology. The potential clinical relevance of this receptor has been suggested from numerous studies that have identified GPER expression in breast, endometrial, ovarian and other cancers. Thus GPER can be considered a candidate biomarker and target for non-invasive imaging and therapy. We have designed and synthesized a series of organometallic tricarbonyl-rhenium complexes conjugated to a GPER-selective small molecule derived from tetrahydro-3H-cyclopenta[c]quinoline. The activity and selectivity of these chelates in GPER-mediated signaling pathways were evaluated. These results demonstrate that GPER targeting characteristics depend strongly on the structure of the chelate and linkage. Ethanone conjugates functioned as agonists, a 1,2,3-triazole spacer yielded an antagonist, and derivatives with increased steric volume exhibited decreased activities. Promising GPER selectivity was observed, as none of the complexes interacted with the nuclear estrogen receptors. Radiolabeling with technetium-99m in aqueous media was efficient and gave radioligands with high radiochemical yields and purity. These chelates have favorable physicochemical properties, show excellent stability in biologically relevant media, exhibit receptor specificity and are promising candidates for continuing development as diagnostic imaging agents targeting GPER expression in cancer.

Rhenium(I) tricarbonyl complexes with multidentate nitrogen-donor derivatives

The reaction of [Re(CO)5X] (X=Cl, Br) with a series of six potentially multidentate nitrogen donor ligands (L1–L6) was studied. The ligands L1–L5 are coordinated bidentately in the neutral complexes of the type fac-[Re(CO)3X(L)] (1–5). The complex salt [Re(CO)3(L6)]Br (6) was formed by the reaction of [Re(CO)5Br] with 2-aminobenzaldehyde (aba), in which the tridentate ligand L6 was formed by the Schiff base condensation of three aba molecules. The crystal structures for complexes 1–6 were determined by X-ray single crystal diffraction. UV–Vis absorption spectra of the complexes show the intraligand and MLCT transitions. Electrochemical behaviour of the complexes was studied with cyclic voltammetry.

Novel imino rhenium(I) tricarbonyl complexes of salicylidene-derived ligands: Synthesis, X-ray crystallographic studies, spectroscopic characterization and DFT calculations

Novel rhenium(I) tricarbonyl complexes of the form fac-[Re(L,L′-Bid)(CO)3(S)] (L,L′10.1016/j.poly.2012.08.059-Bid=N,O-Sal-type bidentate ligand, S=coordinating methanol or pyridine) were obtained by the reaction of the fac-[Re(CO)3]+ moiety with a range of 2-(“T”-iminomethyl)-5-methylphenol Schiff-base ligands. Various biological functional groups (“T”) with different electronic and steric properties were introduced at the imino nitrogen atom. The complexes were characterized spectroscopically by IR, 1H and 13C NMR. Three solid state structures were elucidated by X-ray diffraction and compared to DFT calculations employing B3LYP functions in combination with LANL2DZ.

Theoretical studies of COOH group effect on the performance of rhenium (I) tricarbonyl complexes with bispyridine sulfur-rich core ligand as dyes in DSSC

The series of rhenium (I) tricarbonyl mixed-ligand complexes ReCl(CO)3(Hnbpydt) (n = 2, 1; n = 4, 2; bpy = bispyridine, dt = 1,3-dithiole) and ReCl(CO)3(HnbpyTTF) (n = 2, 3; n = 3, 4; TTF = Tetrathiafulvalene) have been investigated theoretically to explore the effect of COOH functional group on their electronic structures, spectroscopic properties and their properties as dye in a solar cell. The calculated geometry structure and absorption spectrum of 1 and 3 are generally consistent with the experimental results. By attaching the COOH groups on both bpy and dt (TTF in 4) moiety in 2, the nature of LUMO is also contributed by both π*(bpy) and π*(dt) (π*(TTF) in 4), and the absorptions have an obvious red shift compared with 1 and 3. In addition, it can be found that the transition terminates at the orbital populated by the COOH-appended moieties, and the performance of 2 and 4 in the dye-sensitized solar cell can be enhanced as compared with 1 and 3.

Flexible coordination of hetero-scorpionate ligands composed of pyrrole/pyridines hybrid in rhenium(I) tricarbonyl complexes

Rhenium(I) coordination of hetero-scorpionate ligands composed of pyrrole/pyridines hybrid with four coordination sites on a single carbon atom afforded a variety of rhenium(I) tricarbonyl complexes. X-ray analyses on the rhenium(I) complexes revealed the flexible coordination of such hetero-scorpionate ligands. Presence of an additional coordinative site adjacent to the tridentate ligands lead to a unique supramolecular complex, anion recognizing complex, and bis-metal complex.

Photophysical and Photoredox Characteristics of a Novel Tricarbonyl Rhenium(I) Complex Having an Arylborane-Appended Aromatic Diimine Ligand

We report the synthesis and photophysical/photoredox characteristics of a novel tricarbonyl rhenium(I) complex having a (dimesityl)boryldurylethynyl (DBDE) group at the 4-position of a 1,10-phenanthroline (phen) ligand, [Re(CO)(3)(4-DBDE-phen)Br] (ReB). ReB in tetrahydrofuran at 298 K showed the metal-to-ligand charge transfer (MLCT) emission at around 681 nm with the lifetime (τ(em)) of 900 ns. The relatively long emission lifetime of ReB compared with that of [Re(CO)(3)(phen)Br] (RePhen, τ(em) = 390 ns) was discussed on the basis of the temperature dependent τ(em) and Franck-Condon analysis of the emission spectra of the two complexes. Emission quenching studies of both ReB and RePhen by a series of electron donors revealed that the photoinduced electron transfer (PET) quenching rate constant of ReB was faster than that of RePhen at a given Gibbs free energy change of the PET reaction (ΔG(ET)(0) > -0.5 eV). All of the results on ReB were discussed in terms of the contribution of the CT interaction between the π-orbital(s) of the aryl group(s) and the vacant p-orbital on the boron atom in DBDE to the MLCT state of the complex.

Rhenium(I) Tricarbonyl Complexes of 5,10,15,20-Tetraphenyl-21-thia and 21-Oxaporphyrins

The hexa-coordinated rhenium(I) tricarbonyl complexes of 5,10,15,20-tetraphenyl-21-thiaporphyrin 1 and 5,10,15,20-tetraphenyl-21-oxaporphyrin 2 have been synthesized by thermal reaction of corresponding free base porphyrin with Re(2)(CO)(10). The compounds 1 and 2 are characterized by HR-MS mass, (1)H, and (13)C NMR, FTIR, UV-vis, and electrochemical techniques and the structures are determined by X-ray single crystal analysis. The X-ray analysis revealed different coordination behavior of Re(CO)(3) with 21-thiaporphyrin and 21-oxaporphyrin. Interestingly, the Re(CO)(3) coordinates to two of the three inner nitrogens and one sulfur instead of three inner nitrogens as generally expected to produce unique compound 1 whereas it coordinates to three inner nitrogens but not with furan oxygen to form compound 2. The 21-thiaporphyrin ring is more distorted in compound 1 compared to 21-oxaporphyrin ring in compound 2 on complexation with Re(CO)(3). The presence of three carbonyl groups in compounds 1 and 2 are verified by (13)C NMR and IR spectroscopy. The absorption spectra of compounds 1 and 2 showed ill-defined Q-bands along with broad Soret band and the extinction coefficients are much lower than their corresponding free base porphyrins. The compounds 1 and 2 showed two reversible porphyrin ring based reductions supporting their electron deficient nature. The compound 1 is very stable under protonation conditions, and the protonation occurs at the uncoordinated pyrrole ring whereas the compound 2 undergoes decomplexation under same conditions. Furthermore, compound 1 showed the fluxional behavior in coordination mode of binding in solution.

Blue-Green Luminescent Rhenium(I) Tricarbonyl Complexes with Pyridine-Functionalized N-Heterocyclic Carbene Ligands

Five rhenium(I) tricarbonyl chloride complexes with pyridine-functionalized N-heterocyclic carbenes, Re(CO)3(L)Cl (L = 3-methyl-1-(2-pyridyl)imidazol-2-ylidene (1), 3-methyl-1-(2-picolyl)imidazol-2-ylidene (2), 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene (3), 3-methyl-1-(2-picoyl)benzimidazolin-2-ylidene (4), 1-methyl-4-(2-pyridyl)-1,2,4-triazoline-5-ylidene (5)), have been synthesized by silver carbene transmetalation and characterized by elemental analysis, 1H NMR, 13C NMR, and IR spectra. The molecular structures of 3–5 have been determined by single-crystal X-ray diffraction. The electrochemical and photophysical properties of complexes 1, 3, and 5 have been studied. In both degassed CH2Cl2 solution and the solid state at room temperature or 77 K, the emission wavelengths (465–511 nm) of complexes 1, 3, and 5 lie in the blue-green region, which are rare in contrast to the reported rhenium(I) tricarbonyl complexes. The photoluminescence lifetime decays of Re(I) complexes 1, 3, and 5 were measured, a...