Rhenium Tricarbonyl Complexes Research Articles

Synthesis and characterisation of luminescent rhenium tricarbonyl complexes with axially coordinated 1,2,3-triazole ligands

A series of 1-alkyl-4-aryl-1,2,3-triazoles (1-methyl-4-phenyl-1,2,3-triazole (1a); 1-propyl-4-phenyl-1,2,3-triazole (1b); 1-benzyl-4-phenyl-1,2,3-triazole (1c); 1-propyl-4-p-tolyl-1,2,3-triazole (1d)) have been prepared through a one-pot procedure involving in situ generation of the alkyl azide from a halide precursor followed by copper catalysed alkyne/azide cycloaddition (CuAAC) with the appropriate aryl alkyne. Cationic Re(I) complexes [Re(bpy)(CO)(3)(1a-d)]PF(6) (2a-d) were then prepared by stirring [Re(bpy)(CO)(3)Cl] with AgPF(6) in dichloromethane in the presence of ligands 1a-d. X-ray crystal structures were obtained for 2a and 2b. In the solid state, 2a adopts a highly distorted geometry, which is not seen for 2b, in which the plane of the triazole ligand tilts by 13° with respect to the Re-N bond as a result of a π-stacking interaction between the Ph substituent and one of the rings of the bpy ligand. This π-stacking interaction also results in severe twisting of the bpy ligand. Infrared spectra of 2a-d exhibit ν(CO) bands at ∼2035 and ∼1926 cm(-1) suggesting that these ligands are marginally better donors than pyridine (ν(CO) = 2037, 1932 cm(-1)). The complexes are luminescent in aerated dichloromethane at room temperature with emission maxima at 542 to 552 nm comparable to that of the pyridine analogue (549 nm) and blue shifted relative to the parent chloride complex. Long luminescent lifetimes are observed for the triazole complexes (475 to 513 ns) in aerated dichloromethane solutions at room temperature.

Studies of the reactions of tripodal pyridine-containing ligands with Re(CO)5Br leading to rheniumtricarbonyl complexes with potential biomedical applications

The complexes formed from the reaction of N-acylated tris-(pyridin-2-yl)methylamine (LH) with [Re(CO)(5)Br] depend on the structure of the ligand and the reaction conditions. Thus, while N-[1,1,1-tris-(pyridin-2-yl)methyl]acetamide coordinates through the three pyridine nitrogens to give a stable cationic complex [LHRe(CO)(3)Br], the analogous N-benzoyl ligand reacts under similar conditions to give a neutral complex [LRe(CO)(3)] with coordination through two pyridine nitrogens and a deprotonated amide. To try to explain these different outcomes, the reactions of some structurally related N-acylated [1,1-bis(pyridin-2-yl)]methylamines (L'H) with [Re(CO)(5)Br] have been studied and the reaction pathways identified. These studies indicate that a neutral complex [L'HRe(CO)(3)Br] is initially formed in which the amide portion of the ligand is uncoordinated, but that this complex under appropriate conditions then rearranges to give a cationic complex [L'HRe(CO)(3)]Br in which the coordinated amide nitrogen either remains protonated or is present in its imidic acid tautomeric form. Elimination of HBr from these complexes either thermally or in the presence of base then gives stable neutral complexes [L'Re(CO)(3)]. The impact of the N-acyl group and any substituent at the apex of the tripodal ligands (L''H) on the relative stabilities of intermediate complexes on the reaction pathway helps provide an explanation for the observed difference in behaviour of the N-acylated tris(pyridin-2-yl)methylamines (LH).

Synthesis and properties of new π-conjugated pyridine ligands with tetrathiafulvalene derivatives and the rhenium(I) tricarbonyl complexes

Three new π-conjugated pyridine ligands with redox-active tetrathiafulvalene (TTF) derivatives, L 1 – L 3 , have been synthesized and characterized. The Diels–Alder reaction is the key step for this multistep synthetic strategy. The crystal structures of L 1 and L 3 have been studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding tricarbonyl rhenium(I) complexes (ReL 1(CO) 3X, X = Cl, 5; X = Br, 6) have also been investigated.

Novel tricarbonyl rhenium complexes of 5,8-quinolinedione derivatives – Synthesis, spectroscopic characterisation, X-ray structure and DFT calculations

The molecular structure of 7-acetamido-2-methyl-quinoline-5,8-dione has been determined and the reactivity of 7-acetamido-2-methyl-quinoline-5,8-dione ( 1) and 6-acetamido-2-methyl-quinoline-5,8-dione ( 2) towards Re(CO) 5Cl has been examined. Two novel tricarbonyl rhenium complexes, fac-[Re(CO) 3(7-acetamido-2-methyl-quinoline-5,8-dione)Cl]·CHCl 3 ( 3·CHCl 3) and fac-[Re(CO) 3(6-acetamido-2-methyl-quinoline-5,8-dione)Cl] 2·CHCl 3 ( 4·CHCl 3), have been synthesized and characterized spectroscopically and structurally. The electronic spectrum of 3 was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.

Synthesis, Characterization and Photophysical Properties of Thiophene-Containing Chloro Re(I) Complex

Two tricarbonyl rhenium complexes with the formula of [Re(CO)3(L)Cl], where L=1,10-phenanthroline (Phen-Re) and 2-(3-thienyl)-imidazo[4,5-f]-1,10-phenanthroline (TIPh-Re), were successfully synthesized and characterized by 1H NMR and UV–Vis with the aim to analyze the effect of the thiophene(TI) moiety on the photophysical properties of TIPh-Re. It was found that the introduction of an π-electron density moiety into diimine ligands leads to a dramatic red shift of the absorption of the corresponding Re(I) complex. At the same time, the results verify that the triplet metal-to-ligand charge-transfer dπ(Re)→π*(N-N) emission (3MLCT) of Phen-Re and TIPh-Re centered at ca. 566 nm and ca.569 nm, respectively.

Tricarbonyl Rhenium(I) and Technetium(I) Complexes with Hydrazones Derived from 4,5‐Diazafluoren‐9‐one and 1,10‐Phenanthroline‐5,6‐dione

AbstractTricarbonylrhenium(I) and ‐technetium(I) halide (halide = Cl and Br) complexes of ligands derived from 4,5‐diazafluoren‐9‐one (df) and 1,10‐phenanthroline‐5,6‐dione (phen) derivatives of benzoic and 2‐hydroxybenzoic acid hydrazides have been prepared. The complexes have been characterized by elemental analysis, MS, IR, 1H NMR and absorption and emission UV/Vis spectroscopic methods. The metal centres (ReI and TcI) are coordinated through the nitrogen imine atoms and establish five‐membered chelate rings, whereas the hydrazone groups stand uncoordinated. The 1H NMR spectra suggest the same behaviour in solution on the basis of only marginal variations in the chemical shifts of the hydrazine protons.

The impact of ligand structure on the rhenium tricarbonyl complexes from tripodal pyridine-containing chelators

The impact of ligand structure on the rhenium tricarbonyl complexes from tripodal pyridine-containing chelators

Lability of monodentate ligand in tricarbonylrhenium(I) complexes with N-methyl-2-piridinecarboxyamide. Flexidentate behaviour of N-methyl-2-pyridinecarboxyamide

Lability of monodentate ligand in tricarbonylrhenium(I) complexes with N-methyl-2-piridinecarboxyamide. Flexidentate behaviour of N-methyl-2-pyridinecarboxyamide

Tricarbonyl rhenium complex of 2,2′-bis(4,5-dimethylimidazole) — Synthesis, spectroscopic characterization, X-ray structure and DFT calculations

Abstract The paper presents a combined experimental and computational study of the tricarbonyl rhenium(I) complex incorporating 2,2′-bis(4,5-dimethylimidazole) (tmbiimH2). The complex has been studied by IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure of [Re(CO)3(tmbiimH2)Cl] has been calculated with the density functional theory (DFT) method, and the electronic spectrum of the complex was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.

Bis(3,5‐dimethyl‐4‐vinylpyrazol‐1‐yl)acetic Acid: A New Heteroscorpionate Building Block for Copolymers that Mimic the 2‐His‐1‐carboxylate Facial Triad

AbstractThe new N,N,O ligand bis(3,5‐dimethyl‐4‐vinylpyrazol‐1‐yl)acetic acid (Hbdmvpza) (4) suitable for copolymerisation was synthesised in a multi‐step synthesis starting from bis(3,5‐dimethylpyrazol‐1‐yl)methane (1). The κ3‐N,N,O facial coordination behaviour of 4 was verified by synthesis and characterisation of the tricarbonyl compounds [Mn(bdmvpza)(CO)3] (5) and [Re(bdmvpza)(CO)3] (6), the ruthenium bisphosphane complex [Ru(bdmvpza)Cl(PPh3)2] (7), as well as the complex [Cu(bdmvpza)2] (8). Copolymerisation of 4 with methyl methacrylate (MMA) or ethylene glycol dimethacrylate (EGDMA) led to solid phases P1a, P1b and P2 with different amounts of incorporated ligand 4. Furthermore, a homopolymer H1 of ligand 4 was successfully synthesised. Copolymer‐bound manganese and rhenium tricarbonyl complexes P1a‐Mn, P1a‐Re, P2‐Mn and P2‐Re have been obtained by reaction of P1a and P2 with the metal precursors [MnBr(CO)5] and [ReBr(CO)5], respectively. The κ3‐N,N,O coordination of the manganese and rhenium centres was verified by IR spectroscopy and the amount of incorporated metal complex was determined by AAS or ICP‐AES measurements. Treatment of the deprotonated copolymer P1a or P2 with copper(II) or iron(II) led to polymers P1a‐Cu, P1a‐Fe and P2‐Fe. A bathochromic shift in the UV spectrum of P1a‐Cu compared to the absorption maximum of the homogeneous complex 8 by 64 nm indicates copper centres with one ligand moiety bound only. AAS analysis of P1a‐Fe and P2‐Fe show that up to 64 % of the ligand sites can be accessed withiron(II). Furthermore, two 2‐oxocarboxylato complexes [Ru(bdmvpza)(BF)(PPh3)] (9) (BF = benzoylformato) and [Ru(bdmvpza)(NOG)(PPh3)] (10) (NOG = N‐oxalylglycine) have been synthesised that mimic the shape of the active sites of 2‐oxoglutarate dependent iron oxygenases. The successful copolymerisation of 9 and 10 with EGDMA was proven by UV spectroscopy.

Syntheses, structures, and properties of tricarbonyl rhenium(I) heteronuclear complexes with the multidentate bridging ligand containing bis(2-pyridine) and carboxylic acid

By deprotonation reaction of the rhenium(I) tricarbonyl complex, ClRe(CO) 3(H 2bpydt) ( 2, H 2dpydt = 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylic acid, our previous work in J. Organomet. Chem. 694 (2009) 763), complex 3, [Bu 4N][ClRe(CO) 3(Hbpydt)], is synthesized and characterized. Using 3 as the starting material, two trinuclear heterometallic complexes M(MeOH) 4[ClRe(CO) 3(Hbpydt)] 2·2MeOH (M = Cu, 4; M = Mn, 5) are obtained. The crystal structures of 2– 5 have been determined by X-ray crystallography. Complexes 4 and 5 are isostructural. Their absorption and emission properties are studied. The magnetic properties of complexes 4 and 5 have also been investigated.

The synthesis and toxicity of tripodal tricarbonyl rhenium complexes as radiopharmaceutical models

We report the synthesis and toxicity of a series of rhenium(I) tricarbonyl complexes incorporating the trisaminomethylethane (TAME) ligand. Compounds with the (TAME)Re(CO) 3 + cation were synthesized via several routes, including by use of Re(CO) 5 X precursors as well as the aqueous cation Re(CO) 3(H 2O) 3 +. Salts of the formula [(TAME)Re(CO) 3] X where X = Br −, Cl −, NO 3 −, PF 6 − and ClO 4 − were evaluated using two cell lines: the monoclonal S3 HeLa line and a vascular smooth muscle cell line harvested from mice. All compounds have isostructural cations and differ only in the identity of the non-coordinating anion. None of the complexes exhibited any appreciable toxicity in the HeLa line up to the solubility limit. In the vascular smooth muscle cell line, the bromide salt exhibited some cytotoxicity, but this observation most likely results from the presence of bromide anion, which has been shown to have limited toxicity.

Design, synthesis, and evaluation of cyclofenil derivatives for potential SPECT imaging agents

To develop technetium- and rhenium-labeled nonsteroidal estrogen imaging agents for estrogen receptor (ER) positive breast tumors, two groups of rhenium and technetium cyclofenil derivatives were synthesized and characterized. The binding affinities of the rhenium complexes for ERs were determined. The tricarbonyl rhenium complex showed the highest binding affinity for ERs (81.2 for ERbeta, 16.5 for ERalpha). Tricarbonyl technetium cyclofenil complexes were obtained in high radiochemical purity and radiochemical yields. The results of studies of their octanol/water partition and in vitro stability are presented. These results demonstrate that these radiolabeled cyclofenil derivatives may be considered as potential breast cancer imaging agents.

New Re(I) tricarbonyl-diimine complexes with N,N′-bis(substituted benzaldehyde)-1,2-diiminoethane Schiff base ligands: Synthesis, spectroscopic and electrochemical studies and crystal structures

The syntheses, structures and spectroscopic properties of tricarbonylrhenium(I) complexes with N,N′-bis(2-bromo, 4-bromo, 4-chloro and 3-methoxybenzaldehyde)-1,2-diiminoethane Schiff base ligands have been investigated in this paper. Characterization of these complexes was carried out with FTIR, NMR, UV–Vis spectroscopy, elemental analysis and X-ray crystallography. The electrochemical behavior of the investigated complexes has been studied by cyclic voltammetry. The crystal structures of the 4-chloro, 4-bromo and 4-methoxy substituted complexes are stabilized by intermolecular C–H⋯Cl and C–H⋯O hydrogen bonds. The remarkable features of the 2-bromo, 4-bromo and 4-chloro substituted complexes are short intermolecular halogen–oxygen contacts. In the 4-bromo complex, short intermolecular Br⋯O and O⋯O contacts link neighboring molecules along the [1 0 0] direction, which are further stabilized by short intermolecular π⋯π interactions. In 2-bromo complex, intermolecular Br⋯O interactions link neighboring molecules into 1D extended chains along the [0 1 0] and [0 0 1] directions, forming a 2D network which is parallel to the bc-plane.

Synthesis, characterization, and photophysical properties of a thiophene-functionalized bis(pyrazolyl) pyridine (BPP) tricarbonyl rhenium(i) complex

A bromo tricarbonyl rhenium(I) complex with a thiophene-functionalized bis(pyrazolyl) pyridine ligand (L), ReBr(L)(CO)(3) (1), has been synthesized and characterized by variable temperature and COSY 2-D (1)H NMR spectroscopy, single-crystal X-ray diffraction, and photophysical methods. Complex 1 is highly luminescent in both solution and solid-state, consistent with phosphorescence from an emissive (3)MLCT excited state with an additional contribution from a LC (3)(pi-->pi*) transition. The single-crystal X-ray diffraction structure of the title ligand is also reported.

Chemical switching behaviour of tricarbonylrhenium(i) complexes of a new redox active ‘Pincer’ ligand

The structures and optoelectronic properties of tricarbonylrhenium(I) complexes of di(2-pyrazolyl-p-tolyl)amine in its neutral and deprotonated (uninegative amido) form were investigated. Reactions of the complexes with Brønsted acids or bases result in distinctive changes of colour and electrochemical activity owing to the non-innocent nature of the ligand.

Tricarbonylrhenium(i) complexes of highly symmetric hexaazatrinaphthylene ligands (HATN): structural, electrochemical and spectroscopic properties

The new mononuclear and dinuclear tricarbonylrhenium(I) complexes [(HATN)Re(CO)(3)Cl] (1-Cl) and [(μ-Me(6)-HATN)[Re(CO)(3)Cl](2)] (2-Cl(2)) of highly symmetric ligands HATN and Me(6)-HATN were synthesized and structurally characterized. X-Ray crystal structures reveal identical strained aromatic systems and out of the plane fac-Re(CO)(3)Cl units for both complexes. The packing geometry in the unit cell of 1 suggests intermolecular π-π association. Infrared spectroelectrochemistry (SEC) experiments confirmed ligand-based reductions. To get more insight into the reduction mechanism the triflate salts, [(HATN)Re(CO)(3)](OTf) (1-OTf) and [(μ-Me(6)HATN){Re(CO)(3)}(2)](OTf)(2) (2-OTf(2)), were synthesized. Their electrochemical and spectroelectrochemical behavior also exhibits reduction of the aromatic systems. The electronic absorption spectral features of the one electron reduced species were studied by UV-vis-NIR spectroscopy, which shows a broad shoulder at 1500 nm, confirming intra-ligand charge transfer (ILCT). Density functional theory (DFT) calculations on the complexes 1-Cl and 2-Cl(2) for structural optimization show good agreement with experimental bond lengths and bond angles. The spin density plot shows a metal based HOMO and HATN ligand centered LUMO.

Studies of rheniumtricarbonyl complexes of tripodal pyridyl-based ligands

The reaction of N-benzoyl and N-acetyl tris(pyridin-2-yl)methylamine 1b and 1c (LH = tpmbaH and tpmaaH) with [Re(CO) 5Br] has been investigated and shown to proceed via the initial formation of a cationic rheniumtricarbonyl complex [(LH)Re(CO) 3]Br in which coordination of the ligand occurs via the three pyridine rings. For tpmbaH 1b, but not tpmaaH 1c, this initial complex 2b readily undergoes the loss of HBr to give a neutral octahedral complex 4b [(L)Re(CO) 3] where coordination occurs via two of the pyridine rings and the deprotonated amide nitrogen. The 1H NMR spectrum of the latter complex 4b is very unusual in that at room temperature the signals for the 3-H protons on the coordinated pyridine rings are not visible due to extreme broadening of these resonances. Comparison with the analogous complex 7 from N-benzoyl bis(pyridin-2-yl)methylamine 6b (bpmbaH) confirms that this is due to rotation of the uncoordinated pyridine ring. The structure of the cationic complex 3d [(LH)Re(CO) 3]Br formed from N-benzyl tris(pyridin-2-yl)methylamine 1d (bz-tpmaH) is also discussed. The crystal structures of complexes [(tpmba)Re(CO) 3] 4b, [(bz-tpmaH)Re(CO) 3]Br 3d and [(bpmba)Re(CO) 3] 7 have been determined. In all complexes the coordination geometry around Re is distorted octahedral with a fac-{Re(CO) 3} + core.

Tricarbonylrhenium(I) and manganese(I) complexes of 2-(pyrazolyl)-4-toluidine

A series of tricarbonyl rhenium(I) and manganese(I) complexes of the electroactive 2-(pyrazolyl)-4-toluidine ligand, H(pzAn Me), has been prepared and characterized including by single crystal X-ray diffraction studies. The reactions between H(pzAn Me) and M(CO) 5Br afford fac-MBr(CO) 3[H(pzAn Me)] (M = Mn, 1a; Re, 1b) complexes. The ionic species { fac-M(CH 3CN)(CO) 3[H(pzAn Me)]}(PF 6) (M = Mn, 2a; Re, 2b) were prepared by metathesis of 1a or 1b with TlPF 6 in acetonitrile. Complexes 1a and 1b partly ionize to {M(CH 3CN)(CO) 3[H(pzAn Me)] +}(Br −) in CH 3CN but retain their integrity in less donating solvents such as acetone or CH 2Cl 2. Each of the four metal complexes reacts with (NEt 4)(OH) in CH 3CN to give poorly-soluble crystalline [ fac-M(CO) 3(μ-pzAn Me)] 2 (M = Mn, 3a; Re, 3b). The solid state structures of 3a and 3b are of centrosymmetric dimeric species with bridging amido nitrogens and with pyrazolyls disposed trans- to the central planar M 2N 2 metallacycle. In stark contrast to the diphenylboryl derivatives, Ph 2B(pzAn Me), none of the tricarbonyl group 7 metal complexes are luminescent.

Tricarbonylrhenium(I) complexes with anionic ligands containing S and O donor atoms – potential radiopharmaceutical precursors

Equilibrium geometry of tricarbonylrhenium(I) thiosalicylate and of methylthiosalicylate has been determined by the X-ray diffraction studies as well as calculated by the semiempirical method using the PM3 functional basis set. Infrared spectra of the species have also been studied in the 4000−800 cm −1 range of wavenumbers. The experimental and theoretical data are in satisfactory agreement.