Rhenium Carbonyl Research Articles

Rhenium Complexes with a Pyridinyl‐Naphthyridine Ligand: Synthesis, Characterization, and Catalytic Activity

AbstractTreatment of [Re2(CO)8(CH3CN)2] with 2,7‐dipyridinyl‐1,8‐naphthyridine (bpnp) thermally provided mononuclear [(N,N′‐bpnp)Re(CO)3Cl] (1). Further reaction of 1 with rhenium carbonyls yielded ortho‐metallation dinuclear rhenium complex 2. Both complexes were characterized by spectroscopic analyses and single‐crystal X‐ray determination. Complex 1 also reacted with [PdMeCl(COD)] and [Ir(COD)Cl]2 by means of ortho‐metallation to yield the corresponding heterodinuclear species. Complex 2 appears to be an excellent precatalyst to promote the insertion of terminal alkynes into acetoacetates, which subsequently undergo cyclization to form 2‐pyranones.

Solid-State Thermolysis of afac-Rhenium(I) Carbonyl Complex with a Redox Non-Innocent Pincer Ligand

The development of rhenium(I) chemistry has been restricted by the limited structural and electronic variability of the common pseudo-octahedral products fac-[ReX(CO)3L2] (L2 = α-diimine). We address this constraint by first preparing the bidentate bis(imino)pyridine complexes [(2,6-{2,6-Me2C6H3N=CPh}2C5H3N)Re(CO)3X] (X = Cl 2, Br 3), which were characterized by spectroscopic and X-ray crystallographic means, and then converting these species into tridentate pincer ligand compounds, [(2,6-{2,6-Me2C6H3N=CPh}2C5H3N)Re(CO)2X] (X = Cl 4, Br 5). This transformation was performed in the solid-state by controlled heating of 2 or 3 above 200 °C in a tube furnace under a flow of nitrogen gas, giving excellent yields (≥95 %). Compounds 4 and 5 define a new coordination environment for rhenium(I) carbonyl chemistry where the metal center is supported by a planar, tridentate pincer-coordinated bis(imino)pyridine ligand. The basic photophysical features of these compounds show significant elaboration in both number and intensity of the d-π* transitions observed in the UV/Vis spec tra relative to the bidentate starting materials, and these spectra were analyzed using time-dependent DFT computations. The redox nature of the bis(imino)pyridine ligand in compounds 2 and 4 was examined by electrochemical analysis, which showed two ligand reduction events and demonstrated that the ligand reduction shifts to a more positive potential when going from bidentate 2 to tridentate 4 (+160 mV for the first reduction step and +90 mV for the second). These observations indicate an increase in electrostatic stabilization of the reduced ligand in the tridentate conformation. Elaboration on this synthetic methodology documented its generality through the preparation of the pseudo-octahedral rhenium(I) triflate complex [(2,6-{2,6-Me2C6H3N=CPh}2C5H3N)Re(CO)2OTf] (7, 93 % yield).

X-ray Absorption Spectroscopy of Ground and Excited Rhenium–Carbonyl–Diimine Complexes: Evidence for a Two-Center Electron Transfer

Steady-state and picosecond time-resolved X-ray absorption spectroscopy is used to study the ground and lowest triplet states of [ReX(CO)(3)(bpy)](n+), X = Etpy (n = 1), Cl, or Br (n = 0). We demonstrate that the transient spectra at both the Re L(3)- and Br K-edges show the emergence of a pre-edge feature, absent in the ground-state spectrum, which is associated with the electron hole created in the highest occupied molecular orbital following photoexcitation. Importantly, these features have the same dynamics, confirming previous predictions that the low-lying excited states of these complexes involve a two-center charge transfer from both the Re and the ligand, X. We also demonstrate that the DFT optimized ground and excited structures allow us to reproduce the experimental XANES and EXAFS spectra. The ground-state structural refinement shows that the Br atom contributes very little to the latter, whereas the Re-C-O scattering paths are dominant due to the so-called focusing effect. For the excited-state spectrum, the Re-X bond undergoes one of the largest changes but still remains a weak contribution to the photoinduced changes of the EXAFS spectrum.

Mechanism of CO Displacement from an Unusually Labile Rhenium Complex: An Experimental and Theoretical Investigation

The displacement of a CO ligand from an unusually labile rhenium carbonyl complex containing a bidentate carboxyaldehyde pyrrolyl ligand by PPh(3) and pyridine has been investigated. The reaction is found to proceed by an associative, preequilibrium mechanism. Theoretical calculations support the experimental data and provide a complete energetic profile for the reaction. While the Re-CO bond is found to be intrinsically weak in these complexes, it is postulated that the unusual lability of this species is due to the presence of a weak aldehyde Re-O link that can easily dissociate to open a coordination site on the metal center and accommodate an incoming ligand prior to CO loss. The resulting intermediate complex has been identified by IR spectroscopy. The presence of the hemilabile pyrrolyl ligand provides a lower-energy reaction channel for the release of CO and may be of relevance in the design of CO-releasing molecules.

Gold and silver nanoparticles surface functionalized with rhenium carbonyl complexes

Gold and silver nanoparticles have been synthesized and stabilized with 3-mercaptopropionic acid (MPA). The resulting MPA capped nanoparticles have been functionalized by attaching rhenium carbonyl species to the MPA carboxylate groups. The whole process have been carried out in a two-step procedure improved from the literature for radiopharmaceutical applications. The resultant rhenium-coated metal (gold or silver) nanoparticles have been studied by a different techniques, as for example X-ray photoelectron spectroscopy, UV–Visible spectroscopy, Z-potential, thermogravimetric analysis and vibrational infrared spectroscopy, which proves that the metal core has been really coated with the rhenium carbonyl species, so X-ray diffraction and transmission electron microscopy have been used to study the structure, size and shape of the obtained nanoparticles.

Synthesis, structure and luminescent properties of rhenium(I) carbonyl complexes containing pyrimidine-functionalized N-heterocyclic carbenes

Synthesis, structures and photophysical properties of a series of neutral fac-[Re(CO)3(C^N)Cl] complexes, where C^N is a pyrimidine-functionalized N-heterocyclic carbene [3-methyl-1-(2-pyrimidine)imidazol-2-ylidene, 1; 3-n-butyl-1-(2-pyrimidine)imidazol-2-ylidene, 2; 3-benzyl-1-(2-pyrimidine)imidazol-2-ylidene, 3; 3-mesityl-1-(2-pyrimidine)-imidazol-2-ylidene, 4] are reported. These complexes have been characterized by 1H NMR, 13C NMR, elemental analysis, and IR spectra. Their electrochemical and photophysical behaviors, along with the X-ray crystal structures of 2 and 4, are also reported. In both degassed CH2Cl2 solutions and solid state at room temperature, complexes 1–4 exhibit the emissions at 515–570nm.

Spin–Orbit Treatment of UV–vis Absorption Spectra and Photophysics of Rhenium(I) Carbonyl–Bipyridine Complexes: MS-CASPT2 and TD-DFT Analysis

The lowest-lying spectral transitions in [ReX(CO)(3)(bpy)] (X = Cl, Br, I; bpy = 2,2'-bipyridine) complexes were calculated by means of spin-orbit time-dependent density functional theory (SO-TD-DFT) and spin-orbit multistate complete active space second-order perturbation theory (SO-MS-CASPT2). Computational results are compared with absorption spectra measured in different solvents and used to qualitatively explain the temperature dependence of the phosphorescence decay parameters that were measured for the whole series of complexes. Spin-orbit excited-state calculations interpret their electronic absorption spectra as arising from a bunch of spin mixed states with a singlet component of only 50-90% (depending on the halide), and attribute the phosphorescence decay to thermal population of spin-mixed states with a substantial singlet character.

ChemInform Abstract: Anion Sensing by Rhenium(I) Carbonyls with Polarized N‐H Recognition Motifs

AbstractReview: 57 refs.

A Versatile Ligand Platform that Supports Lewis Acid Promoted Migratory Insertion

A helping hand: Incorporation of Group 2 Lewis acids into a macrocycle appended to a phosphine ligand attached to a rhenium carbonyl complex promotes otherwise unfavorable transformations of coordinated CO (see scheme; M=Ca, Sr). These Lewis acids form relatively weak M-O bonds, thereby enabling release of organic products from the metal center.

New Bioconjugated Rhenium Carbonyls by Transmetalation Reaction with Zinc Derivatives

The transmetallation reaction between zinc dithiocarbamates and rhenium carbonyls has been used as a new strategy to link biomolecules to transition metals. The zinc(II) dithiocarbamate of isonipecotic acid (1) and the succinimidyl ester derivative (2) were prepared by straight forward procedures and were fully characterized by spectroscopic and X-ray diffraction methods, showing in both cases the presence of dinuclear complexes. Complex 2 reacted with all the primary and secondary amines studied (glycine methyl ester, β-alanine methyl ester, 1-(2-methoxyphenyl)piperazine and D-(+)-glucosamine) through the activated succinimidyl ester group, linking the metallic fragment with the biomolecule by the formation of a peptidic bond, and leading to the respective bioconjugated zinc complexes 3-6. In all cases, these zinc complexes could be isolated from the reaction medium by simple precipitation. These results evidence the potential of complex 2 to be used as a synthon to link the zinc dithiocarbamate fragment to biomolecules that contain an amine group. Complexes 3-6 were characterized by the usual spectroscopic methods and all data agree with the proposed structures, which do not contain significant interactions between the zinc fragment and the functional groups of these biomolecules. The transmetallation reaction between the zinc complexes 3-6 and the rhenium carbonyl [ReBr₃(CO)₃]²⁻ led to the expected rhenium dithiocarbamates 7-10 with no change in the organic dithiocarbamate fragments, confirming the viability of this reaction as a tool for linking biomolecules to transition elements. All complexes were characterized by spectroscopic methods and the crystal structure of 8 was studied by X-ray diffraction analysis. All data demonstrated that the biomolecule is positioned far away from the fac-{Re(CO)₃} fragment and the octahedral coordination around the metal is completed by the functionalized dithiocarbamate and a phosphine ligand. Finally, the analysis by ESI-MS spectrometry of the reaction between the zinc complex 4 and a water solution of [Re(H₂O)₃(CO)₃]+ at a very low concentration (10 ppm) showed that the transmetallation reaction took place even though the solubility of the zinc complex in water medium was as low as 0.66 ppm. This preliminary result supports the viability of this approach for the preparation of rhenium and technetium target specific radiopharmaceuticals since the preparation of these compounds are always performed in water medium.

Synthesis of Polyyne Rotaxanes

Active-metal templating has been used to synthesize rotaxanes consisting of a phenanthroline-based macrocycle threaded around a C8, C12, or C20 polyyne chain. The crystal structure of the C12 rotaxane has been determined. In the rhenium(I) carbonyl complex of this rotaxane, with Re(CO)(3)Cl coordinated to the phenanthroline macrocycle, the proximity of the polyyne chain quenches the luminescence of the rhenium. These rotaxanes offer a new approach to controlling the environment and interactions of a polyyne chain.

Development of Novel and Highly Efficient Methods to Construct Carbon–Carbon Bonds Using Group 7 Transition-Metal Catalysts

Abstract Rhenium- or manganese-catalyzed transformations based on the cleavage of inactive bonds, such as carbon–hydrogen and carbon–carbon bonds are discussed. Such transformations are recognized as key methods to realize efficient and powerful reactions. We also reveal novel regio- and/or stereodefined cycloaddition reactions using a rhenium or manganese catalyst. Most of the catalytic activities are typical of rhenium and manganese carbonyl complexes.

Catalytic Hydrosilylation of Carbonyls via Re(CO)5Cl Photolysis

The hydrosilylation reaction between silanes and various carbonyl substrates such as aldehyde, ketone, ester, and carbonate has been catalyzed by Re(CO)5Cl UV photolysis. Kinetic studies have shown that the reaction is favored for the least sterically hindered silanes with aldehydes followed by aliphatic ketones. The IR spectrum of the rhenium carbonyl dimer HRe2(CO)9(SiR3) has been recorded in the reaction mixture. This complex is believed to be the resting state of the active catalyst Re(CO)4SiR3, which could be released upon photactivation. A catalytic mechanism involving this species has been proposed and shown to be thermodynamically feasible using computational studies. In addition, the relative hydrosilylation rates among the various carbonyl substrates can be explained using the same mechanism.

Rhenium(I) carbonyl complexes with redox non-innocent 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole ligands: An experimental and theoretical studies

The new rhenium(I) carbonyl complexes containing {Re(CO)3}+ fragment with redox non-innocent ligands L1/L2 (L1, 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole and L2, 1-ethyl-2-{(o-thioethyl)phenylazo}imidazole) having general formula fac-[ReX(CO)3(L1/L2)] (1/2) (X=Cl (1) and Br (2)) have been synthesized and characterized by both experimental and theoretical studies. The structural confirmation has been carried out for 1a. The complexes show one irreversible ReI/ReII oxidation and one reversible along with an irreversible ligand reduction in the cyclic voltammetric studies. The electronic structure and the nature of Re–CO bonding has been explained by means of DFT and NBO calculations. The spin allowed singlet–singlet electronic transitions of 1a and 2a have been calculated with TDDFT method, and the experimental spectra of the complexes have been discussed on this basis.

Phosphorescent Organic Light‐Emitting Diodes with Outstanding External Quantum Efficiency using Dinuclear Rhenium Complexes as Dopants

The photophysical and electroluminescence properties of two dinuclear rhenium(I) carbonyl complexes bearing 1,2-diazines are comprehensively investigated. The bromo-bridged complex is successfully used as triplet emitter for the preparation of vacuum-processed OLEDs with outstanding external quantum efficiencies, reaching a value of 10%.

New rhenium(i) complexes with substituted diimine ligands for highly efficient phosphorescent devices fabricated by a solution process

A series of new carbonyl rhenium(I) complexes chelated by a substituted 1,10-phenanthroline ligand with the general formula Re(CO)3LCl, where L = 2-(2′-methoxyphenyl)-1,10-phenanthroline (L11), 2-(4′-methoxyphenyl)-1,10-phenanthroline (L22) and 2-(4′-diphenylaminophenyl)-1,10-phenanthroline (L33), have been systemically synthesized. The molecular structure of complex 1 was determined by single crystal X-ray diffraction studies, showing that the complex adopts a distorted octahedral geometry. The electrochemical, photophysical, and thermal properties, as well as the electroluminescent behaviors of three rhenium(I) complexes, were investigated. The solution processable complex 1, 2 or 3 was used as a yellow emitting dopant to fabricate electrophosphorescent devices with a polymer host. The device based on complex 3 exhibits a maximum current efficiency of 12.2 cd A−1 and a peak brightness in excess of 7300 cd m−2, respectively. Even at a high luminance of 5000 cd cm−2 with current density of 81 mA cm−2, the current efficiency of this device remains as high as 6.4 cd A−1. These results represent the best values reported for electophosphorescent devices based on solution processable rhenium(I) complexes.

Beyond click chemistry: spontaneous C-triazolyl transfer from copper to rhenium and transformation into mesoionic C-triazolylidene carbene

The exceptional versatility of the 1,2,3-triazole ring in tridentate carbonyl rhenium complexes has been explored starting from a "click chemistry" unexpected product obtained from the spontaneous copper to rhenium transmetalation, which opens the way to successive transformation to C-triazolyl and triazolylidene mesoionic carbene.

Fabrications of potential imaging probes based on a β-alkyl substituted porphyrin with a terpyridine external coordination site

We report synthesis and coordination properties of β-alkyl porphyrin derivatives bearing terpyridylphenyl substituents at the meso-position and propionate side chains at the β-positions. Rhenium(I) carbonyl ion was encapsulated not in the core but in the external terpyridyl ligand. Such porphyrin–terpyridine hybrid porphyrins can be potentially available for less-invasive imaging like SPECT.

Edge‐Bridging and Face‐Bridging Hydrogen Atoms in Trinuclear Rhenium Carbonyl Hydrides

AbstractThe structures of the trinuclear rhenium carbonyl hydrides H3Re3(CO)n (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). The only structure found for H3Re3(CO)12 is the experimentally known structure with each approximately 3.3 Å edge of a singly bonded Re3 triangle bridged by a hydrogen atom and all terminal carbonyl groups. The two lowest energy H3Re3(CO)11 structures lie within 0.5 kcal/mol in energy and are derived from this H3Re3(CO)12 structure by loss of a carbonyl group with retention of the central Re3(μ‐H)3 core. A higher energy H3Re3(CO)11 structure, closely related to the experimental structure for the isoelectronic dianion H3Re3(CO)102–, is also found in which one of the Re=Re edges of double bond length (2.79 Å) is bridged by two hydrogen atoms. Loss of a carbonyl group from this H3Re3(CO)11 structure with concurrent conversion of one of the edge‐bridging hydrogen atoms to a face‐bridging hydrogen atom gives the lowest energy H3Re3(CO)10 structure. Further loss of a carbonyl group from this (μ3‐H)(μ‐H)2Re3(CO)10 structure with concurrent conversion of a second edge‐bridging hydrogen atom to a face‐bridging hydrogen atom leads to the lowest energy H3Re3(CO)9 structure. This (μ3‐H)2(μ‐H)Re3(CO)9 structure with a central Re3(μ3‐H)2 trigonal bipyramid appears to be a very favorable structure since it not only is the lowest energy H3Re3(CO)9 structure but lies more than 22 kcal/mol below the next lowest energy H3Re3(CO)9 structure.

Synthesis and electrochemiluminescence studies of tricarbonylrhenium(I) complexes with a cationic 2,2′-bipyridyl ligand

Two new rhenium(I) carbonyl complexes with cationic 2,2′-bipyridyl ligands were synthesized and characterized. The electrogenerated chemiluminescence (ECL) of the rhenium(I) carbonyl complexes was first investigated in aqueous solution using the co-reactant tri- n-propylamine (TPrA). The ECL behavior of the complexes was also studied in the presence of several surfactants. The oxidation of both TPrA and the rhenium(I) complexes was facilitated in the presence of Triton X-100, and the ECL intensity was enhanced 300-fold at a Au electrode.