Oxorhenium Complexes Research Articles

Transition-Metal Oxos as the Lewis Basic Component of Frustrated Lewis Pairs.

The reaction of oxorhenium complexes that incorporate diamidopyridine (DAP) ligands with B(C6F5)3 results in the formation of classical Lewis acid-base adducts. The adducts effectively catalyze the hydrogenation of a variety of unactivated olefins at 100 °C. Control reactions with these complexes or B(C6F5)3 alone did not yield any hydrogenated products under these conditions. Mechanistic studies suggest a frustrated Lewis pair is generated between the oxorhenium DAP complexes and B(C6F5)3, which is effective at olefin hydrogenation. Thus, we demonstrate for the first time that the incorporation of a transition-metal oxo in a frustrated Lewis pair can have a synergistic effect and results in enhanced catalytic activity.

Production of Adipic Acid from Sugar Beet Residue by Combined Biological and Chemical Catalysis

AbstractAdipic acid is one of the most important industrial dicarboxylic acids and is used mainly as a precursor to nylon‐6,6. Currently, commercial adipic acid is produced primarily from benzene by a chemical route that is associated with environmental, health, and safety concerns. Herein, we report a new process to produce adipic acid from an inexpensive renewable feedstock, sugar beet residue by combining an engineered Escherichia coli strain and Re‐based chemical catalysts. The engineered E. coli converted d‐galacturonic acid to mucic acid, which was precipitated easily with acid, and the mucic acid was further converted to adipic acid by a deoxydehydration reaction catalyzed by an oxorhenium complex followed by a Pt/C‐catalyzed hydrogenation reaction under mild conditions. A high selectivity to the free acid products was achieved by tuning the acidity of the Re‐based catalysts. Finally, adipic acid was produced directly from sugar beet residue that was hydrolyzed enzymatically with engineered E. coli and two chemical catalysts in a yield of 8.4 %, which signifies a new route for the production of adipic acid.

Synthesis, characterization and DFT calculations of a Re(V)-thiazolidine-2,4-dione complex

This article presents a combined experimental and computational study of a new oxorhenium(V) complex of thiazolidine-2,4-dione (HTDO). The complex has been synthesized by direct reaction of NH4ReO4 with thiazolidine-2,4-dione in the presence of Na2S2O6 as a reducing agent. The complex [ReO(TDO)(H2O)3](S2O8) has been characterized by spectroscopy (FT-IR, NMR, UV-vis, mass), thermogravimetry, microanalysis, and HPL chromatography. The complex was geometrically optimized by DFT with B3LYP level of theory and satisfactory theoretical–experimental agreement was achieved for analysis of IR and NMR data of the complex. Additional information about binding between rhenium and oxo ligand in the complex has been obtained by NBO analysis. The antibacterial activity of the investigated complex has been tested and evaluated.

ChemInform Abstract: Synthesis of Air‐ and Moisture‐Stable, Storable Chiral Oxorhenium Complexes and Their Application as Catalysts for the Enantioselective Imine Reduction.

AbstractThe new catalysts are applied to the asymmetric reduction of a wide range of ketimines, the syntheses of enantiopure α‐amino esters, γ‐ and δ‐lactams, isoindolinones, and pharmaceutically relevant targets, such as (R)‐(+)‐salsolidine and (R)‐(+)‐crispine A.

Deoxygenation of carbonyl compounds using an alcohol as an efficient reducing agent catalyzed by oxo-rhenium complexes

The catalytic system 3-pentanol/ReOCl3(SMe2)(OPPh3) was very efficient for the deoxygenation of carbonyl compounds.

N-H cleavage as a route to new pincer complexes of high-valent rhenium.

A novel PNN-type pincer ligand has been accessed via imine reduction with LiAlH4 to provide the phosphine diamino proligand, PNHNH (1). The ligand, 1, as well as PNHP can be metallated directly, via N-H cleavage, with L2ReOX2(OEt) precursors to access six-coordinate (PNP)ReOCl2 (2) and (PNNH)ReOX2 (3-Cl, X = Cl; 3-Br, X = Br) in good yield. 3-Cl and 3-Br undergo dehydrohalogenation upon treatment with NEt3, furnishing the five-coordinate phosphine/diamido PNN-type compounds (PNN)ReOX (4-Cl, X = Cl; 4-Br, X = Br) in excellent yield, presenting as a mixture of rotameric diasteromers. The reversibility of this deprotonation, and the coordinative unsaturation of 4-Cl is shown in reactions with HCl(aq) and PMe3 providing 3-Cl and 4-PMe3, respectively. Treatment of 4-Cl with AgOAc, AgOTf, or NaHBEt3 lead to formation of (PNN)ReO(OAc) (4-OAc), (PNN)ReO(OTf) (4-OTf), and (PNN)ReO(H) (4-H), all isolated in excellent yields in varying diasteromeric ratios. The nature of the isomerism was analyzed based on solid-state structural studies and solution NMR data.

Synthesis and DFT calculations of oxido and phenylimido-rhenium(V) complexes incorporating the N, O donor ligand 2-[(2-hydroxyethylimino)methyl]phenol

The reactions of equimolar amounts of trans-[ReOC13(PPh3)2] or trans-[Re(NPh)(PPh3)2Cl3] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H2L) result in the formation of cis-[ReO(HL)PPh3Cl2] (1a) and trans-[Re(NPh)(HL)(PPh3)Cl2] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10−4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b.

Specific features of the structures of monomeric octahedral d 2 rhenium(V) oxo complexes with oxygen atoms trans to the oxo ligands: Complexes with neutral ligands OER3 (E = P, As; R3 = Ph3, PhEt2) trans to O(oxo)

Specific features of the structures of mononuclear octahedral rhenium(V) oxo complexes with oxygen atoms of neutral ligands OER3 (E = P, As; R3 = Ph3, PhEt2) trans to the multiply bonded oxo ligands have been considered. The complexes contain halide ligands, as well as organic monoand bidentate ligands, in the equatorial plane. The Re–O(OER3)trans bonds are elongated owing to the structural manifestation of the trans influence of multiply bonded oxo ligands.

ChemInform Abstract: Rhenium(V) Oxocomplexes [ReOX(N‐O)2] and [ReOL(N‐O)2]+‐Synthesis, Structure, Spectroscopy and Catalytic Properties

AbstractReview: 51 refs.

ChemInform Abstract: Efficient Deoxygenation Methodologies Catalyzed by Oxo‐Molybdenum and Oxo‐Rhenium Complexes

AbstractReview: 80 refs.

Enantioselective Imine Reduction Catalyzed by Chiral Oxorhenium Complexes

Enantioselective Imine Reduction Catalyzed by Chiral Oxorhenium Complexes

Mechanism and Mitigation of the Decomposition of an Oxorhenium Complex-Based Heterogeneous Catalyst for Perchlorate Reduction in Water.

A biomimetic heterogeneous catalyst combining palladium nanoparticles and an organic ligand-coordinated oxorhenium complex on activated carbon, Re(hoz)2-Pd/C, was previously developed and shown to reduce aqueous perchlorate (ClO4-) with H2 at a rate ∼100 times faster than the first generation ReOx-Pd/C catalyst prepared from perrhenate (ReO4-). However, the immobilized Re(hoz)2 complex was shown to partially decompose and leach into water as ReO4-, leading to an irreversible loss of catalytic activity. In this work, the stability of the immobilized Re(hoz)2 complex is shown to depend on kinetic competition between three processes: (1) ReV(hoz)2 oxidation by ClO4- and its reduction intermediates ClOx-, (2) ReVII(hoz)2 reduction by Pd-activated hydrogen, and (3) hydrolytic ReVII(hoz)2 decomposition. When ReV(hoz)2 oxidation is faster than ReVII(hoz)2 reduction, the ReVII(hoz)2 concentration builds up and leads to hydrolytic decomposition to ReO4- and free hoz ligand. Rapid ReV(hoz)2 oxidation is mainly promoted by highly reactive ClOx- formed from the reduction of ClO4-. To mitigate Re(hoz)2 decomposition and preserve catalytic activity, ruthenium (Ru) and rhodium (Rh) were evaluated as alternative H2 activators to Pd. Rh showed superior activity for reducing the ClO3- intermediate to Cl-, thereby preventing ClOx- buildup and lowering Re complex decomposition in the Re(hoz)2-Rh/C catalyst. In contrast, Ru showed the lowest ClO3- reduction activity and resulted in the most Re(hoz)2 decomposition among the Re(hoz)2-M/C catalysts. This work highlights the importance of using mechanistic insights from kinetic and spectroscopic tests to rationally design water treatment catalysts for enhanced performance and stability.

ChemInform Abstract: Structures of Monomeric Octahedral D2 Rhenium(V) Oxo Complexes with Oxygen Atoms trans to the Oxo Ligands: Complexes with Ethoxo Ligands trans to O(oxo)

AbstractReview: 56 refs.

ChemInform Abstract: Structures of Monomeric Octahedral D2 Rhenium(V) Oxo Complexes with Oxygen Atoms trans to the Oxo Ligands: Complexes with Methoxo Ligands trans to O(oxo)

AbstractReview: 54 refs.

Synthesis of air- and moisture-stable, storable chiral oxorhenium complexes and their application as catalysts for the enantioselective imine reduction.

Air-/moisture-stable, crystalline, and storable chiral salicyloxazoline based oxorhenium(V) complexes have been synthesized and their catalytic application for the asymmetric reduction of ketimines using hydrosilane as hydride source is disclosed. A broad substrate scope, high yields, and excellent enantioselectivities (up to 99 %) are attained. Furthermore, the syntheses of enantiopure α-amino esters, γ- and δ-lactams, and isoindolinones have also been carried out using this methodology. Finally, the method has been applied to synthetic targets of pharmaceutical relevance, such as R-(+)-salsolidine and R-(+)-crispine A.

Characterization of Rhenium(V) Complexes with Phenols Using Mass Spectrometry with Selected Soft Ionization Techniques

The synthesis, characterization, and mass spectra of oxorhenium(V) complexes with 1,2-dihydroxybenzene, 1,2,3-trihydroxybenzene, and 2,3-dihydroxynaphtalene are reported. Electrospray ionization, atmospheric pressure photoionization, and laser desorption/ionization mass spectra of the complexes showed abundant negatively charged molecular anions and low fragmentation. Calculated similarity indexes showed significant conformity between the computed and experimental isotopic patterns of selected ions and confirmed correct assignment of elemental composition to m/z values. Electrospray tandem mass spectrometry provided essential information about fragments from molecular ions of studied complexes, making it possible to distinguish among fragment ions and the ions arising from compounds present in the reaction mixture. Based on the results, mass spectrometry utilizing soft common ionization techniques is useful for monitoring complex formation reaction kinetics and the stabilities of the complexes. Representative spectra were recorded for micromolar concentrations of the analytes.

Structural details of monomeric octahedral d 2-rhenium(V) oxo complexes with oxygen atoms in the trans-positions to oxo ligands. Complexes with the anionic ligands OR n− (n = 1, 2) in trans-positions to O(oxo)

The paper considers details of the structures of mononuclear octahedral rhenium(V) oxo complexes with oxygen atoms of aromatic (phenolic) and other similar cyclic ligands OR− (R = Ph, Cy, C6H4R′ (R′ = OH, OMe), C10H6OH) and with other structurally studied anionic ligands ORn− (n = 1, 2) (R = P(O)(OMe)2, C(O)(CF3), OC(Me(CF3)2, BF3) located in the trans-position to the multiply bonded oxo ligands. The complexes contain halide ligands and organic mono-, bi-, and tetradentate ligands in the equatorial plane. The Re-O(OR)trans bonds as well as the bonds with aliphatic alkoxo ligands (ORalk)trans (R = Me, Et, Pr) are not elongated due to the trans-effect of doubly bonded oxo groups but are substantially shortened (with one exception). This is attributable to the fact that these Re-O(OR) bonds, like Re-O(oxo) bonds, have a higher order, i.e., d2-rhenium(V) complexes of this type should be treated as pseudo-dioxo compounds [Re(=O)(=OR)]3 − n (n = 1, 2).

Carbon nanofibers decorated with oxo–rhenium complexes: Highly efficient heterogeneous catalyst for oxidation of amines with hydrogen peroxide

Pyridine functionalized carbon nanofibers (Py-CNFs) were synthesized, characterized and used for the grafting of oxo–rhenium complex i.e., methyltrioxorhenium (MTO) via acid-base ionic interaction. The grafting of MTO to Py-CNFs was confirmed by FTIR, UV–vis, SEM, TEM and TGA analyses. The determination of rhenium content by ICP-AES further suggested the successful immobilization of MTO to the support. The developed heterogeneous material i.e., MTO@Py-CNFs was found to be an efficient catalyst for the oxidation of various secondary as well as tertiary amines to corresponding nitrones or N-oxides, respectively by using hydrogen peroxide. The developed catalyst was readily recovered by centrifugation and reused for subsequent ten runs without any significant loss in catalytic activity.

Structural features of monomeric octahedral d 2 rhenium(V) oxo complexes with oxygen atoms in trans-positions to oxo ligands: Complexes with propoxo ligands in trans-positions to O(oxo)

Some structural features of mononuclear octahedral rhenium(V) oxo complexes with oxygen atoms of propoxo ligands O(Pr-iso)− in trans-positions to multiply bonded oxo ligands are considered. The complexes contain monodentate inorganic or organic ligands or bi- and tetradentate organic ligands in the equatorial plane. Re-O(OPr) trans bonds, as well as the other bonds with (ORalkoxo) trans alkoxo ligands (R = Me, Et), are considerably shortened, instead of being elongated, due to the structural manifestation of the trans-effect of multiply bonded oxo ligands. This is explained by that these Re-O(ORalkoxo) bonds also have an increased multiplicity; that is, d 2 rhenium(V) monooxomonoalkoxo complexes should be considered as pseudo-dioxo Re(=O)(=ORalkoxo) compounds.

Necroptosis-inducing rhenium(V) oxo complexes.

Rhenium(V) oxo complexes of general formula [ReO(OMe)(N^N)Cl2], where N^N = 4,7-diphenyl-1,10-phenanthroline, 1, or 3,4,7,8-tetramethyl-1,10-phenanthroline, 2, effectively kill cancer cells by triggering necroptosis, a non-apoptotic form of cell death. Both complexes evoke necrosome (RIP1-RIP3)-dependent intracellular reactive oxygen species (ROS) production and propidium iodide uptake. The complexes also induce mitochondrial membrane potential depletion, a possible downstream effect of ROS production. Apparently, 1 and 2 are the first rhenium complexes to evoke cellular events consistent with programmed necrosis in cancer cells. Furthermore, 1 and 2 display low acute toxicity in C57BL/6 mice and reasonable stability in fresh human blood.