Redox properties of a bis-pyridine rhenium carbonyl derived from an anthracene scaffold

We report the synthesis of a novel bis-pyridine chelate derived from an anthracene scaffold. Complexation of the N2 ligand with rhenium carbonyl affords the Re tricarbonyl bromide complex [(Anth-N2)Re(CO)₃Br]. In THF solution, the title complex exhibits two quasi-reversible reductions located near − 2.1 and − 2.5 V vs Fc/Fc⁺, which are similar to those observed in the free Anth-N2 ligand, suggesting the non-innocent behavior of the complexed anthracene scaffold. Under CO₂ atmosphere, the title complex exhibits an electrocatalytic response consistent with CO₂ → CO reduction, and the presence of electrocatalytically generated CO was confirmed by bulk electrolysis. These results suggest that alternate locations of redox activity (other than at the Re metal center, pyr donors, or bpy framework) can lead to interesting electrochemical behavior.     

Towards near-IR emissive rhenium tricarbonyl complexes: Synthesis and characterisation of unusual 2,2′-biquinoline complexes

Diethyl-2,2′-biquinoline-4,4′-dicarboxylate (debq) reacts with pentacarbonylbromorhenium in toluene to give fac-[Re(CO)₃(debq)Br]; subsequent reaction with AgOTf in MeCN affords the cationic complex fac-[Re(CO)₃(debq)(MeCN)]OTf. X-ray crystallographic data on fac-[Re(CO)₃(debq)Br] show that the debq ligand is coordinated in a bidentate fashion at an angle of 32° from the equatorial plane of the complex: DFT calculations confirm this as the lowest energy conformation. fac-[Re(CO)₃(debq)Br] and fac-[Re(CO)₃(debq)(MeCN)]OTf both possess ¹MLCT absorptions in the visible region, the former most red-shifted to ca. 465 nm. Both complexes demonstrated unusual luminescent properties: in solution, emission appears to be dominated by ligand-centred processes, whereas only ³MLCT emission, tailing into the near-IR, was observed in the solid state at 671 (τ = 59 ns) and 711 nm (τ = 19 ns) for fac-[Re(CO)₃(debq)(MeCN)]OTf and fac-[Re(CO)₃(debq)Br], respectively. However, the debq ligand is not labile in these complexes, which are robust to competing ligands and coordinating solvents.     

Synthesis and characterization of some metal carbonyls with 2-hydroxyacetophenone ethanesulfonylhydrazone

Five new complexes, [M(CO)₅(apesh)] [M=Cr; (1), Mo; (2), W; (3)], [Re(CO)₄ Br(apesh)] (4) and [Mn(CO)₃(apesh) ] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)₆] (M=Cr, Mo, W), [Re(CO)₅ Br], and [Mn(CO)₃ Cp] with 2-hydroxyacetophenone ethanesulfonylhydrazone (apesh). The complexes have been characterized by elemental analysis, mass spectrometry, FT-IR, ¹H NMR spectroscopy. The spectroscopic studies show that apesh behaves as a monodentate ligand coordinating via imine N donor atom in (1)–(4) and as tridentate ligand in (5).     

A rhenium(I) compound bearing a dimerized chromone NO bidentate chelator

Herein, we communicate the synthesis of a novel rhenium(I) complex, fac-[Re(CO)₃(chrpychr)Br] (1) from the equimolar reaction between 2-(4-oxo-4H-chromen-3-yl)-5H-chromeno[2,3-d]pyrimidin-5-one (chrpychr) and [Re(CO)₅Br]. The metal complex 1 was characterized via ¹H NMR-, IR- and UV–Vis spectroscopy and conductivity measurements. Single crystal X-ray analysis provides definitive confirmation in the structural elucidation of 1. DFT studies of 1 aided in the interpretation of its experimental IR spectrum.     

The roles of H-bonding, π-stacking,and antiparallel CO ⋯ CO interactions in the formation of a new Gd(III) coordination polymer based on pyridine-2,6-dicarboxylic acid

This study reports the synthesis of a new catenane Gd(III) complex using pyridine-2,6-dicarboxylic acid (H₂pydc) as ligand. The structure of [Gd(pydc)(Hpydc)(H₂O)₂]_n (1) was characterized by IR spectroscopy, X-ray diffraction methods and the elemental analysis to check the purity of the compound. On the basis of crystallographic data, compound 1 contains a Gd(III) metal center that is coordinated to seven oxygen atoms of two tridentate and one monodentate H₂pydc ligands and two coordinated water molecules. Other lanthanoid complexes involving this ligand are available in the literature; however, this is the first example where a combination of monoanionic (Hpydc⁻) and dianionic (pydc^2 −) forms of the ligand counterbalance the Gd^3 + metal center. The intermolecular interactions in this novel system consist of different kinds of H-bonding and π-stacking interactions in addition to antiparallel CO ⋯ CO interactions which have been analyzed using DFT calculations and the Bader's theory of “atoms in molecules”.     

EXAFS characterization of supported metal-complex and metal-cluster catalysts made from organometallic precursors

Nearly uniform (nearly molecular) supported metals made from molecular organometallic precursors are ideally suited to characterization by EXAFS spectroscopy at the metal edge. Among the most thoroughly investigated mononuclear metal complexes on metal oxide and zeolite supports are MgO-supported rhenium subcarbonyls, approximately Re(CO)₃{OMg}₃ (where the braces denote groups terminating the bulk of the support). These were made, e.g., from [HRe(CO)⁵] and from [H₃Re₃(CO)₁₂]; the Re–O_surface distance determined by EXAFS spectroscopy is 2.15 ± 0.03 Å the support is a tridentate ligand. The Re–O_surface distances in related supported complexes of Groups 7 and 8 metals are all in the range of 2.1–2.2 Å, matching those in molecular analogues. HTa{OSi}₂, prepared from [Ta(CH₂C(CH₃)₃)₃(=CHCCH₃)₃] on SiO₂, catalyzes a new reaction, propane metathesis. Supported complexes made from [HRe(CO)⁵] catalyze alkene hydrogenation but not cyclopropane hydrogenolysis, whereas catalysts made from [H₃Re₃(CO)₁₂] catalyze both these reactions, and EXAFS data indicate neighboring Re centers on the latter (but not the former), which are implicated in the catalysis. EXAFS data similarly indicate supported Mo and W pair sites as catalysts. Supported metal clusters made by decarbonylation of metal carbonyl clusters, e.g., Ir₄/γ-Al₂O₃ and Ir₆/γ-Al₂O₃ or Rh₆/zeolite NaY, are indicated by EXAFS data to be tetrahedra and octahedra, respectively. Such clusters are the species detected by EXAFS spectroscopy at 298 K in the presence of propene and H₂ undergoing catalytic hydrogenation, and they are identified as the catalytically active species. The catalytic activities of the clusters for toluene hydrogenation and alkene hydrogenation are almost unaffected by changes in metal oxide support composition, but they depend on the cluster size, although the catalytic reaction is structure insensitive. Thus, supported metal clusters offer new catalytic properties.     

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 metal-chain complexes (X)[Os(CO)3(CNBut)]3Mn(CO)5 (X=Cl,Br, I)

In what is a new metal-chain forming reaction, (X)[Os(CO)₃(CNBu^t)]₃Mn(CO)₅ (X=Cl, Br, I) complexes have been prepared by the successive addition of Os(CO)₄(CNBu^t) to Mn(CO)₅(X) in hexane. The crystal structure of the iodo derivative reveals it to contain an approximately linear Os₃ Mn chain of metal atoms.     

The metal-chain complexes (X)[Os(CO)3(CNBu)]3Mn(CO)5 (X=Cl, Br, I)

In what is a new metal-chain forming reaction, (X)[Os(CO)₃(CNBu^t)]₃Mn(CO)₅ (X=Cl, Br, I) complexes have been prepared by the successive addition of Os(CO)₄(CNBu^t) to Mn(CO)₅(X) in hexane. The crystal structure of the iodo derivative reveals it to contain an approximately linear Os₃ Mn chain of metal atoms.     

Electrocatalytic reduction of CO2 using rhenium complexes with dipyrido[3,2-a:2′,3′-c]phenazine ligands

A series of rhenium(I) complexes (1–4) with substituted dipyrido[3,2-a:2′,3′-c]phenazine (dppz) ligands were synthesized and analyzed as electrocatalysts for CO₂ reduction. Cyclic voltammetry study shows that complexes 1–4 exhibit dppz ligand-based and metal center-based quasi-reversible reductions under N₂. Under a CO₂ atmosphere, complexes 1–4 exhibit electrocatalytic response consistent with CO₂ → CO reduction with the presence of the gaseous phase product CO confirmed by gas chromatography (GC). Re(2,2′-bpy)(CO)₃Br (Lehn catalyst), a benchmark for electrocatalytic reduction of CO₂ to CO, was also prepared and tested for electrocatalytic properties for comparison. The results suggest that chemical modification on the dppz ligand leads to interesting electrocatalytic properties and the large conjugation of the dppz ligand can help store multiple electrons and lower the energy barrier for CO₂ reduction.     

Rhenium(I) complexes with aliphatic Schiff bases appended to bio-active moieties

Novel facial tricarbonylrhenium(I) complexes, fac-[Re(urca)₂(CO)₃Cl] (1) and fac-[Re(bzta)(CO)₃Cl] (2) were isolated from the coordination reactions of 5-((5-hydroxypentylimino)methyl)uracil (urca) and 2-((5-hydroxypentylimino)methyl)benzothiazole (bzta) with [Re(CO)₅Cl], respectively. Spectral characterization of metal complexes 1 and 2 were supported by their X-ray crystal structures. DNA interactions were assessed via UV–Vis calf-thymus (CT)-DNA binding titrations and gel electrophoresis. Redox properties of the metal complexes were probed using voltammetry.     

A novel dirhenium(III) complex with bridging picolinate and methoxide ligands from the reaction between cis-Re2(μ-O2CCH3)2Cl4(H2O)2 and picolinic acid

The reaction of cis-Re₂(μ-O₂CCH₃)₂Cl₄(H₂O)₂ with picolinic acid (Hpic) affords either the diamagnetic, metal–metal bonded, dirhenium(III) complex Re₂(μ-OMe)(μ:η²-pic)(η²-pic)₃Cl (1) or the mononuclear rhenium(V) complex ReO(η²-pic)₂Cl (2), depending on whether mixed methanol/ethanol or acetone/ethanol solvent mixtures are used. The structures of 1 and 2 have been established by X-ray crystallography. Complex 1 is unusual in having a bridging methoxide and bridging picolinate ligand in an edge-sharing bioctahedral structure in which the Re–Re bond distance of 2.4588(4) Å is unusually short for what is a formal Re–Re double bond.     

Synthesis, characterization and crystal structure of cis,mer-[ReH(CO)2{PPh(OMe)2}3]

The dicarbonylhydride complex cis,mer-[ReH(CO)₂{PPh(OMe)₂}₃] (1) was serendipitously obtained when, in an attempt to replace a CO ligand by the phosphonite ligand PPh(OMe)₂ in [ReH(CO)₃(L)] (L = PPh₂OCH₂CH₂OPPh₂), this complex was treated with PPh(OMe)₂ under UV irradiation. The complex 1 was characterized by IR, ¹H and ³¹P{¹H} NMR spectroscopy and by crystal structure determination. The spectroscopic features are consequent with the cis,mer configuration showed by the X-ray crystallographic analysis of the complex. The environment of the metal centre is a distorted octahedron.     

Synthesis of the dimeric μ2-O aminoalkoxy complexes of rhenium [(CO)3Re(μ2-O∩NH2)]2 and their condensation products with acetone [(CO)3Re(μ2-O∩N=CMe2)]2

The allyl rhenium complex Re(CO)₄(η³-C₃H₅) (1) reacts with the amino alcohols 2-amino ethanol, 1-amino-propane-2-ol, 2-amino phenol and 2-amino benzyl alcohol (2a–d) to give the dimeric μ₂-O-bridged tricyclic aminoalkoxy complexes of rhenium of the type [(CO)₃Re(μ₂-O^∩NH₂)]₂ (3a–d). The acidic NH₂ ligand undergoes a condensation reaction with acetone at r.t. forming the corresponding ketimine complexes [(CO)₃Re(μ₂-O^∩N=CMe₂)]₂ (4a–d). The compounds have been characterized by spectroscopic (IR, NMR, MS), analytical (C, H, N) and X-ray diffraction analyses (4a–d).     

Silberkomplexe von 3-disubstituierten 1-Methyl-perhydro-1,2,4-triazin-5,6-dithionen

Silver(I) Complexes of 3-Substituted 1-Methyl-perhydro-1,2,4-triazine-5,6-dithiones Heterocyclic triazine compounds such as 1-methyl-perhydro-1,2,4-triazin-5,6-dithiones react with silver salts forming complex species [AgL₂]⁺ (L = triazinedithione). In water the complexes are unstable owing to ligand hydrolysis. Stable solid complex [AgL₂]Br(L = 1,3,3-trimethyl-perhydro-1,2,4-triazine-5,6-dithione) can be obtained by the digestion of AgBr-microcrystals with the triazinedithione in methanol. As shown by X-ray crystal structure analysis the silver ion in this complex is coordinated trigonal pyramidal by four sulfur donor atoms.     

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

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.     

A unique diruthenium(II,III) unit surrounded by tridentate ligands of N-(2-pyridyl)-2-oxy-5-chlorobenzylaminate

A new metal–metal bonded diruthenium(II, III) compound with a dianionic tridentate ligand, N-(2-pyridyl)-2-oxy-5-chlorobenzylaminate (5-Clsalpy²⁻), was synthesized and structurally characterized as Li₂(THF)₄Cl[Ru₂(5-Clsalpy)₃] (1). The 5-Clsalpy²⁻ ligand that acts as a bridging/chelating co-ligand afforded a unique coordination mode of [M–M bridging/equatorial-chelating] in addition to the “common” mode of [M–M bridging/axial-chelating] around the diruthenium unit of 1.     

Synthesis, structure and magnetic properties of the first copper(II) complex with an (E)-4-aryl-4-oxo-2-butenoato ligand

A new binuclear Cu(II) complex with an (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato ligand (L) was successfully synthesized and characterized by elemental analysis and IR-spectroscopy. The structures of (E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoic acid (HL), and the corresponding (tetrakis)-μ-[(E)-4-(2,4-diisopropylphenyl)-4-oxo-2-butenoato]-bis(ethanol)-copper(II) complex, [Cu₂L₄(C₂H₅OH)₂], were determined by single crystal X-ray analyses and are preliminarily discussed. This is the first complex of a transition metal with ligand L, as well as the first determined crystal structure of a metal complex with this type of ligand. Analysis of the magnetic susceptibility measurements of the isolated [Cu₂L₄(C₂H₅OH)₂] · H₂O complex shows the existence of a strong anti-ferromagnetic intradimer coupling, with an exchange integral value 2J of −260 cm⁻¹.     

Photocatalytic activation of CO2 under visible light by Rhenium complex encapsulated in molecular sieves

The photocatalytic activation of CO₂ over molecular sieve-encapsulated cationic rhenium complex has been investigated under visible light (λ>350 nm). The cationic rhenium complex, [Re(I)(CO)₃(bpy)(py)]⁺(bpy=2,2′bipyridine, py=pyridine), has been encapsulated by ion-exchange method using the aqueous solution of [Re(I)(CO)₃ (bpy)(py)]⁺PF₆ ^- into the microporous NaY and the mesoporous A1MCM-41 molecular sieve acting as supramolecular heterogeneous host. To confirm the encapsulation of [Re(IXCO)₃(bpy)(py)]⁺ into the pores of molecular sieve, XeNMR and FT-IR spectroscopies have been applied before and after the [Re(I)(CO)₃(bpy)(py)]⁺ encapsulation. To investigate the photophysical and photochemical properties, molecular sieve-encapsulated cationic rhenium complex has been studied by UV-Visible diffuse reflectance spectroscopy (UV-DRS) with photoirradiation (λ>350 nm) at room temperature. By monitoring the photoreaction of CO₂ over the photocatalysts, the conversion of CO₂ into CO and carbonate species has been observed by usingin-situ FT-IR and time-resolved mass spectroscopy. From the experimental results, the photocatalytic activation mechanism of CO₂ on the catalyst under visible light (λ>350 nm) could be proposed via the photo-induced reaction of two electrons and two protons, resulting from water decomposition.     

How the electronic and steric properties of the ligand can determine the stability of the asymmetric dinuclear carbonyl-phosphite Rh(0) complex (CO)2(P(O-o-tBuPh)3)Rh-Rh(P(O-o-tBuPh)3)(CO)3

Theoretical studies have shown that the low basicity of the phosphite ligand P(O-o-^tBuPh)₃ in the Rh(0) complex (CO)₂(P(O-o-^tBuPh)₃)Rh-Rh(P(O-o-^tBuPh)₃)(CO)₃ favours the non-bridged structure over the bridged one, but is not responsible for the absence of the expected sixth carbonyl in the structure. The steric effects of the bulky ligand play an important role in the unusual stability of the asymmetric complex.