Furan Complexes Research Articles

Cation−π Complexes of Silver Studied with Photodissociation and Velocity-Map Imaging

Ag+(aromatic) ion-molecule complexes of benzene, toluene, or furan are generated in the gas phase by laser vaporization in a supersonic expansion. These ions are mass selected in a time-of-flight spectrometer and studied with ultraviolet laser photodissociation and photofragment imaging. UV laser excitation results in dissociative charge transfer (DCT) for these ions, producing neutral silver atom and the respective aromatic cation as the photofragments. Velocity-map imaging and slice imaging techniques are employed to investigate the kinetic energy release in these photodissociation processes. In each case, DCT produces significant kinetic energy, and evidence is also found for excitation of the internal rovibrational degrees of freedom for the molecular cations. Analysis of the kinetic energy release together with the known ionization energies of silver and the molecular ligands provides new information on the cation-π bond energies.

A theoretical study of X‐H∙∙∙π and X∙∙∙π interactions in the complexes of furan, thiophene, pyrrole and hydrogen halides

AbstractBy using ab initio geometry optimization calculations we obtained thirteen stable complexes containing H∙∙∙π and X∙∙∙π interactions between Furan, Thiophene, Pyrrole and HX (X = F, Cl, Br) at the MP2/6‐311++G(3df,2pd) high level of theory. The interaction energies corrected for only ZPE and both ZPE and BSSE range from ‐7.92 to ‐28.47 kJ.mol‐1 and ‐3.28 to ‐22.33 kJ.mol‐1, respectively. The results show that for the same HX, the stability of complexes decreases in going from Pyrrole to Thiophene and finally to Furan moiety, and increases in the order of HF < HCl < HBr monomer with the same π‐system. The obtained results from AIM and MEP analyses indicate that the H∙∙∙π interaction is more stable than X∙∙∙π one in all the investigated complexes. It is found that the electrostatic, dispersion and induction energy terms significantly contribute to strength of the studied complexes, in which two formers are for H∙∙∙π hydrogen bonded complexes and two latters are for X∙∙∙π halogen bonded complexes.

Intermolecular dissociation energies of hydrogen-bonded 1-naphthol complexes.

We have measured the intermolecular dissociation energies D 0 of supersonically cooled 1-naphthol (1NpOH) complexes with solvents S = furan, thiophene, 2,5-dimethylfuran, and tetrahydrofuran. The naphthol OH forms non-classical H-bonds with the aromatic π-electrons of furan, thiophene, and 2,5-dimethylfuran and a classical H-bond with the tetrahydrofuran O atom. Using the stimulated-emission pumping resonant two-photon ionization method, the ground-state D 0(S 0) values were bracketed as 21.8 ± 0.3 kJ/mol for furan, 26.6 ± 0.6 kJ/mol for thiophene, 36.5 ± 2.3 kJ/mol for 2,5-dimethylfuran, and 37.6 ± 1.3 kJ/mol for tetrahydrofuran. The dispersion-corrected density functional theory methods B97-D3, B3LYP-D3 (using the def2-TZVPP basis set), and ωB97X-D [using the 6-311++G(d,p) basis set] predict that the H-bonded (edge) isomers are more stable than the face isomers bound by dispersion; experimentally, we only observe edge isomers. We compare the calculated and experimental D 0 values and extend the comparison to the previously measured 1NpOH complexes with cyclopropane, benzene, water, alcohols, and cyclic ethers. The dissociation energies of the nonclassically H-bonded complexes increase roughly linearly with the average polarizability of the solvent, (S). By contrast, the D 0 values of the classically H-bonded complexes are larger, increase more rapidly at low (S), but saturate for large (S). The calculated D 0(S 0) values for the cyclopropane, benzene, furan, and tetrahydrofuran complexes agree with experiment to within 1 kJ/mol and those of thiophene and 2,5-dimethylfuran are ∼3 kJ/mol smaller than experiment. The B3LYP-D3 calculated D 0 values exhibit the lowest mean absolute deviation (MAD) relative to experiment (MAD = 1.7 kJ/mol), and the B97-D3 and ωB97X-D MADs are 2.2 and 2.6 kJ/mol, respectively.

Structure and Spectroscopy of Furan:H2O Complexes.

An analysis of the 1:1 complex of furan and water is presented. In this study, computation and matrix isolation FTIR were used to determine stable complexes of furan:water. Density functional theory and Møller-Plesset second-order, perturbation theory calculations found four, unique geometries for the complex. Two complexes were characterized by C-H···O interactions, one complex was characterized by O-H···O, and the fourth complex was characterized by O-H···π. Optimizations completed using B3LYP, B3LYP-GD3BJ, M05-2X, and MP2 showed the most stable species to be bound by O-H···O interactions. Matrix isolation experiments of mixtures of furan and water held in nitrogen at 15 K showed evidence of stable complexes when probed by FTIR. These signatures grew in intensity when matrices were annealed at 30 K. These vibrational features were predominately associated with perturbation of the water monomer. Additionally, the spectra of complexes containing water isotopologues were recorded. Analysis of spectral features pointed to the presence of a single geometry formed in the matrix, which is best described as a 1:1 complex stabilized by a O-H···O interaction.

Dinuclear palladium(I) sandwich complexes of furan and toluene

The reaction of a dinuclear palladium complex [Pd 2 (CH 3 CN) 6 ][X] 2 (X = BF 4 , PF 6 ) with excess furan afforded the sandwich-type bis-furan dinuclear palladium(I) complex [Pd 2 (μ-furan) 2 (CH 3 CN) 2 ][X] 2 . The substitutionally labile bridging furan ligands in the dipalladium sandwich complex can be readily replaced with toluene to give the bis-toluene dipalladium(I) sandwich complex [Pd 2 (μ-toluene) 2 (CH 3 CN) 2 ][X] 2 .

Sensitivity of Noble Gas NMR Parameters to the Heterocyclic Ring Proximity. Density Functional Theory Studies of Ne–Furan and Ar–Furan Complexes

Theoretical modeling of noble gas interaction with furan as a simple heterocyclic ring was performed. The structures of neon–furan and argon–furan complexes were calculated at the MP2, M06-2X, CAM-B3LYP, APFD, and VSXC levels of theory using 6-311++G** basis set. The predicted 21Ne and 39Ar NMR chemical shifts for the Ne–furan and Ar–furan complexes calculated with pcS-3 and aug-pcS-3 basis sets were sensitive to the presence of the aromatic furan ring. Our results indicate a higher sensitivity of the neon and argon NMR probes than the previously reported 3He NMR spectroscopic parameters in studies of small heterocyclic rings containing the oxygen atom.

Substituent Effects on the Electrochemical, Spectroscopic, and Structural Properties of Fischer Mono- and Biscarbene Complexes of Chromium(0)

A series of ten ferrocenyl, furyl, and thienyl mono- and biscarbene chromium(0) complexes were synthesized and characterized spectroscopically and electrochemically. The single crystal structure of the biscarbene complex [(CO)5Cr═C(OEt)-Fu'-(OEt)C═Cr(CO)5] (4a) was determined: C20H12Cr2O13; triclinic; P1; a = 6.2838(5), b = 12.6526(9), c = 29.1888(19) Å, α = 89.575(2), β = 88.030(2), γ = 87.423(2)°; Z = 4. Results from an electrochemical study in CH2Cl2 were mutually consistent with a computational study in showing that the carbene double bond of 1-6 is reduced to an anion radical, (-)Cr-C• at formal reduction potentials < -1.7 V vs FcH/FcH(+). The Cr centers are oxidized in two successive one electron transfer steps to Cr(II) via the Cr(I) intermediate. Only Cr(I) oxidation is electrochemically irreversible. Dicationic Cr(II) species formed upon two consecutive one-electron oxidation processes are characterized by a peculiar bonding situation as they are stabilized by genuine CH···Cr agostic interactions. With respect to aryl substituents, carbene redox processes occurred at the lowest potentials for ferrocene derivatives followed by furan complexes. Redox process in the thiophene derivatives occurred at the highest potentials. This result is mutually consistent with a (13)C NMR study that showed the Cr═C functionality of furyl complexes were more shielded than thienyl complexes. The NHBu carbene substituent resulted in carbene complexes showing redox processes at substantially lower redox potentials than carbenes having OEt substituents.

Structures of Fischer multi-carbene complexes of furan and thiophene

Structures of Fischer multi-carbene complexes of furan and thiophene

Comparisons of the halogen-bonded and hydrogen-bonded complexes of furan, thiophene and pyridine with Lewis acids (ClF, HCl)

The geometries, interaction energies, tautomerization processes, electron density and Laplacian properties of the weak interaction systems formed by heteroaromatic rings (C 4H 4O, C 4H 4S and C 5H 5N) and Lewis acids (ClF, HCl) have been studied at the spin-restricted DFT method (X3LYP) with the aug-cc-pVTZ basis sets. Two types of interactions are observed among these systems: the σ-type and the π-type geometry. The low energy barriers (<2.3 kcal/mol) demonstrate that the σ-type and π-type angular geometries of C 4H 4O/C 4H 4S⋯ClF/HCl complexes are easily transformed from each other. The nature of the intramolecular interactions has been also investigated through both the theory of atoms in molecules (AIM) and energy decomposition analysis.

Structure, properties, and nature of the pyridine-XY (X, Y=F, Cl, Br) complexes: An ab initio study

Structure and properties (energies, electronic, and thermodynamic properties) of complexes pyridine-XY (X, Y = F, Cl, Br) have been investigated at the MP2/aug-cc-pVDZ level. Two types of geometries (pi-halogen bonded and sigma-halogen bonded) are observed. In contrast with the previous results on similar furan and thiophene complexes, the sigma-halogen bonded structures are more stable and the reasons are discussed. Charge transfer is found to be important in the formation of title system and the possible existing complexes under experimental conditions have been forecasted too. A symmetry-adapted perturbation theory energy decomposition analysis reveals that the pyridine-XY complexes are dominantly inductive in nature.

Study on the nature of interaction of thiophene with various hydrides

The nature of interactions of thiophene with various hydrides (Y) (Y = HF, HCl, H 2O, H 2S, NH 3, PH 3) is investigated using ab initio calculations. In contrast with the previous results on similar furan complexes, only the π-type is observed for the thiophene complexes. Variations in complexes geometry can be accounted for by the differences in the electrostatic potential on the aromatic ring. To further study the nature of the intermolecular interactions, an SAPT (the symmetry-adapted perturbation theory) energy decomposition analysis was carried out and the results indicate that the dispersion and electrostatic interactions dominate the thiophene complexes.

Ruthenium complexes of furan- and thiophene-thiolates: Structure of CpRu(dppe)SThi

Complexes of ruthenium containing 2-furan- and 2-thiophene-thiolates with phosphine ligands have been prepared and characterized. The bis(triphenylphosphine) complexes CpRu(PPh 3) 2SR (R = C 4H 3O: Fu ( 1a), C 4H 3S: Thi ( 1b)) were prepared by the reaction of thiolato anions (FuS − or ThiS −) with CpRu(PPh 3) 2Cl. The one-pot reaction of CpRu(PPh 3) 2Cl, thiolato anions and L ligands gave CpRu(L)SR (L = bis(diphenylphosphino)methane: dppm ( 2); bis(diphenylphosphino)ethane: dppe ( 3)). The newly prepared complexes have been characterized by spectroscopic techniques (FT-IR, 1H NMR and 31P NMR) and by elemental analysis. The crystal structure of CpRu(dppe)SThi ( 3b) has been determined by X-ray diffraction.

Synthesis, characterisation and antimicrobial studies of CuII, NiII and CoII complexes of furan- and thiophene-2-aldoximes

Complexes of Cu II , Ni II and Co II with furan- and thiophene-2-aldoximes have been synthesized. The structures of the synthesised compounds have been established by spectral and magnetic studies. All the synthesised complexes have been screened for their antimicrobial activities.

Rhenium(I) η2-Coordinated Furan Complexes: Converting Furan into a 1,3-Carbon Dipole

TpRe(CO)(MeIm)(η2-2-methylfuran) (1; Tp = hydridotris(pyrazolyl)borate and MeIm = N-methylimidazole) and TpRe(CO)(MeIm)(η2-2,5-dimethylfuran) (9) undergo Lewis acid promoted cyclopentannulation reactions with enones and enals to generate 3-acetylcyclopentene complexes. During the reaction, a rearrangement occurs such that the α- and β-carbons of the enone or enal are incorporated into the new carbocycle. The reactions are completely regioselective. Yields vary from 26 to 78%, depending on reaction conditions. Diastereomer ratios vary from 50:50 to >95:5. In a similar fashion, these furan complexes undergo reactions with aldehydes to form acetyldihydrofuran complexes, where a new dihydrofuran ring is generated from the aldehyde and C3−C5 of the original furan. These dihydrofuran complexes are readily converted into the corresponding trisubstituted furans via oxidative demetalation. Attempts to synthesize TpRe(CO)(MeIm)(η2-2-methoxyfuran) for the synthesis of cyclopentene esters resulted in the formation of a novel rhenium carbene.

Structure and stability of thiophene–hydrogen halide complexes: An ab initio molecular orbital study

The structures of thiophene–hydrogen halide (HX) complexes are examined at the second-order Møller-Plesset (MP2) level to understand hydrogen bonding and intermolecular interactions of a heteroaromatic ring as the hydrogen bond acceptor. In contrast with the previous results on similar furan complexes, only the face-on geometry type is observed for the thiophene complexes. Variations in complex geometry can be accounted for by the differences in the electrostatic potential on the aromatic ring. A decomposition of interaction energy reveals that thiophene–hydrogen halide is bounded largely by orbital and electrostatic energy contributions.

Theoretical Study of Stable Intermolecular Complexes of Furan with Hydrogen Halides

The intermolecular complexes of furan with hydrogen halides are examined using ab initio calculations performed at the second-order Moller-Plesset perturbation approximation with the 6-311++G(d,p) basis set. Two types of geometry are observed: the atom-on geometry, featuring a roughly planar complex with C2v symmetry and a hydrogen bond between the furan oxygen and the hydrogen halide; and the face-on geometry, in which the hydrogen halide lies above the furan ring in an orientation almost perpendicular to the plane of the ring. The furan−HF and furan−HI complexes are each found to have one minimum geometry, of the atom-on and face-on type, respectively. Both geometry types are obtained for the HCl− and HBr−furan complexes. With the exception of furan−HCl, the HX subunits of the atom-on complexes deviate slightly from the furan ring plane. Each of the face-on complexes shows interaction between the hydrogen of the halide subunit and the formal π-bond between C2 and C4 of the furan ring. An electrostatic ...

Complexation of Gas-Phase Metal Ions with Furan: Experimental and Quantum Chemical Binding Energies

Binding of metal ions to furan in the gas phase to form M+(furan) complexes was studied by radiative association kinetics (RAK) in the Fourier transform ion cyclotron resonance (FT-ICR) spectrometer, and by density functional theory (DFT) calculations of the structures and binding energies. Three main-group metals and the first-row transition metal series were included. Binding energies were compared with previous studies of cation-π binding to the aromatic π face involving benzene and pyrrole ligands. It was found that furan is a somewhat weaker π-binding ligand than benzene for all of the metal ions (by an amount of the order of 5 kcal mol-1), in contrast to pyrrole, which is stronger than benzene in most cases. This was rationalized as a largely electrostatic effect. Furan presents the competing possibility of metal-ion binding to the oxygen, but it was found that the oxygen binding site has lower affinity than the π site for all metal ions. The preference for the π site is of the order of 6 kcal mol-1 for metal ions without active d electrons, and of the order of 20 kcal mol-1 for the transition metal ions with partially filled d-orbital shells. A quantitative model was developed and applied to separate out the electrostatic contributions to ion/ligand interaction from other types of interactions.

Rhenium-promoted diastereo- and enantioselective cyclopentannulation reactions: furans as 1,3-propene dipoles.

The rhenium furan complexes TpRe(CO)(MeIm)(eta2-2-methylfuran) (1) and TpRe(CO)(MeIm)(eta2-2,5-dmethylfuran) (2) undergo Lewis acid-promoted cyclopentannulation reactions with enones and enals to generate 3-acetylcyclopentene complexes. During the reaction, a rearrangement occurs such that the alpha and beta carbons of the enone are incorporated into the new carbocycle. Treatment of these complexes with an oxidant (H2O2 or silver triflate) liberates the acetylcyclopentene. When a resolved form of the rhenium complex is used, the acetylcyclopentenes can be obtained enantioselectively.

Stereoselective Aldehyde Addition to Rhenium-Coordinated Furans

Dihapto-coordinated furan complexes of the form TpRe(CO)(t-BuNC)(2,3-η2-furan) (Tp = hydridotris(pyrazolyl)borate) react with aldehydes in the presence of BF3·OEt2 to yield dihydrofuran complexes. Depending on the reaction conditions, these products take one of three forms: a dihapto-coordinated trans-2-alkyl-3-acyl-2,3-dihydrofuran, trans-2,3-dialkyl-2,3-dihydrofuran, or 4a,7a-dihydro-4H-furo[2,3-d][1,3]dioxine. The first two are formed exclusively as trans-disubstituted products, whereas the last exhibits cis stereochemistry at the ring fusion. These are isolated as mixtures of coordination diastereomers, which are separable by chromatography. Of the two diastereomers of the trans-2-alkyl-3-acyl-2,3-dihydrofuran product obtained in each case, only the major isomer undergoes an interfacial isomerization under ambient conditions. Attempts to decomplex the dihydrofurans were unsuccessful.

The Relationship between Binding Models of TMA with Furan and Imidazole and the Molecular Electrostatic Potentials: DFT and MP2 Computational Studies

The theoretical investigation of tetramethylammonium (TMA)−imidazole and TMA−furan complexes has been performed to justify the preferred structure of the cation−aromatic complexes predicated by the analysis of molecular electrostatic potential (MEP) maps of isolated aromatic systems. Such maps have been shown to be helpful in predicting the cation binding sites in cation−aromatic complexes. Our computational results show that a large part of the binding energies in the systems studied are contributed by the classical cation−π interaction. However, the optimized structure obtained in the MP2 method might be different from that obtained by the DFT method due to the influence of dispersion forces. Dispersion forces have been found to be important in the systems studied, increasing the binding energies by ∼7% and 20% for the TMA−imidazole and TMA−furan systems, respectively.