Benzene Complexes Research Articles

Theoretical studies on the charge transfer complexes of aromatic hydrocarbons with chloranil

Molecular orbital and molecular mechanics calculation have been done to obtain informations about some general physicochemical proportion of charge transfer complexes of benzene, naphthalene and anthracene with chloranil.The semi-emperical quantum chemical programme MOPAC and the AMI 1 , 2 method has been used.

Solvent effect on the ligand exchange between bis(diethyldithiocarbamato)copper(II) and bis(diethyldiselenocarbamato)copper(II)

EPR study on the products of ligand exchange taking place on mixing bis(diethyldiseleno-carbamato)copper(II), Cu(dsc) 2, and bis(diethyldithiocarbamato)copper(II), Cu(dtc) 2, solutions is reported. EPR spectra monitored at room temperature for 1 month period reveal a stable equilibrium among the parents (chromophores CuS 4 and CuSe 4) and the obtained mixed-chelate Cu(dtc)(dsc) complex (chromophore CuS 2Se 2) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl 4 and CHCl 3, two new additional EPR spectra appear attributed to the mixed-chelate complexes with chromophores Cu(SSe 3)S and Cu(S 3Se)S. The intensities of all five EPR spectra slowly decrease with the time in CHCl 3 after 1 month monitoring at room temperature, or one week at 60 °C whereas in CCl 4 only the spectrum of Cu(dtc) 2 remains at room temperature on keeping the sample solution for 1 week after mixing or 1 h at 60 °C. The reaction mechanism of formation of both additional complexes with chromophores Cu(SSe 3) and Cu(S 3Se) is discussed. It is assumed that the new mixed-chelates observed in CCl 4 and CHCl 3 are obtained in a reaction of Cu(dtc)(dsc) or Cu(dtc) 2 with the ester of diselenocarbamic acid which is formed in a parallel reaction of Cu(dsc) 2 with CCl 4 or CHCl 3.

Charge donation to and dearomatization of benzene attending complexation: DFT estimates of binding energies of TpMXO(L) with benzene, for Tp = hydridotris(pyrazolyl) borate, MXO = MoNO, ReCO, and WNO, and L = ammonia, N‐methylimidazole, pyridine, phosphine, methyl isocyanide, and carbon monoxide

By density functional methods we characterize the bonding and charge distribution in complexes of benzene with dearomatizing agents tpReCO(L), tpMoNO(L), and tpWNO(L), where tp = hydrido Tris (pyrazolyl)borate), for a range of ligands L. Our LSDA and B3LYP density functional calculations use the Spartan LACVP+ basis and pseudopotential on Re, Mo, and W and 6-31G* on light atoms. The binding energy is strongly dependent on the nature of the ligand L, being greatest for L = ammonia and N-methylimidazole and weakest for CH3NC and CO. We find a correlation between strength of binding and electron transfer from the dearomatizing agents toward benzene. For the most strongly bound systems we find substantial (up to 500 millielectrons) charge transfer towards benzene, while for the most weakly bound systems charge is withdrawn from benzene. Structural details illustrate the ability of Re, Mo, and W species to dearomatize complexed benzene, which is extensive for all but the most weakly bound species with L = MeNC and CO. Re and W dearomatizing agents, which are computed and observed to form stable complexes with benzene, may be economic alternatives to osmium dearomatizing agents.

The Crystalline Enol of 1,3-Cyclohexanedione and Its Complex with Benzene: Vibrational Spectra, Simulation of Structure and Dynamics and Evidence for Cooperative Hydrogen Bonding

The inelastic incoherent neutron scattering spectra of 1,3-cyclohexanedione (CHD) in its crystalline enol form and its cyclamer complexes with benzene and benzene-d6 are compared with each other, with IR and Raman spectra and with the results of calculations using density functional theory (DFT). The crystal packing of the CHD enol is a linear hydrogen-bonded chain with conjugated donor and acceptor groups analogous to that found in peptide hydrogen bonding. The benzene complex is a closed hexameric hydrogen-bonded cycle. A DFT treatment is applied to the full hexamer of the benzene complex. The CHD chain is treated as a series of finite linear clusters by DFT, while the infinite one-dimensional chain and the three-dimensional crystal are treated by periodic DFT. Comparison is made with both the observed crystal structures and the vibrational spectra. The very good to excellent agreement of the computed vibrational spectra with experiment demonstrates that the models and computational treatments used are reliable. The theoretical treatment of the linear chain clusters exhibits a continuous change in structure with increasing chain length, converging to values near the observed structure. Emphasis is placed on the cooperative nature of hydrogen bonding in CHD as revealed by these systematic trends. The ability of DFT methods to treat hydrogen bonding in solids appears to be roughly as accurate as the crystal structure determinations.

Triosmium clusters with bridging terpenic thioureato-like ligands

The reaction of acetone-4-(2-methoxy-phenyl)thiosemicarbazone with triosmium cluster Os 3(CO) 11(NCMe) results in the formation of the cluster with the μ 2 chelate-bridging ligand coordinated by S and N 1 atoms, which was studied by X-ray diffraction analysis. Reaction of ( 3aR, 3bR, 4aR, 5aS)-5a-hydroxy-3,4,4-trimethyl-3a,3b,4,4a,5,5a-hexahydrocyclopropa[3, 4]cyclopenta[1,2-c]pyrazole-1-carbothioic acid amide with Os 3(CO) 11(NCMe) gives rise to the complex with the bridging ligand coordinated by sulphur atom. Further transformation of the complex in hot benzene results in tautomeric rearrangement of the organic ligand and the cleavage of the pyrazolinol cycle to form an open chain tautomer. Unusual silica gel induced oxidative cleavage of the cyclopropane ring in the open chain derivative and epoxidation of cycloalcane C–C bond are observed on the air.

P-benzoquinone-benzene clusters as potential nanomechanical devices: a theoretical study.

The equilibrium structures and binding energies of the benzene complexes of p-benzoquinones (PBQ) and its negatively charged anionic species (PBQ- and PBQ2-) have been investigated theoretically using second-order Møller-Plesset calculations. While neutral p-benzoquinone-benzene clusters (PBQ-Bz) prefer to have a parallel displaced geometry (P-c), CH...pi interactions (T-shaped geometries) prevail in the di-anionic PBQ-benzene (PBQ2- -Bz) complexes (T-e2-). Studies on dianionic p-benzoquinone-benzene clusters showed that two nonbonded intermolecular interactions compete in the most stable conformation. One is H-bonding interaction (C-H...O type) between carbonyl oxygen of p-benzoquinone and one of the hydrogen atoms of benzene, and the other is a pi-H interaction between pi-electron cloud of PBQ2- and another hydrogen atom of benzene. Blueshifted H-bonds were observed in T-shaped clusters. The changes in the geometrical preference of PBQ-Bz complex upon addition of electrons would be useful in designing optimized molecular mechanical devices based on the edge-to-face and face-to-face aromatic interactions.

Cation-π versus anion-π interactions: a comparative ab initio study based on energetic, electron charge density and aromatic features

Several complexes of benzene with cations and hexafluorobenzene with anions have been optimized at the MP2/6-31++G**, B3LYP/6-31++G** and HF/6-31++G** levels of theory. Different aspects of the cation-π interaction have been compared to those of anion-π, including changes in the aromaticity of the ring upon complexation, charge-transfer effects using the Merz–Kollman charges and the contribution of dispersion energies by comparing the complexation energies computed at the B3LYP and MP2 levels of theory.

Structures and its dipole moments of half-sandwich type metal–benzene (1:1) complexes determined by 2-m long electrostatic hexapole

The transition metal–benzene (1:1) complexes are synthesized by laser evaporation method followed by the size and structure selection with 2-m long electrostatic hexapole field. Electric dipole moments of half-sandwich type binary complexes for a series of the transition metals, i.e. Ti, V, Co, and Ni, with benzene molecule were determined by measuring the focusing curves, namely the dependence of the focused beam intensity upon the hexapole field strength. It is found that the dipole moments of Ti–C6H6 and V–C6H6 are larger than the ones of Co–C6H6 and Ni–C6H6. Such large dipole moments of Ti–C6H6 and V–C6H6 can be ascribed to the strong orbital interaction due to charge transfer between the metal atom and benzene molecule.

Geometry and electronic structure of Vn(Bz)m complexes.

First-principles calculations based on the generalized gradient approximation to the density functional theory are performed to explore the global geometries, ground-state spin multiplicities, relative stabilities, and energetics of neutral and anionic V(n)(Bz)(m) (n=1-3, m=1-4, with n<m) complexes. The calculated results show that the V(n)(benzene)(m) complexes clearly prefer sandwich structures to rice-ball structures. The ground-state spin multiplicities of the V(n)(benzene)(n+1) complexes increased linearly with the size of the system (i.e., n). In the anionic complexes, the V(benzene)(2) complex is found to be unstable against the autodetachment of the extra electron. The energy difference between adiabatic and vertical electron affinities is found to be very less, indicating negligible ionization-induced structural changes in the ground-state geometries of V(n)(benzene)(n+1) complexes.

Dearomatization of Benzene, Deamidization of N,N-Dimethylformamide, and a Versatile New Tungsten π Base

The first group VI η2-coordinated benzene complex, TpW(NO)(PMe3)(η2-benzene), is reported. The bound arene is activated toward Diels−Alder cycloaddition, and substitution of the arene with DMF yields a rare example of a η2-coordinated amide.

Mechanistic Proposals for Direct Benzene Hydroxylation over Fe−ZSM-5 Zeolite

A mechanism of direct benzene hydroxylation over Fe−ZSM-5 zeolite is discussed from B3LYP density functional theory computations. We demonstrate using a mononuclear iron model supported at the AlO4- site of zeolite that Fe−ZSM-5 zeolite reasonably catalyzes the conversion of benzene to phenol with N2O. A key in this catalytic reaction is that benzene hydroxylation and N2O decomposition occur at the same active site in a well-balanced manner. In the initial stages of the reaction, a reactive oxygen species referred to as “α-oxygen” is formed upon decomposition of N2O at the iron active site. The first reaction step is the formation of a complex between benzene and the α-oxygen species. The C−H activation of benzene leads to an intermediate that involves OH and C6H5 groups as ligands. After forming this intermediate, the reaction has a junction that leads to two possible pathways, depending on the concentration of N2O. The recombination between the OH and C6H5 ligands, which leads to a complex of phenol, can occur when the concentration of N2O is low, whereas the decomposition of nitrous oxide can occur on the intermediate involving OH and C6H5 groups when the N2O concentration is sufficiently high. Calculated potential energy diagrams and reaction kinetics show that the latter pathway is energetically more favorable than the former. We propose that benzene hydroxylation over Fe−ZSM-5 zeolite should proceed in the following way: (1) the formation of the benzene complex at the iron active site, (2) the hydrogen abstraction from benzene, (3) the decomposition of N2O at the active site, (4) the recombination between the OH and C6H5 ligands, and (5) the release of product phenol.

Molecular orbital calculations of the substituent effect on intermolecular CH/π interaction in C 2H 3X–C 6H 6 complexes (X=H, F, Cl, Br, and OH)

The effect of a substituent group in dimeric complexes of benzene with ethylene and its four derivatives on the intermolecular CH/π interaction was studied theoretically. The hydrogen-bonding nature of the CH/π interaction is confirmed by the bond critical point analysis within the atoms-in-molecules (AIM) theory. It has been found that the CH⋯π access angle depends on the exchange repulsion and the induction effect from the substituent group. The effect of the charge transfer interaction by the substituent group is energetically insignificant. However, the charge density can be varied by substitution, and this contribution cannot be ignored.

N-methylformamide-benzene complex as a prototypical peptide N-H...pi hydrogen-bonded system: density functional theory and MP2 studies.

Although the existence of peptide N-H...pi hydrogen bonds recently has been reported in protein structures, little is known about their strength and binding nature and, therefore, the relative importance of the interaction. To shed light on this binding, the N-methylformamide-benzene complex, as a model of the peptide N-H...pi hydrogen bonding, was studied by using density functional theory and Møller-Plesset second-order perturbation (MP2) methods. The geometry of the complex was fully optimized at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels. The optimized interaction distances are about 3.6 and 3.2 A, respectively, at the two levels. The binding energy corrected by basis set superposition error with the MP2/cc-pVTZ method based on the MP2/6-31G geometry is -4.37 kcal/mol, which is as strong as the conventional hydrogen bonding. The calculated results suggest that the peptide N-H...pi hydrogen bonding is of sufficient strength to play an important role in the stabilization of protein structures. These results are helpful to better understand the characteristics and nature of the peptide N-H...pi interaction as well as to modify current force fields to better represent this special interaction.

Octahedral Ru(II) amido complexes TpRu(L)(L')(NHR) (Tp = hydridotris(pyrazolyl)borate; L = L' = P(OMe)3 or PMe3 or L = CO and L' = PPh3; R = H, Ph, or tBu): synthesis, characterization, and reactions with weakly acidic C-H bonds.

The octahedral Ru(II) amine complexes [TpRu(L)(L')(NH(2)R)][OTf] (L = L' = PMe(3), P(OMe)(3) or L = CO and L' = PPh(3); R = H or (t)Bu) have been synthesized and characterized. Deprotonation of the amine complexes [TpRu(L)(L')(NH(3))][OTf] or [TpRu(PMe(3))(2)(NH(2)(t)Bu)][OTf] yields the Ru(II) amido complexes TpRu(L)(L')(NH(2)) and TpRu(PMe(3))(2)(NH(t)Bu). Reactions of the parent amido complexes or TpRu(PMe(3))(2)(NH(t)Bu) with phenylacetylene at room temperature result in immediate deprotonation to form ruthenium-amine/phenylacetylide ion pairs, and heating a benzene solution of the [TpRu(PMe(3))(2)(NH(2)(t)Bu)][PhC(2)] ion pair results in the formation of the Ru(II) phenylacetylide complex TpRu(PMe(3))(2)(C[triple bond]CPh) in >90% yield. The observation that [TpRu(PMe(3))(2)(NH(2)(t)Bu)][PhC(2)] converts to the Ru(II) acetylide with good yield while heating the ion pairs [TpRu(L)(L')(NH(3))][PhC(2)] yields multiple products is attributed to reluctant dissociation of ammonia compared with the (t)butylamine ligand (i.e., different rates for acetylide/amine exchange). These results are consistent with ligand exchange reactions of Ru(II) amine complexes [TpRu(PMe(3))(2)(NH(2)R)][OTf] (R = H or (t)Bu) with acetonitrile. The previously reported phenyl amido complexes TpRuL(2)(NHPh) [L = PMe(3) or P(OMe)(3)] react with 10 equiv of phenylacetylene at elevated temperature to produce Ru(II) acetylide complexes TpRuL(2)(C[triple bond]CPh) in quantitative yields. Kinetic studies indicate that the reaction of TpRu(PMe(3))(2)(NHPh) with phenylacetylene occurs via a pathway that involves TpRu(PMe(3))(2)(OTf) or [TpRu(PMe(3))(2)(NH(2)Ph)][OTf] as catalyst. Reactions of 1,4-cyclohexadiene with the Ru(II) amido complexes TpRu(L)(L')(NH(2)) (L = L' = PMe(3) or L = CO and L' = PPh(3)) or TpRu(PMe(3))(2)(NH(t)Bu) at elevated temperatures result in the formation of benzene and Ru hydride complexes. TpRu(PMe(3))(2)(H), [Tp(PMe(3))(2)Ru[double bond]C[double bond]C(H)Ph][OTf], [Tp(PMe(3))(2)Ru=C(CH(2)Ph)[N(H)Ph]][OTf], and [TpRu(PMe(3))(3)][OTf] have been independently prepared and characterized. Results from solid-state X-ray diffraction studies of the complexes [TpRu(CO)(PPh(3))(NH(3))][OTf], [TpRu(PMe(3))(2)(NH(3))][OTf], and TpRu(CO)(PPh(3))(C[triple bond]CPh) are reported.

Computational study of the halogen atom-benzene complexes.

The structures of halogen atom-benzene complexes were investigated by modern DFT and ab initio computational methods. The spectroscopic properties of the complexes are also predicted and are in good agreement with experiment where such data have been reported. The fluorine atom-benzene complex is predicted to be a sigma complex due to the strength of a C-F bond. The chlorine atom-benzene complex is predicted to have an eta(1) pi complex structure, which is only slightly more favorable (1.1 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than a sigma complex but is significantly more stable (4.4 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than the eta(6) pi complex. The bromine and iodine benzene complexes are also predicted to prefer an eta(1) pi complex structure.

Structural Effects of Group VI Metal Tricarbonyl Binding to Benzenoid Rings: Interruption of Conjugation or Enhanced Aromaticity?

AbstractThe effect of tricarbonyl (group VI metal) complexation on the geometric aromatic character of benzenoid rings is studied as a function of bond‐length alternation (localization) in the parent arene. Good agreement between theory and experiment is established for (η6‐benzene) tricarbonylchromium, ‐molybdenum, and ‐tungsten. It is found that, whereas the electrons of benzene become slightly more localized upon tricarbonyl metal complexation, those of ‘cyclohexatriene' mimics, like in‐starphenylene, become more delocalized. A combination of ab initio quantum‐mechanical and high‐accuracy X‐ray methods leads to a linear structurestructure correlation between the free and metal‐bound arene bond‐alternation geometry. In all cases, the average bond length in the arene increases upon complexation. The computational observation that the average bond length increases more in benzene complexes than in in‐starphenylene implies stronger back bonding in the benzene complexes and coincides with the experimental observation that more‐delocalized arenes form thermodynamically favored complexes. The rotational barriers about the tricarbonylmetal‐to‐arene axis were computed for 1‐Cr, 1‐Mo, and 1‐W as well as for 5‐Cr, 5‐Mo, and 5‐W. Barriers for the former group are characteristically low, almost negligible (0.05 kcal/mol for 1‐Cr; 0.01 kcal/mol for 1‐Mo; 0.27 kcal/mol for 1‐W), whereas for the latter group they are substantial (11.2 kcal/mol for 5‐Cr; 15.2 kcal/mol for 5‐Mo; 13.6 kcal/mol for 5‐W). The higher barriers found in 5‐M compounds are consistent with previous findings.

N−H···π Interactions in Indole···Benzene-h6,d6 and Indole···Benzene-h6,d6 Radical Cation Complexes. Mass Analyzed Threshold Ionization Experiments and Correlated ab Initio Quantum Chemical Calculations

Indole−benzene complexes in the neutral and cationic forms were investigated by resonance enhanced two-photon ionization (REMPI) and mass analyzed threshold ionization (MATI) experiments and nonemp...

Benzene and Haze Formation in the Polar Atmosphere of Jupiter

Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the polar atmosphere, giving rise to intense auroras [Clarke et al., 1996; Grodent et al., 2000]. An important consequence of this energy influx is the production of a dark haze [Pryor and Hord, 1991], the formation mechanism of which was hitherto poorly known. Recent observations of benzene on Jupiter [Bézard et al., 2001; Flasar, 2002] provide new clues for a chemical and aerosol model for the formation of heavy hydrocarbon aerosols. The chemistry begins with the destruction of methane by energetic particles, followed by neutral and ion reactions, ultimately leading to the formation of benzene and other complex hydrocarbons, including multi‐ring compounds which subsequently condense. High temperatures and effective eddy mixing engendered by the auroras enhance the formation of heavy hydrocarbons and aerosols. This mechanism may be relevant in the atmospheres of Saturn and extrasolar giant planets, and is an example of how a planetary magnetosphere may influence the chemical composition and climate forcing of the upper atmosphere.

Interactions of Atomic Iron Cation with Pyridine and Benzene: A Theoretical Study on an Unresolved Controversy of Bond Energies and Electronic Ground‐State Structures

AbstractThe binding energies, geometries, and electronic structures of cationic ironbenzene and ironpyridine complexes have been studied by the two hybrid DFT‐HF approaches mPW1PW91 and B3LYP, as well as the AQCC and MR‐AQCC extension. The AQCC results confirm the experimental binding energies derived from threshold‐CID experiments reported by Meyer et al., and Rodgers et al. as well as the previously reported C2v‐symmetric quartet ground state of ironbenzene. The ironpyridine complex is coordinated via the N‐atom lone‐pair and has a sextet ground state. Bond energies determined by the kinetic method apparently yield a dissociation energy corresponding to the first excited quartet ironpyridine complex. Both DFT methods fail to predict the correct ground state for cationic iron pyridine.

Competition between π- and σ-based interactions in metal ion complexes of the phenyl radical

Hybrid density functional theory (B3-LYP and B3-PW91) and counterpoise-corrected ab initio (MP2) calculations have been performed for the adducts of the main-group metal ions Na +, Mg +, Al +, K +, and Ca + with the phenyl radical C 6H 5. While the calculated bond dissociation energies (BDEs) and complexation geometries of the alkali metal ion adducts do not differ substantially from those determined for the analogous M +/benzene π-complexes, the alkaline earth ions exhibit a strong preference for σ-bond formation at the bare C atom of the phenyl ring, with calculated BDEs exceeding those determined for benzene complexation by approximately 80 and 150 kJ mol −1 for Mg + and Ca +, respectively. This σ-coordination is only feasible when the unpaired spins on the reactant Mg + (or Ca +) and C 6H 5 radicals are opposed, thereby leading to a closed-shell (singlet state) adduct ion. When the unpaired spins are aligned, the triplet-state adduct thus produced adopts π-complex minimum energy geometry with a BDE significantly below that of the corresponding M +/benzene complex. Both π- and σ-coordination are also found to be local minima on the AlC 6H 5 + potential energy surface, with the BDE of the Al +/C 6H 5 σ-complex being approximately 50 kJ mol −1 larger than that of the corresponding π-complex, and about 20 kJ mol −1 above the BDE for Al +/benzene. The overall results of our study show that the phenyl radical exhibits a much greater degree of selectivity between the main-group metal ions represented here than is evident for benzene. The phenyl radical BDEs range from 59.7 (K +) to 264.7 kJ mol −1 (Ca +) according to calculations at the B3-PW91/6-311+G(2df,p) level of theory, which contrasts with the 65.5 (K +) to 147.9 kJ mol −1 (Al +) BDE values determined for benzene at the same level of theory.