Phenyl-phenyl Bond Research Articles

Adatoms in the Surface-Confined Ullmann Coupling of Phenyl Groups.

Despite the importance of the on-surface Ullmann coupling for synthesis of atomically precise carbon nanostructures, it is still unclear whether this reaction is catalyzed by surface atoms or adatoms. Here, the feasibility of the adatom creation and adatom-catalyzed Ullmann coupling of chloro-, bromo-, and iodobenzene on Cu(111), Ag(111), and Au(111) surfaces is examined using density functional theory modeling. The extraction of a metal atom is found to be greatly facilitated by the formation of strong phenyl-metal bonds, making the extraction energy barrier comparable to, and in the case of Ag(111) even lower than, that for the competing surface-catalyzed phenyl-phenyl bond formation. However, if the phenyl-adatom bonds are too strong, as on Cu(111) and Ag(111), they create an insurmountable barrier for the subsequent adatom-catalyzed C-C coupling. In contrast, Au adatoms do not bind phenyl groups strongly and can catalyze the C-C bond formation almost as efficiently as surface atoms.

Analytical strategies for successful enantioselective separation of atropisomeric polybrominated biphenyls 132 and 149 in environmental samples

Some of the polybrominated biphenyls (PBBs) found in the environment are axially chiral, due to hindered rotation about the interannular phenyl-phenyl bond. This applies for PBB congeners having two or more bromine substituents in ortho-position to this bond. In this study analytical methods were developed that allow determining the enantiomer fraction (EF) of axially chiral (atropisomeric) PBBs in environmental samples. A white-tailed sea eagle egg was used as test sample. The egg extract was purified and further fractionated by normal phase (NP) high performance liquid chromatography (HPLC), yielding enriched fractions of axially chiral PBB 132 and PBB 149. Gas chromatographic (GC) enantioseparation of the atropisomers of PBB 149 was achieved on one of nine tested modified cyclodextrin phases. Due to coelution with an unknown brominated compound, conventional GC/ECNI-MS, which is based on the detection of the bromide ion, did not allow for the establishment of the EF. However, by means of GC/EI-MS-MS it was possible to verify an EF of 0.42-0.43, i.e. a significant enantiomeric enrichment of the second eluting atropisomer of PBB 149 in the white-tailed sea eagle egg. This is the first proof of non-racemic proportions of a chiral PBB in environmental samples. Despite the testing of nine different chiral stationary phases, GC enantioseparation of PBB 132 or other atropisomeric PBB congeners failed. For this reason, an enantioselective reversed-phase HPLC method was developed. This method proved to be a powerful tool for the separation of PBB atropisomers. It was found that even a standard of the di-ortho substituted PBB 153 could be partially separated into atropisomers at 0 degrees C but already enantiomerized at 5 degrees C. For establishing the EF of PBB 132 in the bird egg sample a combination of enantioselective HPLC followed by non-chiral gas chromatography was employed. Using enantioselective HPLC, the atropisomers of PBB 132 were quantitatively targeted into two separate fractions at room temperature (20 degrees C). After addition of internal standards for volume adjustment the relative amounts of the atropisomers in the isolated fractions were quantified by using non-chiral GC/EI-MS analysis. A deviation from the racemic mixture of the atropisomers of PBB 132 in the egg extract could not be statistically proven.

Synthesis, characteristics and luminescence properties of oligo(phenylenevinylene) dimers with a biphenyl linkage center.

Building a new structual oligo(phenylenevinylene) by linking trimeric phenylenvinylene (TPV) through the phenylphenyl bond of a central phenylene ring was reported. The resultant TPV dimers exhibit weak intermolecular interactions and intense blue photoluminescence in the solid state as well as high phase transition temperatures up to 250 degrees C. Organic light-emitting devices (OLEDs) based on these materials display blue emission with low turn-on voltage (about 3 V), maximum luminance approaching 2000 cd m(-2) and efficiency up to 1.6 cd A(-1).

Synthesis and characterization of square planar nickel(II)-arylthiolate complexes with the biphenyl-2,2'-dithiolate ligand.

Two new NiIIS4 complexes with the biphenyl-2,2'-dithiolate ligand (L) are reported. The dinuclear complex 1, [Ni2L3]2-, was formed in the reaction of 2-3 equiv of Na2L and [NiCl4]2- and the mononuclear complex [NiL2]2- (2) by using 4-10 equiv of Na2L. Complexes 1 and 2 have been crystallographically characterized. (Et4N)2[1].0.5S2Ph2, CH3CN: C60H71N3Ni2S7, triclinic, P1, a = 13.806(2) A, b = 14.267(2) A, c = 16.873(2) A, alpha = 69.263(10) degrees, beta = 69.267(8) degrees, gamma = 83.117(10) degrees, Z = 2, R1 = 0.0752 (wR2 = 0.2011). (Et4N)(Na.CH3CN)[2]: C34H39N2NaNiS4, triclinic, P1, a = 9.9570(10) A, b = 13.2670(10) A, c = 13.9560(10) A, alpha = 108.489(7) degrees, beta = 90.396(6) degrees, gamma = 103.570(4) degrees, Z = 2, R1 = 0.0390 (wR2 = 0.0995). Both complexes are square planar about the nickel ion in the solid state as well as in solution. Most Ni(II)-thiolate complexes are square planar except the tetrahedral mononuclear complexes with monodentate arylthiolate ligands that cannot force a square planar geometry. The ligand (L) has some flexibility to change its bite angle via the phenyl-phenyl bond and should not force a planar geometry on its complexes either. Therefore, it is interesting that 2 has adopted a square planar structure. Complex 2 readily converts to 1 in solution when not in the presence of excess L in a process that is presumably similar to that known for other mononuclear, bidentate ligated Ni(II) complexes. Both complexes, at least in the solid state, appear to have an inclination to bind another metal ion on one face of the complex (Ni2+ in 1, Na+ in 2). We hope to take advantage of this in future work to synthesize relevant model complexes for the active sites of the nickel-iron hydrogenases after suitable modifications are made to L.

Structure and Properties of Novel Asymmetric Biphenyl Type Polyimides.

Asymmetric biphenyl type polyimides (PI) were prepared by thermal imidization of polyamic acids (PAA) derived from 2, 3, 3′, 4′- biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4, 4′-oxydianiline (ODA). The degrees of molecular orientation, film densities, and dynamic mechanical properties of these PIs were compared with those of familiar PIs based on symmetric 3, 4, 3′, 4′- biphenyltetracazboxylic dianhydride (s-BPDA). PI(a-BPDA/PDA) cured at 350°C showed a Tg close to that of PI(s-BPDA/PDA) prepared under the same condition in spite of the bent chain structure of the former. Comparison of the PIs cured at 400°C manifested that PI(a-BPDA/PDA) has a Tg at 410°C (abrupt decrease in E′) whereas PI(s-BPDA/PDA) show no distinct Tg. Similar result was also observed for the ODA systems. The unexpectedly high Tgs of a-BPDA-based PIs were explained in terms of the restricted conformational change around the phenyl-phenyl bond in the a-BPDA unit. The difference of the E′ decrement at the Tg for both type of PIs are probably attributed to the difference of the intensity of intermolecular interactions. In PI(a-BPDA/PDA) thin film cured on a substrate, the segments unexpectedly align slightly to the film plane.

Relationship between structure and retention of polychlorinated diphenyl ethers (PCDE) in HRGC in comparison with other groups of halogenated aromatic compounds

The GC-retention of 106 polychlorinated diphenyl ethers (PCDE) has been examined on five different stationary phases representing a broad range of polarities: CP Sil8/10%C18 (Sil8-type with 10% of octadecyl groups), SE 54 (methyl-/5% phenyl-polysiloxane), OV 1701 (7% phenyl-/7% cyanopropyl-polysiloxane), DB Dioxin (a polysiloxane phase, which incorporates 44% methyl, 28% phenyl, 20% cyanopropyl and 8% polyethylene groups) and SP 2331 (90% biscyanopropyl-/10% phenylcyanopropyl (1:1)-polysiloxane). Standard narrow-bore columns (0.2–0.3 mm i.d.) were used. Structural principles for the retention of the PCDEs in gas chromatography were compared with the retention behaviour of the closely related polychlorinated biphenyls (PCB) and the tetrachloro-methyl-diphenylmethanes (tetrachlorobenzyltoluenes, TCBT). The structure-retention behaviour of the PCDEs is partly similar to the TCBTs in spite of the differences in polarity. The differences between the structure-retention behaviour of the PCDEs and the PCBs can best be explained with the increasing possibility of a coplanar arrangement of PCBs with a decreasing number of chlorine substituents in the ortho positions of the phenyl-phenyl bond.

The magnetic properties of ferrocene based macromolecules

Magnetic susceptibility data for conjugatively linked biferrocenes and a methylene bridged ferrocene polymer are presented. In 9,10-di((2-ferrocenyl)vinyl)anthracene a rigid divinylanthracene bridge is connecting two ferrocene units, and the oxidation of both iron centers leads to an antiferromagnetic coupling. In contrast, ferromagnetic coupling between iron centers is indicated for 2,2'-cis,trans-di((2-ferrocenyl)vinyl)biphenyl, where a twist around the phenyl-phenyl bond in the divinylbiphenyl bridging molecule is likely to occur.

Reversed-phase thin-layer chromatography of polynuclear aromatic hydrocarbons and chlorinated biphenyls : Relationship with hydrophobicity as measured by aqueous solubility and octanol-water partition coefficient

Reversed-phase thin-layer chromatography with methanol-water as eluent was used to study relationships between retention and hydrophobicity of non-polar aromatic compounds. For polynuclear aromatic hydrocarbons, n-alkyl- and chloro-substituted benzenes, good correlation was observed between R m values and log P octanol . Significantly different correlations were obtained for polychlorinated biphenyls (PCBs) containing chlorine atoms in the positions ortho to the phenyl-phenyl bond. This effect could not be explained by the measured lower π octanol values for ortho chlorine in PCBs. Estimation of hydrophobicity from aqueous solubility, S, combined with melting point data is restricted to S values higher than 1 μg/l. A group-contribution approach, including a retention index scale, will be very useful for correlation and prediction of reversed-phase retention, hydrophobicity and environmental and toxicological properties of chemicals.

A 13C NMR study of the solution dynamics of 1,3,5-triphenylbenzene; analysis of motion about the phenyl-phenyl bond

Carbon-13 spin-lattice relaxation rates were determined for 1,3,5-triphenylbenzene in CDCl 3 over a temperature range of 86°C, and the results interpreted in terms of the molecular dynamics. Dynamic models appropriate to the problem, including the effects of anisotropic motion and internal jumping between two or four states, were derived and the results evaluated comparatively for several different models. Similarities in the activation energies based on temperature-dependent measurements for all carbons suggests that either fortuitously similar barriers characterize both overall and internal motion, or that all relaxation rates depend primarily on a single type of motion, with the individual T 1 differences reflecting geometric factors. The latter interpretation leads to a rapid internal jump motion with a range of ∼60°, as would be predicted on the basis of theoretical conformational energy calculations. Application of a four-state jump model in which the jump rates are assumed to depend on the 0 and 90° theoretically determined rotational barriers allow an estimation of the rates of internal motion consistent with the relaxation data. The physical basis for complex terms which occur in the bistable (and tristable) jump models is discussed.

Accumulation and elimination kinetics of di-, tri- and tetra chlorobiphenyls by goldfish after dietary and aqueous exposure

Bioaccumulation kinetics of five di-, tri- and tetrachlorobiphenyls from water and food were studied in laboratory experiments with goldfish ( Carassius auratus). First order rate constants for uptake from water and clearance were determined after simultaneous administration of the five compounds in constant concentration, and were related to bioconcentration factors obtained in a static fish-water equilibration system. Biomagnification by retention of the PCB's from food was studied in a separate experiment. The difference in clearance rates for the chlorobiphenyls is the main reason for the different bioconcentration and biomagnification factors. Absorption efficiencies from water and food are higher than 40%. Clearance half lives vary from 10 days for 2,5-dichlorobiphenyl to 60 days for 2,3′,4′5-tetrachlorobiphenyl, which is correlalated with the decreasing aqueous solubilities of the compounds. Bioconcentration factors are between 0.4 × 10 6 and 1.5 × 10 6, biomagnification factors between 0.2 and 1.7, based on extractable lipids. Substitution of chlorine in the position para to the phenyl-phenyl bond influences hydrophobicity and bioaccumulation of the PCB's more strongly than substitution in ortho position. A kinetic model is developed which accounts for the influence of the lipid content of the fish on the clearance rate of a chemical. Reproducible determination of the bioconcentration potential of environmental chemicals is possible by use of an “internal bioaccumulation standard” in a kinetic test system. Food chain accumulation in fish is likely to be an important process only for persistent chemicals with extremely low water solubility.

Relation between phenyl-phenyl bond length and interplanar angle in substituted diphenyls

A statistical examination of available experimental data gives some weak support for a linear relation between phenyl-phenyl bond length and interplanar angle in substituted diphenyls proposed by Cook. Two theoretical models are proposed. The first does not give the observed relation; within experimental error the second does.