Preparation of models and oligomers of metal alkynyls: NMR, GPC and X-ray structural characterization of building blocks for the construction of molecular devices

A systematic study has been carried out for the use of the palladium-based Extended One Pot (EOP) synthetic protocol toward the preparation of metal alkynyl oligomers of general formula [CCArCCM(L)_m]_n (M=Pt, Pd). Model compounds of type trans-M(PBu₃)₂(CCC₆H₅)₂ have been prepared by the reaction of tributyltinethynylbenzene with trans-M(PBu₃)₂Cl₂, in the absence of palladium catalysis, since the presence of catalytic Pd(PPh₃)₄ yields reaction mixtures containing starting material, product and intermediate complex trans-MCl(PBu₃)₂(CCC₆H₅). Palladium catalysis has been used for the formation of the bistinacetylide compounds Bu₃SnCCArCCSnBu₃ (Ar=C₆H₄; bis(2,5-n-octyloxy)C₆H₄). Subsequent coupling of these compounds with MCl₂(PBu₃)₂ in the absence of palladium catalyst yields metal alkynyl oligomers. Comparison of ³¹P-NMR and gel permeation chromatography (GPC) analyses indicates that the GPC technique represents a reliable method to estimate polymer chain lengths for polymers bearing branched aromatic spacers, in spite of the rigid-rod shape of the polymer backbone. Single crystal X-ray determinations of model compounds demonstrate the essential role of side substituents in the aromatic ring to control the supramolecular order and, as a consequence, the optoelectronic properties of materials.     

Synthesis and characterisation of new platinum ethynyl dimers and polymers with pendant ferrocenyl groups

The square-planar platinum(II) complex trans-[(Ph₂FcP)₂PtCl₂] (1) (Fc=ferrocenyl), that is a metal-containing polymer precursor, has been synthesised and its single crystal structure determined. Using 1, new ferrocene-containing platinum ethynyl dimers trans-[(Ph₂FcP)₂Pt(CCR)₂] {R=SiMe₃ (2), C₆H₅ (3) and C₆H₄-p-NO₂ (4)} and a polymer [(Ph₂FcP)₂Pt(CCC₆H₂-p-(OC₈H₁₇)₂CC)]_n (5) have been formed by the reaction of the metal precursor with the appropriate mono- and bis-ethynyl ligands. Single crystal X-ray studies of 4 have shown it to exist as two different polymorphic forms, both having trans-geometry with respect to the ferrocenyl phosphines and ethynyl ligands. GPC measurements on the polymer show a high degree of polymerisation with an average molecular weight of ca. 88?000.     

Synthesis, characterization and electrochemistry of diruthenium complexes linked by aryl acetylide bridges

The reactions between Ru₂(ap)₄Cl and the appropriate lithiated aryl acetylene resulted in the complexes Ru₂(ap)₄(CC4-C₆H₄CCX) with X as SiMe₃ (1), H (2) and Ru₂(ap)₄ (3), 1,3-[Ru₂(ap)₄(CC)]₂(C₆H₄) (4), 1,3-[{Ru₂(ap)₄(CC)}₂]C₆H₃5-CCH (5) and 1-[Ru₂(ap)₄(CC)]C₆H₃3,5-(CCH)₂ (6), where ap is 2-anilinopyridinate. The spectroscopic and electrochemical properties of the new complexes have been assessed. Complexes 3, 4 and 6 display two-electron oxidation and reductions, implying the absence of any significant electronic interaction between the two Ru₂(ap)₄ units in these complexes.     

Preparation and molecular structures of some complexes containing C5 chains

Complexes containing a Co₃ cluster linked to SiMe₃, Au(PPh₃), W(CO)₃Cp and Fc groups by a C₅ chain have been prepared by elimination of AuBr(PR₃) (R=Ph, tol) in the reactions between Co₃(μ₃-CBr)(μ-dppm)(CO)₇ and {(R₃P)Au}CCCCX [X=SiMe₃, W(CO)₃Cp] or {(OC)₇(μ-dppm)Co₃}CCC{Au(PPh₃)} and FcCCI (X=Fc). Subsequent auro-desilylation of the SiMe₃ compound affords {(OC)₇(μ-dppm)Co₃}CCCCC{Au[P(tol)₃]}. Single-crystal X-ray structures of the W(CO)₃Cp, Au{P(tol)₃} and Fc complexes are reported. The C₅ chain shows little departure from a formal CCCCC fragment.     

Benzene ring assembly promoted by a camphor derived palladium complex

Trans-[PdCl₂L₂] (1, L=3-NNMe₂C₁₀H₁₄O), under mild reaction conditions, acts as a catalyst for the cyclic trimerization of alkynes. The best performance is achieved for the reaction with PhCCMe that affords 1,3,5-trimethyl-2,4,6-triphenyl benzene with high activity and selectivity (ca. 99%). As a general trend the catalytic activity is higher for internal (PhCCMe, PhCCPh) than for terminal alkynes (HCCPh, HCC^tBu, HCCCO₂Me). Under more drastic experimental conditions the reaction of 1 with PhCCPh yields trans-[PdCl₂(PhCCPh)₂] and no catalytic activity is observed. The molecular structure of 1,3,5-trimethyl-2,4,6-triphenyl benzene was confirmed by X-ray diffraction analysis. The molecules were characterized by ¹H- and ¹³C-NMR spectroscopies, FAB-MS and, in some cases, elemental analyses.     

First principle study of magnetic and electronic properties of single X (X = Al,Si) atom added to small carbon clusters (C<Subscript> <Emphasis Type="Italic">n</Emphasis> </Subscript>X, <Emphasis Type="Italic">n</Emphasis> = 2–10)

In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C_nX; X = Al, Si; n = 2–10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO–LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C_nSi clusters have more stability compared to C_nAl clusters. In addition, our magnetic calculations were shown that the C_nAl isomers are magnetic objects whereas C_nSi clusters are nonmagnetic objects.     

Chromatographic properties of fullerene modified with liquid crystal p, p′-azoxyphenetol

Stationary phases for gas chromatography based on liquid crystal p,p′-azoxyphenetol applied onto Chromaton N-AW bearing a layer of C₆₀ fullerene were studied. The thermodynamic properties of the adsorption of n-alkanes and n-alcohols on the mesogen surface were studied at low occupancies. Test mixtures of structural isomers of substituted benzene and polycyclic aromatic hydrocarbons were analyzed in a wide temperature range from 100 to 240°C.     

The crystal structure of bis(N-pentafluorophenyl)tetraphenyl-cyclodisilazane-tetrabenzene, (Ph2SiNC6F5)2 · 4C6H6

The disilazane (Ph₂SiNC₆F₅)₂ crystallises from benzene solution with four molecules of solvent in the orthorhombic space group Pnna with a 18.182(6), b 21.480(8) and c 13.631(5) Å, Z = 4. The structure was solved by direct methods and refined by least-squares to R 0.069 for 937 observed reflections. The Si₂N₂ ring is planar with NSiN and SiNSi angles of 85.2 and 95.5° respectively; the mean SiN distance is 1.755 Å. The C₆F₅ groups are twisted by ca. 16° from the Si₂N₂ plane and the benzene molecules are arranged face-on above and below each of the C₆F₅ groups. There are, in addition, short intermolecular contacts between four fluorines of each C₆F₅ group and hydrogen atoms from both solvate benzene and the phenyl groups of a symmetry related silazane. Attempts to refine the related (Me₂SiNC₆F₅)₂ structure were not successful, probably due to disorder.     

Reactions of dodecamethylcyclohexasilane and polydimethylsilane with metal chlorides

The reactions of dodecamethylcyclohexasilane and high-molecular-weight polydimethylsilane with chlorides of I, II, IV-VI and VIII Group metals at high temperature in the absence of a solvent were studied. The interaction of (Me₂Si)₆ with metal chlorides proceeds with the cleavage of SiSi and SiC bonds with the formation of chloro derivatives of linear and cyclic permethyloligosilanes. The reactions of polydimethylsilane with metal chlorides afford mixtures of α,ω-dichlorooligosilanes, Cl(Me₂Si)_nCl (n=2-9). The influence of the reaction conditions (temperature, reaction time and the reagent ratio) on the composition and yields of the reaction products was examined.     

Synthesis and solution properties of sulfate-type hybrid surfactants with a benzene ring

Nine novel sulfate-type hybrid surfactants, C_mF_2m+1C₆H₄CH(OSO₃Na)C_nH_2n+1 (FmPHnOS: m=4, 6, 8; n=3, 5, 7; C₆H₄: p-phenylene), with a benzene ring in their molecules were synthesized. Alkanoyl chlorides were allowed to react with iodobenzene in the presence of aluminum chloride to give the corresponding aromatic ketones. The reaction of the ketones with perfluoroalkyl iodides yielded 1-[4-(perfluoroalkyl)phenyl]-1-alkanones as intermediates. The intermediates were allowed to react with methanol in tetrahydrofuran in the presence of sodium borohydride to yield 1-[4-(perfluoroalkyl)phenyl]-1-alkanols. The desired hybrid surfactants were obtained by the reaction of 1-[4-(perfluoroalkyl)phenyl-1-alkanols with sulfur trioxide/pyridine complex in pyridine and by the subsequent neutralization of the products with sodium hydroxide solution. When compared with the conventional hybrid surfactants, C_mF_2m+1C₆H₄COCH(SO₃Na)C_nH_2n+1 (FmHnS: m=4, 6; n=2, 4, 6; C₆H₄: p-phenylene), the new hybrid surfactants thus synthesized were found to have a comparable ability to lower the surface tension of water and a high hydrophilicity. The cmc of FmPHnOS obeyed Kleven’s rule and their occupied areas per molecule increased with increasing m and n with the values between 0.66 and 1.05 nm². The aggregation number for FmPHnOS micelles ranged from 6 to 45 and the hydrodynamic radius of the micelles was in the range of 1.4-3.1 nm.     

Effect of TiO2 modification with fluorine on the physicochemical properties and activity in the photocatalytic oxidation of pollutants in air under UV irradiation

The influence of the modification of the TiO₂ surface with F^? ions on the physicochemical properties of the catalysts and efficiency in the photooxidation of gaseous molecules under atmospheric conditions and under UV irradiation was studied by IR spectroscopy. The fluorine-containing samples adsorb more water molecules than unmodified TiO₂. The amount of adsorbed water increases with increasing content of surface fluoride ions. The fluorination of the TiO₂ surface first leads to the substitution of the terminal OH groups by F^? ions and to an increase in acidity of the bridging acidic OH groups remained on the surface. The modification also results in the structural rearrangement of the surface involving defective and surface Ti⁴⁺ sites. Fluorine modification increases the activity of TiO₂ in the photocatalytic oxidation of ethanol, acetaldehyde, acetic acid, and acetone. At the same time, benzene and H₂S are oxidized more rapidly on unmodified TiO₂. The presence of fluorine on the TiO₂ surface exerts almost no effect on the oxidation rate of chlorine-containing substrates C₃H₇Cl and C₂H₄Cl₂.

     

Micelle formation by N-alkyl-N-methylpyrrolidinium bromide in ethylammonium nitrate

The aggregation behavior of long-chain pyrrolidinium ionic liquids, N-alkyl-N-methylpyrrolidinium bromide (C_nMPB, n = 12, 14, and 16) was investigated by surface tension measurements in a protic room temperature ionic liquid, ethylammonium nitrate (EAN), at various temperatures. A series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ_CMC), effectiveness of surface tension reduction (Π_CMC), maximum surface excess concentration (Γ_max), and the area occupied per surfactant molecule at the air/solution interface (A_min) were estimated. From these parameters, we demonstrated that the surface activity of C_nMPB is much lower in EAN than that in water. Comparing C_nMPB with alkylimidazolium bromides and alkylpyridinium bromides, the effect of the cationic group on micellization in EAN was also investigated. The thermodynamic analysis of micellization revealed that the micelle formation process for C_nMPB (n = 12, 14, and 16) is entropy-driven at low temperature and enthalpy-driven at high temperature. The micelle aggregation number estimated from the ¹H NMR data is about 21 for C₁₂MPB in EAN, which is much less than that in water. The results of the surface tension measurements and ¹H NMR spectra indicate that the [CH₃CH₂NH₃]⁺ cations of EAN exist around the head groups of C_nMPB when micelles are formed and the NO₃⁻ ions are adsorbed at the micelle surface.     

Polyvinyl- and polyphenylsilsesquioxanes and their films: an investigation by X-ray diffractometry, positron diagnostics, and 29Si NMR spectroscopy

Polyvinyl- and polyphenylsilsesquioxanes (RSiO_1,5) _n were synthesized by hydrolytic polycondensation. The cross section surface areas of the polymer chain were measured and the sizes of ??traps?? of the free and ordered volumes and the ratio of the T₂ and T₃ units in (RSiO_1,5) _n were determined by time positron diagnostics, ²⁹Si NMR spectroscopy, and X-ray diffractometry. The density of polyvinyl- and polyphenylsilsesquioxanes was determined picnometrically and from the X-ray phase analysis data, and the content of hydroxyl groups was found by thermogravimetry. The cross section surface area of the silsesquioxane chains containing vinyl and phenyl radicals at Si were calculated by the Miller-Boyer method. The elementary volumes of the chain segments determined by different methods were compared. The geometric models for ??traps?? of the free volume were proposed. The optical properties and morphology of the polyvinylsilsesquioxane films were studied by atomic force microscopy and UV spectroscopy.     

Benchmarking of DFT functionals for the kinetics and mechanisms of atmospheric addition reactions of OH radicals with phenyl and substituted phenyl‐based organic pollutants

^•OH addition reactions play a pivotal role in the atmospheric transformation of a number of phenyl and substituted phenyl‐based persistent and toxic organic pollutants. Here, we screened appropriate DFT functionals to predict reaction mechanisms and rate constants (k_OH) of the ^•OH additions by taking benzene and substituted benzenes (C₆H₅F, C₆H₅Cl, C₆H₅Br, C₆H₅CH₃, C₆H₅OH) as model compounds. By comparing the k_OH values calculated with DFT methods to experimental values, we found that the ωB97 functional is the best among the 18 functionals considered (using the basis sets 6‐31 + G(d,p) for optimizations and 6‐311++G(3df,2pd) for single point energy calculations) in the temperature range of 230‐330 K. In addition, we found that some other functionals performed well in specific conditions, e.g., BMKD3 is good for benzene, halogenated benzenes and C₆H₅CH₃, and CAM‐B3LYP is good for the reaction of C₆H₅OH at room temperature. Based on the diversity of the electronic structures of the selected model compounds and the frequent occurrence of certain substituents ( CH₃,  OH,  F,  Cl, and  Br) in the target compounds, the functionals recommended here can be used for future study of the reaction mechanisms and k_OH values for ^•OH addition to phenyl and substituted phenyl‐based persistent and toxic organic pollutants.     

Phase transitions in paraffins, <Emphasis Type="Italic">n</Emphasis>-alkane alcohols,and <Emphasis Type="Italic">α,ω</Emphasis>-alkane diols with different chain lengths

A comparative analysis of phase transitions in paraffins (C _n H_2n+2), n-alkane alcohols (C _n H_2n+1OH), and α,ω-alkane diols ?ubC _n H_2n (OH)₂?ub; has been performed via differential scanning calorimetry. The elimination of methodical errors makes it possible to calculate the true values of thermodynamic parameters of phase transitions and to gain insight into their nature. Methods of finding true heat capacity jumps in the region of low-temperature solid-phase transitions of the first order and high-temperature order-disorder transitions of the second-order have been proposed. The quantitative analysis of heat capacity jump profiles has been performed within the framework of the first-order diffuse transition theory and Landau’s theory of order-disorder transitions.     

Theoretical study of C60(OH)20 and C60(OH)18 fullerenols and B12(OH) 12 2? , Si20O30(OH)20, and Ti20O30(OH)20 polyhydroxyl clusters and their Li-substituted derivatives

The equilibrium geometric parameters and the energetic characteristics of fullerenol molecules C₆₀(OH)₂₀ and C₆₀(OH)₁₈ and fullerenol-like inorganic clusters B₁₂(OH) ₁₂ ^2? , Si₂₀O₃₀(OH)₂₀, and Ti₂₀O₃₀(OH)₂₀ and their derivatives C₆₀(OH)_{20 ? n} (OLi) _n , C₆₀(OH)_{18 ? n} (OLi) _n , B₁₂(OH)_{12 ? n} (OLi) _n ^2? , Si₂₀O₃₀(OH)_{20 ? n} (OLi) _n , and Ti₂₀O₃₀(OH)_{20 ? n} (OLi) _n , in which the H atoms of all or one-half of hydroxyl groups are replaced by Li atoms, have been calculated by the density functional theory B3LYP/6-31G* method. It has been found that partial energies ??E(H/Li) per single substitution of Li for H in the reactions C₆₀(OH)₂₀ + nLiAc ?? C₆₀(OH)_{20 ? n} (OLi) _n + nHAc and C₆₀(OH)₁₈ + nLiAc ?? C₆₀(OH)_{18 ? n} (OLi) _n + nHAc (Ac is acetate) and the energies averaged over the entire series of changes in n, as well as over its first and second halves, do not exceed a few kilocalories per mole. It has been predicted that at least one-half (or more than one-half) of OH groups can be replaced by OLi without noticeable changes in energy; however, with a further increase in n, substitutions become endothermic and require ever-increasing energy inputs. In the completely hydroxylated closo-dodecaborane dianion with an icosahedral [B₁₂] cage and more polar B-O-H bonds, analogous H/Li substitutions are slightly exothermic so that the reaction can proceed somewhat smoother and further (toward larger n values) than in fullerenols, other conditions being the same. In the inorganic clusters Si₂₀O₃₀(OH)₂₀ and Ti₂₀O₃₀(OH)₂₀ with the [Si₂₀] and [Ti₂₀] cages, respectively, and with even more polar Si-O-H and Ti-O-H moieties, the substitutions are even more exothermic (their partial energies ??E(H/Li) increase to 4?C6 kcal/mol). For sodium and potassium analogues, the qualitative pattern persists, but H/Na and H/K substitutions are somewhat less exothermic than the H/Li substitutions. The results are compared to the data of previous calculations of stepwise H/Li and H/Na substitutions in the reactions C60(OH)24 + nLAc ?? C60(OH)_{24 ? n} (OL) _n + nHAc (L = Li, Na).     

Photoelectron spectroscopic investigation of phenyl isocyanato silanes

Summary The HeI photoelectron spectra of compounds C₆H₅(CH₃) _n Si(NCO)_3–n were recorded and analysed using semiempirical AM1 quantum chemical calculations. The interaction between phenyl and pseudohalide groups is minimal. The splitting of bands originated from pseudohalide groups is not sensitive to the Si-N-C bond angle.

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Photoelektronenspektroskopische Untersuchungen von Phenyl-isocyanato-silanen

Zusammenfassung Es wurden die Photoelektronenspektren von Verbindungen C₆H₅(CH₃) _n Si(NCO)_3-n aufgenommen und die Spektren mit der Hilfe von semiempirischen quantenchemischen AM1 Rechnungen ausgewertet. Die Wechselwirkung zwischen den Phenyl- und Pseudohalogenidgruppen erwiesen sich als minimal. Die Aufspaltung der infolge der Pseudohalogenidgruppe entstandenen Bänder ist gegen den Bindungswinkel von Si-N-C unempfindlich.

     

Gas phase structure and conformational properties of trifluoroacetic anhydride, CF3C(O)OC(O)CF3

The geometric structure of trifluoroacetic anhydride, CF₃C(O)OC(O)CF₃, has been studied by gas electron diffraction (GED) and quantum chemical calculations (MP2 and B3LYP with 6-31G^* basis sets). The GED analysis results in a single conformer with synperiplanar orientation of the two CO bonds. This analysis, however, cannot discriminate between a planar equilibrium structure (C_2v symmetry) with large amplitude torsional motions around the OC bonds and a nonplanar equilibrium structure (C₂ symmetry) with a low barrier at the planar arrangement. An effective dihedral angle φ(COCO=18(4)° is obtained. Both quantum chemical methods predict a nonplanar equilibrium structure of C₂ symmetry and φ(COCO)=16.5° and 13.9°, respectively.     

Excess enthalpies of some aromatic aldehydes in n-hexane, n-heptane and benzene

Calorimetric measurements of molar excess enthalpies, H^E, at 298.15 K, of mixtures containing aromatic aldehydes of general formula C₆H₅(CH₂)_mCHO (with m = 0, 1 and 2) + n-hexane, n-heptane or benzene are reported, together with the values of H^E at equimolar composition compared with the corresponding values of H^E for the aromatic ketones in the same solvents. The experimental results clearly indicate that the intermolecular interactions between the carbonyl groups (CHO) are influenced by the intramolecular interactions between the carbonyl and phenyl groups, particularly for the mixtures containing benzaldehyde.