Kinetik der Bromierung von Phenolen und phenolischen Mekrkernverbindungen

The bromination of 15 dinuclear phenolic compounds (dihydroxydiphenylmethanes, methylene bisphenols) by molecular bromine in acetic acid was studied kinetically at 22°C. In all compounds the electrophilic substitution occurred inortho-position to the phenolic hydroxy group of the methyl phenol unit while the non reacting neighboring unit was differently substituted by H, CH₃,t-Bu and NO₂. A decrease in the reaction rate was observed in 2,2′-dihydroxydiphenylmethanes, where the +M-effect of the hydroxy group is diminished by an intramolecular hydrogen bond. The strength of this hydrogen bond may be influenced mainly by steric factors. Strong electron withdrawing substituents like NO₂ show a rate decreasing influence on the reactivity of the neighboring unit also in 2,4′- and 4,4′-dihydroxydiphenylmethanes.     

Electrochemical reduction of transition metal-substituted silicon,germanium and tin derivatives: I. Cobalt or cobalt and iron complexes

The complexes Ph₃ECo(CO)₃L (E = Si, Ge; L = CO, PPh₃ P(OPh)₃) have been studied by electrochemistry. The reduction potential of these derivatives is less affected by the nature of the ligand L than in the case of [CO(CO)₃L]₂. The electrochemical reduction of the tin complexes [Co(CO)₄]_n[Fe(CO)₂Cp]_3?nSnCl (n = 1–3) showed that the formation of the radical anion occurred with tin-cobalt rather than tin-chloride bond rupture. Electrolysis of these tin derivatives did not give any distannane containing transition metal groups. However it can be noted that the Fe(CO)₂Cp group stabilized these tin complexes.     

Dipole moments of compounds containing a cobalttin bond

The molecular electric dipole moments are reported for the series of tin-substituted tetracarbonyl cobalt compounds R_nY_m?nSn{Co(CO)₄}_4?m (m = 1–3; n ? m; R = alkyl, phenyl; Y = halogen). The effect of the substituents at the tin atom on the nature of the CoSn bond is established on calculating the (CO)₄CoSn group dipole moments. It is shown that the charge transfer in the CoSn bond is mainly determined by the inductive properties of the ligands attached to tin.     

Synthese von Cp(CO)2 MnTCNE aus [Cp(CO)2MnXPh]n (X = S,Se, Te; n = 1,2); Festkörperstruktur und Magnetismus

Cp(CO)₂MnTCNE (1) which was first reported by M. Herberhold et al., has been obtained from the reaction of [Cp(CO)₂MnXPh]_n (X = S, n = 1; X = Se, Te, n = 2) with TCNE. The synthesis of the relevant organometallic sulfur, selenium and tellurium derivatives is described. An X-ray diffraction study of the TCNE compound reveals that two Cp(CO)₂MnNCC(CN)C(CN)₂ (1) molecules form centrosymmetric dimers containing a coordinated centrosymmetric (TCNE)₂^x− pair. The bond lenghts, the v(CN) spectra and a solid state magnetism of μ_eff = 1.1 μ_B (293 K) are all consistent with this structural finding.     

Elucidating the N−N and C−N Bond-breaking Mechanism in the Photoinduced Formation of Nitrile Imine

In this study, we revealed the significance of chemical bonding for the photochemically induced mechanism of 2-phenyl tetrazole derivatives generating nitrile imines. The correlated electron localization function shows that the formation of imine nitrile involves two key bond events: (i) the heterolytic C−N breakage taking place in the T₁ state and (ii) the homolytic N−N rupture occurring in the T₂ excited state. In particular, a cation-radical specie results from the C−N cleavage, whereas the N−N rupture creates a biradical resonant form of imine nitrile. Additionally, we noticed that the substantial pair delocalization of the C−C-N bonded structure could play a significant role in the conversion of the biradical imine nitrile into both the propargylic and allenic forms via the T₁→S₀ deactivation.     

On the mechanism of polymerization of cyclic esters induced by tin(II) octoate

Mechanism of initiation and propagation in polymerization of ϵ‐caprolactone and L,L‐dilactide induced with tin(II) octoate (Sn(Oct)₂) and Sn(Oct)₂/n‐butyl alcohol system is presented. Tin(II) alkoxide bond formation is required in reaction of Sn(Oct)₂ with hydroxyl group containing compound to form a true initiator. Then tin(II) alkoxide end group is an active centre in the further propagation.     

Carbonylation. 9. Alkoxycarbonylation of pent-3-ene nitrile with homogeneous Co−Ru catalysts: The respective roles of cobalt and ruthenium

Addition of ruthenium compounds (Ru(acac)₃, Ru₃(CO)₁₂) to cobalt catalysts for pent-3-ene nitrile alkoxycarbonylation increases both activity and selectivity in the production of cyanoesters by (i) reducing the amount of Co(II) and facilitating the generation of the active carbonylation species, HCo(CO)_n, and (ii) improving the isomerisation of pentene nitriles, providing significant amounts of pent-4-ene nitrile for the formation of the ω-ester.     

Influence of electronic effects from bridging groups on synthetic reaction and thermally activated polymerization of bisphenol‐based benzoxazines

Six bis‐benzoxazines based on bisphenols with different bridging groups, ? C(CH₃)₂? , ? CH₂? , ? O? , ? CO? , ? SO₂? , and single bond, were synthesized in toluene. The influence of electronic effects from bridging groups on ring‐forming reaction and thermal ring‐opening polymerization were relatively discussed in detail. Their structures were characterized by high‐performance liquid chromatography, Fourier transform infrared, ¹H NMR, differential scanning calorimetry, and elementary analysis. The quantum chemistry parameters of the bisphenols and bis‐benzoxazines were calculated by molecular simulation. The results indicated that the electron‐withdrawing groups inhibited the synthetic reaction by decreasing the charge density of α‐Cs of bisphenols and increasing energy barriers of the synthetic reactions. However, the electron‐withdrawing groups promoted the thermally activated polymerization, which resulted from their activation energy and curing temperature decrease by increasing the bond length and lowering the bond energy of C? O on oxazine rings. Besides, because of stronger electron‐withdrawing sulfone group, there were more arylamine methylene Mannich bridge structure in the polybenzoxazine. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Cationic palladium(II)–acetylacetonate complexes bearing pyridinyl imine ligands as catalysts for the hydroamination of phenylacetylene and polymerization of norbornene

Acetylacetonate palladium(II) complexes bearing pyridinyl imine ligands [Pd(acac)(L)]BF₄ were synthesized via nitrile displacement in [Pd(acac)(MeCN)₂]BF₄ by the bidentate ligands L of type 2-C₅H₄N–CH=N–(CH₂)_nOMe or 2-C₅H₄N–CH=N–Ar. The structures of complexes were analyzed by X-ray diffractometry, NMR, and DFT. The complexes catalyze hydroamination of phenylacetylene with aniline to give the Markovnikov imine product as well as polymerization of norbornene.     

Solid-State 13C NMR Evidence for Long Multicenter Intradimer Bonding in Zwitterion-like Structures

The principal values of the ¹³C chemical shift tensor for the β and δ polymorphs of π-[TTF⋅⋅⋅TCNE] (TTF=tetrathiafulvalene; TCNE=tetracyanoethylene) have been analyzed to understand the abnormally long intra-dimer bonding of singlet π-[TTF^δ+⋅⋅⋅TCNE^δ−]. These structures possess 12 intradimer contacts <3.40 Å, with the shortest intra π-[TTF⋅⋅⋅TCNE] separations involving 2-center (2c) C−S and 3c C−C−C orbital overlap contributions between the [TTF]^δ+ and [TCNE]^δ−. This solid-state NMR study compares the [TTF⋅⋅⋅TCNE] ¹³C tensor data against previously reported π-[TTF]₂²⁺ and π-[TCNE]₂²⁻ homo-dimers to determine how the tensor principal values change as a function of electronic structure for both TTF and TCNE moieties. In the β and δ phases of [TTF⋅⋅⋅TCNE], the TCNE ethylenic ¹³C shift tensors predict TCNE oxidation states of −0.46 and −0.73, respectively. The TTF sites are less similar to benchmark ¹³C data with the β-phase differing primarily in the ethylenic π-electrons. The δ form differs significantly from the homo-dimer data at all principal values at both the ethylenic and CH sites, indicating changes to both the π-electrons and σ-bonds. In both hetero-dimer phases, the NMR changes supports long bond formation at nitrile and CH sites not observed in homo-dimers.     

Preparation,structure, and reactivity of 1,3,4,6-tetrakis-(isopropylthio)thieno[3,4-c]thiophene-palladium complex with tetracyanoethylene

The reaction of 1,3,4,6-tetrakis(isopropylthio)thieno[3,4-c]thiophene ( 1 ) with the palladium complex Pd₂(dba)₃CHCl₃ (dba = dibenzylideneacetone) and tetracyanoethylene (TCNE) gave a new palladium complex in which two isopropylthio groups of 1 and the double bond of TCNE were trigonally coordinated to palladium. The X-ray analysis revealed the electron donation from palladium to TCNE, leading to a lengthening of the C?C double bond in TCNE and distortion of TCNE from planarity. The radical cation of 1 and the radical anion of TCNE were detected by ESR spectroscopy in methylene dichloride solution of the complex, although the radical content was estimated from the paramagnetic susceptibility to be less than 1%. The reaction of the complex with aniline gave the same product as that in the reaction of the radical cation of 1 with aniline.     

Infrared study of the hydrogen bonding site in a poly-functional schiff base: N(sp2) or N(sp)?

The hydrogen bond complexes between phenol derivatives and the Schiff base [(diphenylmethylene)amino]-acetonitrile have been studied by infrared spectroscopy in carbon tetrachloride solution. The thermodynamic data and the infrared spectra investigated in the ν_OH, ν_CN and ν_CN region indicate that complex formation occurs at the nitrogen atom of the nitrile function. The hydrogen bonding site is in this case governed by the accessibility of the lone pair which is markedly higher for the N(sp) than the N(sp²) electrons.     

VINYL MONOMERS BEARING CHROMOPHORE MOIETIES AND THEIR POLYMERS——Ⅹ.INITIATION AND PHOTOCHEMICAL PROPERTIES OF p-(N,N-DIMETHYLAMINO)STYRENE AND ITS POLYMERS*

A vinyl monomer having an electron-donating moiety, p-(N,N-dimethylamino)styrenc (DMAS),was synthesized. It was combined with benzoyl peroxide (BPO) to form a redox initiation system to initiatethe polymerization of methyl methacrylate (MMA). UV spectra measurements show that DMAS enters thePMMA chain as well. Both DMAS and its polymer P(DMAS) display strong fluorescence, and thefluorescence can be quenched by electron-deficient compounds such as methacrylonitrile, fumaronitrile andmethyl methacrylate etc. Moreover, DMAS can also form charge transfer complex (CTC) with strongelectron acceptors such as tetracyanoethylene (TCNE). The difference between the photochemical propertiesof DMAS and P(DMAS) were explained in terms of molecular structure change and polymer conformationeffect in solution. In addition, the CTC and exciplex formation of DMAS or P(DMAS) with C_(60) were alsostudied.     

Nano ceria catalyzed Ullmann type coupling reactions

Ullmann type intermolecular coupling of aryl halide with hetero-aromatic compounds, such as phenols, amines, and thiophenols are key reactions for the formation of carbon-heteroatom bond in organic synthesis. We report a robust and novel method that provides an efficient and economic route for the synthesis of O, N, and S-arylation via Ullman coupling by using nano cerium oxide (ceria, CeO₂). CeO₂ is a cheaper catalyst compared to related copper based catalysts. This method provides a wide range of substrate applicability in the case of phenols and amines. Less reactive chlorobenzene substituted with strong electron withdrawing groups such as 4-nitrochlorobenzene and 4-cyanochlorobenzene favor the reaction. This protocol avoids the use of ligand and gives arylated product in satisfactory yields.     

Study of Unusually High Rotational Barriers about S?N Bonds in Nonafluorobutane‐1‐sulfonamides: The Electronic Nature of the Torsional Effect

Slow rotation about the S? N bond in N,N‐disubstituted nonafluorobutane‐1‐sulfonamides 1 can easily be detected by NMR measurements at room temperature. This effect causes magnetic nonequivalence of otherwise identical geminal substituents in symmetrical staggered ground‐state conformation A . The torsional barriers determined (62–71 kJ?mol^?1) proved to be the highest ever observed for sulfonamide moieties. They are comparable to the values routinely measured for carboxylic acid amides or carbamates. The restricted rotation is interpreted as result (n_N? d_S)‐π and of n_N? σ interactions, which develop substantial S,N double‐bond character in sulfonamides 1 . The S,N binding interaction is increased by the highly electron‐withdrawing effect of the perfluorobutyl group. The anticipated symmetry of the ground‐state conformation A and the considerable shortening of the S? N bond (1.59 Å) compared to the mean value in sulfonamides (1.63 Å) are confirmed by single‐crystal X‐ray study of N,N‐dibenzylnonafluorobutane‐1‐sulfonamide ( 1c ).     

One- and two-dimensional coordination networks of the tetracyanoethylene anion-radicals with potassium counter-ions

Potassium-mirror reduction of tetracyanoethylene (TCNE) acceptor in tetrahydrofuran affords K(THF)₂ TCNE salt (1) showing double TCNE/K chains assembled via unusual μ₃-TCNE-bridging of potassium cations. These parallel ladder-type chains are further tethered by pairs of THF bridges between potassium centers and by intermolecular π-bonding in (TCNE)₂^2? dimers, and this results in formation of quasi-2-D coordination networks. In the presence of crown-ether ligand, the same potassium-mirror reduction lead to formation of [K(18-crown-6)(THF)₂]TCNE salt (2) in which monomeric tetracyanoethylene anion-radicals are positioned between bulky [K⁺(18-crown-6)(THF)₂] counter-ions. In comparison, crystallization of tetracyanoethylene anion-radicals with K⁺(18-crown-6) counter-ions in dichloromethane affords K(18-crown-6)TCNE salt (3) consisting of 1-D chains with 1,2-(N,N’)-TCNE bindings of potassium cations (nested in the crown-ether cavities). Temperature-dependent magnetic susceptibility study revealed essentially isolated tetracyanoethylene anion-radicals (S = 1/2) in this 1-D coordination polymer.     

Synthesis and characterization of a novel ambipolar polymer semiconductor based on a fumaronitrile core as an electron‐withdrawing group

Two conjugated polymers containing stilbene and fumaronitrile moieties were synthesized to investigate their electronic properties by the existence of electron‐withdrawing cyano groups on a vinylene backbone. The cyclic voltammetry investigation and time‐dependent density functional theory calculations indicated that the cyano substituents lowered the lowest unoccupied molecular orbital (LUMO) energy level by about 0.65 and 0.63 eV, respectively. The lowering of the LUMO energy levels due to the electron‐withdrawing properties of the cyano substituents could enhance electron injection capability. Furthermore, bithiophene‐fumaronitrile (donor‐acceptor) intermolecular interaction facilitates the self‐assembly of the polymer chains. Organic field‐effect transistors (OFETs) based on PBTSB without the electron‐withdrawing group only exhibit hole transport, while OFETs based on PBTFN with cyano substituents exhibit ambipolar characteristics. The growth of PBTFN crystalline fibrils was observed with increasing annealing temperature, which enhanced hole and electron mobility. A complementary‐like inverter using PBTFN with ambipolar properties exhibited good symmetry with an inverting voltage nearly half that of the power supply with a gain of 9 at V_DD = 100 V. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A comparative computational study of the homolytic and heterolytic bond dissociation energies involved in the activation step of ATRP and SET‐LRP of vinyl monomers

A quantum‐chemical calculation of the homolytic and heterolytic bond dissociation energies of the model compounds of the monomer and dimer is reported. These model compounds include the dormant chloride, bromide, and iodide species for representative activated and nonactivated monomers containing electron‐withdrawing groups as well as for a nonactivated monomer containing an electron‐donor group. Two examples of sulfonyl and N‐halide initiators are also reported. The homolytic inner‐sphere electron‐transfer bond dissociation is known as atom transfer and is responsible for the activation step in ATRP. The heterolytic outer sphere single electron transfer bond dissociation is responsible for the activation step in single electron transfer mediated living radical polymerization (SET‐LRP). The results of this study demonstrated much lower bond dissociation energies for the outer sphere single electron transfer processes. These results explain the higher rate constant of activation, the higher apparent rate constant of propagation, and the lower polymerization temperature for both activated and nonactivated monomers containing electron‐withdrawing groups in SET‐LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1607–1618, 2007     

Polymers from nitriles. VII. Polymerization of fumaronitrile with triethylamine as initiator

The reaction of fumaronitrile with triethylamine in bulk at 295–353 K gives in high yields dark-colored polymers. The polymerization occurs at one of the two nitrile groups and not at the (C? C) double bond. The kinetics of the reaction were investigated and the polymers characterized analytically.     

PHOTOINDUCED CHARGE TRANSFER POLYMERIZATION OF STYRENE INITIATED BY ELECTRON ACCEPTOR

Photoinduced charge transfer polymerization of styrene (St) with electron acceptor asinitiator was investigated. In case of fumaronitrile (FN) or maleic anhydride (MA) asinitiator the polymerization takes place regularly, whereas the tetrachloro-1, 4-benzenequinone (TCQ), 2, 3-dichloro-5, 6-dicyano-1, 4-benzenequinone (DDQ). ortetracyano ethylene (TCNE) as initiator the polymerization proceeds reluctantly only afterthe photoaddition reaction. A mechanism was proposed that free radicals would be formedfollowing the charge and proton transfer in the exciplex formed between St and electronacceptors.