Synthesis and mesogenic properties of a novel family of oligothiophene derivatives

With the aim of developing new oligothiophene-based liquid crystals involving hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-distearyl-2,2' : 5',2"-terthiophene-5,5"-dicarboxamide (DNC₁₈3T) and N,N'-dialkyl-5,5"-dibromo-2,2' : 5',2"-terthiophene-4,4"-dicarboxamides (DNC_nDBr3T, n = 5, 8, 16, 18), were designed and synthesized, and their thermal behaviour examined. While DNC₁₈3T did not exhibit liquid crystallinity, DNC_nDBr3T compounds with n = 8, 16, 18 were found to form smectic A phases. In addition to liquid crystal behaviour, crystal polymorphism was also observed for DNC₁₆DBr3T. It is shown that both the position of the amido group and the alkyl chain length greatly affect liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of liquid crystal phases in the DNC_nDBr3T system.     

Synthesis and Mesogenic Properties of Novel Terthiophene Derivatives

To develop novel oligothiophene‐based liquid crystals involving hydrogen bonding, new terthiophene derivatives containing a stearylamide group, N,N′‐distearyl‐5,5″‐dicyano‐2,2′∶5′,2″‐terthiophene‐4,4″‐dicarboxamide (DNC₁₈DCN 3T) and N,N′‐distearyl‐5,5′‐dipropyl‐2,2′∶5′,2′‐terthiophene‐4,4″‐dicarboxamide (DNC₁₈ DP3T), were designed and synthesized, and their thermal behavior examined. Although DNC₁₈DP3T did not exhibit liquid crystallinity, DNC₁₈DCN3T was found to form smectic A phase.     

新型低聚噻吩衍生物的设计、合成及其液晶性能的研究

设计、合成了一系列新型低聚噻吩衍生物N,N’-双烷烃基-5,5’-二溴基-2 ,2’：5’,2’-三噻吩-4,4’-二酰胺[N,N’-dialkyl-5,5’-dibromo-2,2’:5 ’,2’-terthiophene-4,4’-dicarboxamide](DNCnDBr3T,n=5,8,6,18)。示差扫描 量热法（DSC）测定的结果及偏光光学显微镜观察的结果显示,DNC18DBr3T, DNC16DBr3T,DNC8DBr3T具有近晶A形液晶性质,DNC5DBr3T不具有液晶性质。为了探 讨分子间氢链对液晶形成的影响,设计、合成了新型低聚噻衍生物4,4“-双烷烃 酯-5,5“-二溴基-2,2’:5’,2’-三噻吩[4,4’-bis(alkyloxycarbonyl)-5,5’ -dibromo-2,2’:5’,2’-terthiophene](DOCnDBr3T,n=5,8,16,18).测定和观察的 结果发现,DOCnDBr3T(n=5,8,16,18）不具有液晶的结果。这个结果表明,酰胺基 的存在于液晶的形成起着重要的作用。测定DNC18DBr3T在结晶状态和液晶状态下的 红外光谱,进一步证实了部分分子间氢键对于液晶的形成起着重要的作用。     

Synthesis and mesogenic properties of a novel family of oligothiophene derivatives

With the aim of developing new oligothiophene-based liquid crystals involving hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-distearyl-2,2' : 5',2"-terthiophene-5,5"-dicarboxamide (DNC₁₈3T) and N,N'-dialkyl-5,5"-dibromo-2,2' : 5',2"-terthiophene-4,4"-dicarboxamides (DNC_nDBr3T, n = 5, 8, 16, 18), were designed and synthesized, and their thermal behaviour examined. While DNC₁₈3T did not exhibit liquid crystallinity, DNC_nDBr3T compounds with n = 8, 16, 18 were found to form smectic A phases. In addition to liquid crystal behaviour, crystal polymorphism was also observed for DNC₁₆DBr3T. It is shown that both the position of the amido group and the alkyl chain length greatly affect liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of liquid crystal phases in the DNC_nDBr3T system.     

Synthesis and characterization of difunctional blue light-emitting molecules containing hole-transporting triphenylamino units

The synthesis of new difunctional (i.e., light-emitting and hole-transporting) fluorophore molecules, 2,2′-difuryl-4,4′-(N,N,N′,N′-tetraphenyl)diaminobiphenyl and 5,5′-bis(4-N,N′-diphenylaminophenyl)-2,2′-bifuryl, which contain hole-transporting triphenylamino units, are reported. These difunctional molecules emit intense blue photoluminescence and further reveal high HOMO energy values as well as high glass transition temperatures.     

Controlled vinyl-addition-type polymerization of norbornene initiated by several cobalt complexes having substituted terpyridine ligands

A series of cobalt(II) complexes having terpyridine derivatives such as 2,2^′:6^′,2″-terpyridine (1), 4,4^′,4″-^tBu₃-2,2^′:6^′,2″-terpyridine (2), 5,5″-Me₂-2,2^′:6^′,2″-terpyridine (3), 6,6″-Me₂-2,2^′:6^′,2″-terpyridine (4) and 6,6″-(3,5-Me₂C₆H₃)₂-2,2^′:6^′,2″-terpyridine (5) was synthesized. The structures of 1, 3, and 4 were confirmed by X-ray crystallography. The coordination sphere around the cobalt center in 1 can be described as pseudo square pyramidal. On the other hand, complex 4 has pseudo trigonal bipyramidal structure. Upon activation with d-MAO (dried-methylaluminoxane), these complexes showed high activities for the polymerization of norbornene (NBE). In particular, polymerization of NBE with 4/d-MAO system at room temperature resulted in quantitative yield within several hours to give the polymers with relatively narrow molecular weight distributions and controlled molecular weight. The polymerizations of NBE with these cobalt catalyst systems proceeded in vinyl addition polymerization, which was confirmed by ¹H NMR spectra of the resulting polymers.     

Reduction of 5-(bromomethyl)-1-pyrrolinium bromides to 2-(bromomethyl)pyrrolidines and their transformation into piperidin-3-ones through an unprecedented ring expansion-oxidation protocol

3,3-Dialkyl-5-(bromomethyl)-1-pyrrolinium bromides, prepared via bromocyclization of N-(2,2-dialkyl-4-pentenylidene)amines by means of bromine in dichloromethane, were reduced to 4,4-dialkyl-2-(bromomethyl)pyrrolidines for the first time using borane dimethyl sulfide in dichloromethane. Furthermore, the latter 2-(bromomethyl)pyrrolidines were transformed into the corresponding piperidin-3-ones through an unprecedented ring expansion-oxidation protocol in dimethylsulfoxide in the presence of potassium carbonate. Reduction of 5,5-dialkylpiperidin-3-ones by means of sodium borohydride in methanol afforded 5,5-dialkyl-3-hydroxypiperidines in good yields.     

Ferromagnetic oxovanadium(IV) complexes chelated with tetrahalosalen ligands

Five oxovanadium(IV) complexes [VO(X₄salen)] have been prepared and characterized, where each benzene ring was substituted with two halogen atoms in salen (H₂salen = N,N′-disalicylideneethylenediamine). The X-ray diffraction study on 3,3′,5,5′-tetrachloro-, 3,3′,5,5′-tetrabromo-, and 4,4′,6,6′-tetrachlorosalen derivatives clarified their polymeric structure with the (-VO-)_n repeating unit. The interatomic V···V distances are 3.710(3), 3.695(3), and 3.749(3) Å, respectively, being shorter than that of known [VO(salpn)] (3.83 Å; H₂salpn = N,N′-disalicylidenepropylenediamine). The exchange coupling parameters (J) were determined by fitting the magnetic susceptibility data to the one-dimensional ferromagnetic model, giving 2J/k_B = 8.2-16 K, which are the largest in the [VO(salen)] and [VO(salpn)] family.     

Atom transfer radical cyclization of O-allyl-2,2-dichlorohemiacetal acetates: an expedient method to dichloro-γ-lactones

3-Alkyl-3-chloro-4-chloromethyl-γ-lactones were synthesized in acceptable yields, exploiting the CuCl-N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyzed atom transfer radical cyclization (ATRC) of O-allyl-2,2-dichlorohemiacetal acetates, starting materials easily prepared from 2,2-dichloroaldehydes. The oxidation of the intermediate dichloro-2-acetoxytetrahydrofurans was completed in a two-step, one-pot procedure: hydrolysis to γ-lactol and final oxidation to lactone with Jones' reagent.     

Synthesis of B-trisubstituted borazines via the rhodium-catalyzed hydroboration of alkenes with N,N′,N″-trimethyl or N,N′,N″-triethylborazine

Hydroboration of terminal and internal alkenes with N,N′,N″-trimethyl- and N,N′,N″-triethylborazine was carried out at 50 °C in the presence of a rhodium(I) catalyst. Addition of dppb or DPEphos (1 equiv.) to RhH(CO)(PPh₃)₃ gave the best catalyst for hydroboration of ethylene at 50 °C, resulting in a quantitative yield of B,B′,B″-triethyl-N,N′,N″-trimethylborazine. On the other hand, a complex prepared from (t-Bu)₃P (4 equiv.) and [Rh(coe)₂Cl]₂ gave the best yield for hydroboration of terminal or internal alkenes.     

Rearrangements in the Scholl oxidation: implications for molecular architectures

Rearrangements readily occur in Scholl oxidations and interfere with the construction of certain molecular architectures. 3,3?,4,4′,4″,4?,5′,5″-Octamethoxy-1,1′,2′,1″,2″,1?-quaterphenyl and 3,3?,4,4′,4′′,4?,5′,5′-octamethyl-1,1′,2′,1″,2″,1?-quaterphenyl, which were conceived as precursors to benzenoid strips, rearranged under Scholl conditions to the unexpected C_2v-substituted products 1,2,5,6,9,10,12,13-octamethoxydibenzo[fg,op]naphthacene and 1,2,5,6,9,10,12,13-octamethyldibenzo[fg,op]naphthacene. This corrects a widely propagated error in the literature in which the assignments of 1,2,5,6,9,10,12,13-octamethoxydibenzo[fg,op]naphthacene (C_2v) and 1,2,5,6,8,9,12,13-octamethoxydibenzo[fg,op] naphthacene (C_2h) are crossed. A mechanism involving the migration of an aryl ring on an arenium cation intermediate is proposed.     

Synthesis and gas transport property of polyimide from 2,2′-disubstituted biphenyltetracarboxylic dianhydrides (BPDA)

A series of dianhydride monomers, 2,2′-disubstituted-4,4′,5,5′-biphenyltetracarboxylic dianhydride (substituents = phenoxy, p-methylphenoxy, p-tert-butylphenoxy, nitro, and methoxy) were synthesized by the nitration of an N-methyl protected 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and subsequent aromatic nucleophilic substitutions with aroxides (NaOAr) or methoxide. These dianhydrides were polymerized with various aromatic diamines in refluxing m-cresol containing isoquinoline to afford a series of aromatic polyimides. The effects of varying 2,2′-substituents of the dianhydride (BPDA) moiety on the properties of polyimides were investigated. It was found that polyimides from the dianhydrides containing phenoxy, p-methylphenoxy, and p-tert-butylphenoxy side groups possessed excellent solubility and film forming capability whereas polyimides from 2,2′-dinitro-BPDA and 2,2′-dimethoxy-BPDA were less soluble in organic solvent. The soluble polymers formed flexible, tough and transparent films. The films had a tensile strength, elongation at break, and Young’s modulus in the ranges 102-168 MPa, 8-21%, 2.02-2.38 GPa, respectively. The polymer gas permeability coefficients (P) and ideal selectivities for N₂, O₂, CO₂ and CH₄ were determined for the -OAr substituted polyimides. The oxygen permeability coefficient (P_O2) and permselectivity of oxygen to nitrogen (P_O2/N2) of the films were in the ranges 3.4-11.3 barrer and 3.8-4.6, respectively. The gas permeability typically increased with increasing free volume in the order of tert-butylphenoxy substituted PI > methylphenoxy substituted PI > phenoxy substituted PI.     

Low-fluorinated homopolymer from heterogeneous ATRP of 2,2,2-trifluoroethyl methacrylate mediated by copper complex with nitrogen-based ligand

We report the preparation of low-fluorinated homopolymer via heterogeneous atom transfer radical polymerization (ATRP) of 2,2,2-trifluoroethyl methacrylate (TFEMA) using 2,2′-bipyridine (bpy), N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA), and tris(2-(dimethylamino)ethyl)amine (Me₆TREN) as representatives for di-, tri-, and tetradentate amine ligands, respectively. The ATRP was better controlled, yielding polymers with controlled molecular weights and low polydispersities (M_w/M_n ca. 1.11) when bpy was used as a ligand than when PMDETA was used. This was further supported by the results of our kinetic and chain extension studies. However, the ATRP of TFEMA had lower monomer conversions and gel formation when Me₆TREN was used as the ligand. Further reported are the thermal-properties, as well as the surface properties of the films from the resulting polymers with different molecular weights.     

Aqueous solution behavior of p(N-isopropyl acrylamide) in the presence of water-soluble macromolecular species

We report here the polymerization of N-isopropyl acrylamide (NIPAM) via the reversible addition fragmentation chain transfer (RAFT) process. Two trithiocarbonates (S,S′-bis(α,α′-dimethyl-α″-acetic acid)-trithiocarbonate and 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid) were used as the chain transfer agents in conjunction with 4,4′-azobis(4-cyanovaleric acid) and 2,2′azobis(2-methylpropionamidine) dihydrochloride as the initiating species. Poly(NIPAM) is a thermo-responsive polymer that has a sharp lower critical solution temperature (LCST). Herein, we investigated the aqueous solution behaviour of well defined p(NIPAM) prepared by the RAFT process as a function of molecular weight (degree of polymerization: 50, 100 and 200) and temperature. Furthermore, we examine the influence of varying concentrations of macromolecular species (neutral polyethylene glycol (M_n - 3400 g/mol) and ionic bovine serum albumin (M_n - 63 000 g/mol)) on the LCST of p(NIPAM). The aqueous solution behaviour was assessed by spectrophotometry, dynamic light scattering and surface tensiometry. The macromolecular additives was found to have a significant effect on the coil to globular transition of the lower molecular weight p(NIPAM).     

Enantioselective phenyl transfer to aldehydes using 1,1′-bi-2-naphthol-3,3′-dicarboxamide as chiral auxiliary

N,N,N′,N′-Tetra-n-butyl-BINOL-3,3′-dicarboxamide 5d was found to promote phenyl transfer from ethylphenylzinc to both aromatic and aliphatic aldehydes with high enantioselectivity up to 96% ee in tert-butyl methyl ether.     

Synthesis and characterization of monomeric siloxo palladium(II) complexes: crystal structure of [Pd(tmeda)(C6F5)(OSiPh3)]

Mononuclear palladium-hydroxo complexes of the type [Pd(N-N)(C₆F₅)(OH)] [(N-N)=2,2^′-bipyridine (bipy), 4,4^′-dimethyl-2,2^′-bipyridine (Me₂bipy), or N,N,N^′,N^′-tetramethylethylenediamine (tmeda)] react with silanols HOSiR₃ in toluene giving the corresponding siloxo complexes [Pd(N-N)(C₆F₅)(OSiR₃)]. The X-ray crystal structure of [Pd(tmeda)(C₆F₅)(OSiPh₃)] has been determined. In one of the two molecules in the asymmetric unit there is an intramolecular interaction by phenyl-pentafluorophenyl π-stacking.     

Crystal structures and spectroscopic properties of a new zinc phosphite cluster and an unexpected chainlike zinc phosphate obtained by hydrothermal reactions

A new zinc phosphite cluster, Zn₂(4,4′-dmbpy)₂(H₂PO₃)₄1, and a new chainlike zinc phosphate, Zn₂(5,5′-dmbpy)₂(HPO₄)(H₂PO₄)₂2, have been synthesized under hydrothermal conditions (4,4′-dmbpy=4,4′-dimethyl-2,2′-dipyridy, 5,5′-dmbpy=5,5′-dimethyl-2,2′-dipyridy). Compound 1 is a molecular zinc phosphite constructed from ZnO₃N₂ trigonal bipyramids, H₂PO₃ pseudo-pyramids and 4,4′-dmbpy ligands. Compound 2 possesses a 1D chainlike framework constructed from ZnO₃N₂ trigonal bipyramids, HPO₄ tetrahedra, H₂PO₄ tetrahedra and 5,5′-dmbpy ligands. Both compounds 1 and 2 exhibit intensive photoluminescence originated from the intraligand π-π* transitions. Crystal data: 1, monoclinic, P2₁/n, , , , β=110.857(3)°, , Z=2, R1=0.0297, wR₁=0.0801; 2, triclinic, P-1, , , , α=64.995(9)°, β=65.952(9)°, γ=65.296(8)°, , Z=2, R₁=0.0418, wR₁=0.1010.     

Heavier alkali metal complexes of the bulky alkyl ligand 2-(bis(trimethylsilyl)methyl)-6-methylpyridine: Crystal structures of [{6-Me(2 Pyr)}(Me3Si)2CNa(pmdta)] and [{6-Me(2-Pyr)}(Me3Si)2CK]∞

Reaction of the bulky pyridyl based ligand 6-Me(2-Pyr)(Me₃Si)₂CH with ⁿBuM (M = Na, K) in the presence of the N donors pmdta (N,N′,N′,N″,N″ pentamethyldiethylenetriamine) and tmeda (N,N,N′,N′ tetramethylethylenediamine) resulted in the formation and crystallisation of the heavy alkali metal complexes, [{6-Me(2-Pyr)}(Me₃Si)₂CNa(pmdta)], 1, and [{6-Me(2-Pyr)}(Me₃Si)₂CK]_∞, 2. Single crystal X-ray diffraction studies show the sodium complex, 1, to be monomeric with a six coordinate metal centre, while the unsolvated potassium complex, 2, is polymeric, involving repeating η³ 1-aza-allyl and allylic interactions of the pyridyl moiety with the potassium cation.     

Synthesis of terpyridine-substituted calix[n]arenes

Calix[n]arenes (n = 4,5) comprising 4-(2,2′:6′,2″-terpyridyl)-phenyl substituents at the upper rim were synthesized for the first time, employing Suzuki-type coupling reactions. All calix[n]arene derivatives were prepared as cone conformers. The single crystal X-ray structure of cone-5,11,17,23-tetra{4-(2,2′:6′,2″-terpyridyl)-phenyl}-25,26,27,28-tetrabutoxycalix[4]arene 4 is analyzed in terms of structural rigidity and potential use of these ligands as novel synthons of cage-type metallosupramolecular assemblies.     

New N-acyl, N-alkyl, and N-bridged derivatives of rac-6,6′,7,7′-tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-bisisoquinoline

The preparation of potential new ligand systems based on the rac-1,1′,2,2′,3,3′,4,4′-octahydro-6,6′,7,7′-tetramethoxy-1,1′-bisisoquinoline skeleton has been investigated. Syntheses of N-(2-bromobenzyl), N-(3-acetoxybenzyl), N-acetyl, N-chloroacetyl, N-chlorocarbonyl, N-ethoxycarbonyl and N-tert-butyloxycarbonyl derivatives and five macrocyclic, polyether containing derivatives are described.