Purine-based carbenes at rhodium and iridium

Purine-based carbenes can be attached to catalysis-related metals like rhodium and iridium through the standard method of in situ deprotonation of the respective azolium salts. Thus, 1,3,7,9-tetramethylxanthinium tetrafluoroborate is obtained by the reaction of trimethyloxonium tetrafluoroborate and caffeine. The salt and 7,9-dimethylhypoxanthinium iodide were used as a consecutive precursor to form rhodium (I) and iridium (I) carbene complexes of the type [M(L)(L_Carbene)₂]I and M(L)(L_Carbene)(I) (M = Rh, Ir, L_Carbene = 1,3,7,9-tetramethylxanthine-8-ylidene, 7,9-dimethylhypoxanthine-8-ylidene, L = η⁴-1,5-COD, CO) (COD = 1,5-cyclooctadiene). All compounds were characterized by ¹H NMR, ¹³C NMR, mass spectrometry and/or elemental analysis.     

Rhodium and iridium complexes of N-heterocyclic carbenes: Structural investigations and their catalytic properties in the borylation reaction

Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)₂Cl]₂ to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)₂][Cl,I] [COD = 1,5-cyclooctadiene, NHC =  1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η⁴-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η⁴-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.     

Synthesis and electroluminescence properties of carbazole-containing 2,6-naphthalene-based conjugated polymers

Three types of carbazole containing 1,5-disubstituted poly(2,6-naphthalene) derivatives, i.e., 2,6-naphthalene homopolymer that has a carbazolyl side chain at 1,5-positions, random copolymers and alternating copolymers consisting of 1,5-dialkoxynaphthalene-2,6-diyl and N-phenylcarbazole-2,7-diyl were newly synthesized by Ni-mediated Yamamoto polycondensation and Pd-catalyzed Suzuki coupling reaction. The number-average molecular weights (M_n) of the polymers and their polydispersity indices (M_w/M_n) were 5.4-8.2 × 10³ and 1.4-1.7, respectively. These polymers exhibited blue photoluminescence in the film states and high fluorescence quantum efficiencies in CHCl₃ (?_fl = 0.70-1.00). The electroluminescence properties of these polymers were investigated by fabricating a PLED device that has a configuration of ITO/PEDOT(PSS)/polymer/CsF/Al. The device fabricated with the random copolymer exhibited highest performances showing a maximum brightness of 8370 cd/m² at 13 V and a maximum efficiency of 2.16 cd/A at 7 V.     

Synthesis of di-, tri-, tetra- and pentacyclic arene complexes of ruthenium(II):[Ru(η-polycyclic arene)-(1-5-η-cyclooctadienyl)]PF6 and their reactions with NaBH4

The phenanthrene complex of ruthenium(II), [Ru(η⁶-phenanthrene)(1,5-η⁵-cyclooctadienyl)]PF₆ (2c), is prepared by the reaction of Ru(η⁴-1,5-COD)(η⁶-1,3,5-COT) (1) with phenanthrene and HPF₆ in 65% yield. Similar treatments with di- tri-, tetra- and pentacyclic arenes give corresponding polycyclic arene complexes, [Ru(η⁶-polycyclic arene)(1-5-η⁵-cyclooctadienyl)]PF₆ [polycyclic arene = naphthalene (2b), anthracene (2d), triphenylene (2e), pyrene (2f) and perylene (2g)] in 46-90% yields. The molecular structure of the perylene complex 2g is characterized by X-ray crystallography. Reaction of 2c with NaBH₄ gives a mixture of the 1,5- and 1,4-COD complexes of ruthenium(0), Ru(η⁶-phenanthrene)(η⁴-1,5-COD) (3c) and Ru(η⁶-phenanthrene)(η⁴-1,4-COD) (4c) in 76% in 1:8 molar ratio. The arene exchange reactions among cationic complexes [Ru(η⁶-arene)(1-5-η⁵-cyclooctadienyl)]PF₆ (2) showed the coordination ability of arenes in the following order: benzene ∼ triphenylene > phenanthrene > naphthalene > perylene ∼ pyrene > anthracene, suggesting the benzo fused rings, particularly those of acenes, decreasing thermal stability of the arene complex.     

Homopolymer and copolymers of 4-nitro-3-methylphenyl methacrylate with glycidyl methacrylate: Synthesis, characterization, monomer reactivity ratios and thermal properties

The novel methacrylic monomer, 4-nitro-3-methylphenyl methacrylate (NMPM) was synthesized by reacting 4-nitro-3-methylphenol dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in the presence of triethylamine as a catalyst. The homopolymer and copolymers of NMPM with glycidyl methacrylate having different compositions were synthesized by free radical polymerization in EMK solution at 70 ± 1 °C using benzoyl peroxide as free radical initiator. The homopolymer and the copolymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility tests were tested in various polar and non-polar solvents. The molecular weight and polydispersity indices of the copolymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in NMPM content. The thermogravimetric analysis of the polymers performed in air showed that the thermal stability of the copolymer increases with NMPM content. The copolymer composition was determined using ¹H NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such Fineman-Ross (r₁ = 1.862, r₂ = 0.881), Kelen-Tudos (r₁ = 1.712, r₂ = 0.893) and extended Kelen-Tudos methods (r₁ = 1.889, r₂ = 0.884).     

Synthesis of a new bidentate ferrocenyl N-heterocyclic carbene ligand precursor and the palladium (II) complex trans-[PdCl2(CfcC)], where (CfcC) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene

A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe₃)₂ and reacted with [PdCl₂ (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl₂(C^∧fc^∧C)], where (cod) = 1,5-cyclooctadiene and (C^∧fc^∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene.     

Dissolution behavior of tetrafluoroethylene-based fluoropolymers for 157-nm resist materials

We have synthesized various main-chain fluorinated polymers and studied base-resin properties, such as transparency at 157 nm, solubility in a standard alkaline developer, and lithographic performance. Main-chain-fluorinated polymers were synthesized by copolymerization of tetrafluoroethylene (TFE) with cyclic monomers, especially newly synthesized norbornene derivatives. We studied the correlation between pK_a(OH) and the solubility of the copolymers of TFE and functional (fluoroalkyl alcohol group) norbornenes. Their solubility depends on the pK_a value of the fluoroalkyl alcohol groups.We studied the impact of the polymerization initiators on base-resin properties. High transparency was obtained by using the fluorocarbon initiator. It was also confirmed that the monocyclic component improves dry-etch resistance and that fluorination at the terminal groups improves alkaline solubility.In addition, we found that the development characteristics of TFE/norbornene copolymers were significantly improved by the stereoselective (endo versus exo) partial protection of the hydroxyl groups in the fluoroalkyl alcohol moiety attached to norbornene unit. The polymer protected only in the exo position of the norbornene unit in the copolymer had a higher R_max and a higher contrast. Positive-working resists based on these fluoropolymers were developed and 55 nm dense lines could be delineated by exposure at 157 nm wavelength with an alternating phase shift mask on a 0.9 NA 157 nm exposure tool.     

Cationic rhodium(I) complexes containing 4,4′-disubstituted 2,2′-bipyridines: A systematic variation on electron density over the metal centre

A series of [Rh(COD)(X₂-bipy)]BF₄ complexes (COD = 1,5-cyclooctadiene; X₂-bipy = 4,4′-disubstituted 2,2′-bipyridines; X = OCH₃, CH₃, H, Cl or NO₂) has been prepared from [Rh(COD)Cl]₂. The complexes for X = OCH₃, Cl and NO₂ have not been described previously in the literature. All complexes have been characterised by elemental analysis, IR, ¹H NMR and UV-Vis spectrometry. This series of complexes presents a wide variation on electron density over the metal centre with virtually no variation on its steric environment which discloses interesting possibilities for catalytic and electro-catalytic studies. A preliminary evaluation of these complexes on the hydroformylation of camphene and β-pinene showed that under the rather drastic conditions employed the complexes acted as a precursor for [Rh(CO)₃H], which accounts for most of the catalytic activity.     

Synthesis, characterization and application of pincer-type nickel iminophosphinite complexes

Two pincer-type nickel iminophosphinite complexes, [(2-(CHNR)-6-(OPR′₂)C₆H₃)NiCl] (R = 2,6-ⁱPr₂C₆H₃, R′ = Ph (2a) or ⁱPr (2b)), were synthesized from the reactions of bis(1,5-cyclooctadiene)nickel(0) and corresponding iminophosphinite ligands. The solid state structures of the nickel pincer complexes were determined by X-ray single crystal diffraction studies. They were successfully employed in the Kumada reaction of non-activated aryl chlorides and phenylmagnesium bromide at room temperature.     

Synthesis and thermochemical properties of NF2-containing energetic salts

Ammonium, 1,5-diamino-4-methyl-tetrazolium and 4-amino-1-methyl-triazolium salts of 5-difluoroaminodifluoromethyl-tetrazolate (TA-CF₂NF₂) were prepared by metathesis reactions of silver 5-difluoroaminodifluoromethyl-tetrazolate and the corresponding iodides. All are thermally stable to ∼150 °C. The ammonium salt has a density of 1.88 g cm⁻³. The combination of the CBS-4 method and isodesmic bond separation reactions was found to be an economical and reliable method to estimate heats of formation for polyfluorinated molecules. The standard heats of formation () of ammonium 5-difluoroaminodifluoromethyl-tetrazolate was calculated to be −53.13 kcal mol⁻¹ using the CBS-4 method. While its detonation pressures (P) and velocities (D) were estimated using Cheetah 4.0: P = 28.78 GPa; D = 8490 m s⁻¹; detonation properties for 1,5-diamino-4-methyl-tetrazolium salts of 5-difluoroaminomethyltetrazolate (TA-CH₂NF₂), 5-difluoroaminotetrazolate (TA-NF₂) and 5-difluoroaminodinitromethyl-tetrazolate (TA-C(NO₂)₂NF₂) are also compared based on predicted densities and computed heats of formation.     

Dinuclear nickel (II) complexes bearing two pyrazolylimine ligands: Synthesis characterization, and catalytic properties for vinyl-type polymerization of norbornene

A series of dinickel (II) complexes of bis-2-(C₃HN₂(R₁)₂-3,5)(C(R₂)N(C₆H₃(CH₃)₂-2,6)Ni₂Br₄ (complex 1: R₁ = CH₃, R₂ = Ph; complex 2: R₁ = CH₃, R₂ = 2,4,6-trimethylphenyl; complex 3: R₁ = R₂ = Ph; complex 4: R₁ = Ph, R₂  = 2,4,6-trimethylphenyl) were synthesized and characterized. The solid-state structures of complexes 1, 2 and 3 have been confirmed by X-ray single-crystal analyses to be in the form of a dinuclear and bromine-bridged structure. However, there is an equilibrium that shifts between the monomer and dimmer in toluene based on the characterization of UV-vis spectrophotometry. Activated by methylaluminoxane (MAO), these complexes are capable of catalyzing the polymerization of norbornene with moderate activity up to 6.64 × 10⁵ gPNBE/(molNi·h). The influences of polymerization parameters such as reaction temperature and Al/Ni molar ratio on catalytic activity and molecular weight of the polynorbornene were investigated in detail. The influence of the bulkiness of the substituents on polymerization activity was also studied. The obtained polynorbornenes were characterized by means of ¹H NMR, FTIR and TG techniques. The analyses results of polymers’ structures indicated that the norbornene polymerization is vinyl-type polymerization rather than ROMP.     

Vinyl polymerization of norbornene catalyzed by a series of bis(β-ketoiminato)nickel (II) complexes in the presence of methylaluminoxane

A series of nickel complexes with β-ketoiminato ligands based on pyrazolone derivative were synthesized and characterized, which are highly active catalyst precursors for norbornene polymerization under mild reaction conditions through a vinyl-type polymerization mechanism. The catalytic activity could be up to 3.38 × 10⁷ g polymer/mol Ni h. The molecular weight distributions of the polynorbornenes (M_w/M_n = 2.05-2.56) indicate the presence of a single active species in the polymerization process.     

Thermotropic polyesters. 2: Synthesis, characterization and thermal transitions of copolyesters containing 4,4′-bis (ω-alkyloxy) biphenyl isophthalate units

Thermotropic copolyesters containing an isophthalate unit and mesogenic 4, 4′-bis (ω-hydroxyalkyloxy) biphenyls (n = 3, 4, 6) with different numbers of methylene units have been synthesized by melt polymerization. The number-average molar mass (M_n) was estimated from end group analysis by ¹H NMR. The copolymer compositions were also obtained from ¹H NMR. The thermal behavior of the copolymers containing even-even (n = 4, 6) and odd-even (n = 3, 4) pairings has been investigated and is also compared with that of the analogous homopolymers. The copolymers exhibit reduced melting point and extending liquid crystalline range identified using polarizing microscopy and DSC. All of the obtained compounds were characterized by conventional spectroscopic methods.     

Synthesis and characterization of new difunctional alkynylated (η-arene)(η-cycloocta-1,5-diene)ruthenium(0) complexes as molecular models for organometallic polymers

The new dialkynylated complexes Ru(η⁶-DEB-Si)(η⁴-COD), 4a, Ru(η⁶-DEBP-Si)(η⁴-COD), 4b1, Ru₂(η⁶,η⁶-DEBP)(η⁴-COD)₂, 4b2 [COD = 1,5-cyclooctadiene; DEB-Si = 1,4-bis(trimethylsilylethynyl)benzene; DEBP-Si = 4,4′-bis(trimethylsilylethynyl)biphenyl] have been synthesized by the arene exchange reaction with the complex Ru(η⁶-naphthalene)(η⁴-COD). The complexes Ru(η⁶-DEB)(η⁴-COD), 5a, and Ru(η⁶-DEBP)(η⁴-COD), 5b1, have been prepared by desilylation of the corresponding compounds 4a and 4b1. All the complexes have been fully characterized by means of spectroscopic techniques.     

An effective route for the synthesis of cationic palladium complexes of general formula [(Acac)PdLL]A

A series of palladium complexes of general formula [(Acac)PdL¹L²]⁺A⁻, where L¹, L² = phosphines and A = BF₄, CF₃SO₃, were synthesized. Preliminary studies show that the complexes are active in selective dimerization of styrene and addition polymerization of norbornene.     

High norbornene incorporation in ethylene-norbornene copolymerization with a bis(α-alkyloxoimine) titanium-MAO catalyst

A novel bis(α-alkyloxoimine) titanium(IV) complex was synthesized and used as a catalyst precursor to catalyze homo- and copolymerization of ethylene and norbornene. The titanium complex activated with methylalumoxane exhibits good activities for the homopolymerizations of ethylene and norbornene under high temperature to produce high-molecular-weight linear polyethylene and vinyl-type polynorbornene, respectively. Ethylene-norbornene copolymers with high molecular weight can also be produced by this catalyst. The incorporation of norbornene from 0 to 76 mol% in the copolymers can be controlled by varying the charged norbornene. ¹³C NMR analyses show that the microstructures of the ethylene-norbornene copolymers with low norbornene incorporation are predominantly alternated and isolated norbornene units, while those with high norbornene incorporation are random polymers containing long norbornene sequences.     

Gallium and indium dithiocarboxylates: Synthesis, spectroscopic characterization and structure of [MeGa(S2Ctol)2]

Several gallium and indium dithiocarboxylate complexes of the type [Me_nM(S₂CR)_3−n] (M = Ga, In; n = 0, 1, 2; R = phenyl (Ph), p-tolyl (tol), mesityl (Mes)) have been synthesized. These complexes were characterized by elemental analysis, IR, UV-vis and NMR (¹H,¹³C{¹H}) spectroscopy. Structure of [MeGa(S₂Ctol)₂] was established by X-ray crystallography. The gallium atom adopts a distorted five coordinate geometry which is intermediate between trigonal bipyramidal and square pyramidal configurations. The complex [Me₂InS₂Ctol] underwent a two-step thermal decomposition leading to the formation of tetragonal β-In₂S₃.     

Ru(η-1,3,5-cyclooctatriene)(η-dimethyl fumarate)2: a novel, versatile zerovalent ruthenium complex with electron-deficient olefinic ligands

The reactivity of a novel zerovalent ruthenium complex, Ru(η⁶-cot)(η²-dmfm)₂ (cot = 1,3,5-cyclooctatriene, dmfm, =dimethyl fumarate), which is readily prepared from Ru(η⁴-cod)(η⁶-cot) (cod = 1,5-cyclooctadiene) and dmfm was examined. The reaction with monodentate phosphine or amine ligands gave Ru(η⁶-cot)(dmfm)(L) (L = ligand) via dissociation of dmfm. Among bidentate phosphines, dppm (dppm = bis(diphenylphosphino)methane) reacted to give Ru(η⁴-cot)(dmfm)(dppm) along with releasing a dmfm ligand. In the case of dppe (dppe = 1,2-bis(diphenylphosphino)ethane), two types of complexes were obtained depending on the reaction conditions, Ru(dmfm)(dppe)₂ and an alkyl alkenyl complex; in the formation of the latter complex, sp² C-H bond activation of dmfm occurred. Ru(η⁴-cot)(dmfm)(N^?N) and Ru(dmfm)₂ (N^?N^?N) were formed by reacting with bidentate and tridentate nitrogen ligands. The reactions with arenes gave π-coordinated complexes, Ru(η⁶-arene)(dmfm)₂. p-Quinones and a p-biqunone reacted to give Ru(η⁶-cot)(p-quinone) and {Ru(η⁶-cot)}₂(p-biquinone), respectively, along with the dissociation of two dmfm ligands. It was found that low-valent ruthenium complexes preferably bear both electron-donating and accepting ligands simultaneously to be thermodynamically stable.     

Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh₃)X], X = OEt, MeCO₂, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs.The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf₂] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh₃)₂] [NTf₂] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.     

Surface structure of thin asymmetric PS-b-PMMA diblock copolymers investigated by atomic force microscopy

Asymmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers of molecular weight M_n = 29,700 g mol⁻¹ (M_PS = 9300 g mol⁻¹M_PMMA = 20,100 g mol⁻¹, PD = 1.15, χ_PS = 0.323, χ_PMMA = 0.677) and M_n = 63,900 g mol⁻¹ (M_PS = 50,500 g mol⁻¹, M_PMMA = 13,400 g mol⁻¹, PD = 1.18, χ_PS = 0.790, χ_PMMA = 0.210) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Atomic force microscopy (AFM) was used to investigate the surface structure of thin films, prepared by spin-coating the diblock copolymers on a silicon substrate. We show that the nanostructure of the diblock copolymer depends on the molecular weight and volume fraction of the diblock copolymers. We observed a perpendicular lamellar structure for the high molar mass sample and a hexagonal-packed cylindrical patterning for the lower molar mass one. Small-angle X-ray scattering investigation of these samples without annealing did not reveal any ordered structure. Annealing of PS-b-PMMA samples at 160 °C for 24 h led to a change in surface structure.