Synthesis and photochemical reaction of 1,4-dialkyl-7-oxa-2,3,5,6-tetrakis(trifluoromethyl)bicyclohepta-2,5-diene

Diels-Alder reaction of 2,5-dialkyl-3,4-bis(trifluoromethyl)furan with hexafluoro-2-butyne gave 1,4-dialkyl-7-oxa-2,3,5,6-tetrakis(trifluoromethyl)bicyclohepta-2,5-diene. Irradiation (uv) of 1,4-diethyl-7-oxa-2,3,5,6-tetrakis(trifluoromethyl)bicyclohepta-2,5-diene afforded 1-ethyl-2,3,4,5-tetrakis(trifluoromethyl)-1,4-cyclopentadiene, ethyl 3-[l-ethyl-2,3,4,5-tetrakis(trifluoromethyl)-1,4-cyclopentadienyl] ketone, and 2,7-diethyl-3,4,5,6-tetrakis(trifluoromethyl)oxepin.     

Chemistry of a 1-silacyclopropene. Thermal production of 1,4-disilacyclohexa-2,5-dienes

Thermolysis of 1,1-dimethyl-2-phenyl-3-trimethylsilyl-1-silacyclopropene in the presence or absence of an alkyne such as diphenylacetylene or ethyl-dimethylsilylphenylacetylene gave a mixture of 1,1,4,4-tetramethyl-2,5-diphenyl-3,6-bis(trimethylsilyl- and 1,1,4,4-tetramethyl-2,6-diphenyl-3,5-bis(trimethylsilyl)-1,4-disilacyclohexa-2,5-diene in high yield. The formation of the 1,4-disilacyclohexa-2,5-diene system can be best rationalized in terms of a mechanism involving direct dimerization of the 1-silacyclopropene.     

Synthesis of macrocyclic polyethers and polyether diesters and preparation of their cationic complexes

New macrocyclic polyethers, 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10-trioxacyclododeca-2,5-diene (I), 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13-tetra oxacyclo pentadeca-2,5-diene (II), and 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13,16-penta oxa cyclo octadeca-2,5-dien (III), and macrocylic lactones 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13-tetraoxacyclopentadeca-2,5-diene-8,15-dione (IV) and 2,3,5,6-bis[5′(5′)-chlorobenzo]-1,7,10,13,16-pentaoxacyclooctadeca-2,5-diene-8,18-dione (V) were synthesized. Complexes of ligands III and V with metal cations were prepared. Furthermore, their metal-picrate extraction with some metal salts was attempted. Structures of the ligands and complexes were confirmed using spectroscopic techniques.     

Sterically encumbered systems for two low-coordinate phosphorus centers

Tetraarylphenyls of the form 2,3,5,6-Ar4C6 (Ar = p-tert-butylphenyl) are investigated as sterically demanding ligands for the syntheses of compounds having two p-phenylene-bridged phosphorus centers. The precursor to such materials, 1,4-diiodo-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (1), is readily obtained via a one-pot procedure in 68% yield. Compound 1 is then used to provide the bis(dichlorophosphine) 1,4-bis(dichlorophosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (2) and the derived bis(phosphine) 1,4-bis(phosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (3) in yields of 56 and 94% respectively. These materials provide access to novel materials containing two low-coordinate phosphorus centers bridged by a sterically encumbered phenylene unit. Compound 2 reacts with benzaldehyde and 2,6-dichlorobenzaldehyde in the presence of excess trimethylphosphine and zinc to produce the new pale yellow crystalline bis(phosphaalkenes) (E,E)-PhC(H)=PAr4C6P=C(H)Ph (4a; 42%) and (E,E)-Ar'C(H)=PAr4C6P=C(H)Ar' (4b; 46%; Ar' = 2,6-dichlorophenyl). The crystal structure of 4a shows a P=C bond length of 1.676(5) A. Compound 2 is also used to provide the unusual red-orange bis(diphosphene) DmpP=PAr4C6P=PDmp (5; 55%; Dmp = 2,6-Mes2C6H3). Compound 5 is structurally characterized, and a P=P bond length of 2.008(2) A is ascertained.     

Synthesis of benzoquinone derivatives containing benzotriazole fragments

2,3,5,6-Tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone was synthesized in 85% yield by reaction of 2,3,5,6-tetrachloro-1,4-benzoquinone with 1H-benzotriazole in pyridine at room temperature. Treatment of 2,3,5,6-tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone with piperidine, ω-amino acids, and aromatic amines gave the corresponding 2,5-diamino-3,6-bis(1H-benzotriazol-1-yl)-1,4-benzoquinones.     

A New Protocol to Generate Catalytically Active Species of Group 4–6 Metals by Organosilicon-Based Salt-Free Reductants

Herein, we provide a new protocol to reduce various transition-metal complexes by using organosilicon compounds in a salt-free fashion with the great advantage of generating pure low-valent metal species and metallic(0) nanoparticles, in sharp contrast to reductant-derived salt contaminants obtained by reduction with metal reductants. The organosilicon derivatives 1,4-bis(trimethylsilyl)-2,5-cyclohexadiene ( 1 a ), 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene ( 1 b ), 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 a ), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 b ), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 c ), and 1,1′-bis(trimethylsilyl)-1H,1′H-4,4′-bipyridinylidene ( 3 ) all served as versatile reductants for early transition-metal complexes and produced only easy-to-remove organic compounds, such as trimethylsilylated compounds and the corresponding aromatics, for example, benzene, toluene, pyrazine, and 4,4′-bipyridyl, as the byproducts. The high solubility of the reductants in organic solvents enabled us to monitor the catalytic reactions directly and to detect any catalytically active species so that we could elucidate the reaction mechanism.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Photochemical Experiments with 2,3-Bis(Tert-Butylsulfonyl)Bicyclo[2.2.2]Octa-2,5-Diene and Related Systems

The irradiation of 2,3-bis(tert-butylsulfonyl)norbornadiene (5) and 2-(tert-butylsulfonyl)norbornadiene (6) yielded the expected quadricyclane derivatives as stable molecules. The irradiation of 2,3-bis(tert-butylsulfonyl)bicyclo[2.2.2]octa-2,5-diene(7) 2,3-bis(tert-butylsulfonyl)-exo-7,8-epoxybicyclo[2.2.2]-octa-2,5-diene (8) and 8,9-bis(tert-butylsulfonyl)-4-anti-phenyl-3,5-dioxa-exo-tricyclo[5.2.2.0^2,6] undeca-8,10-diene 9a and its syn-isomer 9b yielded the corresponding tetracyclic and pentacyclic systems, respectively. The photoproducts of 8 and 9 reverted to the starting products slowly at room temperature. The half-life of the photoproduct of 7 was determined to be 34 min at 50 °C. Compound 9a reacted with n-BuLi to yield the unexpected desulfonylation product 27a.     

Rh(II) and Rh(I) two-legged piano-stool complexes: structure,reactivity, and electronic properties

The ligand 1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene, 3, was used to synthesize a mononuclear Rh(II) complex [(eta(1):eta(6):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh][PF(6)](2), 6+, in a two-legged piano-stool geometry. The structural and electronic properties of this novel complex including a single-crystal EPR analysis are reported. The complex can be cleanly interconverted with its Rh(I) form, allowing for a comparison of the structural properties and reactivity of both oxidation states. The Rh(I) form 6 reacts with CO, tert-butyl isocyanide, and acetonitrile to form a series of 15-membered mononuclear cyclophanes [(eta(1):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CO)(3)][PF(6)] (8), [(eta(1):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CNC(CH(3))(3))(2)][PF(6)] (10), and [(eta(1):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CO)(CH(3)CN)][PF(6)] (11). The Rh(II) complex 6+ reacts with the same small molecules, but over shorter periods of time, to form the same Rh(I) products. In addition, a model two-legged piano-stool complex [(eta(1):eta(6):eta(1)-1,4-bis[3-(diphenylphosphino)propoxy]-2,3,5,6-tetramethylbenzene)Rh][B(C(6)F(5))(4)], 5, has been synthesized and characterized for comparison purposes. The solid-state structures of complexes 5, 6, 6+, and 11 are reported. Structure data for 5: triclinic; P(-)1; a = 10.1587(7) A; b = 11.5228(8) A; c = 17.2381(12) A; alpha = 96.4379(13) degrees; beta = 91.1870(12) degrees; gamma = 106.1470(13) degrees; Z = 2. 6: triclinic; P(-)1; a = 11.1934(5) A; b = 12.4807(6) A; c = 16.1771(7) A; alpha = 81.935(7) degrees; beta = 89.943(1) degrees; gamma = 78.292(1) degrees; Z = 2. 6+: monoclinic; P2(1)/n; a = 11.9371(18) A; b = 32.401(5) A; c = 12.782(2) A; beta = 102.890(3) degrees; Z = 4. 11: triclinic; P(-)1; a = 13.5476(7) A; b = 13.8306(7) A; c = 14.9948(8) A; alpha = 74.551(1) degrees; beta = 73.895(1) degrees; gamma = 66.046(1) degrees; Z = 2.     

Synthesis of π-conjugated poly(arylene)s by polycondensation of 1,4-bis(3-methylpyridin-2-yl)benzene and aryl dibromides through regiospecific C-H functionalization process

On the basis of the Ru-catalyzed regiospecific direct double arylation of benzene rings possessing 3-methylpyridin-2-yl substituents to produce 1-aryl-2-(3-methylpyridin-2-yl)benzene derivatives, the synthesis of poly(p-phenylene) derivatives having 2,5-bis(3-methylpyridin-2-yl) substituents is described. The reaction of 1,4-bis(3-methylpyridin-2-yl)benzene with bromobenzene (2 equiv) was carried out in the presence of [RuCl₂(η⁶-C₆H₆)]₂ (5 mol %) in 1-methyl-2-pyrrolidone at 120°C for 24 h to produce 1,4-bis(3-methylpyridin-2-yl)-2,5-diphenylbenzene in 99% yield as a sole product. Neither 2,6-diphenylated nor further phenylated products was produced under the examined conditions. This regiospecific double arylation process was then applied to the synthesis of π-conjugated polymers by use of aryl dibromides such as 1,4-dibromobenzene, 2,7-dibromo-9,9-dihexylfluorene, and 2,5-dibromothiophene. For example, a polymer was obtained in 73% yield by using 1,4-dibromobenzene, whose M_n and M_w/M_n were estimated to be 3300 and 1.51, respectively. The bathochromic shift of the ultraviolet (UV)–visible absorption spectrum with respect to that of the model compound, 1,4-bis(3-methylpyridin-2-yl)-2,5-diphenylbenzene, indicated the extension of the π-conjugation. The blue fluorescence was also observed for the polymer upon the UV irradiation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2771–2777     

Synthesis of pyrazine acetals by the biased reaction of symmetric 2,5-bis(chloromethyl) or 2,3,5,6-tetrakis(chloromethyl) substituents on pyrazine ring with sodium alkoxides

2,5-Bis(chloromethyl)pyrazine reacted with sodium alkoxide to give unexpected 2-dialkoxymethyl-5-methylpyrazine along with normal substitution product, 2,5-bis(alkoxymethyl)pyrazine. The reaction of 2,3,5,6-tetrakis(chloromethyl)pyrazine with sodium alkoxide afforded similar results to yield 2,6-bis(dialkoxymethyl)-3,5-dimethylpyrazine along with other alkoxymethylpyrazines. The ratio of products depended on the solvent and alkoxide used. A general discussion of the mechanism of such a pyrazine acetal synthesis in the basic conditions is given.     

Enantioselective photocyclization of amides to beta-lactam derivatives in inclusion crystals with an optically active host

Irradiation of inclusion crystals of 2-(N-acyl-N-alkylamino)cyclohex-2-enones and N,N-dimethylphenylglyoxylamide with chiral host molecules gave the optically active N-alkyl-1-azaspiro[3.5]-nonane-2,5-diones and 3-hydroxy-1-methyl-3-phenylazetidin-2-one, respectively. The crystal structure of the 1:1 inclusion complex of N,N-dimethylphenylglyoxylamide with (-)-trans-1,4-bis[3-(o-chlorophenyl)-3-hydroxy-3-phenylprop-1-ynyl]-2,3,5,6- tetrachloro-2,5-cyclohexadiene-1,4-diol was analyzed by X-ray diffraction.     

A Simple and Convenient Method for Syntheses of Phenolic Amino Aldehyde Ligands,enalH2 and tnalH2

New efficient methods for synthesis of enalH₂ or 1,6-bis(2-pyridyl)-2,5-bis(2-hydroxy-3-formyl-5-methylbenzyl)-2,5-diazahexane 1a and of tnalH₂ or 1,7-bis(2-pyridyl) -2,6-bis(2-hydroxy-3-formyl-5-methylbenzyl)-2,6-diazaheptane, 1b are described     

Photoinduced self-substitution of haloquinones

A series of novel oligo(halobenzoquinoid) compounds have been obtained from the photoinduced self-substitution of 2,5-dibromo-1,4-benzoquinone (1a), 2,6-dibromo-1,4-benzoquinone (1b), 2-chloro-1,4-benzoquinone (1c), 2-bromo-5-chloro-1,4-benzoquinone (1d), 2,3,5,6-tetrachloro-1,4-benzoquinone (1e) and 1,4-benzoquinone (1f) in the presence of N,N-dimethyl-t-butylamine (2) in acetonitrile. Dimers, trimers and/or pentamers of these haloquinones were found to be the major products.     

Synthesis of 1,4-annulated cyclooctatetraenophanes based on a novel cubane building block approach

A general synthetic approach to strained 1,4-annulated cyclooctatetraene-based cyclophanes is described. A key feature in this approach is exploitation of the cubane core as a masked cyclooctatetraene synthon. Thus, 1,4-disubstituted cubanes 3 and 4 used as precursors to cyclooctatetraenophanes have been prepared in four steps from the readily available 1,4-cubanedicarboxaldehyde (5). The synthesis of 3 was effected by palladium/copper-mediated coupling of 1,4-bis[(Z,Z)-2-iodovinyl]cubane (6) and 1,4-bis[(Z,Z)-but-1-en-3-ynyl]cubane (8). For the synthesis of 4, on the other hand, modified Eglington-Glaser coupling was applied for the macrocyclization step. The general characteristic of Rh(I) to induce [2 + 2] cycloreversion of the cubane core to syn-tricyclo[4.2.0.0(2,5)]octa-3,7-diene followed by thermal rearrangement to cyclooctatetraene was applied as a key structural transformation toward targeted cyclooctatetraenophanes 1 and 2.     

Synthesis and characterization of novel fluorophosphazene-derived cobaltacyclopentadienyl metallacycles: reagents for assembly of aryl-bridged fluorophosphazenes

Reaction of (beta-phenylethynyl)pentafluorocyclotriphosphazene, F5P3N3C identical with CPh, with in situ generated eta5-(MeOC(O)C5H4)Co(PPh3)2 resulted in the formation of two isomers of cobaltacyclopentadienylmetallacycles, (eta(5)-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,5-bis(pentafluorocyclotriphosphazenyl)-3,4-diphenyl cobaltacyclopentadiene (1) and (eta5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,4-bis(pentafluorocyclotriphosphazenyl)-3,5-diphenyl cobaltacyclopentadiene (2), along with the sandwich compound [eta5-carbomethoxycyclopentadienyl]-[eta4-1,3-bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene]cobalt (3). Formation of cobaltacyclopentadienylmetallacycles or cyclobutadienylmetallocene having two fluorophosphazene units on vicinal carbon atoms of the rings was not observed in this reaction. Reaction of 1 with diphenylacetylene resulted in the formation of a novel aryl-bridged fluorophosphazene, 1,4-bis(pentafluorocyclotriphosphazenyl)-2,3,5,6-tetraphenyl benzene (4), and the conversion of cobaltametallacycle to the sandwich compound, [eta5-(MeOC(O)C5H4]Co(eta4-C4Ph4) (5). Reaction of 1 with phenylacetylene resulted in the formation of aryl-bridged fluorophosphazene, 1,4-bis(pentafluorophosphazenyl)-2,3,5,-triphenyl benzene (6). New compounds 1-4 were structurally characterized. In compound 1, the two fluorophosphazene units were oriented in gauche form with respect to each other. However, in compounds 2 and 3, they were eclipsed to each other, and in compound 4, they were oriented anti to each other.     

The Preparation of Dicompartmental Multifunctional Group Ligands

A convenient method for the preparation of the phenol-based ligands 1,6-bis(2-thiophenyl)-2,5-bis(2-hydroxy-3-hydroxymethyl-5-methylbenzyl)-2,5-diazahexane and 1,6-bis(5-methyl-2-thiophenyl)-2,5-bis(2-hydroxy-3-hydroxymethyl-5-methyl-benzyl)-2,5-diazahexane possessing two dissimilar compartments having multifunctional groups is reported. To synthesize these ligands, an equivalent of 1,6-bis(2-thiophene)-2,5-diazahexane or 1,6-bis(5-methyl-2-thiophene)-2,5-diazahexane and two equivalents of 2,2-dimethyl-6-methyl-8-(chloromethyl)benzo-1,3-dioxin were reacted in the presence of Na₂CO₃ in 1,4-dioxane, followed by acid hydrolysis of an acetonide-protecting group. Characterization data for the new compounds is reported.     

Z-Selective and Syndioselective Ring-Opening Metathesis Polymerization (ROMP) Initiated by MonoAryloxidePyrrolide (MAP) Catalysts

We report the Z-selective and syndioselective polymerization of 2,3-bis(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene (NBDF6) and 3-methyl-3-phenylcyclopropene (MPCP) by monoaryloxide monopyrrolide imido alkylidene (MAP) catalysts of Mo. The mechanism of polymerization with syn-Mo(NAd)(CHCMe(2)Ph)(Pyr)(OHIPT) (1; Ad = 1-adamantyl, OHIPT = O-2,6-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)) as the initiator is proposed to consist of addition of monomer to the syn initiator to yield a syn first insertion product and propagation via syn insertion products. In contrast, the mechanism of polymerization with syn-Mo(NAr)(CHCMe(2)Ph)(Pyr)(OTPP) (4; Ar = 2,6-i-Pr(2)C(6)H(3), OTPP = 2,3,5,6-Ph(4)C(6)H) as the initiator at -78 °C consists of addition of monomer to the syn initiator to yield an anti first insertion product and propagation via anti insertion products. Polymerizations of NBDF6 and MPCP at room temperature initiated by 4 led to polymers without a regular structure. We propose that the syndiotacticity of cis polymers is the consequence of the required inversion at the metal center with each insertion of monomer, i.e., stereogenic metal control of the polymer structure. We also propose that the two mechanisms for forming cis,syndiotactic polymers arise as a consequence of the relative steric bulk of the imido and phenoxide ligands.     

The electrochemical properties of a series of phenylene-thienyl polymers in tetramethylene sulfone based electrolytes

Electronically conducting polymers based on polythiophene and polyparaphenylene exhibit generally, both n-doping and p-doping. In most cases, however, the n-doping process is associated usually with poor reversibility and stability. One approach to improve the doping behavior is to modify the structure of the monomer repeat unit at the molecular level. In this paper we report on the electrochemical properties of the polymer series: pTHP, pTFP (1,4-bis(2-thienyl)-2-fluorobenzene), pTF₂P (1,4-bis(2-thienyl)-2,5-difluorobenzene), and pTF₄P (1,4-bis(2-thienyl)-2,3,5,6-tetrafluorobenzene) in tetramethylene sulfone (sulfolane) TBABF₄ based electrolytes.     

2,3,5,6-Tetra(vinylthio)difluorobenzene in Reactions with Difunctional Nucleophiles

Reaction of 2,3,5,6-tetra(vinylthio)difluorobenzene with ethylene glycol affords 1,4-bis[2,3,5,6-tetra(vinylthio)-4-fluorophenoxy-1-ethyloxy-]-2,3,5,6-tetra(vinylthio)benzene, with diethylene glycol arises 2,3,5,6-tetra(vinylthio)-4-(4-hydroxyethoxyethyloxy)-1-fluorobenzene, with 1,5-diaminopentane forms 1,5-bis[2,3,5,6-tetra(vinylthio)-4-fluoroanilino]pentane; in reactions with 2-aminoethanethiol and 2-mercaptoethanol occurs substitution of two fluorine atoms by RS groups.