87-85-4Relevant articles and documents
Valence Isomerization of Hexamethyl(Dewar benzene) Radical Cation. Pulse Radiolytic Investigation
Gebicki, Jerzy,Marcinek, Andrzej,Mayer, Jozef
, p. 3098 - 3099 (1989)
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Koptyug et al.
, p. 673 (1968)
Koser,Cyr
, p. 4452,4453 (1973)
Accurate oxidation potentials of 40 benzene and biphenyl derivatives with heteroatom substituents
Luo, Pu,Feinberg, Elizabeth C.,Guirado, Gonzalo,Farid, Samir,Dinnocenzo, Joseph P.
, p. 9297 - 9304 (2014)
The redox equilibrium method was used to determine accurate oxidation potentials in acetonitrile for 40 heteroatom-substituted compounds. These include methoxy-substituted benzenes and biphenyls, aromatic amines, and substituted acetanilides. The redox equilibrium method allowed oxidation potentials to be determined with high precision (≥ ±6 mV). Whereas most of the relative oxidation potentials follow well-established chemical trends, interestingly, the oxidation potentials of substituted N-methylacetanilides were found to be higher than those of the corresponding acetanilides. Density functional theory calculations provided insight into the origin of these surprising results in terms of the preferred conformations of the amides versus their cation radicals.
Photo-activated Valence Isomerization of Hexamethyl(Dewar benzene) (HMDB) assisted by Arene - Iron(II) Complexes: Luminescence Properties of 5-C5R5)Fe+(η6-arene)>* Adducts
Roman, Enrique,Hernandez, Sergio,Barrera, Mauricio
, p. 1067 - 1068 (1984)
Hexamethyl(Dewar benzene) (HMDB) isomerizes to hexamethylbenzene (HMB) under visible light irradiation in the presence of stoicheiometric or catalytic amounts of the cationic complexes 5-C5R5)Fe(η6-arene)>+X-, (R = H, Me; X = BF4-, PF6-), (1a - e) and (2), in dichloromethane solutions at 273 K; mixtures of HMDB and (1b - e) or (2) in dichloromethane exhibit a luminescence band at 530 - 540 nm probably due to formation of the corresponding exciplex.
Hogeveen,Volger
, p. 1133 (1967)
Tsutsui,Zeiss
, p. 825,826 (1961)
Zeiss, H.,Herwig, W.
, p. 2913 - 2913 (1958)
Mechanistic studies of olefin and alkyne trimerization with chromium catalysts: Deuterium labeling and studies of regiochemistry using a model chromacyclopentane complex
Agapie, Theodor,Labinger, Jay A.,Bercaw, John E.
, p. 14281 - 14295 (2007)
A system for catalytic trimerization of ethylene utilizing chromium(III) precursors supported by diphosphine ligand PNPO4 = (o-MeO-C 6H4)2PN(Me)P(o-MeO-C6H 4)2 has been investigated. The mechanism of the olefin trimerization reaction was examined using deuterium labeling and studies of reactions with α-olefins and internal olefins. A well-defined chromium precursor utilized in this studies is Cr(PNPO4)-(o,o′- biphenyldiyl)Br. A cationic species, obtained by halide abstraction with NaB[C6H3(CF3)2]4, is required for catalytic turnover to generate 1-hexene from ethylene. The initiation byproduct is vinylbiphenyl; this is formed even without activation by halide abstraction. Trimerization of 2-butyne is accomplished by the same cationic system but not by the neutral species. Catalytic trimerization, with various (PNPO4)Cr precursors, of a 1:1 mixture of C2D 4 and C2H4 gives isotopologs of 1-hexene without H/D scrambling (C6D12, C6D 8H4, C6D4H6, and C 6H12 in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. Using a SHOP catalyst to perform the oligomerization of a 1:1 mixture of C2D4 and C2H4 leads to the generation of a broader distribution of 1-hexene isotopologs, consistent with a Cossee-type mechanism for 1-hexene formation. The ethylene trimerization reaction was further studied by the reaction of trans-, cis-, and gem-ethylene-d2 upon activation of Cr(PNPO4)(o,o′-biphenyldiyl)Br with NaB-[C6H 3(CF3)2]4. The trimerization of cis- and trans-ethylene-d2 generates 1-hexene isotopomers having terminal CDH groups, with an isotope effect of 3.1(1) and 4.1(1), respectively. These results are consistent with reductive elimination of 1-hexene from a putative Cr(H)[(CH2)4CH=CH2] occurring much faster than a hydride 2,1-insertion or with concerted 1-hexene formation from a chromacycloheptane via a 3,7-H shift. The trimerization of gem-ethylene-d 2 has an isotope effect of 1.3(1), consistent with irreversible formation of a chromacycloheptane intermediate on route to 1-hexene formation. Reactions of olefins with a model of a chromacyclopentane were investigated starting from Cr(PNPO4)(o,o′-biphenyldiyl)Br. α-Olefins react with cationic biphenyldiyl chromium species to generate products from 1,2-insertion. A study of the reaction of 2-butenes indicated that β-H elimination occurs preferentially from the ring CH rather than exo-CH bond in the metallacycloheptane intermediates. A study of cotrimerization of ethylene with propylene correlates with these findings of regioselectivity. Competition experiments with mixtures of two olefins indicate that the relative insertion rates generally decrease with increasing size of the olefins.
SYNTHESES OF METAL CARBONYLS. XVII. FORMATION OF A HETERONUCLEAR ORGANOMETALLIC CLUSTER CONTAINING RUTHENIUM AND RHODIUM; CRYSTAL AND MOLECULAR STRUCTURE OF (3(μ3-CO)2)
Hughes, Russell P.,Rheingold, Arnold L.,Herrmann, Wolfgang A.,Hubbard, John L.
, p. 361 - 368 (1985)
Ru(C6Me6)(C2H4)2 reacts with Rh(C5Me5)(CO)2 to give the known dinuclear complex 2 and the new heteronuclear cluster complex (3(μ3-CO)2) which has been fully characterized by a single crystal X-ray diffraction study.
Wavelength and Solvent Effects on Ionic Photodissociation of Charge-Transfer Complexes. The Hexamethyl(Dewar benzene) System
Jones II, Guilford,Becker, William G.
, p. 4630 - 4632 (1981)
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Photosensitized Isomerization of Hexamethyl (Dewar benzene) by Interactions with 1,4-Dicyanonaphthalene-Arene Exciplexes. An Adiabatic Triplex Pathway
Masaki, Yasuhiro,Uehara, Yoshikazu,Yanagida, Shozo,Pac, Chyongjin
, p. 1339 - 1342 (1990)
The isomerization of Hexamethyl (Dewar benzene) to hexamethylbenzene is photosensitized by 1,4-dicyanonaphthalene-arene exciplexes.Spectroscopic and quantum-yield studies suggest that the isomerization proceeds mostly through an adiabatic pathway from hypothetical termolecular excited complexes (triplexes).
Case Study of N-iPr versus N-Mes Substituted NHC Ligands in Nickel Chemistry: The Coordination and Cyclotrimerization of Alkynes at [Ni(NHC)2]
Tendera, Lukas,Helm, Moritz,Krahfuss, Mirjam J.,Kuntze-Fechner, Maximilian W.,Radius, Udo
supporting information, p. 17849 - 17861 (2021/11/17)
A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)2] (NHC=iPr2ImMe 1Me, Mes2Im 2) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni2(iPr2ImMe)4(μ-(η2 : η2)-COD)] B/ [Ni(iPr2ImMe)2(η4-COD)] B’ or [Ni(Mes2Im)2] 2, respectively, with alkynes afforded complexes [Ni(NHC)2(η2-alkyne)] (NHC=iPr2ImMe: alkyne=MeC≡CMe 3, H7C3C≡CC3H7 4, PhC≡CPh 5, MeOOCC≡CCOOMe 6, Me3SiC≡CSiMe3 7, PhC≡CMe 8, HC≡CC3H7 9, HC≡CPh 10, HC≡C(p-Tol) 11, HC≡C(4-tBu-C6H4) 12, HC≡CCOOMe 13; NHC=Mes2Im: alkyne=MeC≡CMe 14, MeOOCC≡CCOOMe 15, PhC≡CMe 16, HC≡C(4-tBu-C6H4) 17, HC≡CCOOMe 18). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p-Tol) and HC≡C(4-tBu-C6H4), 11 and 12, which were formed by addition of a C?H bond of one of the NHC N-iPr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2-butyne, 4-octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1-pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1Me is not a good catalyst. The reaction of 2 with 2-butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)2]. DFT calculations reveal that the differences between 1Me and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2, and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N-alkyl substituted NHC, to enhanced Ni-alkyne backbonding due to a smaller CNHC?Ni?CNHC bite angle, and to less steric repulsion of the smaller NHC iPr2ImMe.
Photocatalytic Oxygenation Reactions with a Cobalt Porphyrin Complex Using Water as an Oxygen Source and Dioxygen as an Oxidant
Hong, Young Hyun,Han, Ji Won,Jung, Jieun,Nakagawa, Tatsuo,Lee, Yong-Min,Nam, Wonwoo,Fukuzumi, Shunichi
supporting information, p. 9155 - 9159 (2019/06/21)
Photocatalytic oxygenation of hexamethylbenzene occurs under visible-light irradiation of an O2-saturated acetonitrile solution containing a cobalt porphyrin complex CoII(TPP) (TPP2- = tetraphenylporphyrin dianion), water, and triflic acid (HOTf) via a one-photon-two-electron process, affording pentamethylbenzyl alcohol and hydrogen peroxide as products with a turnover number of >6000; in this reaction, H2O and O2 were used as an oxygen source and a two-electron oxidant, respectively. The photocatalytic mechanism was clarified by means of electron paramagnetic resonance, time-resolved fluorescence, and transient absorption measurements as well as 18O-labeling experiments with H218O and 18O2. To the best of our knowledge, we report the first example of efficient photocatalytic oxygenation of an organic substrate by a metal complex using H2O as an oxygen source and O2 as a two-electron oxidant.
Coupling of Methanol and Carbon Monoxide over H-ZSM-5 to Form Aromatics
Chen, Zhiyang,Ni, Youming,Zhi, Yuchun,Wen, Fuli,Zhou, Ziqiao,Wei, Yingxu,Zhu, Wenliang,Liu, Zhongmin
supporting information, p. 12549 - 12553 (2018/09/11)
The conversion of methanol into aromatics over unmodified H-ZSM-5 zeolite is generally not high because the hydrogen transfer reaction results in alkane formation. Now circa 80 % aromatics selectivity for the coupling reaction of methanol and carbon monoxide over H-ZSM-5 is reported. Carbonyl compounds and methyl-2-cyclopenten-1-ones (MCPOs), which were detected in the products and catalysts, respectively, are considered as intermediates. The latter species can be synthesized from the former species and olefins. 13C isotope tracing and 13C liquid-state NMR results confirmed that the carbon atoms of CO molecules were incorporated into MCPOs and aromatic rings. A new aromatization mechanism that involves the formation of the above intermediates and co-occurs with a dramatically decreased hydrogen transfer reaction is proposed. A portion of the carbons in CO molecules are incorporated into aromatic, which is of great significance for industrial applications.
