- Evaluation of the Transferability of the “Flexible Steric Bulk” Concept from N-Heterocyclic Carbenes to Planar-Chiral Phosphinoferrocenes and their Electronic Modification
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The concept of “flexible steric bulk” is discussed at 2-phenylvinyl-1-phosphinoferrocenes. The introduction of freely rotatable 1'-silyl groups increases the catalytic productivity within the synthesis of tri-ortho-substituted biaryls by Suzuki–Miyaura C,C cross-coupling reactions, giving higher yields with 1/4 of catalyst concentration than for the non-silylated derivatives. Electronic modification of the P and the vinyl donor functionalities was investigated by introducing substituents in the para positions of both groups. Therein, electron-withdrawing phosphines increased the yield from 78 to 91 percent for a given biaryl, by changing from a diphenylphosphino to the P(p-CN-C6H4)2 unit. Opposite results, obtained from electron-donating and sterically demanding phosphines, were in accordance with the 1J(31P,77Se) values. However, the electron density of the ferrocenyl backbone, expressed by the redox potential of the first ferrocenyl-related redox process, cannot be correlated with the donor-properties at the P atom. Changing from a PPh2-substituted ferrocene to a (RA)-1,1'-binaphthyl-containing phosphonite, a complex interaction between the axial- and the planar-chiral motifs occurs, resulting a change of the absolute biaryl configuration.
- Korb, Marcus,Schaarschmidt, Dieter,Grumbt, Martin,K?nig, Matthias,Lang, Heinrich
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supporting information
p. 2968 - 2982
(2020/07/02)
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- Chromium- and Cobalt-Catalyzed, Regiocontrolled Hydrogenation of Polycyclic Aromatic Hydrocarbons: A Combined Experimental and Theoretical Study
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Polycyclic aromatic hydrocarbons are difficult substrates for hydrogenation because of the thermodynamic stability caused by aromaticity. We report here the first chromium- and cobalt-catalyzed, regiocontrolled hydrogenation of polycyclic aromatic hydrocarbons at ambient temperature. These reactions were promoted by low-cost chromium or cobalt salts combined with diimino/carbene ligand and methylmagnesium bromide and are characterized by high regioselectivity and expanded substrate scope that includes tetracene, tetraphene, pentacene, and perylene, which have rarely been reduced. The approach provides a cost-effective catalytic protocol for hydrogenation, is scalable, and can be utilized in the synthesis of tetrabromo- and carboxyl-substituted motifs through functionalization of the hydrogenation product. The systematic theoretical mechanistic modelings suggest that low-valent Cr and Co monohydride species, most likely from zerovalent transition metals, are capable of mediating these hydrogenations of fused PAHs.
- Han, Bo,Ma, Pengchen,Cong, Xuefeng,Chen, Hui,Zeng, Xiaoming
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supporting information
p. 9018 - 9026
(2019/06/13)
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- SYNTHESIS OF PHOSPHINE LIGANDS BEARING TUNABLE LINKAGE: METHODS OF THEIR USE IN CATALYSIS
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A series of novel linked indolyl phosphine ligands for transition metals, the synthesis thereof and their use in catalytic coupling reactions are provided. The ligands provide improvements of trasition-metal-catalyzed reactions, including the range of substrates scope, reaction conditions and efficieny.
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Page/Page column 16; 17
(2017/12/02)
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- (Planar-Chiral) Ferrocenylmethanols: From Anionic Homo Phospho-Fries Rearrangements to α-Ferrocenyl Carbenium Ions
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The reaction of FcCH2OH with chlorophosphates gave ferrocenyl phosphates FcCH2OP(O)(OR)2 [Fc = Fe(η5-C5H5)(η4-C5H4)], which readily separate into phosphate anions and ferrocenyl carbo-cations. The latter species undergoes consecutive reactions, for example, electrophilic aromatic substitutions. When nitriles, instead of alcohols, are treated with FcLi or tBuLi and chlorophosphates, chiral-pool based ferrocenylimino phosphoramidates Fc-CR=N-P(O)(OR*)2 are formed, which are promising candidates for anionic homo phospho-Fries rearrangements. Moreover, the sterically demanding chiral chlorophosphate with R* enabled oxidative couplings of the imines to form a diferrocenylazine. Similarly, the reaction of Fc–Li with 9-anthrylnitrile produced a 10-ferrocenyl-substituted product, contrary to a reaction at the C≡N functionality. A planar-chiral ortho-P(S)Ph2-functionalized ferrocenylmethanol also gave carbo-cations under acidic conditions. These species can be sulfurized in a unique way giving thio ethers, whereby the in situ formed 1,2-P(S)Ph2,CH2+ ferrocene cation acts as the sulfur and electron source. However, lowering the substrate concentration prevents sulfur migration, resulting in electrophilic substitution reactions with aromatic solvents. Planar-chiral ferrocenylmethyl thio or anisyl derivatives were applied as ligands in Pd-catalyzed Suzuki–Miyaura C,C cross-couplings for the atroposelective synthesis of hindered biaryls with up to 26 % ee at low catalyst loadings (1 mol-% Pd).
- Korb, Marcus,Mahrholdt, Julia,Lang, Heinrich
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supporting information
p. 4028 - 4048
(2017/09/20)
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- Resorcinarene-Based o-Biarylphosphines in Palladium-Catalysed Suzuki–Miyaura Cross-Coupling Reactions of Bulky Substrates
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Two o-biarylphosphines, in which the arene ring remote from the phosphorus atom is part of a resorcin[4]arene cavitand, have been synthesised, characterised by X-ray diffraction and assessed in the cross-coupling reactions of bulky aryl chlorides with sterically hindered arylboronic acids. Only atropisomers with externally located P atoms were obtained. The resorcinarene ligand with the o-PCy2C6H4substituent was found to be more efficient than the Buchwald analogue SPhos in catalysing coupling reactions, reacting around 1.4 times faster. Its superior performance has been attributed to the permanent exo positioning of the metal centre, which engenders steric interactions with two pentyl substituents and therefore facilitates the reductive elimination step.
- Elaieb, Fethi,Sémeril, David,Matt, Dominique
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supporting information
p. 685 - 693
(2017/02/05)
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- An efficient indenyl-derived phosphine ligand for the Suzuki-Miyaura coupling of sterically hindered aryl halides
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An air-stable aryl substituted indenyl phosphine used in combination with Pd(OAc)2 provides a highly efficient catalyst for the Suzuki-Miyaura cross-coupling reaction of sterically hindered aryl halides with aryl boronic acids.
- Liu, Yan,Peng, Hui,Yuan, Jia,Yan, Meng-Qi,Luo, Xue,Wu, Qing-Guo,Liu, Sheng-Hua,Chen, Jian,Yu, Guang-Ao
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supporting information
p. 4664 - 4668
(2016/06/09)
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- The Influence of Imidazolylidene Ligands with Bulky Resorcinarenyl Substituents on Catalysts for Suzuki-Miyaura Coupling
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PEPPSI-type imidazolylidene palladium complexes having their carbenic ring N-substituted with an aryl ring and a cavity-shaped unit [25,26,27,28-tetrapropyloxycalix[4]aren-5-yl or 6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]aren-5-yl (TPR)] have been prepared and assessed in Suzuki-Miyaura cross-couplings. Remarkable efficiency in the coupling of aryl chlorides with sterically hindered arylboronic acids was observed for the carbene ligand having its N atoms (N1, N2) substituted by a mesityl and a TPR group, respectively. This good performance possibly arises from strong steric interactions between the pentyl-substituted cavitand unit and the catalytic centre, which favours reductive elimination. Two of the imidazolium salts used for complex synthesis were characterised by X-ray diffraction analysis.
- Kalo?lu, Murat,Sémeril, David,Brenner, Eric,Matt, Dominique,?zdemir, Ismail,Toupet, Lo?c
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p. 1115 - 1120
(2016/03/15)
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- Arylcalixarenyl Phosphines in Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions
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Two electron-rich arylcalixarenylphosphines have been synthesized in three steps from the appropriate 5-bromocalix[4]arene precursor 1. The combination of 5-(2-diisopropylphosphinophenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (5) and 5-(2-dicyclohexylphosphinophenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (6), respectively, with [Pd2(dba)3] (dba = dibenzylideneacetone) generated effective catalysts for the cross-coupling reactions of hindered aryl chlorides and arylboronic acids. Dicyclohexylphosphino-substituted ligand 6 had a higher activity that that of 5, and the structures of ligand 5 and [AuCl·5] were determined by single-crystal X-ray diffraction studies. The solid-state structure of [AuCl·5] revealed that the gold atom lies above the outer face of the calixarene unit, with distances of 3.08 and 3.28 ? between the gold atom and the two closest aromatic carbon atoms of the calixarene moiety.
- Elaieb, Fethi,Hedhli, Ahmed,Sémeril, David,Matt, Dominique
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supporting information
p. 1867 - 1873
(2016/05/09)
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- A Planar-Chiral Phosphino(alkenyl)ferrocene for Suzuki-Miyaura C-C Coupling Reactions
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Planar-chiral phosphinoferrocene [Fe(η5-C5H3-1-PPh2-2-(E)-CH=CHPh)(η5-C5H5)] (4) was applied in the presence of palladium in Suzuki-Miyaura couplings for the synthesis of sterically congested biaryls. The catalytic activity arises from homogeneous palladium phosphine complexes, of which the potential pre-catalyst [Pd(4)2Cl2] was characterized structurally. The catalytic system is excellently suited for the synthesis of tri-ortho-substituted biaryls under mild conditions (0.1 mol-%, 50-100 C), whereas its application towards the synthesis of tetra-ortho-substituted biaryls is quite limited. Comparing the performance of the reaction with 4 as catalyst and a range of substrates with differing ortho substituents suggests that transmetalation is rate determining. Complex (Sp)-4 was used in atropselective couplings, wherein enantioenrichments of up to 36 % were achieved. The stereoselectivity depends to some extent on the steric properties of the boronic acids; however, slight changes at the aryl halides influence the enantioselectivity.
- Schaarschmidt, Dieter,Grumbt, Martin,Hildebrandt, Alexander,Lang, Heinrich
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supporting information
p. 6676 - 6685
(2016/02/19)
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- Suzuki-Miyaura cross-coupling of bulky anthracenyl carboxylates by using pincer nickel N-heterocyclic carbene complexes: An efficient protocol to access fluorescent anthracene derivatives
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A series of fluorescent (hetero)-aryl substituted anthracene derivatives were readily accessible from the corresponding bulky anthracen-9-yl carboxylates via Suzuki-Miyaura cross-coupling reactions by using pincer nickel N-heterocyclic carbene complex 1 even at the catalyst loading as low as 0.1 mol% in the presence of catalytic amounts of PCy3.
- Xu, Mizhi,Li, Xingbao,Sun, Zheming,Tu, Tao
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supporting information
p. 11539 - 11541
(2013/12/04)
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- METHOD FOR PRODUCING UNSATURATED ORGANIC COMPOUND
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A method for producing an unsaturated organic compound represented by the formula (3): [in-line-formulae](Y1)m-1—R1—R2—(Y2)n-1??(3)[/in-line-formulae] wherein Y1 represents R2 or X1, and Y2 represents R1 or B(X2)2, which comprises reacting a compound represented by the formula (1): [in-line-formulae]R1(X1)m??(1)[/in-line-formulae] wherein R1 represents an aromatic group or the like, X1 represents a leaving group and m represents 1 or 2, with a compound represented by the formula (2): [in-line-formulae]R2{B(X2)2}n??(2)[/in-line-formulae] wherein R2 represents an aromatic group or the like, X2 represents a hydroxyl group or the like, and n represents 1 or 2, in the presence of(a) a nickel compound selected from a nickel carboxylate, nickel nitrate and a nickel halide,(b) a phosphine compound such as 1,4-bis(dicyclohexylphosphino) butane,(c) an amine selected from a primary amine and a diamine such as N,N,N′,N′-tetramethyl-1,2-ethanediamine, and(d) an inorganic base.
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Page/Page column 10; 12
(2011/04/14)
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- Highly efficient carbazolyl-derived phosphine ligands: Application to sterically hindered biaryl couplings
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A new family of phosphine ligands bearing a bulky carbazolyl scaffold is described. With the combination of ligand 2a and Pd(OAc)2, difficult tri-ortho-substituted biaryl couplings are accomplished smoothly. In particular, the catalyst loading as low as 0.02 mol% of Pd for non-activated 2,6-disubstituted aryl chloride coupling can be achieved.
- Chun To, Sheung,Yee Kwong, Fuk
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supporting information; experimental part
p. 5079 - 5081
(2011/06/10)
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- LUMINESCENT COMPOUNDS AND ELECTROLUMINESCENT DEVICE USING THE SAME
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The present invention relates to organic electroluminescent compounds and organic electroluminescent devices employing the same. More specifically, the invention relates to organic electroluminescent compounds containing an anthracenyl group or an aryl group having an anthracenyl substituent m the aryl ring of fluorene or indenofluorene, as a blue electroluminescent material in an organic electroluminescent layer. The electroluminescent compounds according to the invention exhibit high luminous efficiency and excellent life property, so that an OLED device having very good operation lifetime can be prepared therefrom.
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- 9,10-diarylanthracenes as molecular switches: Syntheses, properties, isomerisations and their reactions with singlet oxygen
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A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at 300°C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step.
- Zehm, Daniel,Fudickar, Werner,Hans, Melanie,Schilde, Uwe,Kelling, Alexandra,Linker, Torsten
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experimental part
p. 11429 - 11441
(2009/12/03)
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- Palladium-phosphinous acid-catalyzed cross-coupling of aryl and acyl halides with aryl-, alkyl-, and vinylzinc reagents
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(Chemical Equation Presented) Several palladium-phosphinous acids have been prepared and employed in cross-coupling reactions of aryl or acyl halides with aliphatic and aromatic organozinc reagents. The POPd7-catalyzed reaction of aryl halides, including electron-rich aryl chlorides, and arylzinc reagents was found to afford biaryls exhibiting alkoxy, alkylthio, amino, ketone, cyano, nitro, ester, and heteroaryl groups in 75-93% yield. Excellent results were obtained with sterically hindered substrates which gave di- and tri-ortho-substituted biaryls in up to 92% yield. Aryl halides also undergo POPd7-catalyzed aryl-vinyl and aryl-alkyl bond formation under mild conditions. Styrenes and alkylarenes were prepared in 79-93% yield from aryl halides and vinyl or alkylzinc reagents. The replacement of aryl halides by acyl halides provides access to ketones which were produced in up to 98% yield when POPd was used as catalyst. This approach overcomes the limited substrate scope, reduced regiocontrol, and low functional group tolerance of traditional Friedel-Crafts acylation methods.
- Xu, Hanhui,Ekoue-Kovi, Kekeli,Wolf, Christian
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p. 7638 - 7650
(2008/12/22)
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- Efficient synthesis of sterically crowded biaryls by palladium-phosphinous acid-catalyzed cross-coupling of aryl halides and aryl grignards
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(Chemical Equation Presented) A series of sterically hindered biaryls have been obtained by palladium- and nickel-phosphinous acid-catalyzed Kumada-Corriu cross-coupling of ortho-substituted aryl halides and Grignard reagents. This method allows formation
- Wolf, Christian,Xu, Hanhui
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p. 162 - 167
(2008/09/17)
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- Reactivity of Polycyclic Aromatic Aryl Radicals
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Results of experimental and theoretical studies of the properties and reactions of polycyclic aromatic aryl radicals are reported.Reactions of phenyl, 1- and 2-naphthalenyl, and 9-anthracenyl radicals with toluene and naphthalene were examined in the gas phase at 400 and 450 deg C.Arylation rates for each radical were measured relative to hydrogen abstraction from toluene (kar/kabs).For reactions with toluene of both phenyl and 2-naphthalenyl radicals, this ratio was 0.20-0.25.For the 1-naphthalenyl and 9-anthracenyl radicals, these ratios were significantlylower (0.05 and 0.01, respectively).Relative rates for arylating the different available positions in toluene and naphthalene, however, were not nearly as different.Differences in arylation/abstraction rates of the different radicals are explained in terms of differing degrees of reversibility for the initial addition step.Results are consistent with literature dissociation rate constants measured by Ladaki and Szwarc for aryl bromides.MNDO calculations on a range of arene-aryl radical pairs suggest that these differences originate primarily from differences in radical stabilities.Calculations also suggest that, on the basis of bond strenghts, aryl radicals can be roughly divided into three groups, which depend on the nature of the two neighboring aromatic carbon atoms and are independent of the size of the aromatic cluster.
- Chen, R. H.,Kafafi, S. A.,Stein, S. E.
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p. 1418 - 1423
(2007/10/02)
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