- Resorcinarene-Based o-Biarylphosphines in Palladium-Catalysed Suzuki–Miyaura Cross-Coupling Reactions of Bulky Substrates
-
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
-
-
Read Online
- An efficient indenyl-derived phosphine ligand for the Suzuki-Miyaura coupling of sterically hindered aryl halides
-
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
-
-
Read Online
- The Influence of Imidazolylidene Ligands with Bulky Resorcinarenyl Substituents on Catalysts for Suzuki-Miyaura Coupling
-
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
-
-
Read Online
- Arylcalixarenyl Phosphines in Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions
-
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
-
-
Read Online
- Photoaddition of water and alcohols to the anthracene moiety of 9-(2′-hydroxyphenyl)anthracene via formal excited state intramolecular proton transfer
-
The title compound undergoes efficient photoaddition of a molecule of a hydroxylic solvent (H2O, MeOH, (Me)2CHOH) across the 9- and 10-positions of the anthracene moiety to give isolable triphenylmethanol or triphenylmethyl ether type products. The reaction is believed to proceed via a mechanism involving water-mediated formal excited state intramolecular proton transfer (ESIPT) from the phenolic OH to the 10-position of the anthracene ring, generating an o-quinone methide intermediate that is observable by nanosecond laser flash photolysis, and is trappable with nucleophiles. A "water-relay" mechanism for proton transfer seems plausible but cannot be proven directly with the data available. Irradiation in deuterated solvents led to incorporation of one deuterium atom at the methylene position in the photoaddition product, and partial deuterium exchange of the 10-position of recovered starting material, consistent with the proposed formal excited state proton transfer mechanism. The deuterium exchange and photoaddition reach maximum quantum efficiency at ~5 M water (in CH3CN or CH 3OH), with no reaction observed in the absence of a hydroxylic solvent, demonstrating the sensitivity of this type of ESIPT to solvent composition.
- Flegel, Mitchel,Lukeman, Matthew,Huck, Lawrence,Wan, Peter
-
-
Read Online
- Evaluation of the Transferability of the “Flexible Steric Bulk” Concept from N-Heterocyclic Carbenes to Planar-Chiral Phosphinoferrocenes and their Electronic Modification
-
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
-
supporting information
p. 2968 - 2982
(2020/07/02)
-
- Chromium- and Cobalt-Catalyzed, Regiocontrolled Hydrogenation of Polycyclic Aromatic Hydrocarbons: A Combined Experimental and Theoretical Study
-
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
-
supporting information
p. 9018 - 9026
(2019/06/13)
-
- TBuLi-Mediated One-Pot Direct Highly Selective Cross-Coupling of Two Distinct Aryl Bromides
-
A Pd-catalyzed direct cross-coupling of two distinct aryl bromides mediated by tBuLi is described. The use of [Pd-PEPPSI-IPr] or [Pd-PEPPSI-IPent] as catalyst allows for the efficient one-pot synthesis of unsymmetrical biaryls at room temperature. The key for this selective cross-coupling is the use of an ortho-substituted bromide that undergoes lithium-halogen exchange preferentially. Bro to Bro: A palladium-catalyzed direct cross-coupling of two distinct aryl bromides mediated by tBuLi is described. The use of [Pd-PEPPSI-IPr] or [Pd-PEPPSI-IPent] as catalyst allows for the efficient one-pot synthesis of unsymmetrical biaryls at room temperature. The key for this selective cross-coupling is the use of an ortho-substituted bromide that undergoes lithium-halogen exchange preferentially.
- Vila, Carlos,Cembellín, Sara,Hornillos, Valentín,Giannerini, Massimo,Fa?anás-Mastral, Martín,Feringa, Ben L.
-
supporting information
p. 15520 - 15524
(2015/11/03)
-
- A Planar-Chiral Phosphino(alkenyl)ferrocene for Suzuki-Miyaura C-C Coupling Reactions
-
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
-
supporting information
p. 6676 - 6685
(2016/02/19)
-
- Palladium-catalysed cross-coupling reaction of ultra-stabilised 2-aryl-1,3-dihydro-1H-benzo[d]1,3,2-diazaborole compounds with aryl bromides: A direct protocol for the preparation of unsymmetrical biaryls
-
There has been a significant interest in organoboron compounds such as arylboronic acids, arylboronate esters and potassium aryltrifluoroborate salts because they are versatile coupling partners in metal-catalysed cross-coupling reactions. On the other hand, their nitrogen analogues, namely, 1,3,2-benzodiazaborole-type compounds have been studied extensively for their intriguing absorption and fluorescence characteristics. Here we describe the first palladium-catalysed Suzuki-Miyaura cross-coupling reaction of easily accessible and ultra-stabilised 2-aryl-1,3-dihydro-1H-benzo[d]1,3,2-diazaborole derivatives with various aryl bromides. Aryl bromides bearing electron-withdrawing, electron-neutral and electron-donating substituents are reacted under the catalytic system furnishing unsymmetrical biaryl products in isolated yields of up to 96% in only 10 minutes.
- Sithebe, Siphamandla,Robinson, Ross S.
-
p. 1107 - 1113
(2014/06/09)
-
- Synthesis and photochemical behaviour of novel uranyl-salophen complexes bearing anthracenyl side arms
-
In this paper, we report the synthesis and physico-chemical investigation of two uranyl-salophen receptors, bearing either one or two anthracenyl moieties appended to the salophen skeleton. Despite the presence of the anthracenyl fluorophores, no fluorescence emission was detected. Photophysical data and cyclic voltammetric experiments show that photoinduced electron transfer from the anthracene-localised first singlet excited state to the metal centre is strongly exergonic, thus suggesting that this is the main fluorescence quenching mechanism in these complexes. The investigated compounds are photoreactive upon UV irradiation, yielding either anthracene photooxidation or photodimerisation products depending on the specific complex and the experimental conditions.
- Mihan, Francesco Yafteh,Bartocci, Silvia,Credi, Alberto,Silvi, Serena,Dalla Cort, Antonella
-
p. 109 - 115
(2013/08/24)
-
- Mixed phosphine/N-heterocyclic carbene palladium complexes: Synthesis, characterization and catalytic use in aqueous Suzuki-Miyaura reactions
-
A series of N-heterocyclic carbene (NHC)/PR3 palladium(ii) and palladium(0) complexes has been synthesized and fully characterized. X-ray crystallographic data have allowed comparison of ligand steric properties. The NHC ligand was found to vary its steric properties as a function of the phosphine co-ligand. These complexes display interesting catalytic properties in the Suzuki-Miyaura reaction performed in aqueous media. The pre-catalyst [PdCl2(IPr)(XPhos)] (IPr = N,N′-bis-(2,6-diisopropylphenyl) imidazol-2-ylidene; XPhos = 2-dicyclohexylphosphino-2′,4′,6′- triisopropylbiphenyl) was found to be the most efficient system, promoting the coupling of a wide range of aryl chlorides with boronic acids in aqueous media with a typical catalyst loading of 0.03 mol%.
- Schmid, Thibault E.,Jones, Dale C.,Songis, Olivier,Diebolt, Olivier,Furst, Marc R.L.,Slawin, Alexandra M.Z.,Cazin, Catherine S.J.
-
supporting information
p. 7345 - 7353
(2013/07/25)
-
- Highly efficient carbazolyl-derived phosphine ligands: Application to sterically hindered biaryl couplings
-
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
-
supporting information; experimental part
p. 5079 - 5081
(2011/06/10)
-
- Tetra-ortho-substituted biaryls through palladium-catalyzed suzuki miyaura couplings with a diaminochlorophosphine ligand
-
Chemical Equetion Presentation A palladium complex derived from a sterically hindered diaminochlorophosphine allowed for Suzuki-Miyaura cross-couplings of chloroarenes with ample scope and provided access to tetra-ortho-substituted bi(hetero)aryls.
- Ackermann, Lutz,Potukuchi, Harish K.,Althammer, Andreas,Born, Robert,Mayer, Peter
-
supporting information; experimental part
p. 1004 - 1007
(2010/06/16)
-
- Efficient synthesis of sterically crowded biaryls by palladium-phosphinous acid-catalyzed cross-coupling of aryl halides and aryl grignards
-
(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
-
p. 162 - 167
(2008/09/17)
-
- Palladium-catalyzed arylation of α,α-disubstituted arylmethanols via cleavage of a C-C or a C-H bond to give biaryls
-
The palladium-catalyzed arylation of α,α-disubstituted arylmethanols with aryl halides proceeds not only via C-H bond cleavage at the ortho-position, but also via cleavage of the sp2-sp3 C-C bond with the liberation of ketones (β-carbon elimination) to give the corresponding biaryls. Both reactions appear to occur through common arylpalladium(II) alcoholate intermediates. The results of systematic studies with respect to which C-C or C-H bond is preferentially cleaved in the arylation are reported. Among the important findings is the selective elimination of ortho-substituted aryl groups even from aryl(diphenyl)methanols due to steric reasons. Thus, various biaryls having ortho-substituents can be produced efficiently by treatment of the corresponding aryl(diphenyl or dimethyl)methanols with aryl bromides and chlorides.
- Terao, Yoshito,Wakui, Hiroyuki,Nomoto, Michiyo,Satoh, Tetsuya,Miura, Masahiro,Nomura, Masakatsu
-
p. 5236 - 5243
(2007/10/03)
-