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Search for "NHC" in Full Text gives 196 result(s) in Beilstein Journal of Organic Chemistry.

The role of silver additives in gold-mediated C–H functionalisation

  • Scott R. Patrick,
  • Ine I. F. Boogaerts,
  • Sylvain Gaillard,
  • Alexandra M. Z. Slawin and
  • Steven P. Nolan

Beilstein J. Org. Chem. 2011, 7, 892–896, doi:10.3762/bjoc.7.102

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  • complexes bearing N-heterocyclic carbenes (NHC) [9][10] as supporting ligands has enabled the isolation of a “golden synthon”, [Au(OH)(IPr)] 1 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), that is able to participate in metalation reactions with aromatic C–H bonds (Scheme 1) [11]. The reactivity
  • stoichiometric reaction between Ag2O and the substrate displayed substitution of one of the protons. However, deuterium incorporation experiments were unsuccessful and mass spectrometry on the product was inconclusive. The reaction depicted in Scheme 2 was performed using a neutral gold(I)-NHC complex. The
  • of 5. This observation clearly shows that silver can have a positive role in the carboxylation of C–H bonds. Conclusion The C–H functionalisation of arenes using (NHC)gold(I) complexes has been shown to be significantly affected by the leaving group on the gold. The gold(I) chloride may only react by
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Published 01 Jul 2011

A comparative study of the Au-catalyzed cyclization of hydroxy-substituted allylic alcohols and ethers

  • Berenger Biannic,
  • Thomas Ghebreghiorgis and
  • Aaron Aponick

Beilstein J. Org. Chem. 2011, 7, 802–807, doi:10.3762/bjoc.7.91

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  • isomerized by Au(I)-NHC complexes to the regioisomeric thermodynamic (and observed) products [26]. Successful implementation of such a strategy would offer an alternative to the use of the highly successful and well-established set of leaving groups employed in π-allylmetal chemistry [27][28][29][30][31][32
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Published 14 Jun 2011

Synthetic applications of gold-catalyzed ring expansions

  • David Garayalde and
  • Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

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  • cyclization events [51]. 1-(1-Alkynyl)cyclopropyl ketones 56 proved to be versatile building blocks for this purpose and gave, in the presence of indoles 57 as dipolarophiles, tetracyclic furans 58 in excellent yields (Scheme 20, reaction 1). NHC carbenes are preferred as ancillary ligands on the metal center
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Published 07 Jun 2011

When cyclopropenes meet gold catalysts

  • Frédéric Miege,
  • Christophe Meyer and
  • Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

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  • dependent and did not operate in the presence of the NHC–gold complex [(IPr)AuOTf]. Thus, when cyclopropene 8 was treated with a stoichiometric quantity of EtOH in the presence of the latter catalyst (5 mol %), the tertiary allylic ether 9a was obtained with high regioselectivity (>99:1), but the yield (51
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Published 30 May 2011

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

  • Lian-jun Liu,
  • Feijun Wang,
  • Wenfeng Wang,
  • Mei-xin Zhao and
  • Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

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  • Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, People’s Republic of China, Fax: 86-21-64166128 10.3762/bjoc.7.64 Abstract Axially chiral mono(NHC)–Pd(II) and mono(NHC)–Au(I) complexes with one side shaped 1,1
  • showed good catalytic activities in the asymmetric intramolecular hydroamination reaction to give the corresponding product in moderate ee. Keywords: chiral mono(N-heterocyclic carbene) complex; Heck–Mizoroki reaction; hydroamination; Suzuki–Miyaura reaction; Introduction N-heterocyclic carbene (NHC
  • ][4][5][6][7][8][9][10][11][12][13]. Numbers of novel chiral NHCs and NHC–metal-catalyzed asymmetric transformations have been developed in a dramatic expansion of this area of chemistry during the past decade; however, up to 2010 only a very few efficient chiral NHCs or NHCs metal catalysts have been
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Published 04 May 2011

Synthesis of Ru alkylidene complexes

  • Renat Kadyrov and
  • Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

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  • precursors for the “second generation” catalysts bearing NHC ligands are the alkylidene ruthenium complexes coordinated with two phosphines [1]. For recent reviews see [2][3][4]. There are several routes for accessing five-coordinated ruthenium(II) alkylidene complexes such as diazo-transfer [5] and the
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Published 21 Jan 2011

Olefin metathesis in nano-sized systems

  • Didier Astruc,
  • Abdou K. Diallo,
  • Sylvain Gatard,
  • Liyuan Liang,
  • Cátia Ornelas,
  • Victor Martinez,
  • Denise Méry and
  • Jaime Ruiz

Beilstein J. Org. Chem. 2011, 7, 94–103, doi:10.3762/bjoc.7.13

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  • an intermediate tetracyclic iron arene complex. Furthermore and interestingly, when the metathesis reaction was carried out in refluxing dichloroethane with the addition of the second-generation Grubbs catalyst [RuCl2(=CHPh)(bis-N-mesityl-NHC)], 7, (Scheme 3, NHC = N-heterocyclic carbene), the di
  • presence of water (but in the absence of dendrimer 11) is due to the slow decomposition of the catalytically active species formed during the RCM catalytic cycle. In particular, it has been shown that the methylene species [Ru(=CH2)Cl2{1,3-bis(mesityl)-NHC}(PCy3)], generated in the catalytic cycle of RCM
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Published 19 Jan 2011

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

  • Carolin Fischer and
  • Burkhard Koenig

Beilstein J. Org. Chem. 2011, 7, 59–74, doi:10.3762/bjoc.7.10

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  • ]. Industrial scale-up of these methods has already been applied on the 100 kg scale for arylpiperazines and different diarylamines [21]. In addition, Nolan et al. and Organ et al. have reported Pd-N-heterocyclic carbene (NHC)-catalysed Buchwald–Hartwig amination protocols that provide access to a range of
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Published 14 Jan 2011

Hoveyda–Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

  • Hynek Balcar,
  • Tushar Shinde,
  • Naděžda Žilková and
  • Zdeněk Bastl

Beilstein J. Org. Chem. 2011, 7, 22–28, doi:10.3762/bjoc.7.4

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  • supports: (a) by exchanging halide ligands X [7][8][9][10][11], (b) by exchanging phosphine and NHC ligands L [12][13], and (c) through the alkylidene ligand [14][15][16][17][18][19]. For these purposes, special ligand molecules with tags suitable for the reaction with the support surface (linkers) are
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Published 06 Jan 2011

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

  • Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

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  • improving the selectivity requires tuning the structure of the active sites to favour one isomer over the other (modification of the first coordination sphere). Hybrid materials containing Ru–NHC units New strategies to develop supported homogeneous catalysts involves the preparation of hybrid organic
  • complexes onto these pendant ligands can then be performed. Using this technology, several materials containing N-heterocyclic metal units (M–NHC) have been prepared, including a system containing a Ru–NHC unit (Scheme 5), which displayed unprecedented activity in the metathesis of ethyl oleate with
  • turnover numbers in excess of 15,000 [47]. Identity of the active sites for these systems could be obtained from stereochemical studies, i.e., the measurement of (E/Z)0. Indeed, comprehensive studies of various Ru–NHC homogeneous catalysts showed that the so-called G-I catalysts (no NHC and PCy3
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Published 05 Jan 2011

The catalytic performance of Ru–NHC alkylidene complexes: PCy3 versus pyridine as the dissociating ligand

  • Stefan Krehl,
  • Diana Geißler,
  • Sylvia Hauke,
  • Oliver Kunz,
  • Lucia Staude and
  • Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

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  • Stefan Krehl Diana Geissler Sylvia Hauke Oliver Kunz Lucia Staude Bernd Schmidt Universität Potsdam, Institut für Chemie, Organische Synthesechemie, Karl-Liebknecht-Straße 24–25, D-14476 Golm, Germany 10.3762/bjoc.6.136 Abstract The catalytic performance of NHC-ligated Ru-indenylidene or
  • propargylic alcohols as alkylidene precursors [10], which resulted in the synthesis of a first generation analogue C with an indenylidene ligand [11][12]. A landmark in the evolution of Ru-metathesis catalysts was the introduction of alkylidene complexes bearing N-heterocyclic carbenes (NHC) [13][14][15], in
  • pyridines as placeholders. Originally, complex G was synthesized as a precursor for mixed NHC-phosphine complexes other than D [25][26][27][28] or, very recently, for the synthesis of Ru-alkylidenes with two different NHC ligands [29]. Comparatively little information is available concerning the catalytic
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Published 15 Dec 2010

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

  • Etienne Borré,
  • Frederic Caijo,
  • Christophe Crévisy and
  • Marc Mauduit

Beilstein J. Org. Chem. 2010, 6, 1159–1166, doi:10.3762/bjoc.6.132

Graphical Abstract
  • been facilitated [2][3][4]. However, many research groups have focused their research on the development of more efficient precatalysts (Figure 1). In 1999, Grubbs (1a) [5] and Nolan (1b) [6] reported ruthenium species bearing one N-heterocyclic carbene (NHC) moiety. Despite the stability enhancement
  • of the active species (due to NHC), these catalysts still required a high catalytic loading (up to 20 mol % in some cases [7]). Later, Hoveyda synthesized a recyclable phosphine-free precatalyst (2a) [8] based on a release/return concept of the benzylidene ether fragment. Electronic or steric
  • Hoveyda-like complexes. Complexes 4a, 4b and 4f can be considered to be activated catalysts, while catalyst 4g bearing a more sterically demanding NHC (SIPr) ligand shows a faster initiation compared to its SIMes analogue catalyst 4b. Additionally, 4g gave the best conversion over a reaction time of one
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Published 06 Dec 2010

Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene

  • César A. Urbina-Blanco,
  • Xavier Bantreil,
  • Hervé Clavier,
  • Alexandra M. Z. Slawin and
  • Steven P. Nolan

Beilstein J. Org. Chem. 2010, 6, 1120–1126, doi:10.3762/bjoc.6.128

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  • 10.3762/bjoc.6.128 Abstract The steric and electronic influence of backbone substitution in IMes-based (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) N-heterocyclic carbenes (NHC) was probed by synthesizing the [RhCl(CO)2(NHC)] series of complexes to quantify experimentally the Tolman
  • electronic parameter (electronic) and the percent buried volume (%Vbur, steric) parameters. The corresponding ruthenium–indenylidene complexes were also synthesized and tested in benchmark metathesis transformations to establish possible correlations between reactivity and NHC electronic and steric
  • parameters. Keywords: N-heterocyclic carbene; olefin metathesis; percent buried volume; ruthenium–indenylidene; Tolman electronic parameter; Introduction The use of N-heterocyclic carbenes (NHC) as spectator ligands in ruthenium-mediated olefin metathesis represents one of the most important breakthroughs
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Published 23 Nov 2010

Light-induced olefin metathesis

  • Yuval Vidavsky and
  • N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2010, 6, 1106–1119, doi:10.3762/bjoc.6.127

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  • respective yields and the required reaction times. In line with the development of ruthenium benzylidene initiators [66][67], the phosphane ligand was replaced by an N-heterocyclic carbene (NHCs) in the photoactivated precatalysts. Accordingly, Noels et al. [68][69] synthesised a range of NHC substituted
  • ruthenium cymene complexes (Figure 8) either by replacing the phosphane ligand in complex 12 by NHC ligands or via direct synthesis from 13. Complexes 15 and 16 were tested as photoactivated ROMP catalysts. In all cases cyclooctene was used as a standard cyclic olefin monomer for the polymerisation studies
  • in the photochemical process; however, the active species and overall mechanism were not elucidated. Both saturated and unsaturated NHC ligands afforded similar results. However, blocking both ortho positions on the aromatic groups of the NHCs was crucial for the performance of the catalyst. The
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Published 23 Nov 2010

Halide exchanged Hoveyda-type complexes in olefin metathesis

  • Julia Wappel,
  • César A. Urbina-Blanco,
  • Mudassar Abbas,
  • Jörg H. Albering,
  • Robert Saf,
  • Steven P. Nolan and
  • Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

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  • -heterocyclic carbenes (NHC) as co-ligands in ruthenium-based carbene complexes for olefin metathesis [1][2][3] in the late nineties of the last century, olefin metathesis has become a powerful carbon-carbon double-bond-forming tool presenting unique synthetic opportunities [4]. Developments in this area can be
  • attributed to a steady and competitive research, focused on improving activity, selectivity and functional group tolerance of the catalysts by changing the leaving co-ligand [4][5], by using tailored carbene ligands [5][6][7], by introducing new NHC ligands [5][8][9], or by variation of the anionic co
  • 16.10 ppm. All other features of the 1H NMR spectrum of 2 are similar to those of 1 indicating slightly hindered rotation of the N-heterocyclic carbene ligand and a trans-disposition of the two halide ligands. In contrast, the rotation of the NHC ligand around the Ru–NHC bond in 3 is hindered as shown
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Published 23 Nov 2010

Total synthesis of (±)-coerulescine and (±)-horsfiline

  • Mukund G. Kulkarni,
  • Attrimuni P. Dhondge,
  • Sanjay W. Chavhan,
  • Ajit S. Borhade,
  • Yunnus B. Shaikh,
  • Deekshaputra R. Birhade,
  • Mayur P. Desai and
  • Nagorao R. Dhatrak

Beilstein J. Org. Chem. 2010, 6, 876–879, doi:10.3762/bjoc.6.103

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  • radical cyclizations [20][21][22][23][24], electrophilic cyclization [25], asymmetric nitroolefination reaction [26], palladium asymmetric allylic alkylation [27], palladium-catalyzed domino Heck–cyanation [28], Pd-catalyzed intramolecular cyanoamidation [29][30], NHC-mediated O- to C-carboxyl transfer
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Published 27 Sep 2010

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF3 and BH3

  • Julien Monot,
  • Louis Fensterbank,
  • Max Malacria,
  • Emmanuel Lacôte,
  • Steven J. Geib and
  • Dennis P. Curran

Beilstein J. Org. Chem. 2010, 6, 709–712, doi:10.3762/bjoc.6.82

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  • carbenes; stable carbenes; Introduction Lewis acid/Lewis base complexes of N-heterocyclic carbenes and boranes (NHC–boranes) are readily prepared from NHC’s and boranes by direct complexation [1][2][3][4]. Unlike many other classes of Lewis base complexes of boranes with neutral molecules (ethers
  • , sulfides, etc.), NHC–borane complexes are highly stable in diverse environments. Complexes such as those shown in Figure 1 are white solids that can often be chromatographed if desired. Many such complexes resist decomplexation, oxidation, and both acidic and basic hydrolysis. Such NHC–boranes are
  • shown in Figure 3. Of special interest are the lengths of the Ccarbene–N bonds. At 1.294(3) Å for 3a and 1.293(3) Å for 3b, these bonds are significantly shorter than analogous bonds on other NHC–BF3 complexes where the carbene carbon has two nitrogen substituents (1.338(5)–1.355(5) Å) [24][25]. Instead
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Published 02 Aug 2010
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  • Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported Pd–NHC complex catalyst has been realized for the first time. The polymer-supported catalyst can be re-used several times still retaining high activity for this transformation
  • general study on the Suzuki–Miyaura reactions of 1-aryltriazenes under heterogeneous catalysis described to date. Previously, we reported an active and recyclable polystyrene-supported Pd–NHC (N-heterocyclic carbene) catalyst 1 (Scheme 1) for the Suzuki–Miyaura cross-coupling reactions of aryl bromides
  • arylboronic acids can be readily effected with our polystyrene-supported Pd–NHC catalyst, which shows high efficiency and can be easily recovered and reused several times still retaining high activity. Results and Discussion The polystyrene-supported Pd–NHC catalyst 1 was prepared according to our reported
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Published 28 Jun 2010

The C–F bond as a conformational tool in organic and biological chemistry

  • Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

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  • . The asymmetric transannular aldol reaction catalysed by trans-4-fluoroproline (41), and its application to the total synthesis of (+)-hirsutene (46). The asymmetric Stetter reaction catalysed by chiral NHC catalysts 49–52. The ring conformations of 50–52 are influenced by σCH→σ*CF hyperconjugation. Cy
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Published 20 Apr 2010

Synthesis of new Cα-tetrasubstituted α-amino acids

  • Andreas A. Grauer and
  • Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

Graphical Abstract
  • (+, 3 C, t-Bu-CH3); 28.4 (+, 3 C, t-Bu-CH3); 32.6 (−, 1 C, CH2); 66.5 (−, 0.1 C, cis-OCH2); 66.6 (−, 0.9 C, trans-OCH2); 67.6 (Cquat, 1 C, NHC); 82.3 (Cquat, 2 C, t-Bu-C); 87.5 (+, 1 C, CH); 154.0 (Cquat, 0.1 C, cis-NHCO); 154.4 (Cquat, 0.9 C, trans-NHCO); 171.2 (Cquat, 0.1 C, cis-COO); 171.3 (Cquat
  • -NHC); 68.2 (Cquat, 0.8 C, trans-NHC); 79.8 (Cquat, 1 C, t-Bu-C); 81.7 (Cquat, 0.2 C, cis- t-Bu-C); 82.0 (Cquat, 0.8 C, trans- t-Bu-C); 82.1 (+, 0.8 C, trans-CH); 82.8 (+, 0.2 C, cis-CH); 154.7 (Cquat, 0.8 C, trans-NHCO); 155.1 (Cquat, 0.2 C, cis-NHCO); 170.6 (Cquat, 0.2 C, cis-COO); 170.7 (Cquat, 0.8
  • , 0.25 C, cis-NHC); 68.2 (Cquat, 0.75 C, trans-NHC); 79.8 (Cquat, 1 C, t-Bu-C); 81.7 (Cquat, 0.25 C, cis- t-Bu-C); 82.0 (Cquat, 0.75 C, trans- t-Bu-C); 84.1 (+, 0.75 C, trans-CH); 84.5 (+, 0.25 C, cis-CH); 154.8 (Cquat, 0.25 C, cis-NHCO); 155.1 (Cquat, 0.75 C, trans-NHCO); 170.6 (Cquat, 0.75 C, trans-COO
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Published 18 Feb 2009

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

  • Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

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  • -dimethylphenyl), precursors to widely used N-heterocyclic carbene (NHC) ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively) by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism
  • prominent members of the family of N-heterocyclic carbenes (NHC) are the sterically encumbered imidazolylidenes IPr and IMes (Figure 1), which can also be considered as analogues of bulky and electron-rich tertiary phosphanes. In contrast to the latter, their synthesis does not involve air-sensitive or
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Published 28 Aug 2007
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