A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

• Vladislav Vasilenko,
• Torsten Roth,
• Clemens K. Blasius,
• Sebastian N. Intorp,
• Hubert Wadepohl and
• Lutz H. Gade

Beilstein J. Org. Chem. 2016, 12, 846–853, doi:10.3762/bjoc.12.83

• neutral κ2-P,N-ligands comprising an imine and a phosphine binding site. These ligands were reacted with rhodium, iridium and palladium metal precursors and the structures of the resulting complexes were elucidated by means of X-ray crystallography. We observed that subtle changes of the ligand backbone

• have a significant influence on the binding geometry und coordination properties of these bidentate P,N-donors. Keywords: P,N-ligands; phosphanylformamidines; phosphine imines; transition metal complexes; Introduction P,N-ligands have been applied in a wide variety of chemical reactions ranging from

• . In addition, the resulting ligand families should provide nitrogen and phosphorus donors with varying donor strength (amidine vs imine, phosphine vs heteroatom-bound phosphorus) and different bite angles (five- vs six-membered chelate rings). Results and Discussion Ligand synthesis We based the

A convenient route to symmetrically and unsymmetrically substituted 3,5-diaryl-2,4,6-trimethylpyridines via Suzuki–Miyaura cross-coupling reaction

• Dariusz Błachut,
• Joanna Szawkało and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2016, 12, 835–845, doi:10.3762/bjoc.12.82

• . The screening was then continued with Pd(OAc)2 and tri-(o-tolyl)phosphine (P(o-tol)3) used as a catalyst in the mixture toluene/water/ethanol as solvent system and with sodium carbonate as a base. In order to control the progress of the process, the mixture was regularly sampled and the components

• )3)4 clearly confirms that the later compound is more active in the cross-coupling reaction [46]. The results of the cross coupling depend on electronic and steric properties of the ligands coordinated to the metal atom. In the case of phosphine-based ligands, the structure of the aryl and alkyl

Asymmetric α-amination of 3-substituted oxindoles using chiral bifunctional phosphine catalysts

• Qiao-Wen Jin,
• Zhuo Chai,
• You-Ming Huang,
• Gang Zou and
• Gang Zhao

Beilstein J. Org. Chem. 2016, 12, 725–731, doi:10.3762/bjoc.12.72

• , Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, People’s Republic of China 10.3762/bjoc.12.72 Abstract A highly enantioselective α-amination of 3-substituted oxindoles with azodicarboxylates catalyzed by amino acids-derived chiral phosphine

• catalysts is reported. The corresponding products containing a tetrasubstituted carbon center attached to a nitrogen atom at the C-3 position of the oxindole were obtained in high yields and with up to 98% ee. Keywords: 3-aminooxindoles; asymmetric catalysis; phosphine catalyst; tetrasubstituted

• novel amino acid-derived chiral bifunctional organophosphine catalysts, which have successfully applied to catalyze various asymmetric reactions [40][41]. As a general concept, a tertiary phosphine adds to an electrophilic reactant to form a zwitterion which serves as either a nucleophile or a Bronsted

Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

• Grzegorz Mlostoń,
• Paulina Pipiak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 716–724, doi:10.3762/bjoc.12.71

• the reaction mixture with tris(diethylamino)phosphine, and the respective ethenes 9 were isolated as the final products. It is worth mentioning that in the case of the non-symmetrical aryl/hetaryl thioketones 1c, 1f–h and 2-diazopropane (7a), the formed 1,3-dithiolanes 10 were isolated as mixtures of

• tris(dimethylamino)phosphine desulfurization leading to the ethane derivative was carried out. Reaction of thioketones 1d–e with (trimethylsilyl)diazomethane (7c) – General procedure: The corresponding thioketones 1d–e (1 mmol) were dissolved in freshly distilled THF (2.5 mL) and the solution was

Copper-mediated arylation with arylboronic acids: Facile and modular synthesis of triarylmethanes

• H. Surya Prakash Rao and
• A. Veera Bhadra Rao

Beilstein J. Org. Chem. 2016, 12, 496–504, doi:10.3762/bjoc.12.49

• report a copper(II) triflate-catalyzed modular synthesis of triarylmethanes by employing diarylmethanols 9 and arylboronic acids 10. It is advantageous to employ a base metal catalyst such as copper(II) triflate instead of palladium [55][56] or nickel (Ni) [57] catalysts and to avoid the use of phosphine

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• ion intermediate through a stabilizing cation–π-interaction. They came to this conclusion, after an extensive catalyst screening. In 2014, Shi and co-workers presented the synthesis of products 243, utilizing substrates 244 and α,β-unsaturated aldehyde 245. Chiral phosphine organocatalyst 246 was

Enantioselective [3 + 2] annulation of α-substituted allenoates with β,γ-unsaturated N-sulfonylimines catalyzed by a bifunctional dipeptide phosphine

• Huanzhen Ni,
• Weijun Yao and
• Yixin Lu

Beilstein J. Org. Chem. 2016, 12, 343–348, doi:10.3762/bjoc.12.37

• of a dipeptide phosphine catalyst, a wide range of highly functionalized cyclopentenes bearing an all-carbon quaternary center were obtained in moderate to good yields and with good to excellent enantioselectivities. Keywords: [3 + 2] annulation; α-substituted allenoate; dipeptide phosphine

• ; enantioselective; Introduction Over the past decade, chiral phosphine catalysts have been utilized extensively for the construction of a broad range of synthetically useful molecular structures [1][2][3][4][5][6][7][8][9][10][11][12][13]. Since the initial discovery of phosphine-catalyzed [3 + 2] annulation of

• examples make use of allenoates without an α-substitution. As demonstrated by Yu, Kwon and their co-workers [34][35][36], this is due to the requirement of a hydrogen atom at the α-position for a proton shift during the reaction cycle. Instead, α-substituted allenoates were shown to interact with phosphine

Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

• Michael Edmunds,
• Mohammed Abdul Raheem,
• Rebecca Boutin,
• Katrina Tait and
• William Tam

Beilstein J. Org. Chem. 2016, 12, 239–244, doi:10.3762/bjoc.12.25

• on their oxidation state and the presence or absence of phosphine ligands (Table 1, entries 1–4). The catalyst lacking a phosphine ligand gave a low yield and the reaction proceeded very slowly (9%, 65 h, Table 1, entry 1). The addition of phosphine exogenously greatly increased the speed and the

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

• Julia Wappel,
• Roland C. Fischer,
• Luigi Cavallo,
• Christian Slugovc and
• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 154–165, doi:10.3762/bjoc.12.17

• behavior in ROMP and especially for their use in the synthesis of poly(dicyclopentadiene) (pDCPD). Bearing either the common phosphine leaving ligand in the first and second Grubbs olefin metathesis catalysts, or the Ru–O bond cleavage for the next Hoveyda-type catalysts, this work is a step forward

• ][59]. Thus this study opens a door to find out new families of olefin metathesis catalysts [60], overcoming the issue of bearing a phosphine or to break a Ru–O bond in the precatalysts [55][61]. The initiators exhibit an excellent stability in the solid state as well as in solution and an outstanding

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

• bond [7][8], which favored the synthesis of new NHCs and to their use as ligands in transition metal complexes. The latter complexes were usually obtained by an easy replacement of a phosphine by the new NHC ligand, displaying a very high stability under many catalytic conditions. Furthermore, NHCs

N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd–NHC complexes: synthesis, characterization and catalytic activity in carbon–carbon bond-forming reactions

• Senem Akkoç,
• Yetkin Gök,
• İlhan Özer İlhan and
• Veysel Kayser

Beilstein J. Org. Chem. 2016, 12, 81–88, doi:10.3762/bjoc.12.9

• ][10][11]. This is because NHC complexes are easily obtained by deprotonating imidazolium or benzimidazolium salts and most are relatively stable in air and moisture. They are weak π-acceptors and strong σ-donors and can form strong M–C bonds with transition metal ions compared to trivalent phosphine

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• metathesis catalysts has been the cardinal factor to distribute olefin metathesis in the synthesis of many important compounds [1][2][3][4]. Commercially available homogeneous complexes, including phosphine-containing Gru-II, Ind-II or phosphine-free Hov-II and Gre-II are usually employed in such cases

• backbone is a much better approach than the previously used ones (e.g., via phosphine or benzylidene ligands). An early example of a non-covalent attachment is complex 4, an activated catalyst deposited on glass polymer Raschig rings, which was tested in various metathesis reactions carried out in batch

Comparison of the catalytic activity for the Suzuki–Miyaura reaction of (η⁵-Cp)Pd(IPr)Cl with (η³-cinnamyl)Pd(IPr)(Cl) and (η³-1-t-Bu-indenyl)Pd(IPr)(Cl)

• Patrick R. Melvin,
• Nilay Hazari,
• Hannah M. C. Lant,
• Ian L. Peczak and
• Hemali P. Shah

Beilstein J. Org. Chem. 2015, 11, 2476–2486, doi:10.3762/bjoc.11.269

• and feature strongly electron-donating and sterically bulky phosphine or N-heterocyclic carbene (NHC) ancillary ligands [6][7]. In particular, precatalysts of the type (η3-allyl)Pd(NHC)(Cl) have shown excellent activity for the Suzuki–Miyaura reaction, with systems incorporating an η3-cinnamyl moiety

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• synthesis of the antimicobacterial agent erogorgiaene (Scheme 12) [31]. One of the key steps of this synthesis involved the conversion of the bicyclic extended Michael acceptor 44 to 45 through a 1,4-selective copper-catalyzed ACA. Copper(I) triflate and chiral phosphine ligand L10 enabled this

Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

• Manuel R. Fructos,
• Juan Urbano,
• M. Mar Díaz-Requejo and
• Pedro J. Pérez

Beilstein J. Org. Chem. 2015, 11, 2254–2260, doi:10.3762/bjoc.11.245

• )]SbF6 (L = tertiary phosphine ligand) abstracted the carbene group :CHPh from a tropilium derivative, and further transferred the gold-bonded carbene group to an olefin [17][18]. This contribution constituted a breakthrough in gold-mediated carbene-transfer reactions since the carbene source lacks of

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

• Kevin Lafaye,
• Cyril Bosset,
• Lionel Nicolas,
• Amandine Guérinot and
• Janine Cossy

Beilstein J. Org. Chem. 2015, 11, 2223–2241, doi:10.3762/bjoc.11.241

• and 5 h 40 min, respectively at 55 °C and the main byproduct CH3PCy3+Cl− was identified using 1H, 13C and 31P NMR data as well as HRMS data. The deactivation of the catalysts was hypothesized to go through ligand dissociation from 1 and 2 followed by a nucleophilic attack of the free phosphine on the

• methylidene derivative that could not be isolated. Thus, the decomposition of G-HII was studied in the presence of ethylene and unidentified ruthenium hydride species were observed by 1H NMR after 24 h. This result indicates that another mode of deactivation that does not involve a phosphine is involved in G

• complex 8 that was isolated and characterized using X-ray diffraction (Scheme 3, reaction 2). In both cases, free PCy3 was observed by NMR confirming amine-induced phosphine displacement. The decomposition of GI was hypothesized to go through a bimolecular coupling from 7. On the contrary, the bulky NHC

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• of the catalyst 6 (Scheme 2), which then was capable of polymerizing unstrained cyclic olefins and to perform reactions with acyclic olefins [37]. Subsequent variations showed that larger and more basic phosphine ligands led to improved activity, and that an order of activity could be established as

• catalyst (9, Scheme 3). The reaction of RuCl2(PPh3)3-4 (3) with phenyldiazomethane (7), followed by a phosphine exchange reaction, afforded complex 9 in high yields. Complex 9 has become the most used metathesis catalyst, because of its good activity, relatively good stability to air (storage of 9 has been

• heteroleptic complexes, bearing one N-heterocyclic carbene (NHC) (16–19, Figure 1) and one phosphine as ligands, represented the second crucial turning point in this chemistry. Following Herrmann’s report on bis-NHC ruthenium complexes (10–15) and their low activity [39], independently and simultaneously the

Chiral Cu(II)-catalyzed enantioselective β-borylation of α,β-unsaturated nitriles in water

• Lei Zhu,
• Taku Kitanosono,
• Pengyu Xu and
• Shū Kobayashi

Beilstein J. Org. Chem. 2015, 11, 2007–2011, doi:10.3762/bjoc.11.217

• ]. Enantioselective boron conjugate addition to α,β-unsaturated nitriles provides one of the most efficient routes to chiral β-boryl nitriles. Several straightforward methods have been developed that rely on chiral Cu(I) complexes with air-sensitive phosphine ligands [11][12][13][14][15]. In contrast, Cu(II)-based

• oxidation with high enantioselectivity. In contrast to well-documented Cu(I) catalytic systems in organic solvents, Cu(II) catalysis in water does not require the use of air-sensitive phosphine ligands or strong bases. Notably, neither the chemical nor physical properties of the α,β-unsaturated nitriles had

Aerobic addition of secondary phosphine oxides to vinyl sulfides: a shortcut to 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides

• Svetlana F. Malysheva,
• Alexander V. Artem’ev,
• Nina K. Gusarova,
• Nataliya A. Belogorlova,
• Alexander I. Albanov,
• C. W. Liu and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2015, 11, 1985–1990, doi:10.3762/bjoc.11.214

• Chemistry, National Dong Hwa University, Hualien 97401, Taiwan 10.3762/bjoc.11.214 Abstract Secondary phosphine oxides react with vinyl sulfides (both alkyl- and aryl-substituted sulfides) under aerobic and solvent-free conditions (80 °C, air, 7–30 h) to afford 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl

• )phosphine oxides in 70–93% yields. Keywords: addition; green method; phosphine oxides; regioselectivity; vinyl sulfides; Findings Tertiary phosphines and phosphine chalcogenides are important organophosphorus compounds that are widely used in industry, organic synthesis, polymer science, medicinal and

• ][20] as well as transition metal catalysts [21][22][23]. Also, examples of the microwave-assisted [24][25] and photoinduced [26] addition are described. Recently, on example of secondary phosphines [27] as well as secondary phosphine sulfides [28] and selenides [29], it has been disclosed that the

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

• Shawna L. Balof,
• K. Owen Nix,
• Matthew S. Olliff,
• Sarah E. Roessler,
• Arpita Saha,
• Kevin B. Müller,
• Ulrich Behrens,
• Edward J. Valente and
• Hans-Jörg Schanz

Beilstein J. Org. Chem. 2015, 11, 1960–1972, doi:10.3762/bjoc.11.212

• hydrophilic phosphine ligands [22][23][24][25], NHC ligands [26][27][28][29], N-donor ligands [30], alkylidene moieties [31][32][33] or combinations of these structural features [34][35][36][37]. Another recent development in homogeneous catalysis, and olefin metathesis in particular, have become switchable

• protonation of the ancillary NMe2 groups was demonstrated to cause a reduced ROMP propagation rate compared the neutral catalyst [62], we hypothesized that a catalyst based on this NHC-motif could still be superior in activity to phosphine-containing catalysts 1–4 in an emulsion ROMP process. It should be

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

• Patrycja Żak,
• Szymon Rogalski,
• Mariusz Majchrzak,
• Maciej Kubicki and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2015, 11, 1910–1916, doi:10.3762/bjoc.11.206

• (Scheme 1) [11]. However, in our hands to get complete transformation 5 equiv of phosphine had to be used. In a next step the complexes (4–6) were subjected to metathesis exchange reaction with 2-(prop-1-enyl)phenol (Scheme 2). The reaction was performed in the presence of an equimolar amount of the

• corresponding phosphine in order to bind the HCl liberated during the reaction, which resulted in a significant increase in the reaction yield. Complexes 8–10 were easily isolated by precipitation with methanol or hexane from concentrated solution in methylene chloride (isolated yields = 86–90%). 1H NMR spectra

• isolated yields of 90% (complex 13) and 92% (complex 14). Catalytic activity The obtained complexes were tested in the ring opening metathesis polymerisation (ROMP) of cyclooctadiene. First, the impact of a phosphine ligand on the catalytic activity was investigated. Preliminary tests performed showed, as

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• -tolyl substituted NHC ligand in [Ru]5 exerts a smaller steric effect than the -PCy3 residue in [Ru]1–4. Furthermore, the bulky phosphine ligand (PCy3) expands away from the transition metal center (coordination sphere), while the N,N’-o-tolyl substituent attached to the central imidazole ring penetrates

Profluorescent substrates for the screening of olefin metathesis catalysts

• Raphael Reuter and
• Thomas R. Ward

Beilstein J. Org. Chem. 2015, 11, 1886–1892, doi:10.3762/bjoc.11.203

• generation-type catalysts 1–4 (Figure 1). These catalysts were mainly chosen because of their high stability towards both air and moisture. Catalysts 1 and 2 are the phosphine-free Grubbs–Hoveyda and Grela-type catalysts bearing different isopropoxystyrene ligands. Catalysts 3 and 4 are phosphine-containing

Cross metathesis of unsaturated epoxides for the synthesis of polyfunctional building blocks

• Meriem K. Abderrezak,
• Kristýna Šichová,
• Nancy Dominguez-Boblett,
• Antoine Dupé,
• Zahia Kabouche,
• Christian Bruneau and
• Cédric Fischmeister

Beilstein J. Org. Chem. 2015, 11, 1876–1880, doi:10.3762/bjoc.11.201

• various cross metathesis reactions, the phosphine-free Hoveyda type second generation Zhan catalyst-1B [30] was selected to conduct this transformation. A recent study by Fogg rationalized the superiority of the Hoveyda catalyst vs the Grubbs catalyst in cross metathesis with acrylates showing that the

• phosphine could interact with the electron-deficient olefin leading to catalyst decomposition [31]. As observed by us and other groups in cross metathesis involving different substrates, double bond migration side-reactions took place during this transformation. This side reaction could be circumvented

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

• Chao Chen,
• Chunxin Lu,
• Qing Zheng,
• Shengliang Ni,
• Min Zhang and
• Wanzhi Chen

Beilstein J. Org. Chem. 2015, 11, 1786–1795, doi:10.3762/bjoc.11.194

• carbenes (NHCs) have been recognized as a class of strong donating ligands which can stabilize various metal complexes of catalytic importance. Transition metal complexes bearing NHCs are more stable to air, moisture, heat, and tolerant toward oxidation compared to phosphine ligands [1][2][3][4][5][6][7

• ]. Among NHCs, functionalized NHC ligands have been extensively studied in recent years because of their intriguing structural diversities and potential applications in coordination chemistry and homogenous catalysis. NHC ligands containing additional phosphine, nitrogen, oxygen, and sulfur donating groups