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

• significantly improve the complex solubility in acidic aqueous media [32]. We have also demonstrated before that acid addition to (DMAP)2Ru–alkylidene complexes 6 and 7 resulted in fast protonation of the N-donor ligand and thus resulting in fast, irreversible and generally complete metathesis initiation [45

• ][46]. For most ROMP processes, this is desirable as a fast initiation typically affords high ROMP activity with low catalyst loadings [57][67]. Hence, hexacoordinate complexes 11 and 12 were also synthesized from their precursor complexes 9 and 10 [61] by ligand exchange according to Scheme 2. These

• complexes now contain pH-responsive groups at the H2ITap ligand to afford solubility in aqueous acid and at the N-donor ligand which affords rapid metathesis initiation. It should be noted that Plenio et al. also reported a Ru–benzylidene complex similar to catalysts 11 and 12 bearing the NEt2-analogue to

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

• . Continuous efforts have been aimed at the search for new catalysts characterized by improved stability and catalytic performance. One of the current challenges is the development of catalysts allowing control of initiation for some metathesis polymerisation processes. For such applications a variety of

• latent catalysts have been reported which permit control of initiation and efficient propagation of the reaction [3][4][5]. Among numerous examples of latent catalysts, the complexes representing the structural motif illustrated in Figure 1 have been relative poorly investigated. Known examples include

Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions

• Andrzej Tracz,
• Mateusz Matczak,
• Katarzyna Urbaniak and
• Krzysztof Skowerski

Beilstein J. Org. Chem. 2015, 11, 1823–1832, doi:10.3762/bjoc.11.198

• anionic ligands. Grubbs et al. showed that the exchange of chlorides for bromides or iodides in the second generation Grubbs’ catalysts facilitated the initiation, but reduced the propagation rate and eventually provided no overall improvement [12]. More recently Slugovc et al. synthesized bromo- and iodo

• - analogues of HII, but no improvement was noted [13][14][15]. Moreover, the presence of iodide ligands reduced initiation rates for Hoveyda second generation complex bearing iodides (HII-I2) in ring-closing metathesis (RCM). Similarly, Schrodi and colleagues did not find any advantages for halide exchanged

• heterogenize catalysts, which resulted in the formation of materials with reduced activity and efficiency [23][24]. It is well recognized that the benzylidene ligand structure strongly influences initiation rates for Hoveyda-type catalysts [25]. As a consequence of the “boomerang effect”, which was recently

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• -2-chloro-3-cyanopyridine, which was cross-coupled with 3-methylpyridin-2-ylzinc bromide catalyzed by PEPPSI-iPr (pyridine-enhanced precatalyst preparation stabilization and initiation or 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride) under microwave

Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

• Maximilian Koy,
• Hagen J. Altmann,
• Benjamin Autenrieth,
• Wolfgang Frey and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 1632–1638, doi:10.3762/bjoc.11.178

• yield is attributed to the comparable low ring strain in M6. Polydispersity indices (PDIs) were in the range of 1.2 to 3.8. Together with the high molecular weights, this is indicative for substantial chain transfer and potentially incomplete initiation of the Ru–alkylidene, particularly with

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• acids, in aqueous solutions, n-butyric acid displayed the highest initiation rate. Some research using carboxylic acids and employing homogeneous PRCs has been reported [51][52]. However, the precedent of the photo-Kolbé reactions implied that radicals generated from carboxylic acids by semiconductor

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

• Thibault E. Schmid,
• Florian Modicom,
• Adrien Dumas,
• Etienne Borré,
• Loic Toupet,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 1541–1546, doi:10.3762/bjoc.11.169

• /catalyst ratios were investigated, and 150 equiv of TFA afforded the best catalytic performance in terms of initiation rate and conversion. In fact, both a decrease (100 equiv) and an increase (200 equiv) of this acid/catalyst ratio led to a significant deterioration of the kinetic profile. Subsequently

• ligand demonstrated modest latency potential with 5% conversion after this period. In both cases, activation of the catalysts with 150 equiv of TFA did not provide full conversion of the benchmark substrate. Notably, despite a faster initiation rate, the SIMes-based catalyst 2 afforded a lower conversion

• RCM of DEDAM [31]. The replacement of TFA by a weaker acid, acetic acid afforded a lower initiation rate and a conversion of only 40% was obtained after 5 h. On the other hand, hydrochloric acid outperformed TFA to complete the reaction in 10 min, as depicted in Figure 4. With the best conditions in

Ruthenium indenylidene “1^st generation” olefin metathesis catalysts containing triisopropyl phosphite

• Stefano Guidone,
• Fady Nahra,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2015, 11, 1520–1527, doi:10.3762/bjoc.11.166

• °C in less than 50 min. These features prompted us to hypothesize an isomerization step from the cis-pre-catalyst 1 to the corresponding trans isomer as reported for cis-Caz-1 (see Supporting Information File 1, section 2) [25]. Under the same conditions, instant pre-catalyst initiation and fast

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

• Karolina Żukowska,
• Eva Pump,
• Aleksandra E. Pazio,
• Krzysztof Woźniak,
• Luigi Cavallo and
• Christian Slugovc

Beilstein J. Org. Chem. 2015, 11, 1458–1468, doi:10.3762/bjoc.11.158

• structures virtually unlimited. Complexes incorporating alkylidene ligands based on aromatic [12][13][14][15] or aliphatic amines [16][17] and Schiff base patterns [18][19][20][21][22] have been prepared so far, exhibiting diverse activities ranging from very fast to very slow initiation. Furthermore, in

• 516.0 kg·mol−1 (PDI = 2.2) and 14 gave the highest conversion (98%) and the shortest polymer strands (Mn = 326.7 kg·mol−1; PDI = 2.2). The Mn values allow for an indirect relative assessment of the initiation efficacy [49][50][51][52][53][54], because they are proportional to the ratio of the

• propagation rate (kp) and the initiation rate constant (ki), provided that no secondary metathesis occurs. In this case, Mn is only dependent on ki, because in all cases the same propagating species occurs and kp is the same. Accordingly, initiator 14 exhibits the highest initiation efficacy and initiator 5a

Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations

• Adriana K. Slavova-Kazakova,
• Silvia E. Angelova,
• Timur L. Veprintsev,
• Petko Denev,
• Davide Fabbri,
• Maria Antonietta Dettori,
• Maria Kratchanova,
• Vladimir V. Naumov,
• Aleksei V. Trofimov,
• Rostislav F. Vasil’ev,
• Giovanna Delogu and
• Vessela D. Kancheva

Beilstein J. Org. Chem. 2015, 11, 1398–1411, doi:10.3762/bjoc.11.151

• results only in aprotic media. Comparative analysis of the results obtained by using different models and structure–activity relationship The initiated oxidation of a model hydrocarbon substrate (model 1) has an advantage that in this system the rate of initiation (RIN) is well controlled (constant value

• all four dimers tested, and this is in a good agreement with the theoretical BDE values, which are rather close. In contrast to the initiated oxidation, during lipid autoxidation (model 2) the rate of initiation increased with time as a result of accelerated hydroperoxide decomposition and of

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• theoretical study, in which the initiation and propagation steps of the copolymerisation were addressed. The initiation started with the coordination of epoxide at a penta-coordinated metal–salen complex, followed by a nucleophilic, SN2-like, back-side attack on such a coordinated epoxide. The propagation

Probing multivalency in ligand–receptor-mediated adhesion of soft, biomimetic interfaces

• Stephan Schmidt,
• Hanqing Wang,
• Daniel Pussak,
• Simone Mosca and
• Laura Hartmann

Beilstein J. Org. Chem. 2015, 11, 720–729, doi:10.3762/bjoc.11.82

• ], leading to longer MA grafting units compared to AA. Another interesting fact is that the kinetics of polymerization initiation is slower compared to propagation in case of AA units whereas the opposite is the case for MA. This behavior further increases the length of MA grafts compared to AA. Furthermore

Morita–Baylis–Hillman reaction of acrylamide with isatin derivatives

• Radhey M. Singh,
• Kishor Chandra Bharadwaj and
• Dharmendra Kumar Tiwari

Beilstein J. Org. Chem. 2014, 10, 2975–2980, doi:10.3762/bjoc.10.315

• acceptor tendency of alkene, which retards the attack of the catalyst on alkene, thus hindering the initiation of a reaction (Figure 1). Thus acrylamide has least contributed to the success of this reaction in the last four decades. In an effort to address the slow reaction rate of acrylamide, Hu et al

Galactan synthesis in a single step via oligomerization of monosaccharides

• Marius Dräger and
• Amit Basu

Beilstein J. Org. Chem. 2014, 10, 2658–2663, doi:10.3762/bjoc.10.279

• longer oligomers were not observed. Moreover, very little of the donor is incorporated into the products, suggesting that self-oligomerization competes effectively with the desired initiation. The use of p-methoxyphenyl 2,4,6-tri-O-benzyl-β-galactopyranoside (11) as the acceptor provided only the product

OligArch: A software tool to allow artificially expanded genetic information systems (AEGIS) to guide the autonomous self-assembly of long DNA constructs from multiple DNA single strands

• Kevin M. Bradley and
• Steven A. Benner

Beilstein J. Org. Chem. 2014, 10, 1826–1833, doi:10.3762/bjoc.10.192

• universal gas constant (1.987 cal/°C·mol) and ΔH and ΔS are the enthalpy and entropy of the base stacking adjusted for initiation factors [14], with ΔS also adjusted for salt concentrations using the formula [15]: AEGIS segments are designed using a bidirectional sliding-window approach. Starting at the

Investigations of thiol-modified phenol derivatives for the use in thiol–ene photopolymerizations

• Sebastian Reinelt,
• Monir Tabatabai,
• Urs Karl Fischer,
• Norbert Moszner,
• Andreas Utterodt and
• Helmut Ritter

Beilstein J. Org. Chem. 2014, 10, 1733–1740, doi:10.3762/bjoc.10.180

• campherchinone/4-(N,N-dimethylamino)benzoate initiation [41]. As evident from Table 1, all investigated thiol derivatives (10b, 14a–c and 17) – except for monomer 10a – outperformed the reference monomer PETMP regarding flexural strength and flexural modulus of elasticity of the photopolymerized thiol–ene

Multivalent scaffolds induce galectin-3 aggregation into nanoparticles

• Candace K. Goodman,
• Mark L. Wolfenden,
• Pratima Nangia-Makker,
• Anna K. Michel,
• Avraham Raz and
• Mary J. Cloninger

Beilstein J. Org. Chem. 2014, 10, 1570–1577, doi:10.3762/bjoc.10.162

• solution. Taken together, these data support aggregate initiation as a response to specific carbohydrate binding interactions between lectin and glycodendrimer. They also reveal the significance of the N-terminal domain in formation of higher order aggregates. The presence of these aggregates was confirmed

Why a diaminopyrrolic tripodal receptor binds mannosides in acetonitrile but not in water?

• Diogo Vila-Viçosa,
• Oscar Francesconi and
• Miguel Machuqueiro

Beilstein J. Org. Chem. 2014, 10, 1513–1523, doi:10.3762/bjoc.10.156

• acetonitrile [51][52] were used. All bonds were constrained using the P-LINCS algorithm [53]. The energy minimization steps were performed using a combination of both steepest descent and limited-memory Broyden–Fletcher–Goldfarb–Shanno methods. The initiation was performed in 3 steps of 100 ps, 200 ps, and 200

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• -adduct. The stereoselectivity of the method determines the conformation at the newly formed chiral centers. The hydrophosphination typically proceeds via thermal [68][69], radical, acidic [70][71][72] or basic [73][74] initiation. Radical addition of secondary phosphines to alkenes can be accomplished by

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• development of new methods for organic synthesis was achieved by use of photolabile protective groups, which could be released under irradiation by light [10][11]. Since many decades in industry, PRG are used in photopolymerization, a field in which the PRG prompt the initiation of the polymerization through

Polyglycerol-functionalized nanodiamond as a platform for gene delivery: Derivatization, characterization, and hybridization with DNA

• Li Zhao,
• Yuki Nakae,
• Hongmei Qin,
• Tadamasa Ito,
• Takahide Kimura,
• Hideto Kojima,
• Lawrence Chan and
• Naoki Komatsu

Beilstein J. Org. Chem. 2014, 10, 707–713, doi:10.3762/bjoc.10.64

• converted to ester (aprotic ones) by initiation of the ring-opening polymerization of glycidol. The immobilization of polypeptides turned the zeta potentials into plus (–36.8 mV → +14.2 to +44.1 mV) due to the protonation to the basic groups in the peptides; imidazole, amine, and guanidine. These zeta

A unified approach to the important protein kinase inhibitor balanol and a proposed analogue

• Tapan Saha,
• Ratnava Maitra and
• Shital K. Chattopadhyay

Beilstein J. Org. Chem. 2013, 9, 2910–2915, doi:10.3762/bjoc.9.327

• residues of a substrate protein by transferring a phosphate group from ATP to the substrate protein [1][2][3]. This phosphorylation induces conformational changes of the substrate protein leading to initiation of a number of cellular events including signal transduction [4][5]. The human PKC enzyme

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

• Luca Valgimigli,
• Daniele Bartolomei,
• Riccardo Amorati,
• Evan Haidasz,
• Jason J. Hanthorn,
• Susheel J. Nara,
• Johan Brinkhorst and
• Derek A. Pratt

Beilstein J. Org. Chem. 2013, 9, 2781–2792, doi:10.3762/bjoc.9.313

• consumption of the sample was measured. From the rate of oxygen consumption during the inhibited period (Rinh), kinh values were obtained by using Equation 6 [44], where R0 is the rate of oxygen consumption in the absence of antioxidants, Ri is the initiation rate (in the range 2–10 × 10−9 Ms−1), 2kt is the

Advancements in the mechanistic understanding of the copper-catalyzed azide–alkyne cycloaddition

• Regina Berg and
• Bernd F. Straub

Beilstein J. Org. Chem. 2013, 9, 2715–2750, doi:10.3762/bjoc.9.308

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• induction period and demonstrated the involvement of radical species in the reaction. The authors proposed a mechanism accounting for the EPR profile of the reaction and for the results of kinetic isotope effect experiments (Figure 21). In this mechanism, rhenium intervenes in the initiation step. It acts