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

• latency towards cyclic olefins. The new pre-catalysts can be triggered using HCl. Due to their extremely good solubility in apolar solvents and substrates they are useful candidates for solvent-free polymerizations. Their latency also makes them very suitable for the polymerization of strained monomers

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• , 1.6 < ÐM < 2.5) in yields >95%, using low catalyst loadings (0.2–0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization. Keywords: latency; N-heterocyclic carbenes; ring-opening organocatalysis

• more suitable under these conditions. Finally, a mixture of 5Me-Me-CO2, BnOH and D4 was tested for thermal latency (Figure 2). Notably, after 72 h at a slightly elevated temperature of 45 °C only negligible conversion was observed. A relatively mild increase to 80 °C, however, triggered a clean jump to

• 5Me-Me-CO2. Note that the fivefold monomer excess was used in case of BnOH being present. Thermal activation of a 5Me-Me-CO2/BnOH/D4 (1:5:500) composition after a latency period of 72 h. NHC-carboxylates part of this study (top) and polymerization scheme with initial thermal decarboxylation and final

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

• time period. The low metathesis activity of Fischer-type Ru–alkylidenes at room temperature is well-documented [66]. The observed acceleration with heat indicates a significant latency for this complex based on slow metathesis initiation. Neither complexes 11 or 12 performed efficiently in the RCM of

• characterized via X-ray diffraction. While in homogeneous organic or aqueous solution, the 2nd generation Grubbs-type catalyst 9 containing a Fischer-type phenylthiomethylidene group exhibited significant latency but proved to be a proficient ROMP and RCM catalyst at elevated temperatures. Catalyst 11 exhibited

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

• 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

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

• exotherm at approx. 60 °C; cf. Figure 9, left) while the highest latency was found for initiator 14 (onset at approx. 75 °C). While initiators 14 and 15 exhibited rather sharp exotherms for the polymerization of monomer 22, a much broader shape was found in the case of 5a. This shape can be explained by

Regulation of integrin and growth factor signaling in biomaterials for osteodifferentiation

• Qiang Wei,
• Theresa L. M. Pohl,
• Anja Seckinger,
• Joachim P. Spatz and
• Elisabetta A. Cavalcanti-Adam

Beilstein J. Org. Chem. 2015, 11, 773–783, doi:10.3762/bjoc.11.87

• , developmental endothelial locus-1; EGF, epidermal growth factor; ICAM, intercellular cell adhesion molecule; iC3b, inactivated complement component C3b; LAP-TGF-β, latency associated peptide transforming growth factor β; MAdCAM-1, mucosal addressin cell adhesion molecule 1; MFG-E8, milk fat globule EGF factor 8

Light-induced olefin metathesis

• Yuval Vidavsky and
• N. Gabriel Lemcoff

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

• latency [60] and did not show any polymerisation of DCPD at 80 °C. Whilst a solution of 4 and DCPD can stand for days with no apparent polymerisation, irradiation with UV light led to fast polymerisation. Ruthenium catalysed photometathesis The first example for PROMP using ruthenium initiators was

• light activated precatalyst in practical applications, latency must be significant also at higher temperatures. Therefore, Buchmeiser et al. concentrated efforts towards the design of 'true' latent photoactivated ruthenium precatalysts for ROMP [70]. These precatalysts, similar to Noels’ complexes

• complexes (Figure 12), as thermo-switchable catalysts for RCM and ROMP [73][74][75][76][77]. The thermal latency of the sulfur chelated complexes make them ideal candidates for photoswitchable applications; especially in light of the well documented photodissociation of ruthenium sulfur ligands. Therefore