301224-40-8Relevant articles and documents
Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand
Samec, Joseph S.M.,Keitz, Benjamin K.,Grubbs, Robert H.
, p. 1831 - 1837 (2010)
The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy3)((κN,O)-picolinate)2RuCHPh (5) and (H2IMes)((κN,O)-picolinate)2RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.
A practical larger scale preparation of second-generation hoveyda-type catalysts
Bieniek, Michal,Michrowska, Anna,Gulajski, LUkasz,Grela, Karol
, p. 1096 - 1099 (2007)
A two-step synthesis of the nitro-substituted Hoveyda-Grubbs olefin metathesis catalyst 4b from the parent first-generation Hoveyda-Grubbs complex 3a has been developed. The second-generation ruthenium catalyst was prepared by mixing together all ingredients, including a NHC ligand precursor and a strong base in an appropriate solvent. The formation of desired product 3b was separated from the liberated phosphine and decomposition products by flash chromatography using CH2Cl2 as the eluent. A good chelating 2-isopropoxybenzylidene fragment in 3b was replaced with the less chelating 5-nitro-2-isopropoxybenzylidene ligand. The resulting mixture was separated by crystallization from EtOAc from CH2Cl2 and finally from methanol. The method does not require extensive use of silica gel chromatography and can be easily scaled up.
Reactivity and selectivity differences between catecholate and catechothiolate ru complexes. Implications regarding design of stereoselective olefin metathesis catalysts
Khan, R. Kashif M.,Torker, Sebastian,Hoveyda, Amir H.
, p. 14337 - 14340 (2014)
The origins of the unexpected finding that Ru catechothiolate complexes, in contrast to catecholate derivatives, promote exceptional Z-selective olefin metathesis reactions are elucidated. We show that species containing a catechothiolate ligand, unlike catecholates, preserve their structural integrity under commonly used reaction conditions. DFT calculations indicate that, whereas alkene coordination is the stereochemistry-determining step with catecholate complexes, it is through the metallacyclobutane formation that the identity of the major isomer is determined with catechothiolate systems. The present findings suggest that previous models for Z selectivity, largely based on steric differences, should be altered to incorporate electronic factors as well.
High-Yield Synthesis of a Long-Sought, Labile Ru-NHC Complex and Its Application to the Concise Synthesis of Second-Generation Olefin Metathesis Catalysts
Day, Craig S.,Fogg, Deryn E.
, p. 4551 - 4555 (2018)
The controlled reaction of [RuCl2(p-cymene)]2 with H2IMes generates the previously challenging precatalyst and Ru synthon RuCl2(p-cymene)(H2IMes) (Ru-2) in 96% isolated yield. Critical to success is inhibiting premature p-cymene displacement. This is achieved by carrying out the synthesis at ambient temperatures, protected from light, and at sufficient dilutions (25 mM in THF) to enable stoichiometric control and inhibit bimolecular decomposition. The ease with which p-cymene loss can be deliberately induced, however, is key to the utility of Ru-2 in both catalysis and catalyst synthesis. The transformation of Ru-2 into two second-generation olefin metathesis catalysts is described. RuCl2(H2IMes)(=CH(o-C6H4-OiPr)) (HII) and RuCl2(H2IMes)(PPh3)(=CHPh) GII′ (a desirable, faster-initiating analogue of GII) are accessible in ca. 80% yield over two steps from commercially available [RuCl2(p-cymene)]2. Synthesis from RuCl2(PPh3)3, in comparison, requires three or four steps for HII or GII′, respectively, and proceeds in lower yields.
Light-Driven gem Hydrogenation: An Orthogonal Entry into “Second-Generation” Ruthenium Carbene Catalysts for Olefin Metathesis
Zachmann, Raphael J.,Fürstner, Alois
, p. 7663 - 7666 (2021)
The newly discovered light-driven gem hydrogenation of alkynes opens an unconventional yet efficient entry into five-coordinate Grubbs-type ruthenium carbene complexes with cis-disposed chloride ligands. Representatives of this class featuring a chelate substructure formed by an iodo-substituted benzylidene unit react with (substituted) 2-isopropoxystyrene to give prototypical “second-generation” Grubbs-Hoveyda complexes for olefin metathesis. The new approach to this venerable catalyst family is safe and versatile as it uses a triple bond rather than phenyldiazomethane as the ultimate carbene source and does not require any sacrificial phosphines.
Cis-Dichloro Sulfoxide Ligated Ruthenium Metathesis Precatalysts
Johns, Adam M.,Fiamengo, Bryan A.,Herron, Jessica R.,Bourg, Jean-Baptiste,Doppiu, Angelino,Karch, Ralf,Pederson, Richard L.
supporting information, p. 218 - 222 (2019/01/14)
Novel sulfoxide-ligated ruthenium complexes were prepared by reacting second-generation metathesis precatalysts with p-toluenesulfonyl chloride in the presence of a small excess of sulfoxide. (SIMes)Ru(S-DMSO)(Ind)Cl2 (M54) and (SIMes)Ru(S-DMSO)(CHPh)Cl2 (M54a) were characterized crystallographically and, in agreement with NMR spectroscopy, were found to adopt an unusual cis-dichloro configuration. Despite having traditionally latent geometry, the new complexes were found to be highly reactive precatalysts for routine metathesis transformations. Additionally, the robustness, scalability, and industrial utility of M54 as a ruthenium synthon are demonstrated.
Activation of olefin metathesis complexes containing unsymmetrical unsaturated N-heterocyclic carbenes by copper and gold transmetalation
Kamal, Fadwa,Colombel-Rouen, Sophie,Dumas, Adrien,Guégan, Jean-Paul,Roisnel, Thierry,Dorcet, Vincent,Baslé, Olivier,Rouen, Mathieu,Mauduit, Marc
supporting information, p. 11583 - 11586 (2019/10/02)
The activation of ruthenium-indenylidene complexes containing two unsymmetrical unsaturated N-heterocyclic carbenes (u2-NHCs) by a transmetalation process is reported. The use of copper(i) or gold(i) chlorides promotes the rapid trapping of one NHC ligand, which releases the catalytically active Ru-species. Impressive initiation rates with full-conversions are observed within one minute. This practical protocol demonstrates excellent catalytic performances in various ring-closing metathesis (RCM) and self-metathesis (SM) reactions.
