Ring closing metathesis in protic media by means of a neutral and polar ruthenium benzylidene complex

The ring closing olefine metathesis in protic solvents using a new ruthenium benzylidene complex is described

Facile Synthesis of Effcient and Selective Ruthenium Olefin Metathesis Catalysts with Sulfonate and Phosphate Ligands

A series of novel, air-stable ruthenium NHC catalysts with sulfonate and phosphate anions have been prepared easily in one pot at high yields using commercially available precursors. The catalysts were found to be effective for ring-opening metathesis polymerization, ring-closing metathesis, and cross-metathesis. The catalysts showed higher cis-selectivity in olefin cross-metathesis reactions as compared to earlier known ruthenium-based olefin metathesis catalysts, with allylbenzene and cis-1,4-diacetoxybutene as substrates

Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis

We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands that catalyze highly Z-selective olefin metathesis. A very simple and convenient procedure for the synthesis of such catalysts has been developed. Intramolecular C–H bond activation of the NHC ligand, promoted by anion ligand substitution, forms the appropriate chelate for stereocontrolled olefin metathesis

50th Anniversary Perspective: Living Polymerization—Emphasizing the Molecule in Macromolecules

The ideal of living polymerization has defined research in polymer chemistry over the past 50 years. In this Perspective, we present the case that this concept has enabled the treatment of polymers as organic molecules, rather than impure mixtures of species, and allowed the translation of methods developed by synthetic organic chemists into ever more accessible living and/or controlled polymerization methods. The concurrent development of rapid analytical methods for screening new polymerization methods for living characteristics, chiefly size exclusion chromatography, has greatly aided in the expansion of living polymerization methods

The Metallacyclopentane-Olefin Interchange Reaction

Tris(triphenylphosphine)tetramethylenenickel(II) and biscyclopentadienyltetramethylenetitanium, prepared from the reaction of a 1,4-dilithiobutane and the transition metal dihalides react with olefins to produce substituted metallacyclopentanes; the stereochemistry and substitution pattern of the metallocycles formed from propene, octa-1,7-diene, and norbornadiene has been determined

Initiation of Olefin Metathesis: Reaction of Deca-2,8-diene with Catalysts formed from Me_4Sn-WC1_6 and Me_3Al_2Cl_3-(Ph_3P)_2(NO)_2Cl_2Mo

The initial product of the metathesis of deca-2,8-diene with metathesis catalysts formed from either Me_4Sn–WCl_6 or Me_3Al_2Cl_3–(Ph_3P)_2(NO)_2Cl_2Mo is propene; labelling of the terminal groups of the diene and the alkylating agents gives a labelling pattern in the propene that is best explained in terms of generation of a carbene in the initiation step from the alkylating agent

A catalytic cycle for oxidation of tert-butyl methyl ether by a double C−H activation-group transfer process

A square-planar, iridium(I) carbene complex is shown to effect atom and group transfer from nitrous oxide and organic azides, releasing the corresponding formate or formimidate and an iridium(I)−dinitrogen adduct. The dinitrogen complex performs C−H activation upon photolysis or thermolysis, regenerating the carbene from tert-butyl methyl ether with loss of H_2. Taken together, these reactions represent a net catalytic cycle for C−H functionalization by double C−H activation to generate metal−carbon multiple bonds. Additionally, the unusual group transfer from diazo reagents underscores the unique nature of the reactivity observed for nucleophilic-at-metal carbene complexes

Synthesis of Telechelic Polyisoprene via Ring-Opening Metathesis Polymerization in the Presence of Chain Transfer Agent

Telechelic polyisoprene was synthesized via the ring-opening metathesis polymerization (ROMP) of 1,5-dimethyl-1,5-cyclooctadiene (DMCOD) in the presence of cis-1,4-diacetoxy-2-butene as a chain transfer agent (CTA). This method afforded telechelic polymer in excellent yield, and the acetoxy groups were successfully removed to yield α,ω-hydroxy end-functionalized polyisoprene with potential for subsequent reactions. Efficient, quantitative incorporation of CTA was achieved, and NMR spectroscopy was utilized to confirm the chemical identity of the polymer end groups. Polymerization of discrete DMCOD monomer generated polyisoprene with excellent regioregularity in the polymer backbone. Successful ROMP of sterically challenging DMCOD in the presence of a CTA for chain end-functionalization was borne out through screening of a variety of Ru-based olefin metathesis catalysts

Ruthenium-Based Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts

The fascinating story of olefin (or alkene) metathesis (eq 1) began almost five decades ago, when Anderson and Merckling reported the first carbon-carbon double-bond rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μετάθεση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia

A Tandem Approach to Photoactivated Olefin Metathesis: Combining a Photoacid Generator with an Acid Activated Catalyst

Combining an acid activated precatalyst with a photoacid generator (PAG) in the presence of ultraviolet light resulted in a highly efficient catalyst for olefin metathesis. The tandem system of precatalyst and PAG was capable of both ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP) in good to excellent conversion. Mechanistic investigations revealed that the catalytically active species is very similar to that of other well-known Ru-based catalysts