Molybdenum imido alkylidene and tungsten oxo alkylidene N-heterocyclic carbene complexes for olefin metathesis

Cationic Group VI Metal Imido Alkylidene N-Heterocyclic Carbene Nitrile Complexes: Bench-Stable, Functional-Group-Tolerant Olefin Metathesis Catalysts

Despite their excellent selectivities and activities, Mo‐and W‐based catalysts for olefin metathesis have not gained the same widespread use as Ru‐based systems, mainly due to their inherent air sensitivity. Herein, we describe the synthesis of air‐stable cationic‐at‐metal molybdenum and tungsten imido alkylidene NHC nitrile complexes. They catalyze olefin metathesis reactions of substrates containing functional groups such as (thio‐) esters, (thio‐) ethers and alcohols without the need for prior activation, for example, by a Lewis acid. The presence of a nitrile ligand was found to be essential for their stability towards air, while no decrease in activity and productivity could be observed upon coordination of a nitrile. Variations of the imido and anionic ligand revealed that alkoxide complexes with electron‐withdrawing imido ligands offer the highest reactivities and excellent stability compared to analogous triflate and halide complexes.

Norbornene, norbornadiene and their derivatives: promising semi-products for organic synthesis and production of polymeric materials

The methods for synthesis of promising norbornene monomers from norbornadiene and quadricyclane are summarized. A strategy for their synthesis is discussed, combining theoretical and experimental approaches to the selection of catalysts and the conditions for carrying out stereoselective reactions. The mechanisms of catalytic reactions of synthesis of norbornene monomers, as well as the progress in the macromolecular design of functional polymeric materials based on them, are considered. The data on industrial processes of production of polynorbornenes and areas of their use are presented.

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Olefin metathesis in air using latent ruthenium catalysts: imidazole substituted amphiphilic hydrogenated ROMP polymers providing nano-sized reaction spaces in water

Imidazole substituted hydrogenated amphiphilic ROMP polymers were used as both surfactants and ligand precursors for olefin metathesis reactions in water.

N-Heterocyclic carbene-induced transmethylation in tungsten imido alkylidene bistriflates: unexpected formation of an N-heterocyclic olefin complex

The reaction of [W(N-2,6-ⁱPr₂C₆H₃)(CHCMe₂Ph)(CF₃SO₃)₂(DME)] (DME = 1,2-dimethoxyethane) with the N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene leads to DME activation and to the formation of an N-heterocyclic olefin complex.

Neutral and Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Reactivity in Selected Olefin Metathesis Reactions and Immobilization on Silica

The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] (3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] (4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] (5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)](+)BArF(-) (6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] (7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] (8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF(-)=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3(-)). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3-8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of α,ω-diynes. In the RCM of α,ω-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100,000, 210,000 and 30,000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3 ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group 6 metal alkylidenes.