Olefin metathesis-distribution of products and carbene complex initiation

Abstract

The metathesis reactions of cycloolefins results in a ring‐chain equilibrium of cyclic oligomers and an acyclic polymer. The distribution of the polymer can be described by a most probable molecular weight distribution. The oligomer distribution differs in the kinetically controlled regime of the reaction from the equilibrium situation. The particular cases of norbornene and norbornadiene are discussed. Carbene complexes may be used as initiators. The more stable the carbene the more strained the cycloolefin has to be in order to be polymerizable. With increasing strain the cis‐stereoselectivity is significantly attenuated. (CO)5CRCR′R″ may initiate the metathesis reaction of cyclic and acyclic vinylethers. The reaction proceeds in a structurally uniform manner, i.e. only vinylethers are formed, and yields the equilibrium ratio of cis and trans double bonds.

SBA-15 Immobilized Ruthenium Carbenes as Catalysts for Ring Closing Metathesis and Ring Opening Metathesis Polymerization

“…The presence of this reaction forced us to use a higher monomer concentration than with NBE. Experiment with COE concentration 0.06 mol/L led to the formation of oligomers only, in accord with [45]. For both NBE and COE, 2b/SiO 2 delivered considerably lower polymer yield than 2b/SBA-15.…”

“…The lower yield may be a result of strong viscosity effect in the catalyst pores, the higher molecular weight may indicate a lower initiation efficiency (not all Ru species in solid catalyst were accessible for monomer molecules). In the case of COE, oligomer fraction was observed in the reaction product indicating the presence of intramolecular (back-biting) reactions [45] due to a high flexibility of the growing chain. The presence of this reaction forced us to use a higher monomer concentration than with NBE.…”

Olefin Metatheses and Related Reactions Initiated by Carbene Derivatives of Metals in Low Oxidation States

“…21 Similarly, in the 2‐butene and 3‐hexene initially formed from cis ‐2‐pentene, the double bonds are almost exclusively cis (97 % and 95 %, respectively); from trans ‐2‐pentene they are largely trans (73 % and 83 % trans , respectively) 1f. In the polymer formed in quantitative yield from bicyclo[4.2.0]oct‐7‐ene, they are 85 % cis 22. Such stereoselectivity is extraordinary.…”

“…(7)] shown in Equation (10) 65. 66 Another, summarized in Scheme , yielded two materials identified as structures 10 and 11 , indications of the mechanistic steps in the scheme 22. 67 Another provided UV spectroscopic evidence for the presence of one diphenylmethylene unit (experimentally 0.8 units) per polymer chain in the product formed when the metathesis of 1‐methyl‐ trans ‐cyclooctene is initiated by diphenylcarbene 1 1e…”

The metathesis reaction of cycloolefins and heterocyclic olefins: Thermodynamics and mechanistic aspects

“…stabilized by heteroatoms, are of particular interest for the metathesis reaction of vinyl ethers and the polymerization of cyclic vinylethers, such as 2,3-dihydrofuran, since the intermediate species resemble very much the structure of the initiating species (lo), (11).…”