Norbornene

About: Norbornene is a research topic. Over the lifetime, 5628 publications have been published within this topic receiving 104495 citations. The topic is also known as: norbornylene & norcamphene.

Zeolite titanium beta as a selective catalyst in the epoxidation of bulky alkenes

Abstract: The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41 in the epoxidation of 1-octene and norbornene. The advantage of the larger pore size of Ti-beta is illustrated by the facile epoxidation of norbornene in which TS-1 displayed no activity. Rate differences in the epoxidation of terminal or internal alkenes are very small for Ti-beta, indicating that the Ti-site is rather spacious. The catalytic properties of Ti-beta were further investigated in the epoxidation of bulky alkenes such as cyclohexenes, cyclic terpenes and allylic alcohols. Ti-beta was found to catalyze the epoxidation of a wide variety of alkenes with aqueous hydrogen peroxide. In the epoxidation of linear alkenes two trends were observed. The lower alkenes were epoxidized fastest and the internal alkenes were slightly faster than the alkenes with a terminal double bond. The reactivity of methylenecyclohexane is about twice that of 1-methylcyclohexene. Based on electronic effects of substituents the reverse order would be expected, which suggests that here steric effects at the titanium site can play a dominant role in determining reactivity. Pronounced electronic effects were observed to be more important in the epoxidation of allylic alcohols: more highly substituted allylic alcohols are more reactive, whereas the reactivity of the substrates bearing a terminal, unsubstituted double bound is over an order of lower magnitude.

Living ROMP of exo-Norbornene Esters Possessing PdII SCS Pincer Complexes or Diaminopyridines

Abstract: Isomerically pure exo-norbornene esters containing either a PdII SCS pincer complex or a diaminopyridine unit were synthesized, polymerized, and copolymerized by ring-opening metathesis polymerization using a ruthenium initiator. All polymerizations are living under mild reaction conditions. A comparison between the pure exo monomers and the commonly employed 80:20 endo/exo mixtures was carried out. The exo-norbornene isomers exhibit significantly higher rates of propagation under milder conditions when compared to the endo/exo mixtures. Kinetic studies have shown that the kp values are highly dependent upon the isomeric purity but completely independent of the terminal diaminopyridine or PdII SCS Pincer functional groups. The living character of the polymerization has allowed for the first block copolymerization of norbornene metal-containing pincer complexes and diaminopyridine-based hydrogen-bonding receptors.