title: Metathesis transformations of natural products: cross-metathesis of natural rubber and mandarin oil by Ru-alkylidene catalysts.
abstract: This study reports on the degradation of natural rubber (NR) via crossmetathesis with mandarin oil and d-limonene, an abundant compound in essential oils; that were used as chain transfer agents (CTAs) and green solvents. Reactions were performed in the presence of the ruthenium-alkylidene catalysts (PCy₃)₂(Cl)₂Ru=CHPh (I) and (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (PCy₃)Cl₂Ru=CHPh (II), respectively. Catalyst II bears an N-heterocyclic carbene ligand (NHC) bounded to the ruthenium atom, which has a strong basic character; therefore it is more active toward trisubstituted olefins in comparison with catalyst I. In both cases, isolated monoterpene-terminated isoprene oligomers were obtained as products of the cross-metathesis degradation of NR. In the presence of catalyst II molecular weight values around M(n) × 10² and yields of 80% were obtained; whereas with catalyst I, the molecular weights of products were about M(n) × 10⁴ with yields ranging 70 to 74%. The composition and yield of NR degradation products were determined by GC/MS (EI) analysis and it was found that the oligomers obtained have primarily one vinyl group and one terpene-monocyclic group at the chain end, with isoprene units A(m) = 2, 3 y 4.
authors.affiliation: Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, CU, Coyoacán, México, D.F. 04510, Mexico.
authors.forename: Araceli
authors.initials: A
authors.lastname: Martínez
authors.forename: Selena
authors.initials: S
authors.lastname: Gutiérrez
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Tlenkopatchev
mesh_terms: D002384:Catalysis; D002957:Citrus / Q000737:chemistry; D053138:Cyclohexenes / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D000077222:Limonene; D019906:Nuclear Magnetic Resonance, Biomolecular; D010938:Plant Oils / Q000737:chemistry*; D012408:Rubber / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013729:Terpenes / Q000737:chemistry*
chemical_list: D053138:Cyclohexenes; D010938:Plant Oils; D013729:Terpenes; D012428:Ruthenium; D012408:Rubber; D000077222:Limonene