![Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F51444.jpg&w=3840&q=50)
Alkene Isomerization Catalyzed by a Mn(I) Bisphosphine Borohydride Complex
Ines Blaha1, Stefan Weber1, Robin Dülger1
1Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163-AC, A-1060 Wien, Austria.
Abstract:
An additive-free manganese-catalyzed isomerization of terminal alkenes to internal alkenes is described. This reaction is implementing an inexpensive nonprecious metal catalyst. The most efficient catalyst is the borohydride complex cis-[Mn(dippe)(CO)2(κ2-BH4)]. This catalyst operates at room temperature, with a catalyst loading of 2.5 mol %. A variety of terminal alkenes is effectively and selectively transformed into the respective internal E-alkenes. Preliminary results show chain-walking isomerization at an elevated temperature. Mechanistic studies were carried out, including stoichiometric reactions and in situ NMR analysis. These experiments are flanked by computational studies. Based on these, the catalytic process is initiated by the liberation of "BH3" as a THF adduct. The catalytic process is initiated by double bond insertion into an M-H species, leading to an alkyl metal intermediate, followed by β-hydride elimination at the opposite position to afford the isomerization product.
Related Concept Videos
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
03:08Hydroboration-Oxidation of Alkenes
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
02:36Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
02:46Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.