![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)
Dehydrocoupling of Phosphine-Borane Adducts Under Ambient Conditions Using Aminoboranes as Hydrogen Acceptors
Matthew A Wiebe1, Anne Staubitz2, Ian Manners1
1Department of Chemistry, University of Victoria, 3800 Finnerty Rd, Victoria, BC, V8P 5C2, Canada.
Abstract:
We report on the reactivity of aminoboranes (R2N=BH2; R = iPr, Et, Me) with phosphine-borane adducts (PhR'PH ⋅ BH3; R' = H, Ph): Sufficiently sterically unencumbered aminoboranes can accept hydrogen from phosphine-borane adducts. The hydrogen transfer results in the formation of amine-borane adducts (R2NH ⋅ BH3) and transient phosphinoboranes (PhR'P-BH2) in situ. These phosphinoboranes undergo subsequent reactivity to yield either polyphosphinoborane, [PhPH-BH2]n, or the linear dimer, Ph2PH ⋅ BH2-Ph2P ⋅ BH3. Unlike metal catalyzed phosphine-borane dehydrocoupling, which occurs at elevated temperatures (2 M, toluene, ≥100 °C, ≥24 h), these dehydrocoupling reactions occur under ambient conditions (2 M, Et2O or C6D6, 20 °C, ≤24 h). We performed a computational mechanistic study in which we identified that this transformation potentially occurs via a P-to-N and B-to-B hydrogen transfer through a 6-membered transition state.
Related Concept Videos
03:08Hydroboration-Oxidation of Alkenes
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...
02:15Preparation of Alcohols via Addition Reactions
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
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.
01:38Preparation of Amines: Reductive Amination of Aldehydes and Ketones
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.