Related Experiment Video
Updated: Oct 25, 2026
Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
Published on: November 9, 2019
Selective Formation of a 1,2-Diborane(4) and Alcohol-Driven B─B Bond Cleavage to Generate H2
Rayni P Noriega1, David J Nelson2, Marcus W Drover1
1Department of Chemistry, Western University, London, Ontario, Canada.
Abstract:
Diborane(4) chemistry continues to reveal new aspects of the reactivity of electron-deficient p-block elements. These systems are capable of bond activation and ligand rearrangement-processes once thought to be exclusive to transition metals. Here, we show that reaction of B2Cat2 (Cat = benzene-1,2-diolate) with mesityllithium (MesLi; Mes = 2,4,6-trimethylphenyl) affords an unusual 1,2-disubstituted diborane(4), Mes-B(μ-Cat)-B-Mes. Structural, spectroscopic, and computational data indicate that the catecholate co-ligand favors formation of the 1,2-isomer. Subsequent reaction with alcohols (ROH) cleaves the B─B bond in this compound to form CatBMes and MesB(OR)2 via B(II) → B(III) oxidation, releasing H2. These results expand the reactive landscape of O,O-chelating diborane(4) systems, establish an entry into 1,2-diborane(4) frameworks, and demonstrate that their distinct reactivity toward alcohols can be exploited to differentiate the chemistry of 1,1- and 1,2-diborane(4) isomers.
Related Concept Videos
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 stereochemistry.
01:17Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
03:08Hydroboration-Oxidation of Alkenes
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
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.