Catalyst‐Free Hydroboration of CO2 With a Nucleophilic Diborane(4). Issue 64 (2nd November 2018)

• Record Type: Journal Article
• Authors: Frick, Markus; Horn, Julian; Wadepohl, Hubert; Kaifer, Elisabeth; Himmel, Hans‐Jörg
• Is Part Of: Chemistry. Volume 24:Issue 64(2018)
• Page Start: 16983
• Page End: 16986
• Publication Date: 2018-11-02
• Subjects: B−B bond -- carbon dioxide -- diborane -- hydroboration -- nucleophilic boron; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201804612
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Hydroboration generally requires the presence of a catalyst to lower the barrier for hydride transfer. This work reports on the first catalyst‐free CO2 hydroboration with a neutral boron compound, the nucleophilic diborane [HB(hpp)]2, 1 (hpp=1, 3, 4, 6, 7, 8‐hexahydro‐2 H ‐pyrimido[1, 2‐a]pyrimidinate). Further hydroboration reactions to bis(boryl)acetals are possible. In acetonitrile, but not in dichloromethane solutions, hydroboration of a first CO2 is followed by hydroboration of a second CO2 molecule. Detailed kinetic measurements for both hydroboration steps were carried out and the influence of the solvent and the addition of a Lewis base on the rate constants analyzed. In contrast to catalyst‐free hydroboration of CO2, hydroboration of the less electrophilic acetone requires the presence of an activating Lewis acid. Abstract : Nucleophilic diboranes enable the hydroboration of electron‐poor substrates, including the first catalyst‐free CO2 hydroboration by a neutral boron compound. Their scope is complimentary to the traditionally applied electrophilic boranes.