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Origins of observed reactivity and specificity in the addition of B2Cl4 and analogues to unsaturated compounds

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posted on 2023-06-09, 15:48 authored by Cristina Pubill Ulldemolins, Elena Fernánez, Carles Bo, John M Brown
In 1954 Schlesinger and co-workers observed the direct reaction of diboron tetrachloride with simple organic compounds under mild conditions, the 1,2 addition product being formed with either ethylene or acetylene. In the following 25 years a series of addition reactions to simple alkenes, alkynes and dienes was demonstrated. B2F4 was shown to react in similar manner, albeit under more forcing conditions. Crucially, it was demonstrated that the addition to (E)- or (Z)-but-2-ene occurred with cis-stereospecificity. Only sporadic interest was shown in this field thereafter until catalysed addition reactions of diboron reagents were realized. Encouraged by this revival of interest through the discovery of transition-metal and nucleophilic catalysis of diboryl additions, DFT analysis of uncatalysed additions of B2X4 has been carried out and interpreted. This includes the relative reactivity of several B–B reagents with ethene, and that of B2Cl4vs. B2F4 additions, including benzene, naphthalene and C60 as reactants. This allows the analysis of relative reactivity vis-à-vis substitution on boron, and also direct comparison with hydroboration by HBCl2. [4 + 2] Addition of diboron reagents to dienes with B–B cleavage competes with direct [2 + 2] addition, favourably so for B2F4. The computational results demonstrate that the stereospecific addition to isomeric but-2-enes is a rare concerted [2ss + 2ps] process

History

Publication status

  • Published

File Version

  • Published version

Journal

Organic and Biomolecular Chemistry

ISSN

1477-0520

Publisher

Royal Society of Chemistry

Issue

37

Volume

13

Page range

9619-9628

Department affiliated with

  • Chemistry Publications

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date

2018-11-09

First Open Access (FOA) Date

2018-11-09

First Compliant Deposit (FCD) Date

2018-11-07

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