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Catalyst-free diboration and silaboration of alkenes and alkynes using bis(9-heterofluorenyl)s †

Gilmer, Jannik, Trageser, Timo, Čaić, Luis, Virovets, Alexander, Bolte, Michael, Lerner, Hans‐Wolfram, Fantuzzi, Felipe, Wagner, Matthias (2023) Catalyst-free diboration and silaboration of alkenes and alkynes using bis(9-heterofluorenyl)s †. Chemical Science, 14 (17). pp. 4589-4596. ISSN 2041-6520. E-ISSN 2041-6539. (doi:10.1039/D3SC01395B) (KAR id:100715)

Abstract

Diboration and silaboration reactions are prominent tools to introduce valuable functional groups into organic substrates. To date, most diboranes(4) and silylboranes used for this purpose are electronically and/or kinetically stabilized and require activation by a catalyst. We show here that the tetraaryl (μ-hydrido)diborane(4) anion [3]− and the silyl (hydrido)borate ([4]−)/Me3SiBr system react spontaneously with the archetypal olefin ethylene in the absence of a catalyst. The actual active species in both cases are the valence isoelectronic intermediates [FluB−B(H)Flu]− ([1]−) and FluB−Si(H)Flu (2), which consist of two 9-heterofluorenyl halves that get attached to the 1 and 2 positions of ethylene. At room temperature, [1]− is present in a dynamic equilibrium with its isolable isomer [3]−, while 2 has to be released in situ at low temperatures by H− abstraction from [4]−. Quantum-chemical calculations show qualitatively identical reaction mechanisms for [1]− and 2. Since the reactions start with π coordination of the ethylene molecule to a vacant B(pz) orbital, the high Lewis-acidity and low steric hindrance of the 9-borafluorenyl fragments are the keys to success. As the reaction proceeds, back-donation from the B−E bond into the ethylene π* orbital becomes increasingly important (E = B, Si). The scope of the reactions has been extended to tBu(H)C=CH2 and tBuC≡CH on the one hand and FluB−Si(Cl)Flu as well as FluB−Si(Cl)Ph2 on the other.

Item Type: Article
DOI/Identification number: 10.1039/D3SC01395B
Uncontrolled keywords: General Chemistry
Subjects: Q Science > QD Chemistry
Divisions: Divisions > Division of Natural Sciences > Chemistry and Forensics
Funders: German Academic Exchange Service (https://ror.org/039djdh30)
Goethe University Frankfurt (https://ror.org/04cvxnb49)
University of Kent (https://ror.org/00xkeyj56)
Depositing User: Felipe Fantuzzi
Date Deposited: 02 Apr 2023 12:42 UTC
Last Modified: 04 Mar 2024 18:56 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/100715 (The current URI for this page, for reference purposes)

University of Kent Author Information

Gilmer, Jannik.

Creator's ORCID:
CReDIT Contributor Roles:

Fantuzzi, Felipe.

Creator's ORCID: https://orcid.org/0000-0002-8200-8262
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