Untangling the Complexity of Mixed Lithium/Magnesium Alkyl/Alkoxy Combinations Utilised in Bromine/Magnesium Exchange Reactions. Issue 14 (26th February 2021)

• Record Type: Journal Article
• Authors: Bole, Leonie J.; Judge, Neil R.; Hevia, Eva
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 14(2021)
• Page Start: 7626
• Page End: 7631
• Publication Date: 2021-02-26
• Subjects: alkoxides -- bromine/magnesium exchange -- lithium -- magnesium -- mixed-aggregates; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202016422
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: While it is known that the addition of Group 1 alkoxides to s ‐block organometallics can have an activating effect on reactivity, the exact nature of this effect is not that well understood. Here we describe the activation of s Bu2 Mg towards substituted bromoarenes by adding one equivalent of LiOR ( R =2‐ethylhexyl), where unusually both s Bu groups can undergo efficient Br/Mg exchange. Depending on the substitution pattern on the bromoarene two different types of organometallic intermediates have been isolated, either a mixed aryl/alkoxide [{LiMg(2‐FG‐C6 H4 )2 (OR)}2 ] (FG=OMe; NMe2 ) or a homoaryl [(THF)4 Li2 Mg(4‐FG‐C6 H4 )4 ] (FG=OMe, F). Detailed NMR spectroscopic studies have revealed that these exchange reactions and the formation of their intermediates are controlled by a new type of bimetallic Schlenk‐type equilibrium between heteroleptic [LiMg s Bu2 (OR)], alkyl rich [Li2 Mg s Bu4 ] and Mg(OR)2, with [Li2 Mg s Bu4 ] being the active species performing the Br/Mg exchange process. Abstract : Combining reactivity, NMR spectroscopy and structural studies has cleared the mist surrounding the complex constitutions of mixed Li–Mg, mixed alkyl–alkoxo complexes used in metal–bromine exchange reactions.