Issue 7, 2021

Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

Abstract

Complexes of the Lewis base-free cations (MeBDI)Mg+ and (tBuBDI)Mg+ with Ph–X ligands (X = F, Cl, Br, I) have been studied (MeBDI = HC[C(Me)N-DIPP]2 and tBuBDI = HC[C(tBu)N-DIPP]2; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand (MeBDI) only complexes with PhF could be isolated. Heavier Ph–X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C6F5)4. For the cations with the bulkier tBuBDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X–Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F–Ph bonding originates from electrostatic attraction between Mg2+ and the very polar Cδ+–Fδ bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph–X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C–X bond breaking.

Graphical abstract: Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

Supplementary files

Article information

Article type
Edge Article
Submitted
17 nov. 2020
Accepted
16 déc. 2020
First published
16 déc. 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2021,12, 2410-2418

Magnesium–halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex

A. Friedrich, J. Pahl, J. Eyselein, J. Langer, N. van Eikema Hommes, A. Görling and S. Harder, Chem. Sci., 2021, 12, 2410 DOI: 10.1039/D0SC06321E

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