Trends in benzene inverse sandwich complexes of the alkaline-earth metals Mg, Ca, Sr and Ba

Abstract

Mechanochemical reduction of β-diketiminate (BDI) barium iodide precursors with K/KI resulted in the first barium inverse sandwich complexes containing the benzene dianion in yields of up to 54%. This most challenging isolation of highly reactive (BDI)Ba-(C6H6)-Ba(BDI) complexes, completes the family of heavier benzene inverse sandwich complexes and allows for a comparison of trends in the series from Mg, Ca, Sr to Ba. Syntheses, stabilities, structures, electronic states and reactivities of the full range are compared. Crucial for isolation of the Ba inverse sandwich complexes are the tBu-substituents in the ligand backbone which push the bulky aryl rings towards the large Ba metal cations. These secondary Ba···(p-Ar) interactions result in an unexpected high stability. Another trend is found for the ring puckering in the bridging benzene2- dianion which steadily increases from Ba to Mg. DFT calculations show the general ionic character of (BDI)Ae-(C6H6)-Ae(BDI) complexes (Ae = Mg, Ca, Sr, Ba) and reveal only small energy differences between closed-shell singlet or open-shell triplet states. The most reactive (BDI)Ba-(C6H6)-Ba(BDI) complexes could be considered the first BaI synthons. They reduce a range of polyaromatic hydrocarbons, H2 or even convert (BDI)MgI precursors into well-known (BDI)Mg-Mg(BDI) complexes. Reactions with heavier (BDI)AeI (Ae = Ca, Sr) gave (BDI)Ae-(C6H6)-Ae(BDI) and (BDI)BaI.

Supplementary files

Article information

Article type
Edge Article
Submitted
18 Jul 2025
Accepted
11 Aug 2025
First published
29 Aug 2025
This article is Open Access

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

Chem. Sci., 2025, Accepted Manuscript

Trends in benzene inverse sandwich complexes of the alkaline-earth metals Mg, Ca, Sr and Ba

D. Jędrzkiewicz, M. Morasch, O. Townrow, B. Rösch, J. Langer, Z. Mathe and S. Harder, Chem. Sci., 2025, Accepted Manuscript , DOI: 10.1039/D5SC05373K

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