Issue 18, 2023

On the existence of low-valent magnesium–calcium complexes

Abstract

DFT-Calculations predict that a low-valent complex (BDI)Mg–Ca(BDI) with bulky β-diketiminate (BDI) ligands is thermodynamically stable. It was attempted to isolate such a complex by salt-metathesis between [(DIPePBDI*)MgNa+]2 and [(DIPePBDI)CaI]2 (DIPePBDI = HC[C(Me)N-DIPeP]2; DIPePBDI* = HC[C(tBu)N-DIPeP]2; DIPeP = 2,6-CH(Et)2-phenyl). Whereas in alkane solvents no reaction was observed, salt-metathesis in C6H6 led to immediate C–H activation of benzene to give (DIPePBDI*)MgPh and (DIPePBDI)CaH, the latter crystallizing as a THF-solvated dimer [(DIPePBDI)CaH·THF]2. Calculations suggest reduction and insertion of benzene in the Mg–Ca bond. The activation enthalpy for the subsequent decomposition of C6H62− into Ph and H is only 14.4 kcal mol−1. Repeating this reaction in the presence of naphthalene or anthracene led to heterobimetallic complexes in which naphthalene2− or anthracene2− anions are sandwiched between (DIPePBDI*)Mg+ and (DIPePBDI)Ca+ cations. These complexes slowly decompose to their homometallic counterparts and further decomposition products. Complexes in which naphthalene2− or anthracene2− anions are sandwiched between two (DIPePBDI)Ca+ cations were isolated. The low-valent complex (DIPePBDI*)Mg–Ca(DIPePBDI) could not be isolated due to its high reactivity. There is, however, strong evidence that this heterobimetallic compound is a fleeting intermediate.

Graphical abstract: On the existence of low-valent magnesium–calcium complexes

Supplementary files

Article information

Article type
Edge Article
Submitted
17 fev 2023
Accepted
13 apr 2023
First published
13 apr 2023
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., 2023,14, 4724-4734

On the existence of low-valent magnesium–calcium complexes

J. Mai, B. Rösch, N. Patel, J. Langer and S. Harder, Chem. Sci., 2023, 14, 4724 DOI: 10.1039/D3SC00909B

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