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Arene Activation by Calcium Hydride/Zinc Amide Equilibration
Kyle G Pearce1, Agustín Morales1, Michael S Hill1
1Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
Journal of the American Chemical Society
|August 2, 2025
Summary
Calcium hydride reacts with zinc complexes, leading to transmetalation and the formation of zinc-based reagents. This enables the synthesis of biphenyls via cross-coupling, showcasing synergistic metal cooperation in C-H activation.
Area of Science:
- Organometallic Chemistry
- Coordination Chemistry
- Catalysis
Background:
- Calcium hydride complexes with β-diketiminate ligands are known reagents.
- Transmetalation reactions involving calcium and zinc are of interest for synthetic applications.
- Deprotonation of arenes by metal complexes can generate valuable organometallic intermediates.
Purpose of the Study:
- To investigate the reactivity of a β-diketiminato calcium hydride complex with different zinc complexes.
- To explore the formation of heterobimetallic species and their role in ligand transfer.
- To develop new methods for arene functionalization and biphenyl synthesis.
Main Methods:
- Reaction of [(BDI)CaH]2 with [Zn{N(SiMe3)2}2] and [Zn(TMP)2].
- Characterization of reaction products, including heterobimetallic complexes.
- Palladium-catalyzed cross-coupling reactions for biphenyl synthesis.
- Density Functional Theory (DFT) calculations to study reaction mechanisms.
Main Results:
- Transmetalation occurs, yielding [(BDI)ZnH] from the silazide system.
- The TMP system leads to Brønsted basicity enhancement and deprotonation of benzene to form [(BDI)Zn(C6H5)].
- The resulting [(BDI)Zn(C6H5)] can be used in palladium-catalyzed cross-coupling with bromobenzene for biphenyl synthesis.
- The protocol is extended to other arenes, with selective C(sp3)-H deprotonation observed for mesitylene.
Conclusions:
- The synergistic cooperation of calcium and zinc metals is crucial for the observed zinc arylation process.
- The developed method provides a versatile route to β-diketiminato arylzinc reagents.
- The synthesized reagents are effective in subsequent cross-coupling reactions for constructing biaryl compounds.
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