Nucleophilic aromatic substitution at benzene with powerful strontium hydride and alkyl complexes

The key to isolation of the first alkylstrontium complex is the synthesis of a strontium hydride complex that is stable towards ligand exchange reactions. This was achieved by using the superbulky ß‐diketiminate ligand DIPePBDI (CH[C(Me)N‐DIPeP]2, DIPeP =2,6‐diisopentylphenyl). Reaction of DIPePBDI‐H with Sr[N(SiMe3)2]2 gave (DIPePBDI)SrN(SiMe3)2 which was converted with PhSiH3 to [(DIPePBDI)SrH]2. Dissolved in C6D6, the Sr hydride complex is stable is up to 70 °C. At 60 °C, H‐D isotope exchange gave full conversion to [(DIPePBDI)SrD]2 and C6D5H. Since H‐D exchange with D2 is also facile, the strontium hydride complex is a catalyst for the deuteration of C6H6 by D2. Reaction of [(DIPePBDI)SrH]2 with ethylene gave [(DIPePBDI)SrEt]2. The high reactivity of this first alkylstrontium complex is demonstrated by facile ethylene polymerization and nucleophilic aromatic substitution with C6D6 giving alkylated aromatic products and (DIPePBDI)SrD]2¬, both processes which proceed at room temperature. DFT calculations illustrate that the latter Et‐D exchange with C6D6 likely involves the highly instable Meisenheimer anion C6D6Et‾ as an intermediate.

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