Stable Strontium Angew
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research highlights METAL ALKYL COMPLEXES Stable strontium Angew. Chem. Int. Ed. https://go.nature.com/2Nugrmp (2019). Et Et Et Ar Ar Ar H N Et Sr[N(SiMe ) ] N N N 3 2 2 PhSiH3 Sr N(SiMe3)2 Sr Sr NH Et N N N Et H Ar Ar Ar 1 2 Et Et Ar Ar Et N N Ethylene polymerization, Sr Sr nucleophilic aromatic N N substitution Et Ethylene Ar Ar Ar Ar H N N 3 Sr Sr N N H Ar Ar 2 D Ar Ar 2 D N N HD– isotope exchange Sr Sr N N D Ar Ar 4 Metal alkyls have a prominent place was not just the result of ligand size, but in organic synthesis. For instance, also due to agostic interactions between Sr organomagnesium and organolithium and the C–H bond in the 3-pentyl group. compounds are among the first choices Addition of PhSiH3 produced the strontium for carbon nucleophiles and bases, as hydride dimer (complex 2), which is also well as taking part in catalytic reactions stable and soluble in apolar solvents. such as the Kumada coupling. But, as you go With this complex in hand the team further down groups 1 and 2 in the periodic could explore its chemistry. The hydride table, the corresponding metal alkyls dimer engaged in H–D isotope exchange become more unstable or, in many cases, in C6D6 solution (leading to the production have not even been isolated. It is only in of deuterated analogue 4), and acted as recent years that unstabilized alkyl–calcium a catalyst for benzene deuteration with compounds have been prepared, by the D2. Significantly, an unstabilized alkyl use of bulky ligands and alkene insertion strontium complex 3 was easily formed by into Ca–H bonds. the addition of ethylene. Initial exploration Now, Sjoerd Harder and colleagues of the reactivity of this species showed that it at the Universität Erlangen–Nürnberg in could polymerize ethylene and also alkylate Germany have achieved this feat in the C6D6 via nucleophilic aromatic substitution. even more challenging case of strontium. Given these initial results, it will certainly be The key step was the use of a super-bulky interesting to see what reactivities develop ligand — bulkier even than those from these species in the future. successfully employed for calcium complexes. Combing such a ligand with Enda Bergin Sr[N(SiMe3)2]2 led to the formation of the surprisingly stable complex 1 (see Fig.). Published online: 13 March 2019 X-ray studies showed that the stabilization https://doi.org/10.1038/s41929-019-0261-3 NatURE CatalysIS | VOL 2 | MARCH 2019 | 177 | www.nature.com/natcatal 177.