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Abstract Attempts to create a novel Mg−Be bond by reaction of ( DIPeP BDI*)MgNa 2 with BeN(SiMe 3 ) 2 2 failed; DIPeP BDI*=HC( t Bu)C=N(DIPeP) 2 , DIPeP=2,6‐Et 2 C‐phenyl. Even at elevated temperatures, no conversion was observed. This is likely caused by strong steric shielding of the Be center. A similar reaction with the more open Cp*BeCl gave in quantitative yield ( DIPeP BDI*)MgBeCp* ( 1 ). The crystal structure shows a Mg−Be bond of 2.469(4) Å. Homolytic cleavage of the Mg−Be bond requires ΔH=69.6 kcal mol −1 (cf. CpBe−BeCp 69.0 kcal mol −1 and ( DIPP BDI)Mg−Mg( DIPP BDI) 55.8 kcal mol −1 ). Natural‐Population‐Analysis (NPA) shows fragment charges: ( DIPeP BDI*)Mg +0.27/BeCp* −0.27. The very low NPA charge on Be (+0.62) compared to Mg (+1.21) and the strongly upfield 9 Be NMR signal at −23.7 ppm are in line with considerable electron density on Be and the formal oxidation state assignment of Mg II −Be 0 . Despite this Mg δ+ −Be δ− polarity, 1 is extremely thermally stable and unreactive towards H 2 , CO, N 2 , cyclohexene and carbodiimide. It reacted with benzophenone, azobenzene, phenyl acetylene, CO 2 and CS 2 . Reaction with 1‐adamantyl azide led to reductive coupling and formation of an N 6 ‐chain. The azide reagent also inserted in the Cp*−Be bond. The inertness of 1 is likely due to bulky ligands protecting the Mg−Be unit.
Berthold et al. (Fri,) studied this question.