Insertion of CO 2 into divalent group 2 and 12 bis(silylamides)

Abstract

Previous studies have shown that CO₂ can insert into divalent Sn and Ge bis(silylamides) to give mixtures of silylated isocyanates and bis(silyl)carbodiimides, albeit rather sluggishly. In order to more effectively utilize the divalent metal bis(silylamides) in synthesis, more active and selective reactions to form only isocyanates or carbodiimides were needed. We have now shown that the more electropositive Group 2 complexes react with CO₂ virtually instantaneously under the very mild conditions of room temperature and atmospheric pressure CO₂. We have also demonstrated that CO₂ can react under high pressure directly with the solid Mg bis(silylamides) to produce an unusual, high melting point solid. Different products are obtained when the cyclic, tied-back complex Mg[N(SiMe₂CH₂)₂]₂(Et₂O)₂ is used in place of Mg[N(SiMe₃)₂]₂(THF)₂. Various Zn bis(silylamides) can be designed to afford either the silyl isocyanate or the bis(alkyl)carbodiimide in near quantitative conversions in ~100% selectivities. Lastly, we have shown that the tied-back Zn complex can react with CO₂ at room temperature and 4 atm CO₂ pressure to cleave CO₂ and generate a product containing a stable, [Zn₄O]⁶⁺ core with a bridging μ₄-O atom.