Insertion of CO2 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 sily- lated 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 con- versions 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 4-O atom.