Insertion of CO2 into divalent group 2 and 12 bis(silylamides)

Abstract

Previous studies have shown that CO 2 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 CO 2 virtually instantaneously under the very mild conditions of room temperature and atmospheric pressure CO 2 . We have also demonstrated that CO 2 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(SiMe 2 CH 2 ) 2 ] 2 (Et 2 O) 2 is used in place of Mg[N(SiMe 3 ) 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 CO 2 at room temperature and 4 atm CO 2 pressure to cleave CO 2 and generate a product containing a stable, [Zn 4 O] 6+ core with a bridging 4 -O atom.

Selective Conversion of CO2 into Isocyanate by Low‐Coordinate Iron Complexes

“…A prominent example of such a scenario is the reaction of metal silylamides with CO 2 . A wide range of metal silylamides have been reported to react with CO 2 to give isocyanates, carbodiimides and metal isocyanato complexes together with the corresponding silyl ethers, metal siloxides or unidentified species (Scheme ). However, amide additions with high selectivity towards the isocyanate under mild conditions are rare .…”

“…A wide range of metal silylamides have been reported to react with CO 2 to give isocyanates, carbodiimides and metal isocyanato complexes together with the corresponding silyl ethers, metal siloxides or unidentified species (Scheme ). However, amide additions with high selectivity towards the isocyanate under mild conditions are rare . Because the formed isocyanate is isoelectronic with CO 2 , metals that strongly activate CO 2 also activate the isocyanate, which is subsequently converted to the carbodiimide or metal isocyanate and silyl ether.…”

Synthesis and Reactivity of Three-Coordinate (dtbpe)Rh Silylamides: CO2 Bond Cleavage by a Rhodium(I) Disilylamide

“…The transformation of CO 2 to OCN – has been reported for several transition-metal silylamides . Deoxygenation of CO 2 by main-group and alkali-metal disilylamides is also known, though the major products are normally silylisocyanates or disilylcarbodiimides resulting from a single Si–N cleavage. In this case, we are able to assign a preliminary mechanism for the transformation (Scheme ) on the basis of the following observations.…”

Low-coordinate first-row transition metal complexes in catalysis and small molecule activation

“…115 Reactions between low-coordinate metal amides and carbon dioxide can afford isocyanates, carbodiimides, or (often) a mixture of the two. While the reaction has been performed with metals from the s-, 116,117 p-, [118][119][120] and f-block, 121,122 zinc-and iron-based systems have shown some of the greatest selectivities, 123,124 with a recent iron silylamide (46) affording the corresponding isocyanate with >95% selectivity at CO 2 pressures as low as 0.01 atm (Scheme 20a). 124 The T-shaped Ni(I) complex 48, which features a rigid acridane-based ligand, was recently investigated by Yoo and Lee.…”