The Reactions of Carbon Monoxide with Silyl and Silenyl Lithium – Synthesis and Isolation of the First Stable Tetra‐Silyl Di‐Ketyl Biradical and 1‐Silaallenolate Lithium

Reactions of carbon monoxide (CO) with tBu2MeSiLi and (E)‐(tBu2MeSi)(tBuMe2Si)C=Si(SiMetBu2)Li⋅2 THF (4) were studied both experimentally and computationally. Reaction of tBu2MeSiLi with CO in hexane yields the first stable tetra‐silyl di‐ketyl biradical [(tBu2MeSi)2COLi].2 (3). Reaction of 4 with CO yields selectively and quantitatively the first reported 1‐silaallenolate, (tBu2MeSi)(tBuMe2Si)C=C=Si(SiMetBu2)OLi⋅THF (5). Both 3 and 5 were characterized by X‐ray crystallography and biradical 3 also by EPR spectroscopy. Silaallenolate 5 reacts with Me3SiCl to produce siloxy substituted 1‐silaallene (tBu2MeSi)(tBuMe2Si)C=C=Si(SiMetBu2)OSiMe3. The reaction of 4 with CO provides a new route to 1‐silaallenes. The mechanisms of the reactions of tBuMe2SiLi and of 4 with CO were studied by DFT calculations. Reaction of carbon monoxide with tBu2MeSiLi yields the first stable tetra‐silyl di‐ketyl biradical 2; with silenyl lithium 1 silaallenolate 3 is obtained. In 3 the bond in the inserted CO molecule is fully cleaved. Both 2 and 3 were characterized by X‐ray crystallography and biradical 2 also by EPR spectroscopy. Density functional theory (DFT) calculations suggest mechanisms for these reactions.