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

Abstract

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.

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

“…[17] Biradical 3 was successfully crystallized and its Xray crystallography structure is presented in Figure 2b. [16] These experiments indicate that reaction of tBu 2 MeSiLi with CO yields both 1 + 3,i na4:1 ratio (according to EPR spectroscopy). 2 and 3 are the first isolated and characterized silyl substituted ketyl radicals.I nb oth, each ketyl unit possesses aperfect planar geometry around the central Catom (AEC1 = 360.08 8); other structural details are given in the Supporting Information.…”

“…Addition of 12-crown-4 to the initial reaction mixture (Scheme 2, step a) yields quantitatively (according to EPR) tetra-silyl diketyl biradical 2 in which the lithium cation is solvated by the crown-ether (Scheme 2, step c). Radical 2 was isolated, crystallized and characterized by X-ray crystallography [16] ( Figure 2a)a nd EPR spectroscopy. [10] When the initial reaction mixture (Scheme 2, step a) is cooled to 110 K inside the EPR cavity,atypical EPR spectrum of at riplet biradical, having axial symmetry,i so bserved ( Figure 1c).…”

“…5 was isolated and characterized by X-ray crystallography (Figure 3). [16] 5 is formed by incorporation of one equivalent of CO into 4. Interestingly,the strong CO triple bond (ca.…”

Recent advances in the chemistry of ketyl radicals

“…DFT and other studies have shown that the spin density mainly resides on the carbon atom of ketyl radical anions. 1 Covering the literature of the past 10 years, this tutorial review highlights exciting developments in the chemistry of ketyl radicals by comparing the varied contemporary -for example, using photoredox catalysts -and more classical approaches for the generation and use of ketyl radicals. The review will focus on different strategies for ketyl radical generation, their creative use in new synthetic protocols, strategies for the control of enantioselectivity, and the proposed mechanisms of reactions involving the reactive intermediates.…”

“…1 ). 1 For example, ketyl radicals are readily generated from carbonyl compounds and thus play a pivotal role in strategies for carbonyl umpolung reactivity. Ketyl radicals and ketyl radical anions are one of the most well-studied reactive intermediates and are commonly exploited in powerful methods for C–C bond formation.…”