Generation and EPR Spectroscopy of the First Silenyl Radicals, R 2 C=Si . −R: Experiment and Theory

Synthesis of Genuine Germenyl Lithiums and the First Persistent Germenyl Radicals

The first isolated genuine germenyl lithiums (R₃Si)(1‐Ad)C=Ge(SiMetBu₂)(Li⋅2 L) (R₃Si=tBu₂MeSi, L=THF (1  a), or L=12‐crown‐4 (1  b) and R₃Si=tBuMe₂Si, L=THF (2  a), or L=12‐crown‐4 (2  b)), were synthesized by reaction of the corresponding acyl germanes 3 and 4, respectively, with tBu₂MeSiLi in THF at 70 °C. The novel 1  a and 2  b were characterized by NMR and UV/Vis spectroscopy, and also by X‐ray crystallography (r(C=Ge)=1.865 Å for 1  a and 1.877 Å for 2  b). Nucleophilic addition reaction of 1  a with MeI and a C−H insertion reactions to the C=Ge bond of 1  a, 2  a and 2  b, are reported. Oxidation of 1  a and 2  b (toluene, 230 K) produces the first persistent germenyl radicals (R₃Si)(1‐Ad)C=Ge⋅‐(SiMetBu₂) (R₃Si=tBu₂MeSi (13  a), R₃Si=tBuMe₂Si (13  b)), which were characterized by EPR spectroscopy (t_1/2≈30 min at 230 K, g=2.029, a_av(⁷³Ge) is 55.0G for 13  a and 60.2G for 13  b). The experimental EPR parameters and DFT calculations indicate that 13  a and 13  b have a strongly bent structure at Ge (calc. ∡(C=Ge−Si)=136.7° (13  a), 135.9° (13  b)), and that the unpaired electron has a substantial s‐character.

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 tBu₂ MeSiLi and (E)-(tBu₂ MeSi)(tBuMe₂ Si)C=Si(SiMetBu₂ )Li⋅2 THF (4) were studied both experimentally and computationally. Reaction of tBu₂ MeSiLi with CO in hexane yields the first stable tetra-silyl di-ketyl biradical [(tBu₂ MeSi)₂ COLi]^. ₂ (3). Reaction of 4 with CO yields selectively and quantitatively the first reported 1-silaallenolate, (tBu₂ MeSi)(tBuMe₂ Si)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 Me₃ SiCl to produce siloxy substituted 1-silaallene (tBu₂ MeSi)(tBuMe₂ Si)C=C=Si(SiMetBu₂ )OSiMe₃ . The reaction of 4 with CO provides a new route to 1-silaallenes. The mechanisms of the reactions of tBuMe₂ SiLi and of 4 with CO were studied by DFT calculations.