Synthesis of Silenyllithiums Li(R′3Si)Si═C(SiR3)(1-Ad) via Transient Silyne–Silylidene Intermediates
摘要:
The first two lithium silenides, Li(tBu(2)MeSi)-Si=C(SiMetBu(2))(1-Ad) (1) and Li(tBuMe(2)Si)Si=C(SiMetBu(2))(1-Ad) (2) were prepared by THF addition to the corresponding lithium-silenolates, [(tBu(2)MeSi)(2)Si=C(OLi)(1-Ad)]center dot(R3SiLi) (3a: R3Si=tBu(2)MeSi, 313: R3Si=tBuMe(2)Si). 1 and 2 were crystallized, and their structures were determined by X-ray crystallography. This process requires the presence of both coaggregated silyllithium (R3SiLi) (3a and 3b) and THF. Based on reaction products and DFT calculations, it is suggested that elimination of tBu(2)MeSiOLi from 3a (or 3b) produces first the corresponding silyne intermediate which rearranges to the corresponding silylidene, which is then trapped by R3SiLi giving 1 (or 2).
A stable lithium stannenolate 7 was synthesized and isolated by the reaction of acylstannane 6 with LDA or tBu2MeSiLi in THF. 7 was characterized by X-ray crystallography and by NMR and UV-Vis spectroscopy. Spectroscopic and structural features, in combination with DFT quantum-mechanical calculations, indicate that 7 is best described as an acyl-substituted stannyl anion, adopting the stannenolate
Two novel germenyllithiums (1 a and 2 b), having a genuine C=Ge bond and substituents with mild electronic effects, were synthesized and structurally characterized. Further oxidation of compounds 1 a (or 2 b) produced the firstpersistentgermenylradicals 13 a (or 13 b) which were characterized by EPR spectroscopy and DFT calculations.
Reaction of silyl substituted dichlorosilanes with lithiosilanes in hexane leads exclusively to the corresponding stable silyl radicals. Two radicals, the new (t-Bu2MeSi)(2)HSi(t-Bu2MeSi)(2)Si center dot (1) and the previously isolated (t-Bu2MeSi)(3)Si center dot (2), were isolated and fully characterized including by X-ray crystallography. This one-step method is general and was applied for the synthesis of other silyl. radicals. Upon irradiation radical 1 (yellow solution in hexane) decays to yield the corresponding disproportionation products, silane and disilene (blue colored). In contrast, radical 2 is photostable in the absence of additives, but it abstracts hydrogen from triethylsilane and 2-propanol upon irradiation. DFT calculations and irradiation experiments with lambda > 400 nm suggest that SOMO-1 square SOMO excitation, which provides better electron accepting properties to the radical, is responsible for the photoreactivity of 1 and 2.