Tris- and Tetrakis(lithiomethyl)silanes:  An Easy Access to New Building Blocks for Organosilicon Compounds

Abstract

Tris(lithiomethyl)silanes, RSi(CH2Li)3, and tetrakis(lithiomethyl)silane, Si(CH2Li)4, were prepared by the reductive C−S bond cleavage with lithium p,p‘-di-tert-butylbiphenylide (LiDBB) and characterized by trapping with Bu3SnCl. The yields of the isolated trapping products were 42−81% (>95% NMR yield of the crude product), indicating a high-yield synthesis of the corresponding poly(lithiomethyl)silane building blocks. Tetrakis(lithiomethyl)silane is the first compound containing four lithioalkyl groups without any stabilization of the metalated carbon atoms by π-systems. Tetrakis(lithiomethyl)silane was used for the synthesis of 2,2,3,3,7,7,8,8-octamethyl-2,3,5,7,8-pentasilaspiro[4,6]nonane (10), a new spirocyclic disilane. The single-crystal X-ray diffraction study of 10 indicates two five-membered rings in envelope conformation with ecliptically arranged methyl groups connected to a spiro compound by a central silicon atom. DFT geometry optimizations [B3LYP/6-31G(d) level] and NMR calculations (GIAO method, HF/6-31+G(d,p) level) of 10 confirm the observed conformation of 10 as an energetic minimum and support the experimental results.

Synthesis and Characterization of Lithiated Dendrimers

“…Generation of Lithiated Dendrimers in Situ. Following the method of Strohmann et al, , we reacted 1 with a slight excess of lithium naphthalenide (LiC 10 H 8 ) at −41 °C, followed by quenching with excess D 2 O. The reaction proceeded rapidly and completely to give the desired deuterated dendrimer Si[(CH 2 ) 3 SiMe 2 CH 2 D] 4 ( 6 ), as was concluded from the 1 H and 13 C NMR spectra of the product after isolation.…”

“…For the synthesis of known bis(lithiomethyl)silanes, a limited number of reports are available in the literature. Recently a report by Strohmann et al described the high-yield synthesis of a series of bis(lithiomethyl)silanes and tetrakis(lithiomethyl)silanes by reductive cleavage of C−S bonds with lithium naphthalenide. Our strategy was to apply the method of Strohmann et al .…”

“…Our strategy was to apply the method of Strohmann et al . , to the synthesis of dendrimers. An important consideration in our strategy was to prevent possible decomposition through β-hydrogen elimination, as well as stabilizing the carbanion, by using a lithiomethyldimethylsilyl group.…”

Organodilithium Intermediates as Useful Dianionic Synthons: Recent Advances

“…The reaction of 184 and 185 with n-Bu3SnCl as electrophile yielded the expected compounds 186 and 187, respectively. The synthetic potential of these intermediates was shown by the preparation of spirosilane 188 by reaction of the intermediate 185 with 1,2-dichloro-1,1,2,2-tetramethyldisilane as electrophile (Scheme 42) [98,99].…”

Synthesis and Characterization of Water-Soluble Tin-Based Metallodendrimers

“…Recently, we systematically opened up the field of organotin dendrimers in analogy to the organosilicon 10 and the organogermanium dendrimers known. Before, already a few triorganotin derivatives could be found in the literature, which are classified as dendrimers but that have not been synthesized from this aspect: E(SnMe 3 ) 4 (E = Sn, Si, C) and E(CH 2 SnMe 3 ) 4 (E = Sn, Si) have been reported in connection with NMR sprectroscopic investigations; Si(CH 2 SnBu 3 ) 4 represents a derivatization product of a novel polylithiated compound . Furthermore, a tin phthalocyanine complex containing four tetraaza macrocycles may be classified as a metallodendrimer with the tin atom located in the core .…”