78907-56-9Relevant articles and documents
Dimere der Ethene Me2E=C(SiMe3)2 (E=Si, Ge, Sn): Auf welchem Wege entstehen sie aus Me2EX-CM(SiMe3)2? Wie sind sie strukturiert?
Wiberg,Passler,Wagner,Polborn
, p. 292 - 303 (2007/10/03)
Alkali metal organyls or silyls MR (e.g. LiMe, LinBu, LitBu, LiPh, LiCH(SiMe3)2, LiC(SiMe3)3, NaSitBu3) convert equimolar amounts of bromomethanes Me2EX-CBr(SiMe3)2 with E=Si, Ge, Sn and electronegative substituents X (e.g. F, Br, OPh) in organic solvents (e.g. pentane, diethyl ether, tetrahydrofuran) (i) by a very fast Br/M exchange into the 'metalation products' Me2EX-CM(SiMe3)2, which thermolyze under formation of 'cyclobutanes' [-Me2E-C(SiMe3)2-]2, and (ii) to a lesser extent by X/R exchange into 'substitution products' Me2ER-CBr(SiMe3)2. As shown by trapping experiments, the unsaturated compounds Me2E=C(SiMe3)2 play the role of short-lived intermediates in both reactions. They are formed from Me2EX-CM(SiMe3)2 by MX elimination and add the present alkalimetal compounds Me2EX-CM(SiMe3)2≡MR′ or MR, respectively. The products Me2ER′-CM(SiMe3)2 with R′=C(EXMe2)(SiMe3)2, obtained in this way, eliminate MX under formation of the mentioned 'cyclobutanes'. On the other hand, the compounds Me2ER-CM(SiMe3)2 convert unreacted Me2EX-CBr(SiMe3)2 in Me2EX-CM(SiMe3)2 under formation of Me2ER-CBr(SiMe3)2. Relative rates of both the metalation reactions and the salt eliminations are determined. X-ray structure analyses of [-Me2E-C(SiMe3)2-]2 (E=Si, Ge, Sn) prove their 1,3-dielementacyclobutane structure with planar four-membered ECEC rings.
Ungesaettigte Silicium- und Germaniumverbindungen XVI. Stabilisierung des Labilen Silaethens Me2Si=C(SiMe3)2 durch Adduktbildung mit Donoren. Reaktivitaet von Me2Si=C(Si(Me3)2NMe3
Wiberg, Nils,Koepf, Hubert
, p. 9 - 18 (2007/10/02)
Silaethene Me2Si=C(SiMe3)3 (1), unstable at -100 degC with regard to dimerization, forms an adduct Me2Si=C(SiMe3)2NMe3 (3) with trimethyl amine, metastable at 0 degC.It decomposes thermally to give 1 and NMe3 and can, therefore, serve as a source of 1.With 1 as an intermediate, the adduct 3 reacts with butadiene, cyclopentadiene, 2,3-dimethylbutadiene, Ph2C=NSiMe3, t-BuN3, isobutene, or acetone giving either cycloadducts or ene reaction products.Adduct 3 reacts with ROH (R0H, Me, t-Bu, Ph) to yield insertion products, probably by way of a proton adduct of 3, but not via 1.Other donors (D) of which NMe3 is an example form adducts 1D, producing a new class of silicon compounds.As the Lewis basicity of D, relative to 1, decrease (F- >NMe3>NEt3>Br->THF), the resistance to decomposition of the adducts 1D to the dimer of 1 and D also decreases.
