103349-32-2Relevant 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.
On the Reactivity of Germaethene Me2Ge=C(SiMe3)2: Mechanistic Aspects of Diels Alder and Ene Reactions [1]
Wiberg, Nils,Wagner, Susanne
, p. 838 - 850 (2007/10/03)
Diels-Alder and ene reactions of germaethene Me2Ge=C(SiMe3)2 (2) with butadienes >C=C + (Combining vertical line above)-C + (Combining vertical line above)=CC=C + (Combining vertical line above)-CH butadiene; 2-methylpropene > propene), and retarded by an increasing bulkyness of substituents in 1.4- or 1,3-positions (e.g. 1-methylbutadiene > 2-methylbutadiene; 1-vinylpropene > propene). It is concluded from these studies that Diels-Alder and ene reactions of 2 occur - like those of Me2Si=C(SiMe3)2 (1) or of ethenes >C=Ca concerted way and are HOMOdiene-LUMOdienophile and HOMOene-LUMOenophile controlled. Thus 2 and 1 behave as carbon analogues. With regard to a specific diene or ene (e.g. anthracene: toluene), 2 is the better dienophile or enophile than 1 or ethenes. With a fixed diene/ene mixture (e.g. butadiene/propene), 2 acts as the better dienophile, while 1 is the better enophile. These results can be explained by the π/π*-energy difference and the double bond polarity decreasing in the direction 1 > 2. Only cis-piperylene gives a [2+2] cycloadduct with 2, besides two [4+2] cycloadducts, and an ene reaction product.
Generation and Evidence of the Germaethene Me2Ge=C(SiMe3)2
Wiberg, Nils,Kim, Chung-Kyun
, p. 2966 - 2979 (2007/10/02)
Bromogermyldisilylmethanes (Me3Si)2(Me2XGe)CBr (3 - 13) are formed as a result of the reaction of (Me3Si)2(Me2PhGe)CBr (14) with bromine (X = Br) and also through the reaction of (Me3Si)2(Me2BrGe)CBr (3) with AgX (X = F, Ph2POn) or MX (M = H, Li, Na; X = OR, SR, R).Lithium organyls RLi convert 3 - 11 (X = Hal, OR, SR, Ph2POn) at low temperatures by Br/Li exchange into protolysable, thermolabile compounds (Me3Si)2(Me2XGe)CLi, and by X/R exchange into (Me3Si)2(Me2RGe)CBr.Thermal decomposition of (Me3Si)2(Me2XGe)CLi in diethyl ether at -110 to 100 deg C leads under LiX elimination to 1,3-digermacyclobutane 2 (24).The reactive intermediate is the germaethene Me2Ge=C(SiMe3)2 (2), the intermediate existence of which has been established through chemical means by trapping 2 with 2,3-dimethyl-1,3-butadiene (formation of a cycloadduct as well as an ene-reaction product).
