The reaction of [C6H4CH2N(CH3)2]2SiCl2 (1) with hydrogen chloride gives the singly protonated adduct 2. Its solid state structure has been determined by single crystal X-ray dif fraction. Centrosymmetric 2 is orthorhombic, space group Pbca, a = 1694.9(2), b = 1161.7(2), c = 2501.7(3) pm; Z -8. Controlled hydrolysis of 1 leads to the 1,3-siloxanediol 4, probably via the precursors 3 a -3 c which could not be isolated. The hydrogen chloride formed during the hydrolysis protonates two of the dimethylamino groups, while the other two dimethylamino functions form hydrogen bonds to the silanol groups. Centrosymmetric 4: monoclinic, space group P 2Jc, a = 980.
(Me3Si0)2Si=CHCH2tBu (4) is obtained by the reaction of (Me3SiO)zSi(C1)CH=CH2 (2) with LitBu. The reaction proceeds via the a-lithiated species 3, which can be intercepted by trimethylsilyl triflate to give 5. Silaethene 4 dimerizes to the E/Z-isomers of disilacyclobutane 7 and adds to Me,SiOMe to give 6. The reactivity of 4 resembles that of ClZSi=CHCH2tBu(1): A [4 + 21 cycloadduct is obtained from the reaction with anthracene, and with 1,3-cyclohexadiene and 1,3-cycloheptadiene mixtures of monosilacyclobutanes (10 and 12) and bicyclic Diels-Alder adducts (9 and 11) are available. Exclusive [2 + 21 cycloaddition reactions take place with styrene (formation of 13), 2,3-dimethyl-l,3-butadiene (--t19), and 1,3-butadiene (+21). Detaillierte Reaktivitatsstudien an Neopentylsilaethenen
The reaction between in situ formed 1.1-dichloro-2-neopentyl-1-silene, Cl2Si=CHCH2tBu (2), and 1,1-dimethylpentafulvene (5) leads to the formation of exo/endo-isomeric [4+2] cycloadducts 9 and [2+2] stereoisomers 10 in good yields. NMR spectroscopic investigations of the product mixture prove the different modes of the silene cycloaddition reactions ([4+2] vs [2+2] addition).Treatment of 9 and 10 with LiAlH4 and LiMe yield the stereo- and regioisomeric derivatives (LiAlH4: 16, 17: MeLi: 18. 19). whereas PhMgBr reacts with 10 to give only the mono substitution, the [4+2] compound 20. and the diphenylated silacyclobutane 21. The reactions of silene 2 with pentafulvenes 6-8 lead to similar results.
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