Speicherung des labilen Silaethens Me₂Si=C(SiMe₃)₂ mit Benzophenon [1] / Storing of the Labile Silaethene Me₂Si = C(SiMe₃)₂ with Benzophenone [1]

Abstract

Benzophenone Ph 2 C=O is able to “store” the silaethene Me 2 Si=C(SiMe 3 ) 2 (1). produced from Me 2 SiX-CLi(SiMe 3 ) 2 (X = F. Br, Ph 2 PO 4 ), under formation of a [2+4] cycloadduct (2b). At about 100 °C, 2b by way of 1 transfers into the [2+2] cycloadduct of 1 and Ph 2 C=O (3b), which in the course of transformation decomposes visibly (in the absence of Me 3 SiCl) or only by traces (in the presence of Me 3 SiCl) to secondary products. In the presence of ROH (R = H. Me. tBu. MeCO) or PhN = NSiMe 3 or RN 3 (R = tBu. Me 3 Si) or 2,3-dimethylbutadiene (dmb) about 100 °C 2b and 3b form by way of 1 insertion products of 1 into the OH bond of ROH or a [2+2] cycloadduct of 1 and PhN = NSiMe 3 or [2 + 3] cycloadducts of 1 and RN 3 or a [2+4] cycloadduct and an ene reaction product of 1 and dmb. The rate constants/half lives of the first order transformation of 2b into 3b or of the first order decomposition of 2b or of 3b in the presence of reactiv traps for 1 (ROH. Me 3 SiN 3 ; benzene as solvent) are in the order of 0.3 × 10 -4 s -1 /τ 1/2 = 7 h (2b→3b; 90 °C) 3 3×10 -4 s -1 /τ 1/2 = 3/4 h (2b + traps; 90 °C), 0.4 × 10 -4 s -1 /τ 1/2 = 5 h (3b + traps. 110 °C).