Thermische Stabilisierung des Silaethens Ph2Si=C(SiMe3)2

Abstract

Thermal Stabilization of the Silaethene Ph2Si=C(SiMe3)2Frühere Mitteilungen: Lit. Herrn Prof. Dr. Manfred Regitz zum 60. Geburtstag gewidmet. Silaethene Ph2Si=C(SiMe3)2 (3) (generated from Ph2SiBr‐C‐Li(SiMe3)2 = 3 · LiBr in Et2O at ‐78·C) reversibly isomerizes fast by methyl migration, then a bit slower by phenyl migration, and finally fast by methyl migration into thermodynamically more stable Me2Si=C(SiMePh2)(SiMe3) (3a), then into medium stable PhMeSi=C(SiMe2Ph)(SiMe3) (3b), and finally into most stable Me2Si=C(SiMe2Ph)2 (3c) (cf. Schemes 1 and 2; Figure 1). Simultaneously with isomerization 3a · 3c [2 + 2] cycloadditions (dimerizations) of 3a and 3c occur (formation of 3a · 3a, 3a · 3c, 3c · 3c; cf. Scheme 2). Over and above that, silaethenes 3a and 3c irreversibly isomerize into disilaindanes 4a, 4b, and 4c (cf. Scheme 6). Certainly, the latter reactions are even slow at 100·C. Thermolysis of 3a · 3a, 3a · 3c, 3c · 3c at 340·C, on the other hand, leads by way of [2 + 2] cycloreversion and the intermediate formation of an equilibrium mixture of 3, 3a, 3b, 3c almost quantitatively to 4. In addition to the thermolysis products mentioned above, products of 3 and its isomers 3a, 3b, 3c with the solvents (for example Et2O; cf. Scheme 7), with the silaethene sources (for example 3 · LiBr; cf. Scheme 8), or with products formed from sources besides silaethene 3 (for example Ph2,C=N‐SiMe3;cf. Scheme 4) are observed.