Thermische Stabilisierung des Silaethens Ph 2 Si=C(SiMe 3 ) 2

Thermal Stabilization of the Silaethene Ph 2 Si=C(SiMe 3 ) 2Frühere Mitteilungen: Lit.Herrn Prof. Dr. Manfred Regitz zum 60. Geburtstag gewidmet. Silaethene Ph 2 Si=C(SiMe 3 ) 2 ( 3 ) (generated from Ph 2 SiBr‐C‐Li(SiMe 3 )2 = 3 · LiBr in Et 2 O 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 Me 2 Si=C(SiMePh 2 )(SiMe 3 ) ( 3a ), then into medium stable PhMeSi=C(SiMe 2 Ph)(SiMe 3 ) ( 3b ), and finally into most stable Me 2 Si=C(SiMe 2 Ph) 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 Et 2 O; 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 Ph 2 ,C=N‐SiMe 3 ;cf. Scheme 4) are observed.