Thermal stabilization of the silaethene Ph(2)Si=C(SiMe(3))(2)

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 degrees 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 degrees C. Thermolysis of 3a . 3a, 3a . 3c, 3c . 3c at 340 degrees 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.