THERMAL STABILIZATION OF THE SILAETHENE P H(2)SI=C(SIME(3))(2)

Silaethene Ph(2)Si=C(SiMe(3))(2) (3) (generated from Ph(2)SiBr-C-Li(Si Me(3))(2)=3 . LiBr in Et(2)O at -78 degrees C) reversibly isomerizes f ast by methyl migration, then a bit slower by phenyl migration, and fi nally 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 isomeriz ation 3a --> 3c [2 + 2] cycloadditions (dimerizations) of 3a and 3c oc cur (formation of 3a . 3a, 3a . 3c, 3c . 3c; cf. Scheme 2). Over and a bove that, silaethenes 3a and 3c irreversibly isomerize into disilaind anes 4a, 4b, and 4c (cf. Scheme 6). Certainly, the latter reactions ar e 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] cyclorev ersion 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 wit h 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.