A Retro-Diels Alder route to Tetramethyldisilene Me2Si=SiMe2 revisited: Flow Pyrolysis of 1,1,2,2-Tetramethyl-1,2-disilacyclohex-4-ene

Reinvestigation of the flow pyrolysis of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene did not identify conditions under which the retro-Diels Alder reaction was the exclusive process. Extrusion of Me₂Si=SiMe₂was confirmed, but dimerization of directly extruded Me₂Si: contributes significantly to its formation. Rearrangement of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene to 1,1,3,3-tetramethyl-1,3-disilacyclohex-4-ene is a major process under a variety of conditions. Computational studies reduced the number of viable pathways. Both experimental and computational results point to stepwise extrusion of Me₂Si=SiMe₂ via a diradical intermediate and to linkage by one or more common intermediates of the extrusion pathway and the pathway leading to rearranged disilacyclohexene. Such a mechanism receives support from the formation of 1,2- and 1,3-disilacyclohex-4-enes, that is both the Diels-Alder product and the rearrangement product, in the addition of Me₂Si=SiMe₂ to butadiene. Dedicated to Professor Mitsuo Kira on the occasion of his being honored for his inspiring work as the recipient of the 2005 Wacker Silicon Award.