Silylenes extrusion from disilanes

During the 1960s and 1970s, clean methods were developed for the generation of silylenes [5]. It required many years, however, for woricers in the field to recognize the connection between the most useful reactions for the production of silylenes, extrusion from disilanes and siliranes, and reactions that efficiently consume them, insertions into cr-bonds and addition to r-bonds. Yet staring us in the face was a phenomenon quite different from carbene chemistry nearly all silylene reactions are reversible [6]. This provides a compact framework within which to present a selection of the reactions that lead to silylenes and those reactions that consume them, as shown in Scheme 1. 

Silylated triphosphanes and triphosphides, synthesis, 31 188-194 yields, 31 194 Silylenes, 29 2-6 addition reactions, 29 4-6 to butadiene, 29 4 to ethylene, 29 4 to hexadienes, 29 5 mechanism, 29 4 nitric oxide scavenging, 29 4 complexes, 25 37, 51, 116, 118 as catalyst intermediates, 25 118 extrusion from disilanes, 25 114, 118 halides, 3 225 from hydridosilanes, 25 14 insertion into element-hydrogen bonds, 29 3-4... 

The much studied photochemistry of aryldisilanes carried out in earlier years has been reviewed51,52. Cleavage of the silicon-silicon bond of the disilyl moiety is always involved, but various other reactions have been observed depending on the structure of the disilane and the conditions employed. Thus cleavage to a pair of silyl radicals, path a of Scheme 15, is normally observed, and their subsequent disproportionation to a silene and silane, path b, is often observed. There is evidence that the formation of this latter pair of compounds may also occur by a concerted process directly from the photoex-cited aryldisilane (path c). Probably the most common photoreaction is a 1,3-silyl shift onto the aromatic ring to form a silatriene, 105, path d, which may proceed via radical recombination52. A very minor process, observed occasionally, is the extrusion of a silylene from the molecule (path e), as shown in Scheme 15. 

The first silylene-metal complex with no base stabilization was prepared by extrusion of SiMe2 from a substituted disilane (384), as in Eq. (165) where R is H or Me. 

---