π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements

The Chemistry of Silenes

Publisher Summary The chapter describes the structure and bonding in the parent hydrides and multiply bonded silicon and germanium compound. Experimental and theoretical studies of unsaturated silicon and germanium compounds have produced a wealth of new and unexpected phenomena, and more is sure to come. Foremost among those already recognized is the enhanced stability of divalent isomers in these systems, but we should include, as well, the trans-bent nature of double- and triple-bonded systems, the curious inversion of single- and double-bond dissociation energies, and the emergence of low lying stable or ground state bridged isomers. Many of these new phenomena are foreshadowed by the properties of the parent hydrides. The reversal of the patterns in the sequential bond dissociation energies of CH, compared to SiH, and GeH, already gives a clue to the lack of any special stability associated with sp2 hybridized bonding environments. Furthermore, the pyramidal nature of silyl and germyl radicals, and the large barriers to linearity in SiH, and certainly GeH, as well, presages the instability of the planar and linear bonding environment customarily seen in alkenes and alkynes, respectively.

K. D. Dobbs

Papers

.pi.-Bond strengths in main-group olefin analogs