STRAINED-RING AND DOUBLE-BOND SYSTEMS CONSISTING OF THE GROUP-14 ELEMENTS SI, GE, AND SN

The organometallic chemistry of the Group 14 elements E = Si, Ge, Sn in the 1980's is highlighted by the successful construction and thorough characterization of three systems previously thought to be too reactive to exist: 1) three-membered ring compounds including cyclotrisilane, cyclotrigermane, and cyclotristannane, 2) molecules containing E-E double bonds including disilene, digermene, and distannene, and 3) strained polycycles containing a skeleton of Group 14 elements, such as bicyclo[1.1.0]tetrasilane, hexagermaprismane, and octasilacubane. The majority of these numerous compounds now available are fully substituted with bulky ligands to suppress the reactivity intrinsic to the systems. These compounds permit examinations of 1) the variation of physical and chemical properties of a system with these elements and also with the ligands and 2) how two systems are interrelated thermally and photochemically with the intermediacy of the divalent (carbene-like) species. Theoretical calculations on virtually all of the parent compounds discussed in this review are evaluated alongside the experimental results. Some polycycles may constitute a stepping-stone on the way to compounds with a triple bond.