Cyclotrimetallenes:  Bridged and Distorted Structures

The geometry and the energetic aspects of the stable isomers of trimetallenes (X₂YR₄:  X, Y = Si, Ge) were investigated, and some exotic di- and monobridge structures were found. Many of the bridge structures were identified as stable intermediates or transition states during the two-step substituent migration reactions. The effect of bulky substituents on the stability and geometry of the monobridge structures was studied. The bulkier bridging substituents cause a larger deviation from the ideal bridge structure. SiH₃ and Si(SiH₃)₃ substituents confer a direct benefit on the bridge geometry, in spite of their bulkiness, via electronic effects. According to these results and considering the electronic effect of the Si(SiC_nH_m)₃-type substituents, there is hope to synthesize bridge silicon compounds with bulky substituents.