Synthesis, characterization and comparison of group 14 pyrrolides and indolides Ph3MX (M = Si, Ge, Sn; X = C4H4N, C8H6N)

The biologically important heterocycles pyrrole, C₄H₄N, and indole, C₈H₆N, ought to be useful as reagents in organic synthesis. Unfortunately, working with them has proved to be difficult because they tend to self-polymerize in solution, especially in the presence of acid catalysts. When the self-polymerization can be controlled, however, the pyrrole and indole units should provide an important route to selective N-metal binding, particularly when these ligands are activated by alkyl-lithium reagents. Using this approach, a general synthesis of the group 14 pyrrolides and indolides, Ph₃MX (M = Si, Ge, Sn; X = C₄H₄N, C₈H₆N), has been developed and the results are reported here. The compounds are formed as high-melting, white crystalline solids and have been characterized by ¹³C-, ²⁹Si- and ¹¹⁹Sn-NMR, Raman and electron-impact mass spectroscopy as well as elemental analysis. A single-crystal X-ray study of Ph₃Si(C₄H₄N) has shown that the compound is disordered in the tetragonal lattice, even at low temperature (100 K).