TORSIONAL DISTORTIONS IN TRIMESITYLSILANES AND TRIMESITYLGERMANES

The crystal structures have been solved for allyltrimesitylsilane (3), trimesitylsilane (4), and trimesitylgermane (5). Steric congestion ca used by the three mesityl groups causes some lengthening of the Si-C a nd Ge-C bonds. The C-Si-C and C-Ge-C bond angles are increased when X is not H. Distortion is relieved by rotating the plane of the phenyl r ings to create a propeller conformation. The same distortion has been found in unpublished data of the reported crystal structures of trimes itylsilyl azide (6) and aminotrimesitylgermane (7). Despite the variet y of substituents (allyl, amino, azido, H) and the two different centr al atoms (Si, Ge), the twist angle of the propeller (compared with a c onformation lacking any twist) lies between 41.6 and 48 degrees for al l five systems. (C) 1998 Elsevier Science S.A. All rights reserved.