TETRA-PARA-TOLYL COMPOUNDS PARA-TOL4SI AND PARA-TOL4GE - CONFIGURATION OF TETRARYL METHANEANALOGS AR4M (M = C,SI,GE,SN,PB)

p-Tol4Si and p-Tol4Ge have been obtained from the reaction of p-TolLi with SiCl4 and of p-TolMgBr with GeCl4, respectively. The crystal structures have been determined and compared with those of the homologous compounds p-Tol4Sn and p-Tol4Pb. The latter two molecules (space group I4BAR) exhibit a S4 axis running between the aromatic groups and are shortened along this axis: all four p-Tol groups are closer together than in an undistorted tetrahedron. In the cases of the silane and germane (space group Pc), the tetrahedron is lengthened along one of the bond axes C-M: only three of the four p-Tol groups are closer together, and the set up of a special molecular symmetry is blocked. All this is caused by the different atomic radii of the central atoms. C-13 NMR data in CDCl3 solution are given.