PUB - Publikationen an der Universität Bielefeld

At variance to an earlier finding, the reaction of Me2SiCl2 with Li[(Me)N-C(Ph)-NH] (1a), in the presence of a base, gives a six-membered ring molecule mu-[(Ph)(MeN)C-N][-SiMe2-N-C(Ph) N(Ph)-SiMe2-] (s3a), whereas with Li[(PrN)-Pr-i-C(Ph)-NH] (1b), a four-mernbered ring molecule mu-[(PrN)-Pr-i(Ph)C-N](2)(SiMe2)(2) (s4b) was formed. In contrast, with Li[(BuN)-Bu-t-C(Ph)-NH] (1c), no such reaction occurred. Obviously, a delicate influence of steric effects has to be taken into account. In fact, the latter amidinate reacts with GeCl2 to form an eight-membered ring molecule [(BuN)-Bu-t-C(Ph)-N-Ge](4) (5c) without adding an additional base. The compounds are fully characterized and their structures determined by X-ray diffraction. DFT calculations confirm the dependence on steric influences. The relative energies of ground and transition states give a rationalization the ease of transformations of the various rings via pathways with penta- and hexacoordinate silicon centers, which in turn relates to the experimental results on penta- and hexacoordinate silicon amidinates and their fluctional behavior in solution. (c) 2007 Elsevier B.V. All rights reserved.