Head-to-head versus head-to-tail dimerizations of transient silenes — the generation and dimerization behavior of 2-(2-dimethylaminoaryl)-1,1-bis(trimethylsilyl)silenes

Abstract

The transient silenes (Me 3Si) 2SiCR 1R 2 ( 4: R 1=H, R 2=2-Me 2N-5-Me–C 6H 3; 11: R 1=Me, R 2=2-Me 2N–C 6H 4; 15: R 1=3,5-Me 2–C 6H 3, R 2=2-Me 2N–C 6H 4; 18: R 1=Me, R 2=2-Me 2N-5-Me–C 6H 3) were generated following the mechanism of the sila-Peterson reaction. Thus, 4 was obtained by base-induced trimethylsilanol elimination from (2-dimethylamino-5-methylphenyl)tris(trimethylsilyl)silylmethanol ( 3). Addition of methyllithium or 3,5-dimethylphenyllithium, respectively, to the carbonyl group of 2-dimethylaminobenzoyl-tris(trimethylsilyl)silane ( 10) and subsequent elimination of Me 3SiOLi led to 11 and 15, respectively. Similarly, (2-dimethylamino-5-methylbenzoyl)-tris(trimethylsilyl)silane ( 17) and MeLi gave 18. The silene 4 underwent a spontaneous head-to-tail cyclodimerization to give a 1,3-disilacyclobutane ( 5), whereas 11 afforded a linear head-to-head dimer ( 12). The dimerization rates of 15 and 18 proved to be slow, thus, under the conditions of the sila-Peterson reaction readdition products of eliminated trimethylsilanolate to the SiC bond of the silenes were obtained ( 16, 19). The structures of the compounds prepared were elucidated on the basis of comprehensive NMR and MS studies; for 5 also the results of an X-ray structural analysis are given. Possible reasons for the different behavior of the similarly structured silenes are discussed.