SYNTHESIS OF VOLATILE CYCLIC SILYLAMINES AND THE MOLECULAR-STRUCTURESOF 2 1-AZA-2,5-DISILACYCLOPENTANE DERIVATIVES

An optimized synthetic procedure for alpha,omega-bis (bromosilyl)alkan es, BrH2Si(CH2)(w)SiH2Br (with n = 2 and 3), is proposed. I,2-Bis(brom osilyl)ethane reacts with ammonia to give aza-2,5-disilacyclopentane-1 -yl)-1,4-disilabutane, traces of a-2,5,7,10,11,14-hexasilabicyclo[4.4. 4]tetradecane and nonvolatile products. The primary reaction products undergo slow redistribution reactions whereby -aza-2,5-disilacyclopent ane-1-yl)-1,4-disilabutane is formed as the major product. Reactions o f alpha,omega-bis(bromosilyl)alkanes, BrH2Si(CH2)(n)SiH2Br (with n = 2 and 3), with isopropylamine afford the heterocycles 1-isopropyl-1-aza -2,5-disilacyclopentane and 1-isopropyl-1-aza-2,6-disilacyclohexane, w hereas the analogous reaction with bis(bromosilyl)methane gives diisop ropyl-1,5-diaza-2,4,6,8-tetrasilacyclooctane rather than a four-member ed ring compound. All compounds have been characterized by elemental a nalysis, mass spectrometry, and IR and NMR spectroscopy [H-1, C-13, N- 15 and Si-29 including the measurement of (1)J((SiN)-Si-29-N-15) coupl ing constants]. The molecular structure of 1-isopropyl-1-aza-2,5-disil acyclopentane, determined by analysis of gas-phase electron-diffractio n data augmented by restraints derived from ab initio calculations, is compared with the molecular structure of the isoelectronic 1-(dimethy lamino)-1-aza-2,5-disilacyclopentane . The latter also was determined by gas-phase electron-diffraction (Supported by nb initio calculations ) and by low-temperature crystallography. The presence of a beta-donor Si...N interaction in the tatter compound, leading to a narrow Si-N-N angle, is apparent from a significant distortion of the molecular str ucture as compared with the isoelectronic reference compound.