HYDROXYLAMINOSILANES - COMPOUNDS WITH BETA-DONOR-ACCEPTOR BONDS

Two series of compounds, HxSi(ONMe2)(4-x) (3a, 2a, 1a) and HxSi(ONEt2) (4-x) (3b, 2b, 1b) (with x = 1, 2, 3), have been prepared by either th e condensation of N,N-dialkylhydroxylamines with halogenosilanes in th e presence of; 2,6-lutidine as an auxiliary base or by the more select ive reaction of the O-lithiohydroxylamines with halogenosilanes at low temperatures. The compounds are very sensitive to hydrolysis, but are not pyrophoric, and are Stable at ambient temperature to a potentiall y very exothermic rearrangement into aminosilanoles. The compounds hav e been characterized by gas-phase IR and solution NMR spectroscopy (H- 1,C-13, N-15, O-17, Si-29) and by mass spectrometry. The IR frequencie s of the simplest compound H3SiONMe2 (1a) have been assigned by compar ison with ab initio frequencies. The NMR data are discussed in the lig ht of P-donor interactions. The Si-29 NMR shifts of the series HxSi(ON Me2)(4-x) are compared with those of the isoelectronic isopropoxysilan es, HxSi(OCHMe2)(4-x), which have been prepared for this purpose. Sing le crystals of H3SiONMe2 (1a), H3SiONEt2 (1b), H2Si(ONMe2)(2) (2a), an d HSi(ONMe2)3 (3a) have been grown by in situ methods, and their struc tures have been determined by X-ray diffraction. All compounds have sm all Si-O-N angles, with the minimum of 95.2 degrees occurring with H2S i(ONMe2)(2) (2a). The crystallographic data are compared with the resu lts of ab initio calculations (MP2/6-311G*) and the crystal structure of the isoelectronic H3SiOCHMe2,which has now been deterinined, and t he earlier reported Si(OCHMe2)(4). H3SiOCHMe2 crsstalizes in a transit ion state geometry according to MP2/6-311G* calculations and has a Si -O-C angle of 118.4(1)degrees. The data show clearly the large differe nces between Si-O-N and Si-O-C angles, which are attributed to the occ urrence of P-donor interactions in SiO-N units. The strength of this i nteraction has been estimatedto be 15 kJ mol(-1) from ab initio calcul ations.