HYDRIDE AND FLUORIDE TRANSFER REACTIONS ACCOMPANYING NUCLEOPHILIC SUBSTITUTION AT PENTACOORDINATE SILICON

摘要

The syntheses of aminoazasilatranes of the type R(2)NSi(R'NCH2CH2)(3)N (R' = H, R = H (2a), CH3 (3a), CH2CH3 (4a), Si(CH3)(3) (6a), R' = CH3, R = H (2b), CH3 (3b), CH2CH3 (4b), Si(CH3)(3) (6b) via nucleophilic substitution reactions of ClSi(R'NCH2CH2)(3)N (R' = H (7a), R' = CH3 (7b), respectively) with amide anions are reported. Reactivities of 7a and 7b;toward other nucleophilic reagents such as alkyllithiums and Group 1 metal alkoxides are also described. It is found that the equatorial NR' functionalities significantly influence the reaction pathways. With strong bases, lithiation of the equatorial NH hydrogens of 7a predominated along with some nucleophilic substitution products and hydride transfer product HSi(HNCH2CH2)(3)N, 1a. With 7b, however, equatorial nitrogen Lithiation is precluded and its reaction with nucleophiles can produce substantial amounts of nucleophilic substitution product as well as hydride transfer product HSi(CH3NCH2CH2)(3)N, 1b. The relative ratios of these products depend substantially on stereoelectronic factors, the nature of the nucleophilic reagents, and the reaction conditions. In the case of the reaction of 7b with BrC5F5-BuLi, three products, namely, C6F5Si(CH3NCH2CH2)(3)N (13b), FSi(CH3NCH2CH2)(3)N (14b), and C6F5Si(CH3NCH2CH2)(2)(o-C6F4CH3NCH2CH2)N (15) formed in;an approximate ratio of 1:2:1. The formation of 15 is attributed to perfluorobenzyne insertion into a Si-N-eq bond of (13b). Interestingly, the plane defined by the axial NSi2 moiety in 6a is found to be fixed at the apical position of the silicon, providing an interesting example of p pi-d pi interaction between a pentacoordinate silicon and a nitrogen. However, the axial moiety in analogue 6b freely rotates around the apical Si-N bond due to steric interactions with nearby methyl groups on the cage. [References: 60]