MULTINUCLEAR MAGNETIC-RESONANCE STUDY OF N,N',N''-TRIS(TRIMETHYLSILYL)BORAZINE

The nuclear spin relaxation rate of the quadrupolar N-14 nuclei in N,N ',N''-tris(trimethylsilyl)borazine (1) is surprisingly slow [T-1(N-14) = 0.1 s]. This allows one to measure (1)J((SiN)-Si-29-N-14) (9.6 Hz) directly from the Si-29 NMR spectra and also to compare signs of coupl ing constants (1)J((SiN)-Si-29-N-14) (<0) and (3)J((NSiCH)-N-14-H-1) ( >0) by 2D Si-29/H-1 HETCOR experiments. Since the transverse relaxatio n time T-2(N-14) in 1 is governed by scaler relaxation of the second k ind, the magnitude of (1)J((NB)-N-14-B-11) can be evaluated (23 +/- 0. 5 Hz). B-11, N-14 and Si-29 NMR data for N,N'-bis(trimethylsilyl)boraz ine (2) were also obtained, and B-11 and N-14 NMR spectra of the paren t borazine [HBNH](3) (3), and of [HBNMe](3) (4) were remeasured. Calcu lation of the tenser components of the N-14 electric field gradient sh ows that eq(zz) in 1 and in 2 for N-14(SS) is significantly smaller th an for other borazines [HBNR](3), ag. with R = H (3) or Me (4), in agr eement with the experimental results.