29Si and 13C chemical shifts and coupling constants of tris(phenyldimethylsilyl)methyl silicon compounds

Abstract

Silicon-29 (δ 29Si) NMR chemical shifts are reported for the first time for a number of tris(phenyldimethylsilyl)methyl silicon compounds (disilylated derivatives), (PhMe 2Si A) 3C αL, where LSi BR 1R 2R 3, where R varies widely in electronegativity. δ 29Si B for these series exhibited to some extent good correlations with the electronegativities of the groups bonded to silicon (particularly, δ 29Si BMe 2X, X H, OH, OCH 3, COCH 3 and Cl). Substitution with electronegative atoms shifts the chemical shift of silicon to high field. The 13C NMR spectra of these compounds have been recorded and assigned. The chemical shifts of the α-carbon (C α) resonances are shown to depend on the type of substituent on the silicon-B, thus 13C α exhibit downfield shifts when X=oxygen ligand. The 13C phenyl resonances have been measured and show the same order of o, m and p signals, viz. δ ortho (downfield)>δ para>δ meta. The variation of 29Si- 1H coupling constants with the electronegativity of X was studied.