Spin-spin coupling constants 1J(27Al,13C) and 1J(13C,11B) in comparable organoaluminum and -boron compounds.: NMR spectroscopy of lithium tetra(tert-butyl)alanate

The C-13, Al-27 and B-11 NMR spectra of tri(tert-butyl)alane, AlBu'(3), and of the corresponding borane, BBu'(3), respectively, were examined in order to determine the magnitude of the coupling constants (1)J(Al-27, C-13) = 94 +/- 5 Hz and (1)J(C-13, B-11) = 52 +/- 2 Hz by measurement of the line widths of the 13 C NMR signals and of the relaxation rates of the quadrupolar Al-27 and B-11 nuclei. This is the first example of (1)J(Al-27, C-13) determined for a monomeric trialkylalane. In addition, the coupling constants were calculated by DFT methods (B3LYP) using the 6-311 +G(d,p) basis set. The H-1, C-13 and 27 At NMR spectra of lithium tetra(tert-butyl)alanate, Li[AlBu'(4)], were measured under various conditions. Ion-pair separation in THF revealed the expected patterns for Al-27-C-13 spin-spin coupling across one and two bonds as well as for the three-bond Al-27-H-1 spin-spin coupling.