2-STANNYLPYRIDINE-BORANE ADDUCTS - MULTINUCLEAR MAGNETIC-RESONANCE STUDY AND X-RAY STRUCTURE DETERMINATION OF A 1,4-DIHYDRO-4A,1,4-AZASTANNABORA-NAPHTHALENE DERIVATIVE

The adduct formation between 2-trimethylstannyl-pyridine (1) and triet hylborane, leading to 2a, and 9-borabicyclo[3.3.1]nonane, leading to 2 b, was studied by H-1, B-11, C-13, N-15 and Sn-119 NMR in solution. Ch anges in the magnitude of the coupling constants J(Sn-119,C-13), with respect to the data for 1, were analysed. The absolute signs have been determined [all coupling constants (n)J(Sn-119,C-13) to methyl and py ridine carbon atoms in 1 to 3 possess a negative sign and the same is true for (n)J(Sn-119,H-1) of the pyridine hydrogen atoms] by various t wo-dimensional NMR experiments, and attributed to the influence of the lone pair of electrons at the nitrogen atom in 1, The NMR spectroscop ic results for the 1,4-dihydro-4a,1,4-azastannabora-naphthalene deriva tive 3, in which structural fragments are present analogous to those i n the borane adducts 2, correspond to those for 1 and 2a,b. The molecu lar structure of 3 has been determined by X-ray analysis [orthorhombic ; P2(1)2(1)2(1); a = 713.9(2), b = 1566.0(2), c = 1578.4(2) pm]. Solid -state C-13 and Sn-119 CP/MAS NMR spectra prove that the molecular str uctures of 3 in the solid state and in solution are very similar.