2-Stannylpyridine-Borane Adducts - Multinuclear Magnetic Resonance Study and X-Ray Structure Determination of a l,4-Dihydro-4 a,l,4-azastannabora-naphthalene Derivative

The adduct formation between 2-trimethylstannyl-pyridine (1) and triethylborane, leading to 2a, and 9-borabicyclo[3.3.1]nonane, leading to 2b, was studied by ’H, “ B, 13C, 15N and 119Sn NMR in solution. Changes in the magnitude of the coupling constants 7(119Sn, 13C), with respect to the data for 1, were analysed. The absolute signs have been determined [all coupling constants " / (119Sn,13C) to methyl and pyridine carbon atoms in 1 to 3 possess a negative sign and the same is true for "y(119Sn,*H) of the pyridine hydrogen atoms] by various two-dimensional NMR experiments, and attributed to the influence of the lone pair of electrons at the nitrogen atom in 1. The NMR spectroscopic results for the 1,4-dihydro4a,l,4-azastannabora-naphthalene derivative 3, in which structural fragments are present analogous to those in 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 [orthor’nombic; P 2 i2121; a = 713.9(2), b = 1566.0(2), c 1578.4(2) pm]. Solid-state 13C and 119Sn CP/MAS NMR spectra prove that the molecular structures of 3 in the solid state and in solution are very similar.