STRUCTURE AND PROPERTIES OF 3-(DIETHYLBORYL)PYRIDINES

3-(Diethylboryl)pyridine (1a), a versatile starting material for the p reparation of arylpyridines, is notable for its stability under ambien t conditions, in spite of little steric hindrance on the boron atom. H -1 and C-13 spectra of 1a indicated that the boryl group does not act as a mere pi-acceptor and that the boron atom is shielded by ca. 50 pp m even when compared with trivalent boron atoms conjugated with the pi -donor. A single-crystal X-ray crystallographic study for la revealed formation of a cyclic-tetramer with a void via the intermolecular boro n-nitrogen coordination bond. Vapor pressure osmometry in various solv ents suggested that la comprises the tetramer in these solutions. In o rder to know the actual structure, synthesis of 3-(2-methoxyethoxy)-5- (diethylboryl)pyridine (1b) and its scrambling experiment with 1a were carried out. Heating at 100 degrees C for 24 h was required to attain the equilibrium of the scrambling of the component molecules in the t etramers. This means that 3-(diethylboryl)pyridines 1a and 1b comprise the rigid cyclic-tetramer in solution at ambient temperature. Compoun d 1b is stable in aerated tetrahydrofuran containing up to 33 % water.