Synthesis and Structural Characterization of (1,4-Dihydropyrid-1-yl)aluminum Complexes

The reaction between LiAlH4 and pyridine, 4-methylpyridine, or 3,5-dimethylpyridine results in hydride transfer
to the pyridine ring to give tetrakis(pyridine)lithium tetrakis(1,4-dihydropyrid-1-yl)aluminate(III), 1, tetrakis(4-methylpyridine)lithium tetrakis(1,4-dihydro-4-methylpyrid-1-yl)aluminate(III), 2, or tetrakis(3,5-dimethylpyridine)lithium tetrakis(3,5-dimethyl-1,4-dihydropyrid-1-yl)aluminate(III), 3, respectively. We claim that 1, instead of
lithium tetrakis(1,4-dihydropyrid-1-yl)aluminate(III), is the compound which is known as Lansbury's reagent.
Treatment of trimethylamine−alane, AlH3·NMe3, with pyridine yields tris(1,4-dihydropyrid-1-yl)(pyridine)aluminum, 4. It could be shown that AlH3·NMe3 initially reduces pyridine to 1,2-dihydropyridine, which is
subsequently converted into its 1,4-isomer. The X-ray crystal structures of 1−4 were determined. While the
differences between Al−N distances within each of the compounds 1−3 are not significant, 4 exhibits two distinctly
different types of Al−N bonds, the dative bond between Al and N(pyridine), d(Al−N) = 1.959(2) Å, and the
covalent bonds between Al and N(1,4-dihydropyrid-1-yl), dav(Al−N) = 1.833 Å.