Synthesis and structural characterization of (1,4-dihydropyrid-1-yl)aluminum complexes

The reaction between LiAlH4 and pyridine, 4-methylpyridine, or 3,5-dimethyl pyridine 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, inst ead of lithium tetrakis(1,4-dihydropyrid-1-yl)aluminate(III), is the compou nd which is known as Lansbury's reagent. Treatment of trimethylamine-alane, AlH3. NMe3, with pyridine yields tris(1,4-dihydropyrid-1-yl)(pyridine)alum inum, 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 bet ween 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 bet ween Al and N(pyridine), d(Al-N) = 1.959(2) Angstrom, and the covalent bond s between Al and N(1,4-dihydropyrid-1-yl), d(av)(Al-N) = 1.833 Angstrom.