Isolation, characterisation, and solution structures of the bis(pyridine) complex of the n-butyllithium-pyridine adduct, Bun(C5H5N)Li·2C5H5N, its mode of decomposition, and ab initio calculations on model systems

The complexed adduct, Bun(C5H5N)Li·2C5H5N (3) has been isolated from the reaction of BunLi with a 3-fold molar excess of pyridine, and characterised fully by analysis and by 1H, 13C NMR spectroscopy. Ab initio calculations on model systems have shown that the formation of 3 probably involves initial complexation of the organolithium to the pyridine nitrogen atom, and that subsequent addition to the aromatic ring is aided by the presence of donor (pyridine) molecules. Cryoscopic molecular mass measurements imply that adduct 3 is essentially monomeric in arene solution, so that the 1/1/1 7Li NMR resonances observed at low temperatures can be provisionally attributed to conformers arising due to the presence of chiral (BunC5H5N)-nitrogen and -C(2) centres. High-field 1H NMR spectra of solutions of 3 of various ages and of various thermal/photochemical histories have shown that conversion of 3 into 2-butylpyridine (1) proceeds at least in part via hydrolysis to 1,2-dihydro-2-butylpyridine (4).