Coordination of the Bis(pyridyl)methyl Substituent to Group 1 and 13 Metals

The bis(pyridy1)methyl derivatives C(thf)~Li(2-NCs&>,CHl[, HzC(~-NC~H~)ZL~(~-NC~&)ZCHI,[Li(l2-crown-4)21[Li((2-NC&4)~CH}2[1N, a(thf)6l[Li{(2-C5H4)2CH}~[lM, eA(2-NC&)2-CHI, and [M~ZG~(~-NC&)~hCavHe ]b een synthesized and characterized by low-temperature X-ray structure determination. Although deprotonated at the central carbon atoms, they are only formally carbanions. All experimental structural parameters indicate that they are better described as amides. The bis(pyridy1)methyl ligand coordinates lithium, aluminum, and gallium with both nitrogen ring atoms. All anions are planar and fully conjugated. Two anions coordinated to a single lithium atom seem favorable, because this structural motif of the overall anion is present in the structure of a lithium lithiate and a sodium lithiate. In the first structure, the lithium cation is complexed by two crown ether molecules, in the latter, the sodium cation is complexed by six thf molecules. Crystals of this compound melt at about -30 "C. At -80 "C, it is possible to isolate an intermediate with lithium coordinated by one bis(pyridy1)methyl anion and one molecule bis(pyridy1)- methane, which donates the lithium atom like a nitrogen base. This intermediate gives direct access to the structural comparison of the starting material and the anion. In all metal complexes, the double bonds of the anion are localized, regardless of group 1 or group 13 metals. Lithium, aluminum, and gallium match in size and fit the bite of the bis(pyridy1)- methyl ligands. The bigger sodium cation is complexed by thf molecules.