The changing structural chemistry of lithium anilide on solvation by pyridine, 4-methylpyridine or 4-tert-butylpyridine

A family of crystalline lithium anilide solvates, [{PhN(H)Li .(pyr)(2)}(2)] 1, [{PhN(H)Li .(4-Me-pyr)(2)}(2)] 2 and [{PhN(H)Li}(4).(4-Bu-t-pyr)(6)] 3 has been synthesised by reacting the aromatic primary amide with two molar equivalents of the appropriate pyridine-based solvent (pyridine, 4-methylpyridine and 4-tert-butylpyridine, respectively) in hexane-toluene solution. X-Ray crystallographic studies have revealed three contrasting structures: 1 adopts a dinuclear, dimeric [(anilido)N-Li](2) ring arrangement with a transoid (anti) conformation of amido substituents; 2 adopts a similar arrangement but with a cisoid (syn) conformation of amido substituents; and 3 adopts a novel tetranuclear arrangement with a central [(anilido)N-Li](2) transoid ring, separating two mixed ligand [(anilido)N-Li-(pyr)N-Li] rings, made possible by the unusual mu-bonding of a 4-tert-butylpyridine ligand. A combination of H-1, Li-7 and C-13 NMR spectroscopic studies at 300 K suggests similar environments exist for corresponding atoms in [H-2(8)]-toluene solutions of 1, 2 or 3. Further examination of the solution of 3 over the temperature window (300-193 K) has detected a fluxional structure involving the intramolecular exchange of two distinct types of anilido ligand, consistent with those present in the molecular structure of crystalline 3.