Structural Features of Lithio[3]ferrocenophane Systems Bearing Stabilizing Dimethylamino Substituents

Treatment of the α-dimethylamino[3]ferrocenophane derivative 3 with n-butyllithium results in a directed o-metalation at the adjacent Cp ring of the ferrocene unit to selectively yield the (R*,R*,p-S*) diastereomer 4. Similarly, lithiation of rac-12 gives (R*,p-S*)-13. Both these compounds form meso-type dimers in the crystal that feature a central C₂Li₂ four-membered-ring moiety. Compound 13 crystallizes with excess n-butyllithium to form a (13·n-BuLi) dimer that was also characterized by X-ray diffraction. Directed lithiation of the nonbridged ferrocene derivative 1-(dimethylaminobenzyl)ferrocene (16) with tert-butyllithium resulted in an opposite stereoselectivity to yield (R*,p-R*)-17, which forms a chiral dimeric structure in the solid state, as was revealed by its X-ray crystal structure analysis.