Oligomeric chain-structures of substituted (dialkylaminomethyl)cyclopentadienyllithium compounds: Structural variations characterized by different involvement of the internal amino donor ligands in the solid state

Treatment of 6-dimethylaminofulvene (8) with propynyllithium (9a) results i n a clean nucleophilic addition at the electrophilic fulvene carbon atom C6 to yield the substituted lithium cyclopentadienide system [C5H4CH(C=CCH3)N CCH3)(2)]Li (10) Likewise,the addition of p-tolyllithium, n-butyllithium, o r phenyllithium resulted in the analogous substituted lithium cyclopentadie nide systems [C5H4CH(R)N(CH3)(2)]Li, 11 (R = p-tolyl), 12 (R = C4H9), or 13 (R = Ph), respectively. These four Li-cyclopentadienide systems were chara cterized by single crystal X-ray structural analyses. This has revealed a s eries of gradually different oligomeric [C5H4CH(R)N(CH3)(2)]Li structural a ggregate types in the solid state. Compound 10 crystallizes with 1 equiv of THF that is coordinated to Li. The metal is eta (5)-coordinated to the Cp ligand and kappaN-bonded to the -N(CH3)(2) substituent of the next ligand ( Li-N 2.118-(7) Angstrom), thereby constructing an oligomeric chain of a (TH F)Li(eta (5)-Cp)(L-kappaN) type. The compound 11 crystallizes without incor poration of solvent. Here the oligomeric chain is constructed by eta (5)-Cp coordination to lithium and again kappaN-bonding of the -N(CH3)(2) donor o f the adjacent ligand to the metal center. In the solvent-free system 11 th e resulting Li-N linkage (2.032(5) Angstrom) is much shorter than in 10. In 12 a beginning coordination of the lithium atom to both its neighboring Cp rings is observed. A Li cation is eta (5)-coordinated to one face of the C 5H4 ring system, whereas another lithium atom in the oligomeric chain struc ture is bonded in a eta (2)-fashion from the other face, assisted by kappaN -coordination of the attached dimethylamino substituent. Eventually, two ve ry different coordination geometries around lithium are characteristic for the oligomeric chain structure of 13: atom Li1 is rather symmetrically eta (5)-coordinated ina metallocene fashion to two cyclopentadienides, whereas the adjacent Li2 atom is coordinated to two -N(CH3)(2) groups, assisted by a weaker eta (2)- to eta (4)-Cp coordination to the attached,Cp ring system s. Supporting quantum chemical calculations have revealed rather shallow mi nima and easy conversions between these structural types. The [C5H4CH(R)NR2 '](-) ligand is thus suited to experimentally realize a whole family of nov el oligomeric (CpLi)(n) structural types.