Synthesis and Structural and Chemical Features of Formimidoyl-Functionalized Lithium Cyclopentadienides

Treatment of 6-dimethylaminofulvene ( 1 ) with lithium anilide ( 2a ) yields lithium [( N -phenylformimidoyl)cyclopentadienide], 3a, by an anilide addition/dimethylamine elimination reaction sequence. Similar treatment of 1 with the reagents Li[HNAr] [Ar = p -tolyl ( 2b ), −2,6-dimethylphenyl ( 2c ), or −2,6-diisopropylphenyl ( 2d )] gave the corresponding Li[C 5 H 4 CH NAr] products 3b, 3c, and 3d in good yields (80−90% isolated) as THF adducts. Crystallization from THF gave 3d ·3THF, which was characterized by X-ray diffraction. It contains monomeric units in the solid state. The lithium atom is coordinated to the imino nitrogen atom and to three THF molecules in a tetrahedral arrangement. The C 5 H 4 unit shows some residual bond alternation. In crystalline 3d it exhibits no contact to the alkali metal. The structural features of 3d can be described by a resonance hybrid of mesomeric structures of iminium-cyclopentadienide (i.e., C 5 H 4 CH N(Li·3THF)Ar, 3A ) and of fulvenoide character (i.e., C 5 H 4 CHN(Li·3THF)Ar, 3B ). The structure of 3c ·3THF in the solid state is analogous. Complex 3a crystallizes with 1 equiv of THF. It exhibits a cyclodimeric structure ( 3a ·THF) 2 in the crystal, where each Li atom is η 5 -Cp- and κN-coordinated to two different C 5 H 4 CH NPh - ligands. The electrostatic nature of the Li−C and Li−N interactions results in very similar structural features of the C 5 H 4 CH NAr - ligands in the complexes 3a, 3c, and 3d . The solution structures of these systems were characterized by temperature-dependent 1 H and 7 Li NMR spectra. The reagents 3a and 3d were employed in the synthesis of the respective bis[1,1‘-( N -aryl)formimidoyl]ferrocenes 4a and 4d (both isolated in ca. 80% yield). The complexes 4a and 4b were characterized by X-ray crystal structure analyses.