Synthesis and structural and chemical features of formimidoyl-functionalized lithium cyclopentadienides

Citation
K. Kunz et al., Synthesis and structural and chemical features of formimidoyl-functionalized lithium cyclopentadienides, ORGANOMETAL, 20(3), 2001, pp. 392-400
Citations number
101
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
0276-7333 → ACNP
Volume
20
Issue
3
Year of publication
2001
Pages
392 - 400
Database
ISI
SICI code
0276-7333(20010205)20:3<392:SASACF>2.0.ZU;2-H
Abstract
Treatment of 6-dimethylaminofulvene (1) with lithium anilide (2a) yields li thium [(N-phenylformimidoyl)cyclopentadienide], 3a, by an anilide addition/ dimethylamine elimination reaction sequence. Similar treatment of 1 with th e reagents Li[HNAr] [Ar = p-tolyl (2b), -2,6-dimethylphenyl (2c), or -2,6-d iisopropylphenyl (2d)] gave the corresponding Li[C5H4 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 co ntains monomeric units in the solid state. The lithium atom is coordinated to the imino nitrogen atom and to three THF molecules in a tetrahedral arra ngement. The C5H4 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 iminiu m-cyclopentadienide (i.e., C5H4CH=N(Li . 3THF)Ar, 3A) and of fulvenoide cha racter (i.e., C5H4=CHN(Li . 3THF)Ar, 3B). The structure of 3c.3THF in the s olid state is analogous. Complex 3a crystallizes with 1 equiv of THF. It ex hibits a cyclodimeric structure (3a.THF)(2) in the crystal, where each Li a tom is eta (5)-Cp- and N-K-coordinated to two different C5H4CH=NPh- ligands . The electrostatic nature of the Li-C and Li-N interactions results in ver y similar structural features of the C5H4CH=NAr- ligands in the complexes 3 a, 3c, and 3d. The solution structures of these systems were characterized by temperature-dependent H-1 and Li-7 NMR spectra. The reagents 3a and 3d w ere employed in the synthesis of the respective bis [1, 1'-(N-aryl)formimid oyl] ferrocenes 4a and 4d (both isolated in ca. 80% yield). The complexes 4 a and 4b were characterized by X-ray crystal structure analyses.