The isocyanate route to cyclopentadienyl-carboxamide- and cyclopentadienyl-amino ester-substituted metallocene complexes

Lithium cyclopentadienide adds to a variety of isocyanates [R-N=C=O, R = tert-butyl (a), n-butyl (b), cyclohexyl (c), phenyl (d), 3-pyridyl (e), 2-tetrahydropyranyl (f), adamantyl (g)] to yield the monocarbamoyl-substituted cyclopentadienides C(5)H(4)CONHR(-) 3 admired with varying amounts of the respective 1,2-dicarbamoyl-substituted C5H3(CONHR)(2)(-) systems 4 and a corresponding quantity of the C5H5- Starting material. Subsequent treatment of these reaction mixtures with anhydrous FeCl2 gave the 1,1'-dicarbamoylferrocenes 6 and the corresponding monocarbamoylferrocenes 5, which were easily separated by chromatography. The carbamoylferrocenes 5b, 5c, and 6d were characterized by X-ray crystal structure analyses. The (N-phenyl- and (N-adamantylcarbamoyl)cyclopentadienides were treated with CpTiCl(3) to give the carboxamide-substituted titanocene dichloride complexes [CP(C(5)H(4)CONHR)TiCl2] 8a (R = Ph) and Sh (R = adamantyl), respectively. Complex 8b was also characterized by X-ray diffraction. The valine ester-derived isocyanate reacts with lithium cyclopentadienide to give the N-valinyl-substituted carbamoylcyclopentadienide 3h. Subsequent treatment with FeCl2 or FeCl2/CpLi, respectively, produces the 1,1'-difunctionalized ferrocene 6h or the monofunctionalized ferrocene 5h. Both complexes were characterized by X-ray crystal structure analyses.