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 admixed with varying amounts of the respective 1,2-dicarbamoyl-substituted C 5 H 3 (CONHR) 2 - systems 4 and a corresponding quantity of the C 5 H 5 - starting material. Subsequent treatment of these reaction mixtures with anhydrous FeCl 2 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)TiCl 2 ] 8a (R = Ph) and 8b (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 FeCl 2 or FeCl 2 /CpLi, respectively, produces the 1,1‘-difunctionalized ferrocene 6h or the monofunctionalized ferrocene 5h . Both complexes were characterized by X-ray crystal structure analyses.