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Treatment of 3-phenylcyclopent-2-enone (1) with either morpholine or pyrrolidine in the presence of 3 Å molecular sieves yielded the corresponding cyclopentadienamines 2a and 2b. Subsequent deprotonation with n-butyllithium followed by the reaction with zirconium tetrachloride led to the formation of the amino-substituted bent metallocenes 4a and 4b. Crystallization furnished the isomerically pure complex meso-bis(phenyl-3-pyrrolidinylcyclopentadienyl)zirconium dichloride (meso-4b), which was characterized by X-ray diffraction. Complex meso-4b exhibits a C(Cp)-N bond length of 1.349(3) Å. A rotational barrier of ∆G q (CN-rot) (248 K) ) 12.1 ( 0.2 kcal mol -1 was measured for meso-4b in solution by dynamic 600 MHz 1 H NMR spectroscopy. Similar treatment of 2-indanone with morpholine, followed by deprotonation and reaction with ZrCl 4 , gave bis(2-morpholinoindenyl)ZrCl 2 (7a), which was also characterized by an X-ray crystal structure analysis (the indenyl-C2/12-N bond lengths are 1.349(5)/1.381(5) Å). Two rotational processes were subsequently frozen out on the 600 MHz 1 H NMR time scale upon decreasing the temperature from ambient to give a C-N rotational barrier of ∆G q (CN-rot) (268 K) ) 12.9 ( 0.2 kcal mol -1 and an activation energy of the rotation about the zirconium-Cp(indenyl) vector of ∆G q (Ind-rot) (178 K) ) 7.6 ( 0.5 kcal mol -1 . In solution and in the solid state only a single C 2 -symmetric metallocene rotamer of 7a was detected. The same is found for bis(2-pyrrolidinoindenyl)ZrCl 2 (7b). By dynamic 1 H NMR spectroscopy the two rotational activation barriers of complex 7b were determined as ∆G q (CN-rot) (338 K) ) 16.4 ( 0.2 kcal mol -1 and ∆G q (Ind-rot) (198 K) ) 9.1 ( 0.5 kcal mol -1 .

New metallocene Ziegler catalysts are generated by activation of the rigid ansa‐metallocenes 2 with methylalumoxane. Complexes 2 are formed by application of an acid‐catalyzed Mannich reaction—a classical reaction from the synthetic organic repertoire—of complexes 1, which are readily available by means of a fulvene route.

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