1H-NMR studies regarding the molecular structure and the conformative mobility of paramagnetic organometallic alkoxy-complexes of uranium(IV): tris(cyclopentadienyl)-n-hexyloxy-, cyclohexyloxy- and cholesteryloxy-uranium(IV)

The properties, particularly the 1 H‐NMR spectra, of three new organometallic complexes (C 5 H 5 ) 3 UOR with R = n-hexyl, cyclohexyl, and cholesteryl (1–3) are described. The 1 H‐NMR spectra of the alkyl groups are split by the paramagnetism of the U IV ion such that each CH 2 and CH 3 group of the open-chain substituent or each individual proton in the cyclohexane ring or in the cholesteryl ring A gives rise to a discrete signal. The signals of the protons on the rigid cholesteryl framework can be assigned based on the geometric factors determined from the model. It is concluded that their paramagnetic shifts, with the exception of the α-proton, are solely due to pseudocontact interaction. The U–O–C arrangement is found to be strongly bent, making rotation around the O–C axis in the cholesteryl complex impossible due to steric hindrance. The shifts of the α-protons of the three complexes can only be interpreted if a strong, negative Fermi contact contribution, aligned with the pseudocontact component, is additionally assumed. The mobility of the C 6 H 11 ring in the cyclohexyl complex is also significantly hindered. A lower limit for the Δ G ° value of the ring inversion is determined to be 2.3 kcal/mol.