November 2023

Journal

Linear versus Bent Uranium(II) Metallocenes─A Local Vibrational Mode Study

By:
Peluzo, Barbara; Makos, Malgorzata Z; Moura jr, Renaldo; Friendorf, Marek; Kraka, Elfi
Journal Name:
Inorganic Chemistry
Page Number:
12510-12524
Volume:
62
Issue Number:
31
Publication Date:
November 2023
View DOI Listing:
https://doi.org/10.1021/acs.inorgchem.3c01761

Abstract

Uranium metallocenes have recently attracted attention driven by their use as catalysts in organometallic synthesis. In addition to bent U(IV) and U(III), an U(II) metallocene [(η5-C5i Pr5)2U] was synthesized with an unusual linear Cp–U–Cp angle. In this work, we investigated 22 U(II) metallocenes, (i) assessing the intrinsic strength of the U-ring interactions in these complexes with a novel bond strength measure based on our local vibrational mode analysis and (ii) systematically exploring what makes these U(II) metallocenes bent. We included relativistic effects through the NESCau Hamiltonian and complemented the local mode analysis with natural bonding orbital (NBO) and quantum theory of atoms in molecules (QTAIM) data. Our study led to the following results: (i) reduction of bulky U-ring ligand substituents does not lead to bent complexes for alkyl substituents (iPr and iBu) in contrast to SiMe3 ring substituents, which are all bent. (ii) The most bent complexes are [(η5-C5H4SiMe3)2U] (130°) and [η5-P5H5)2U] (143°). (iii) Linear complexes showed one hybridized NBO with s/d character, while bent structures were characterized by s/d/f mixing. (iv) We did not observe a correlation between the strength of the U-ring interaction and the amount of the ring-U-ring bend; the strongest interaction was found for [η5-Cp)2U] and the weakest for [η5-P5H5)2U]. In conclusion, our results provide a foundation for the design of U(II) metallocenes with specific physicochemical properties and increased reactivity.