Redox-Active vs Redox-Innocent: A Comparison of Uranium Complexes Containing Diamine Ligands

Scott A Pattenaude; Kimberly C Mullane; Eric J Schelter; Maryline G Ferrier; Benjamin W Stein; Sharon E Bone; Juan S Lezama Pacheco; Stosh A Kozimor; Phillip E Fanwick; Matthias Zeller; Suzanne C Bart

doi:10.1021/acs.inorgchem.8b00663

Redox-Active vs Redox-Innocent: A Comparison of Uranium Complexes Containing Diamine Ligands

Inorg Chem. 2018 Jun 4;57(11):6530-6539. doi: 10.1021/acs.inorgchem.8b00663. Epub 2018 May 11.

Affiliations

¹ H. C. Brown Laboratory, Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , United States.
² P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104 , United States.
³ Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.
⁴ Department of Earth System Science , Stanford University , Stanford , California 94305 , United States.
⁵ Department of Chemistry , Youngstown State University , Youngstown , Ohio 44555 , United States.

PMID: 29749729
DOI: 10.1021/acs.inorgchem.8b00663

Abstract

Uranium complexes (^MesDAE)₂U(THF) (1-DAE) and Cp₂U(^MesDAE) (2-DAE) (^MesDAE = [ArN-CH₂CH₂-NAr]; Ar = 2,4,6-trimethylphenyl (Mes)), bearing redox-innocent diamide ligands, have been synthesized and characterized for a full comparison with previously published, redox-active diimine complexes, (^MesDAB^Me)₂U(THF) (1-DAB) and Cp₂U(^MesDAB^Me) (2-DAB) (^MesDAB^Me = [ArN═C(Me)C(Me)═NAr]; Ar = Mes). These redox-innocent analogues maintain an analogous steric environment to their redox-active ligand counterparts to facilitate a study aimed at determining the differing electronic behavior around the uranium center. Structural analysis by X-ray crystallography showed 1-DAE and 2-DAE have a structural environment very similar to 1-DAB and 2-DAB, respectively. The main difference occurs with coordination of the ene-backbone to the uranium center in the latter species. Electronic absorption spectroscopy reveals these new DAE complexes are nearly identical to each other. X-ray absorption spectroscopy suggests all four species contain +4 uranium ions. The data also indicates that there is an electronic difference between the bis(diamide)-THF uranium complexes as opposed to those that only contain one diamide and two cyclopentadienyl rings. Finally, magnetic measurements reveal that all complexes display temperature-dependent behavior consistent with uranium(IV) ions that do not include ligand radicals. Overall, this study determines that there is no significant bonding difference between the redox-innocent and redox-active ligand frameworks on uranium. Furthermore, there are no data to suggest covalent bonding character using the latter ligand framework on uranium, despite what is known for transition metals.