title: Investigation of the electronic ground states for a reduced pyridine(diimine) uranium series: evidence for a ligand tetraanion stabilized by a uranium dimer.
abstract: The electronic structures of a series of highly reduced uranium complexes bearing the redox-active pyridine(diimine) ligand, (Mes)PDI(Me) ((Mes)PDI(Me) = 2,6-(2,4,6-Me3-C6H2-N═CMe)2C5H3N) have been investigated. The complexes, ((Mes)PDI(Me))UI3(THF) (1), ((Mes)PDI(Me))UI2(THF)2 (2), [((Mes)PDI(Me))UI]2 (3), and [((Mes)PDI(Me))U(THF)]2 (4), were examined using electronic and X-ray absorption spectroscopies, magnetometry, and computational analyses. Taken together, these studies suggest that all members of the series contain uranium(IV) centers with 5f (2) configurations and reduced ligand frameworks, specifically [(Mes)PDI(Me)](•/-), [(Mes)PDI(Me)](2-), [(Mes)PDI(Me)](3-) and [(Mes)PDI(Me)](4-), respectively. In the cases of 2, 3, and 4 no unpaired spin density was found on the ligands, indicating a singlet diradical ligand in monomeric 2 and ligand electron spin-pairing through dimerization in 3 and 4. Interaction energies, representing enthalpies of dimerization, of -116.0 and -144.4 kcal mol(-1) were calculated using DFT for the monomers of 3 and 4, respectively, showing there is a large stabilization gained by dimerization through uranium-arene bonds. Highlighted in these studies is compound 4, bearing a previously unobserved pyridine(diimine) tetraanion, that was uniquely stabilized by backbonding between uranium cations and the η(5)-pyridyl ring.
authors.affiliation: †H.C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Nickolas H
authors.initials: NH
authors.lastname: Anderson
authors.affiliation: ‡Department of Chemistry, Supercomputing Institute, and Chemical Theory Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Samuel O
authors.initials: SO
authors.lastname: Odoh
authors.affiliation: §P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Ursula J
authors.initials: UJ
authors.lastname: Williams
authors.affiliation: §P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Lewis
authors.affiliation: ∥Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Wagner
authors.affiliation: ⊥School of Earth Sciences, Environmental Earth System Science Department, Stanford University, Stanford, California 94305-4216, United States.
authors.forename: Juan
authors.initials: J
authors.lastname: Lezama Pacheco
authors.affiliation: ∥Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.affiliation: ‡Department of Chemistry, Supercomputing Institute, and Chemical Theory Center, University of Minnesota, Minneapolis, Minnesota 55455, United States.
authors.forename: Laura
authors.initials: L
authors.lastname: Gagliardi
authors.affiliation: §P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Schelter
authors.affiliation: †H.C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Bart
mesh_terms: D019281:Dimerization; D004583:Electrons; D008024:Ligands; D060328:Magnetic Phenomena; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D014501:Uranium / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D014501:Uranium; C023666:pyridine