Elucidating the Mechanism of Uranium Mediated Diazene N?N Bond Cleavage
By Kiernicki, John J.; Higgins, Robert F.; Kraft, Steven J.; Zeller, Matthias; Shores, Matthew P.; Bart, Suzanne C.
Published in Inorganic Chemistry
2016
Abstract
Investigation into the reactivity of reduced uranium species toward diazenes has revealed key intermediates in the four-electron cleavage of azobenzene. Trivalent Tp*2U(CH2Ph) (1a) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) and Tp*2U(2,2?-bpy) (1b) both perform the two-electron reduction of diazenes affording ?2-hydrazido complexes Tp*2U(AzBz) (2-AzBz) (AzBz = azobenzene) and Tp*2U(BCC) (2-BCC) (BCC = benzo[c]cinnoline) in contrast to precursors of the bis(Cp*) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide) ligand framework. The four-electron cleavage of diazenes to give trans-bis(imido) species was possible by using Cp*U(MesPDIMe)(THF) (3) (MesPDIMe = 2,6-((Mes)N?CMe)2-C5H3N, Mes = 2,4,6-trimethylphenyl), which is supported by a highly reduced trianionic chelate that undergoes electron transfer. This proceeds via concerted addition at a single uranium center supported by both a crossover experiment and through addition of an asymmetrically substituted diazene, Ph-N?N-Tol. Further investigation of 3 and its substituted analogue, Cp*U(tBu-MesPDIMe)(THF) (3-tBu) (tBu-MesPDIMe = 2,6-((Mes)N?CMe)2-p-C(CH3)3-C5H2N), with benzo[c]cinnoline, revealed that the four-electron cleavage occurs first by a single electron reduction of the diazene with the redox chemistry performed solely at the redox-active pyridine(diimine) to form dimeric [Cp*U(BCC)(MesHPDIMe)]2 (5) and Cp*U(BCC)(tBu-MesPDIMe) (6). While a transient pyridine(diimine) triplet diradical in the formation of 5 results in H atom abstraction and p-pyridine coupling, the tert-butyl moiety in 6 allows for electronic rearrangement to occur, precluding deleterious pyridine-radical coupling. The monomeric analogue of 5, Cp*U(BCC)(MesPDIMe) (7), was synthesized via salt metathesis from Cp*UI(MesPDIMe) (3-I). All complexes have been characterized by 1H NMR and electronic absorption spectroscopies, X-ray diffraction, and, where pertinent, EPR spectroscopy. Further, the electronic structures of 3-I, 5, and 7 have been investigated by SQUID magnetometry.
Microsoft is Ending Support for Windows 7
Microsoft will discontinue support for Windows 7 on January 14, 2020 which means Gamry will also be discontinuing support for Windows 7. If you are upgrading to Windows 10, like many companies and institutions, you need to be running Version 7 of our s oftware . Please note that only USB and Ethernet-based instruments can run in Version 7. Eligible users can download the latest version of our software through our online Client Portal .
If you haven't already registered your instrument, you can do so through the Client Portal .
Please email Technical Support if you have any questions regarding this transition. Please be sure to include your instrument model and serial number when contacting us.