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Issue 26, 2012
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Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U–OAr2 and U–SAr2 bonding

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Abstract

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H2[TXA2], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using nBuLi provided Li2(DME)2[TXA2] (2), and subsequent reaction with UCl4 afforded [Li(DME)3][(TXA2)UCl3] (4). The analogous NON-donor ligated complex [(XA2)UCl3K(DME)3] [3; XA2 = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K2(DME)x[XA2] with UCl4. A cyclic voltammogram (CV) of 3 in THF/[NBu4][B(C6F5)4] at 200 mV s−1 showed an irreversible reduction to uranium(III) at Epc = −2.46 V versus FeCp20/+1, followed by a product wave at E1/2 = −1.83 V. Complex 4 also underwent irreversible reduction to uranium(III) [Epc = −2.56 V], resulting in an irreversible product peak at Epa = −1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA2)UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA2)U(DME)Cl2Li(DME)2] (6), respectively. The U–S distances in 4 and 6 are uncommonly short, the C–S–U angles are unusually acute, and the thioxanthene backbone of the TXA2 ligand is significantly bent. By contrast, the xanthene backbone in XA2 complexes 3 and 5 is planar. However, κ3-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA2)UCl3] (3B), [(TXA2)UCl2(DME)] (6B) and [(TXA2)UCl(DME)] (6C) to probe the extent of covalency in U–SAr2 bonding relative to U–OAr2 bonding.

Graphical abstract: Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U–OAr2 and U–SAr2 bonding

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Article information


Submitted
02 Feb 2012
Accepted
26 Mar 2012
First published
08 May 2012

Dalton Trans., 2012,41, 8175-8189
Article type
Paper

Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U–OAr2 and U–SAr2 bonding

B. Vidjayacoumar, S. Ilango, M. J. Ray, T. Chu, K. B. Kolpin, N. R. Andreychuk, C. A. Cruz, D. J. H. Emslie, H. A. Jenkins and J. F. Britten, Dalton Trans., 2012, 41, 8175
DOI: 10.1039/C2DT30247K

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