Structure, Reactivity, and Density Functional Theory Analysis of the Six-Electron Reductant, [(C₅Me₅)₂U]₂(μ-η⁶:η⁶-C₆H₆), Synthesized via a New Mode of (C₅Me₅)₃M Reactivity

Abstract

The sterically crowded (C(5)Me(5))(3)U complex reacts with KC(8) or K/(18-crown-6) in benzene to form [(C(5)Me(5))(2)U](2)(mu-eta(6):eta(6)-C(6)H(6)), 1, and KC(5)Me(5). These reactions suggested that (C(5)Me(5))(3)U could be susceptible to (C(5)Me(5))(1-) substitution by benzene anions via ionic salt metathesis. To test this idea in the synthesis of a more conventional product, (C(5)Me(5))(3)U was treated with KN(SiMe(3))(2) to form (C(5)Me(5))(2)U[N(SiMe(3))(2)] and KC(5)Me(5). 1 has long U-C(C(5)Me(5)) bond distances comparable to (C(5)Me(5))(3)U, and it too is susceptible to (C(5)Me(5))(1-) substitution via ionic metathesis: 1 reacts with KN(SiMe(3))(2) to make its amide-substituted analogue [[(Me(3)Si)(2)N](C(5)Me(5))U](2)(mu-eta(6):eta(6)-C(6)H(6)), 2. Complexes 1 and 2 have nonplanar C(6)H(6)-derived ligands sandwiched between the two uranium ions. 1 and 2 were examined by reactivity studies, electronic absorption spectroscopy, and density functional theory calculations. [(C(5)Me(5))(2)U](2)(mu-eta(6):eta(6)-C(6)H(6)) functions as a six-electron reductant in its reaction with 3 equiv of cyclooctatetraene to form [(C(5)Me(5))(C(8)H(8))U](2)(mu-eta(3):eta(3)-C(8)H(8)), (C(5)Me(5))(2), and benzene. This multielectron transformation can be formally attributed to three different sources: two electrons from two U(III) centers, two electrons from sterically induced reduction by two (C(5)Me(5))(1-) ligands, and two electrons from a bridging (C(6)H(6))(2-) moiety.

Rare Earth Arene-Bridged Complexes Obtained by Reduction of Organometallic Precursors

“…(Diaconescu and Cummins, 2012) In the case of uranium all reduced arene complexes had an analogous electronic structure, featuring  overlap between LUMOs of one phenyl ring and the 83 two uranium centers. Other related diuranium inverse sandwich benzene or toluene complexes that were synthesized with different supporting ligands adhere to similar bonding considerations (Arnold et al, 2012;Diaconescu et al, 2000;Evans et al, 2004;Monreal et al, 2011;Mougel et al, 2012;Patel et al, 2011).…”

“…This suggestion, based on the Lewis acid character of thorium is in line with what is described in section 2, where several benzene/arene polyanions stabilized by coordination to lanthanides are presented. For actinides, several groups reported that benzene or its derivatives can serve as a bridging ligand between two uranium ions (Arnold et al, 2012;Diaconescu et al, 2000;Diaconescu and Cummins, 2012;Evans et al, 2004;Monreal et al, 2011;Patel et al, 2011).…”

“…Magnetic susceptibility measurements, X-ray absorption near edge structure (XANES) spectroscopy, and DFT studies showed that most of these complexes can be described as having a 70 benzene (or a substituted benzene) dianion bridging two U(III) centers (Diaconescu and Cummins, 2012;Evans et al, 2004 (Patel et al, 2011;Patel et al, 2013) biphenyl (Scheme 7) and was crystallographically characterized (Figure 18) .…”

“…U 2 -biph is from reference (Diaconescu and Cummins, 2012). U 2 -tol is from reference (Evans et al, 2004). Calcd.…”

A six-carbon 10π-electron aromatic system supported by group 3 metals

“…For actinides, several groups reported that benzene or its derivatives can serve as a bridging ligand between two uranium centers 11,[14][15][16][17][18][19] . Magnetic susceptibility measurements, X-ray absorption near edge structure (XANES) spectroscopy and density functional theory (DFT) studies showed that most of these complexes can be described as having a benzene (or a substituted benzene) dianion bridging two U(III) centers 14,16 . A [toluene] 4 À uranium complex was reported by Liddle and coworkers 11 ; the evidence presented there, however, does not allow an irrefutable interpretation of its electronic structure.…”