Experimental and Computational Studies on an Actinide Metallacyclocumulene Complex

Abstract

Reduction of (η 5 -C 5 Me 5 ) 2 ThCl 2 (1) with potassium graphite (KC 8 ) in the presence of 1,4-diphenylbutadiyne (PhCCCCPh) yields the first actinide metallacyclocumulene, the thorium metallacyclopentatriene (η 5 -C 5 Me 5 ) 2 Th(η 4 -C 4 Ph 2 ) (2). The structure and reactivity of 2 were investigated in detail; structural parameters and density functional theory (DFT) studies confirm the presence of a metallacyclopentatriene unit in 2. Furthermore, DFT computations also indicate a notable contribution of the 5f orbitals to the bonding of the metallacyclopentatriene Th−(η 4 -CCCC) moiety. While complex 2 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as isothiocyanates, carbodiimides, aldehydes, ketones, nitriles, pyridines, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, in comparison to group 4 metals, the thorium metallacyclopentatriene 2 exhibits distinctively different reactivity patterns.

δ and φ back-donation in AnIV metallacycles

“…Geometry. Our DFT optimized geometries for the metallacyclopropene and metallacyclocumulene complexes (henceforth referred to as 'propene' and 'cumulene', respectively, for brevity) match published crystal structures, with bond distances and angles generally within experimental uncertainty for both Group 4 transition metals [33][34][35][36][37][38][39] and actinides (Th and U); [27][28][29][30][31][32] see Supplementary Tables 1, 2. The calculated IR spectrum matches the measured spectra of U-cumulene, including the strong C α -C β stretch peak at 1590 cm -1 discussed in the literature 32 .…”

“…Based on recent syntheses reports [27][28][29][30][31][32] and our chemical bonding models for Th and U complexes of metallacyclopropenes and metallacyclocumulenes, we predict three more actinide compounds of Pa, Np, and Pu, which also help to fully understand the electronic structures of the Th and U complexes. Specifically, we demonstrate that the direct L-M σ and π donations combined with the M-L δ or φ back-donation are crucial in explaining the non-classical trend of the M-L bond lengths in both series, thus underscoring the significance of these δ and φ interactions.…”

Synthesis and characterization of a new and electronically unusual uranium metallacyclocumulene, (C5Me5)2U(η4-1,2,3,4-PhC4Ph)

“…This is a modification of a literature procedure. [22] A 20-mL scintillation vial equipped with a stir bar was charged with KC 8 (0.103 g, 0.762 mmol), (C 5 Me 5 ) 2 ThCl 2 (0.208 g, 0.363 mmol), 1,4-diphenylbutadiyne (0.073 g, 0.363 mmol), and toluene (5 mL). The slurry was heated to 50 °C for 3 h, after which it was filtered through a Celitepadded coarse-porosity fritted funnel and was extracted with toluene (2 x 3 mL) until the washings ran clear.…”

“…Interestingly, unlike most uranium complexes, the 13 C{ 1 H} NMR spectrum for 1 can be obtained, but only five out of the expected resonances are observed. [32] The IR spectrum for (C 5 Me 5 ) 2 U(η 4 -1,2,3,4-PhC 4 Ph) (1) shows a strong absorption band at 1590 cm -1 , which corresponds to the C α -C β stretching mode of the butatriene unit, [22,27,33] and compares well with the data obtained for the structurally similar metallcyclocumulene complexes (C 5 Me 5 ) 2 Th( 4 -1,2,3,4-PhC 4 Ph) (1600 cm -1 ), (C 5 Me 5 ) 2 Th( 4 -1,2,3,4-Me 3 SiC 4 SiMe 3 ) (1582 cm -1 ), and (C 5 Me 5 ) 2 U( 4 -1,2,3,4-Me 3 SiC 4 SiMe 3 ) (1572 cm -1 ).…”

Synthesis of Actinide Materials for the Study of Basic Actinide Science and Rapid Separation of Fission Products

“…115 There are several examples in the literature of recent thorium-sulfide compounds, 108,111,113,114,[116][117][118][119][120][121] . 123 Sattelberger published the original synthesis and the structural characterization of (C5Me5)2ThS5 (4) in 1986, 113 and it was recently reported by the Kiplinger group that 4 can be prepared using an actinide hydride route. 15…”