Synthesis of Thorium(IV) and Uranium(IV) Salicylaldiminate Pseudo‐Halide Complexes

Abstract

To explore the coordination chemistry of salicylaldiminate ligands as a non‐cyclopentadienyl ligand framework, we report the synthesis of their ThIV and UIV complexes. Deprotonation of (NC5H4)N=C(H)(3,5‐tBu2C6H2)OH (1), (NC9H6)N=C(H)(3,5‐tBu2C6H2)OH (2), and (CH3SC6H4)N=C(H)(3,5‐tBu2C6H2)OH (3) with sodium hydride and the subsequent addition of 0.5 equivalents of [UI4(1,4‐dioxane)2] yielded [{(NC5H4)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2UI2] (4), [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2UI2] (5), and [{(CH3SC6H4)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,S)}2UI2] (6), respectively. The reaction of 3 equivalents of the sodium salt of 1 afforded [{(NC5H4)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}3U]I3 (7). By using [ThCl4(dme)2], [{(NC5H4)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2ThCl2] (8) and [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2ThCl2] (9) were isolated. The metathesis of both chloride ligands in 9 with NaN3 led to a rare thorium azide product, [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2Th(N3)2] (10). The reaction of 5 with AgOTf (OTf = O3SCF3) afforded [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2U(OTf)2] (11), and the subsequent reaction of 11 with 2 equivalents of NaN3 provided [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2U(N3)2] (12). The reaction of 5 with 2 equivalents of AgNO3 produced [{(NC9H6)N=C(H)(3,5‐tBu2C6H2)O‐κ3(O,N,N′)}2U{NO3‐κ2(O,O)}2] (13). Each complex was characterized by 1H NMR and IR spectroscopy and, with the exception of 11, their structures were determined by X‐ray crystallographic analysis.

Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis

“…However, the observed differences are within or close to the error range and thus will not be discussed in detail. Moreover, a correlation of the vibrational characteristics and the bonding strength has been questioned by recent quantum chemical calculations and is also not apparent for other isostructural tetravalent actinide azido complexes although those are limited to thorium and uranium. ,, …”

“…Moreover, a correlation of the vibrational characteristics and the bonding strength has been questioned by recent quantum chemical calculations 81 and is also not apparent for other isostructural tetravalent actinide azido complexes although those are limited to thorium and uranium. 79,80,82 UV/vis/NIR spectra have been recorded for the tetravalent f element complexes 1, 2, and 4 (see Figure S45 in the SI) showing characteristic bands related to f-f transitions in the tetravalent uranium complex 2 83−85 and intense and very broad ligand-to-metal charge-transfer (LMCT) bands for the tetravalent cerium complex 4. 86−88 Multinuclear NMR spectroscopy evidenced that the solidstate structures are largely preserved in solution.…”

Synthesis, Spectroscopy, and Theoretical Details of Uranyl Schiff-Base Coordination Complexes

“…Schiff-base ligands and their derivatives are of popular interest because of their ability to coordinate to many different metal ions and stabilize them in a variety of oxidation states. , More recently, Schiff-base ligands coordinated to f -elements have received increased attention because of the ability to tune the electronic characteristics of the ligands. − The coordination chemistry of uranyl cations with these ligands has also been probed because of potential applications in the remediation of nuclear waste from reactor fuels as well as the extraction of uranium from seawater, groundwater, and soil. − Additionally, uranyl ions have been studied for decades because of their rich coordination behavior, reactivity, and unusual interactions with a wide variety of ligands − as well as their potential optical, magnetic, catalytic, and ion-exchange applications. , Generally, U VI prefers to bind to axial O atoms to form the linear UO 2 2+ species and forms stable complexes with various O-, N-, and S-donor ligands. ,− These uranyl complexes are able to adopt a variety of coordination environments and have been observed in structures with coordination numbers ranging from 6 to 8. ,, …”

Experimental and Theoretical Comparison of Transition-Metal and Actinide Tetravalent Schiff Base Coordination Complexes

“…Schiff base ligands have been heavily utilized for their ability to stabilize metals in various oxidation states and control the behavior of metals during catalysis . In addition, their steric and electronic properties are highly modular . Salen ligands and their derivatives have been crystallized and characterized with transition metals, ,− lanthanides, ,− early actinides (Th and U), − and very few studies with transuranium elements. − By utilizing a phenyl-based rigid backbone N , N ′-bis­[(4,4′-diethylamino)­salicylidene]-1,2-phenylenediamine ( H 2 L ), isolable, crystalline homoleptic compounds of Pu­(IV) and Ce­(IV) have been studied, eq .…”