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. 2023 Oct 16;14(43):12255-12263.
doi: 10.1039/d3sc04857h. eCollection 2023 Nov 8.

Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride

Robert J Ward  1 , Pokpong Rungthanaphatsophon  1 , Patrick Huang  2 , Steven P Kelley  1 , Justin R Walensky  1
Affiliations

Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride

Robert J Ward et al. Chem Sci. .

Abstract

Cooperative chemistry between two or more metal centres can show enhanced reactivity compared to the monometallic fragments. Given the paucity of actinide-metal bonds, especially those with group 13, we targeted uranium(iii)-aluminum(i) and -gallium(i) complexes as we envisioned the low-valent oxidation state of both metals would lead to novel, cooperative reactivity. Herein, we report the molecular structure of [(C5Me5)2(MesO)U-E(C5Me5)], E = Al, Ga, Mes = 2,4,6-Me3C6H2, and their reactivity with dihydrogen. The reaction of H2 with the U(iii)-Al(i) complex affords a trihydroaluminate complex, [(C5Me5)2(MesO)U(μ2-(H)3)-Al(C5Me5)] through a formal three-electron metal-based reduction, with concomitant formation of a terminal U(iv) hydride, [(C5Me5)2(MesO)U(H)]. Noteworthy is that neither U(iii) complexes nor [(C5Me5)Al]4 are capable of reducing dihydrogen on their own. To make the terminal hydride in higher yields, the reaction of [(C5Me5)2(MesO)U(THF)] with half an equivalent of diethylzinc generates [(C5Me5)2(MesO)U(CH2CH3)] or treatment of [(C5Me5)2U(i)(Me)] with KOMes forms [(C5Me5)2(MesO)U(CH3)], which followed by hydrogenation with either complex cleanly affords [(C5Me5)2(MesO)U(H)]. All complexes have been characterized by spectroscopic and structural methods and are rare examples of cooperative chemistry in f element chemistry, dihydrogen activation, and stable, terminal ethyl and hydride compounds with an f element.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Thermal ellipsoid plot of 2 (left) and 3 (right) shown at the 50% probability level. The hydrogen atoms have been omitted for clarity.
Fig. 2
Fig. 2. (Left) U–Al dative bond from NBO analysis and (Right) Ga 4s lone pair (red isosurface) donating to an empty U valence orbital (green isosurface).
Scheme 1
Scheme 1. Formation of complexes 2–7.
Scheme 2
Scheme 2. Reaction of 1 with [(C5Me5)Ga] and the resulting complex, 3, with H2.
Fig. 3
Fig. 3. Thermal ellipsoid plot of 4 shown at the 50% probability level. Only the hydrogen atoms bridging between U1 and Al1 are shown for clarity.
Scheme 3
Scheme 3. Synthesis of terminal alkyl, [(C5Me5)2(MesO)U(R)], R = Et, 8; Me, 9, and hydride, [(C5Me5)2(MesO)U(H)], 5, complexes.
Fig. 4
Fig. 4. Thermal ellipsoid plot of 8 (left) and 9 (right) shown at the 50% probability level. The hydrogen atoms have been omitted for clarity.
See this image and copyright information in PMC

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