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Abstract Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO22+is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An=U, Np, Pu). The thioether calixarene TC4A (4‐tert‐butyltetrathiacalix[4]arene) binds equatorially to the actinyl cation forming a conical pocket that differentiates the twotrans‐oxo groups. The ‘ate’ complexes, [A]2[UO2(TC4A)] (A=[Li(DME)2], HNEt3) and [HNEt3]2[AnO2(TC4A)] (An=U, Np, Pu), enable selective oxo chemistry. Silylation of the UVIoxo groups by bis(trimethylsilyl)pyrazine occurs first at only the unencapsulatedexooxo and only one silylation is needed to enable migration of theendooxo out of the cone, whereupon a second silylation affords the stable UIVcis‐bis(siloxide) [A]2[U(OSiMe3)2(TC4A)]. Calculations confirm that only one silylation event is needed to initiate oxo rearrangement, and that the putativecisdioxo isomer of [UO2(TC4A)]2−would be stable if it could be accessed synthetically, at only 23 kcal.mol−1in energy above the classicaltransdioxo. Calculations for the transuraniccis[AnO2(TC4A)]2−(An=Np, Pu) are at higher energies, 30–35 kcal.mol−1, retaining the U complexes as the more obvious target for acis‐dioxo actinyl ion. The aryloxide (OAr) groups of the macrocycle are essential in stabilizing this as‐yet unseen uranyl geometry as further bonding in the TC4A U‐OArgroups stabilizes the U=O ‘yl’ bonds, explaining the stability of the putativecis[UO2(TC4A)]2−in this ligand framework.
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Reaction Pathway for the Aerobic Oxidation of Phosphines Catalyzed by Oxomolybdenum Salen Complexes
Abstract Catalysis ofO‐atom transfer (OAT) reactions is a characteristic of both natural (enzymatic) and synthetic molybdenum‐oxo and ‐peroxo complexes. These reactions can employ a variety of terminal oxidants, e. g. DMSO,N‐oxides, and peroxides, etc., but rarely molecular oxygen. Here we demonstrate the ability of a set of Schiff‐base‐MoO2complexes (cy‐salen)MoO2(cy‐salen=N,N’‐cyclohexyl‐1,2‐bis‐salicylimine) to catalyze the aerobic oxidation of PPh3. We also report the results of a DFT computational investigation of the catalytic pathway, including the identification of energetically accessible intermediates and transition states, for the aerobic oxidation of PMe3. Starting from the dioxo species, (cy‐salen)Mo(VI)O2(1), key reaction steps include: 1) associative addition of PMe3to an oxo‐O to give LMo(IV)(O)(OPMe3) (2); 2) OPMe3dissociation from2to produce mono‐oxo complex (cy‐salen)Mo(IV)O (3); 3) stepwise O2association with3via superoxo species (cy‐salen)Mo(V)(O)(η1‐O2) (4) to form the oxo‐peroxo intermediate (cy‐salen)Mo(VI)(O)(η2‐O2) (5); 4) theO‐transfer reaction of PMe3with oxo‐peroxo species5at the oxo‐group, rather than the peroxo unit leading, after OPMe3dissociation, to a monoperoxo species, (cy‐salen)Mo(IV)(η2‐O2) (7); and 5) regeneration of the dioxo complex (cy‐salen)Mo(VI)O2(1) from the monoperoxo triplet37or singlet17by a concerted, asynchronous electronic isomerization. An alternative pathway for recycling of the oxo‐peroxo species5to the dioxo‐Mo1via a bimetallic peroxo complex LMo(O)‐O−O‐Mo(O)L8is determined to be energetically viable, but is unlikely to be competitive with the primary pathway for aerobic phosphine oxidation catalyzed by1.
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- Award ID(s):
- 2102071
- PAR ID:
- 10481133
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- European Journal of Inorganic Chemistry
- Volume:
- 27
- Issue:
- 4
- ISSN:
- 1434-1948
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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