Addition of [UI 2 (THF) 3 (μ-OMe)] 2 ·THF (2·THF) to THF solutions containing 6 equiv. of K[C 14 H 10 ] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF) 2 ] 2 [U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 ·4THF (118C6·4THF) and {[K(THF) 3 ][U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)]} 2 (1THF) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 118C6·4THF and 1THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 118C6·4THF and 1THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1THF but absent in 118C6·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U( iv ) formal assignments for the metal centres in both 118C6·4THF and 1THF, though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1THF (3.74 μ B ) is significantly lower than that of 118C6·4THF (4.40 μ B ) at 300 K. Furthermore, the XANES data shows the U L III -edge absorption energy for 1THF to be 0.9 eV higher than that of 118C6·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 } 2− (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.
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Intra- and intermolecular interception of a photochemically generated terminal uranium nitride
The photochemically generated synthesis of a terminal uranium nitride species is here reported and an examination of its intra- and intermolecular chemistry is presented. Treatment of the U( iii ) complex L Ar UI(DME) ((L Ar ) 2− = 2,2′′-bis(Dippanilide)- p -terphenyl; Dipp = 2,6-diisopropylphenyl) with LiNIm Dipp ((NIm Dipp ) − = 1,3-bis(Dipp)-imidazolin-2-iminato) generates the sterically congested 3N-coordinate compound L Ar U(NIm Dipp ) ( 1 ). Complex 1 reacts with 1 equiv. of Ph 3 CN 3 to give the U( iv ) azide L Ar U(N 3 )(NIm Dipp ) ( 2 ). Structural analysis of 2 reveals inequivalent N α –N β > N β –N γ distances indicative of an activated azide moiety predisposed to N 2 loss. Room-temperature photolysis of benzene solutions of 2 affords the U( iv ) amide ( N -L Ar )U(NIm Dipp ) ( 3 ) via intramolecular N-atom insertion into the benzylic C–H bond of a pendant isopropyl group of the (L Ar ) 2− ligand. The formation of 3 occurs as a result of the intramolecular interception of the intermediately generated, terminal uranium nitride (L Ar )U(N)(NIm Dipp ) ( 3′ ). Evidence for the formation of 3′ is further bolstered by its intermolecular capture, accomplished by photolyzing solutions of 2 in the presence of an isocyanide or PMe 3 to give (L Ar )U[NCN(C 6 H 3 Me 2 )](NIm Dipp ) ( 5 ) and ( N , C -L Ar *)U(NPMe 3 )(NIm Dipp ) ( 6 ), respectively. These results expand upon the limited reactivity studies of terminal uranium–nitride moieties and provide new insights into their chemical properties.
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- Award ID(s):
- 1827875
- NSF-PAR ID:
- 10148953
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 11
- Issue:
- 9
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 2381 to 2387
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Catalysis of
O ‐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 from2 to produce mono‐oxo complex (cy‐salen)Mo(IV)O (3 ); 3) stepwise O2association with3 via 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 species5 at 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 triplet3 7 or singlet1 7 by a concerted, asynchronous electronic isomerization. An alternative pathway for recycling of the oxo‐peroxo species5 to the dioxo‐Mo1 via a bimetallic peroxo complex LMo(O)‐O−O‐Mo(O)L8 is 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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Abstract The trichromium cluster (tbsL)Cr3(thf) ([tbsL]6−=[1,3,5‐C6H9(NC6H4‐
o ‐NSit BuMe2)3]6−) exhibits steric‐ and solvation‐controlled reactivity with organic azides to form three distinct products: reaction of (tbsL)Cr3(thf) with benzyl azide forms a symmetrized bridging imido complex (tbsL)Cr3(μ 3‐NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (tbsL)Cr3(μ 1‐NMes); whereas the reaction with mesityl azide in THF leads to terminal N‐atom excision from the azide to yield the nitride complex (tbsL)Cr3(μ 3‐N). The reactivity of this complex demonstrates the ability of the cluster‐templating ligand to produce a well‐defined polynuclear transition metal cluster that can access distinct single‐site and cooperative reactivity controlled by either substrate steric demands or reaction media. -
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Abstract The trichromium cluster (tbsL)Cr3(thf) ([tbsL]6−=[1,3,5‐C6H9(NC6H4‐
o ‐NSit BuMe2)3]6−) exhibits steric‐ and solvation‐controlled reactivity with organic azides to form three distinct products: reaction of (tbsL)Cr3(thf) with benzyl azide forms a symmetrized bridging imido complex (tbsL)Cr3(μ 3‐NBn); reaction with mesityl azide in benzene affords a terminally bound imido complex (tbsL)Cr3(μ 1‐NMes); whereas the reaction with mesityl azide in THF leads to terminal N‐atom excision from the azide to yield the nitride complex (tbsL)Cr3(μ 3‐N). The reactivity of this complex demonstrates the ability of the cluster‐templating ligand to produce a well‐defined polynuclear transition metal cluster that can access distinct single‐site and cooperative reactivity controlled by either substrate steric demands or reaction media. -
The masked Ti( ii ) synthon ( Ket guan)(η 6 -Im Dipp N)Ti ( 1 ) oxidatively adds across thiophene to give ring-opened ( Ket guan)(Im Dipp N)Ti[κ 2 - S (CH) 3 C H] ( 2 ). Complex 2 is photosensitive, and upon exposure to light, reductively eliminates thiophene to regenerate 1 – a rare example of early-metal mediated oxidative-addition/reductive-elimination chemistry. DFT calculations indicate strong titanium π-backdonation to the thiophene π*-orbitals leads to the observed thiophene ring opening across titanium, while a proposed photoinduced LMCT promotes the reverse thiophene elimination from 2 . Finally, pressurizing solutions of 2 with H 2 (150 psi) at 80 °C leads to the hydrodesulphurization of thiophene to give the Ti( iv ) sulphide ( Ket guan)(Im Dipp N)Ti(S) ( 3 ) and butane.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9SC05992J
