Redox-switchable carboranes for uranium capture and release.

The uranyl ion (UO22+; U(VI) oxidation state) is the most common form of uranium found in terrestrial and aquatic environments and is a central component in nuclear fuel processing and waste remediation efforts. Uranyl capture from either seawater or nuclear waste has been well studied and typically relies on extremely strong chelating/binding affinities to UO22+ using chelating polymers1,2, porous inorganic3-5 or carbon-based6,7 materials, as well as homogeneous8 compounds. By contrast, the controlled release of uranyl after capture is less established and can be difficult, expensive or destructive to the initial material2,9. Here we show how harnessing the redox-switchable chelating and donating properties of an ortho-substituted closo-carborane (1,2-(Ph2PO)2-1,2-C2B10H10) cluster molecule can lead to the controlled chemical or electrochemical capture and release of UO22+ in monophasic (organic) or biphasic (organic/aqueous) model solvent systems. This is achieved by taking advantage of the increase in the ligand bite angle when the closo-carborane is reduced to the nido-carborane, resulting in C-C bond rupture and cage opening. The use of electrochemical methods for uranyl capture and release may complement existing sorbent and processing systems.

Exploring Spin-Orbit Effects in a [Cu6Tl]+ Nanocluster Featuring an Uncommon Tl-H Interaction.

Reaction of [CuH(PPh3)]6 with 1 equiv. of Tl(OTf) results in formation of [Cu6TlH6(PPh3)6][OTf] ([1]OTf]), which can be isolated in good yields. Variable-temperature 1H NMR spectroscopy, in combination with density functional theory (DFT) calculations, confirms the presence of a rare Tl-H orbital interaction. According to DFT, the 1H chemical shift of the Tl-adjacent hydride ligands of [1]+ includes 7.7 ppm of deshielding due to spin-orbit effects from the heavy Tl atom. This study provides valuable new insights into a rare class of metal hydrides, given that [1][OTf] is only the third isolable species reported to contain a Tl-H interaction.

Measuring Metal-Metal Communication in a Series of Ketimide-Bridged [Fe2]6+ Complexes.

Reaction of Fe(acac)3 with 3 equiv of Li[N═C(R)Ph] (R = Ph, tBu) results in the formation of the [Fe2]6+ complexes, [Fe2(µ-N═C(R)Ph)2(N═C(R)Ph)4] (R = Ph, 1; tBu, 2), in low to moderate yields. Reaction of FeCl2 with 6 equiv of Li(N═C13H8) (HN═C13H8 = 9-fluorenone imine) results in the formation of [Li(THF)2]2[Fe(N═C13H8)4] (3) in good yield. Subsequent oxidation of 3 with ca. 0.8 equiv of I2 generates the [Fe2]6+ complex, [Fe2(µ-N═C13H8)2(N═C13H8)4] (4), along with free fluorenyl ketazine. Complexes 1, 2, and 4 were characterized by 1H NMR spectroscopy, X-ray crystallography, 57Fe Mössbauer spectroscopy, and SQUID magnetometry. The Fe-Fe distances in 1, 2, and 4 range from 2.803(7) to 2.925(1) Å, indicating that no direct Fe-Fe interaction is present in these complexes. The 57Fe Mössbauer spectra for complexes 1, 2, and 4 are all consistent with the presence of symmetry-equivalent high-spin Fe3+ centers. Finally, all three complexes exhibit a similar degree of antiferromagnetic coupling between the metal centers (J = -26 to -30 cm-1), as ascertained by SQUID magnetometry.

Photolytic C-Diazeniumdiolate Disassembly in the ß-Diketiminate Complexes [MeLM(O2N2CPh3)] (M = Fe, Co, Cu).

The reaction of [K(18-crown-6)][O2N2CPh3] with [MeLCo(µ-Br)2Li(OEt2)] (MeL = {(2,6-iPr2C6H3)NC(Me)}2CH) generates the trityl diazeniumdiolate complex, [MeLCo(O2N2CPh3)] (1), in moderate yield. Similar metathesis reactions result in the formation of the Fe and Cu analogues, [MeLM(O2N2CPh3)] (Fe, 2; Cu, 3), which can also be isolated in moderate yields. Complexes 1-3 were characterized by ultraviolet-visible (UV-vis) spectroscopy, and their solid-state structures were determined by X-ray crystallography. These complexes were further characterized via 1H NMR spectroscopy (in the case of 1 and 2) or EPR spectroscopy (in the case of 3). Irradiation of complexes 1 and 2 with 371 nm light generates the known dinitrosyl complexes, [MeLM(NO)2] (M = Co, 4; Fe, 5), along with Ph3CH and 9-phenylfluorene. We propose that 4 and 5 are formed via the putative hyponitrite intermediates, [MeLM(κ2-O,O-ONNO)], which are formed by photoinduced homolysis of the C-N bond of the [O2N2CPh3] ligand. In contrast, irradiation of complex 3 with 371 nm light, in the presence of 1 equiv of PPh3, led to the formation of the Cu(I) complexes, [MeLCu(PPh3)], [(ArNCMeC(NO)CMeNAr)Cu(PPh3)] (6), and [(ArNCMeC(NO)CMeNAr)Cu]2 (7), of which the latter two are products of γ-nitrosation of the ß-diketiminiate ligand. Also formed in this transformation are Ph3CN(H)OCPh3, Ph3PO, and N2O, along with trace amounts of NO.

Evaluating f-Orbital Participation in the UV═E Multiple Bonds of [U(E)(NR2)3] (E = O, NSiMe3, NAd; R = SiMe3).

The reaction of 1 equiv of 1-azidoadamantane with [UIII(NR2)3] (R = SiMe3) in Et2O results in the formation of [UV(NR2)3(NAd)] (1, Ad = 1-adamantyl) in good yields. The electronic structure of 1, as well as those of the related U(V) complexes, [UV(NR2)3(NSiMe3)] (2) and [UV(NR2)3(O)] (3), were analyzed with EPR spectroscopy, SQUID magnetometry, NIR-visible spectroscopy, and crystal field modeling. This analysis revealed that, within this series of complexes, the steric bulk of the E2- (E═O, NR) ligand is the most important factor in determining the electronic structure. In particular, the increasing steric bulk of this ligand, on moving from O2- to [NAd]2-, results in increasing U═E distances and E-U-Namide angles. These changes have two principal effects on the resulting electronic structure: (1) the increasing U═E distances decreases the energy of the fσ orbital, which is primarily σ* with respect to the U═E bond, and (2) the increasing E-U-Namide angles increases the energy of fδ, due to increasing antibonding interactions with the amide ligands. As a result of the latter change, the electronic ground state for complexes 1 and 2 is primarily fφ in character, whereas the ground state for complex 3 is primarily fδ.

Quantifying Actinide-Carbon Bond Covalency in a Uranyl-Aryl Complex Utilizing Solution 13C NMR Spectroscopy.

Reaction of [UO2Cl2(THF)2]2 with in situ generated LiFmes (FmesH = 1,3,5-(CF3)3C6H3) in Et2O resulted in the formation of the uranyl aryl complexes [Li(THF)3][UO2(Fmes)3] ([Li(THF)3][1]) and [Li(Et2O)3(THF)][UO2(Fmes)3] ([Li(Et2O)3(THF)][1]) in good to moderate yields after crystallization from hexanes and Et2O, respectively. Both complexes were characterized by X-ray crystallography and NMR spectroscopy. DFT calculations reveal that the Cispo resonance in [1]- exhibits a deshielding of 51 ppm from spin-orbit coupling effects originating at uranium, which indicates an appreciable covalency in the U-C bonding interaction.

NO and N2O Release from the Trityl Diazeniumdiolate Complexes [M(O2N2CPh3)3]- (M = Fe, Co).

Reaction of MBr2 with 3 equiv of [K(18-crown-6)][O2N2CPh3] generates the trityl diazeniumdiolate complexes [K(18-crown-6)][M(O2N2CPh3)3] (M = Co, 2; Fe, 3) in good yields. Irradiation of 2 and 3 using 371 nm light led to NO formation in 10 and 1% yields (calculated assuming a maximum of 6 equiv of NO produced per complex), respectively. N2O was also formed during the photolysis of 2, in 63% yield, whereas photolysis of 3 led to the formation of N2O, as well as Ph3CN(H)OCPh3, in 37 and 5% yields, respectively. These products are indicative of diazeniumdiolate fragmentation via both C-N and N-N bond cleavage pathways. In contrast, oxidation of complexes 2 and 3 with 1.2 equiv of [Ag(MeCN)4][PF6] led to N2O formation but no NO formation, suggesting that diazeniumdiolate fragmentation occurs exclusively via C-N bond cleavage under these conditions. While the photolytic yields of NO are modest, they represent a 10- to 100-fold increase compared to the previously reported Zn congener, suggesting that the presence of a redox-active metal center favors NO formation upon trityl diazeniumdiolate fragmentation.

Metal-Metal-Bonded Fe4 Clusters with Slow Magnetic Relaxation.

Reaction of FeBr2 with Li(N═CtBu2) (0.5 equiv) and Zn0 (2 equiv) results in the formation of the formally mixed-valent cluster [Fe4Br2(N═CtBu2)4] (1) in moderate yield. The subsequent reaction of 1 with Na(N═CtBu2) results in formation of [Fe4Br(N═CtBu2)5] (2), also in moderate yield. Both 1 and 2 were characterized by zero-field 57Fe Mössbauer spectroscopy, X-ray crystallography, and superconducting quantum interference device magnetometry. Their tetrahedral [Fe4]6+ cores feature short Fe-Fe interactions (ca. 2.50 Å). Additionally, both 1 and 2 display S = 7 ground states at room temperature and slow magnetic relaxation with zero-field relaxation barriers of Ueff = 14.7(4) and 15.6(7) cm-1, respectively. Moreover, AC magnetic susceptibility measurements were well modeled by assuming an Orbach relaxation process.

Assessing the 4f Orbital Participation in the Ln-C Bonds of [Li(THF)4][Ln(C6Cl5)4] (Ln = La, Ce).

The reaction of [Ln(NO3)3(THF)4] (Ln = La, Ce) with 4 equiv of LiC6Cl5 in Et2O resulted in the formation of the homoleptic lanthanide-aryl "ate" complexes [Li(THF)4][La(C6Cl5)4] ([Li][1]) and [Li(THF)4][Ce(C6Cl5)4] ([Li][2]). These complexes represent the first isolated homoleptic perchlorophenyl complexes for the lanthanides. In the solid state, both [Li][1] and [Li][2] exhibit octa-coordinate lanthanide centers, with four Ln-C σ-bonds and four Cl → Ln dative interactions involving the ortho-Cl atoms of the C6Cl5 ligands. Despite this apparent steric saturation, both [Li][1] and [Li][2] are highly temperature sensitive and quickly decompose in solution at room temperature. Density functional calculations show that the Ln-Cipso donation bonds feature only weak 4f participation (e.g., ∼1% 4f weight for [1]-). Nonetheless, the 13C chemical shift of the Cipso nuclei of [1]- includes ca. 8 ppm of deshielding from the spin-orbit interaction due to the participation of the 4f (and 5d) orbitals in the La-C bonds.

Structural and Spectroscopic Characterization of a Zinc-Bound N-Oxyphthalimide Radical.

Thermolysis of a 1:1:1 mixture of MeLH (MeL = {(2,6-iPr2C6H3)NC(Me)}2CH), N-hydroxyphthalimide (HOPth), and diethylzinc in toluene at 77 °C provided [MeLZn(OPth)] (1) in good yield after workup. The subsequent reduction of 1 with 1.3 equiv of KC8 and 1 equiv of 2.2.2-cryptand, in tetrahydrofuran, provided [K(2.2.2-cryptand)][MeLZn(OPth)] (2) in 74% yield after workup. Characterization of 2 via X-ray crystallography and electron paramagnetic resonance spectroscopy reveals the presence of an S = 1/2 radical on the N-oxyphthalimide ligand. Importantly, these data represent the first structural and spectroscopic confirmation of the redox activity of a metal-bound N-oxyphthalimide fragment, expanding the range of structurally characterized redox-active ligands.

Photolytic or Oxidative Fragmentation of Trityl Diazeniumdiolate (O2N2CPh3-): Evidence for Both C-N and N-N Bond Cleavage.

Exposure of [K(18-crown-6)(THF)2][CPh3] (THF = tetrahydrofuran; Ph = phenyl) to an atmosphere of nitric oxide (NO) cleanly generates [K(18-crown-6)][O2N2CPh3] (1) in excellent yields. A subsequent reaction of [ZnCl2(THF)2] with 3 equiv of 1 affords the C-diazeniumdiolate complex [K(18-crown-6)][Zn(O2N2CPh3)3] (2). Both 1 and 2 were characterized by 1H and 13C{1H} NMR spectroscopy, and their structures were confirmed by X-ray crystallography. Photolysis of 2 using 371 nm light resulted in the formation of three trityl-containing products, namely, Ph3CH, 9-phenylfluorene, and Ph3CN(H)OCPh3 (3). In addition, we detected nitrous oxide (N2O), as well as small amounts of NO in the reaction mixture. In contrast, oxidation of 2 with 1.2 equiv of [Ag(MeCN)4][PF6] resulted in the formation of O(CPh3)2 as the major trityl-containing product; N2O was also detected in the reaction mixture, but NO was not apparently formed in this case. The observation of these fragmentation products indicates that the [O2N2CPh3]- ligand is susceptible to both C-N bond and N-N bond cleavage. Moreover, the different product distributions suggest that [O2N2CPh3]- is susceptible to different modes of fragmentation.

Understanding the Early Stages of Nickel Sulfide Nanocluster Growth: Isolation of Ni3 , Ni4 , Ni5 , and Ni8 Intermediates.

Addition of sub-stoichiometric quantities of PEt3 and diphenyl disulfide to a solution of [Ni(1,5-cod)2 ] generates a mixture of [Ni3 (SPh)4 (PEt3 )3 ] (1), unreacted [Ni(1,5-cod)2 ], and [(1,5-cod)Ni(PEt3 )2 ], according to 1 H and 31 P{1 H} NMR spectroscopic monitoring of the in situ reaction mixture. On standing, complex 1 converts into [Ni4 (S)(Ph)(SPh)3 (PEt3 )3 ] (2), via formal addition of a "Ni(0)" equivalent, coupled with a CS oxidative addition step, which simultaneously generates the Ni-bound phenyl ligand and the µ3 -sulfide ligand. Upon gentle heating, complex 2 converts into a mixture of [Ni5 (S)2 (SPh)2 (PEt3 )5 ] (3) and [Ni8 (S)5 (PEt3 )7 ] (4), via further addition of "Ni(0)" equivalents, in combination with a series of C-S oxidative addition and CC reductive elimination steps, which serve to convert thiophenolate ligands into sulfide ligands and biphenyl. The presence of 1-4 in the reaction mixture is confirmed by their independent syntheses and subsequent spectroscopic characterization. Overall, this work provides an unprecedented level of detail of the early stages of Ni nanocluster growth and highlights the fundamental reaction steps (i.e., metal atom addition, CS oxidative addition, and CC reductive elimination) that are required to grow an individual cluster.

Synthesis and Characterization of Two Uranyl-Aryl "Ate" Complexes.

Reaction of [UO2 Cl2 (THF)3 ] with 3 equivalents of LiC6 Cl5 in Et2 O resulted in the formation of first uranyl aryl complex [Li(Et2 O)2 (THF)][UO2 (C6 Cl5 )3 ] ([Li][1]) in good yields. Subsequent dissolution of [Li][1] in THF resulted in conversion into [Li(THF)4 ][UO2 (C6 Cl5 )3 (THF)] ([Li][2]), also in good yields. DFT calculations reveal that the U-C bonds in [Li][1] and [Li][2] exhibit appreciable covalency. Additionally, the 13 C NMR chemical shifts for their Cipso environments are strongly affected by spin-orbit coupling-a consequence of 5f orbital participation in the U-C bonds.

[Ni23Se12(PEt3)13] Revisited: Isolation and Characterization of [Ni23Se12Cl3(PEt3)10].

The reaction of [Ni(1,5-COD)2] (1.0 equiv), PEt3 (0.04 equiv), SePEt3 (0.52 equiv), and [NiCl2(PEt3)2] (0.07 equiv) in a mixture of toluene and THF results in the formation of [Ni23Se12Cl3(PEt3)10] (1), which can be isolated in moderate yield after workup. Complex 1 was characterized by NMR spectroscopy, ESI-MS, and X-ray crystallography. This open-shell nanocluster features a central [Ni13]7+ anticuboctahedral kernel, which is encapsulated by a [Ni10(µ-Se)9Cl3]- shell, along with ten PEt3 ligands and three (µ4-Se)2- ligands. On the basis of our spectroscopic and crystallographic analysis, coupled with in situ spectroscopic monitoring, we believe that the previously reported nanocluster, [Ni23Se12(PEt3)13], is actually better formulated as [Ni23Se12Cl3(PEt3)10].

Homoleptic Perchlorophenyl "Ate" Complexes of Thorium(IV) and Uranium(IV).

The reaction of AnCl4(DME)n (An = Th, n = 2; U, n = 0) with 5 equiv of LiC6Cl5 in Et2O resulted in the formation of homoleptic actinide-aryl "ate" complexes [Li(DME)2(Et2O)]2[Li(DME)2][Th(C6Cl5)5]3 ([Li][1]) and [Li(Et2O)4][U(C6Cl5)5] ([Li][2]). Similarly, the reaction of AnCl4(DME)n (An = Th, n = 2; U, n = 0) with 3 equiv of LiC6Cl5 in Et2O resulted in the formation of heteroleptic actinide-aryl "ate" complexes [Li(DME)2(Et2O)][Li(Et2O)2][ThCl3(C6Cl5)3] ([Li][3]) and [Li(Et2O)3][UCl2(C6Cl5)3] ([Li][4]). Density functional calculations show that the An-Cipso σ-bonds are considerably more covalent for the uranium complexes vs the thorium analogues, in line with past results. Additionally, good agreement between experiment and calculations is obtained for the 13Cipso NMR chemical shifts in [Li][1] and [Li][3]. The calculations demonstrate a deshielding by ca. 29 ppm from spin-orbit coupling effects originating at Th, which is a direct consequence of 5f orbital participation in the Th-C bonds.

Synthesis of Parent Acetylide and Dicarbide Complexes of Thorium and Uranium and an Examination of Their Electronic Structures.

The reaction of [AnCl(NR2)3] (An = U or Th; R = SiMe3) with NaCCH and tetramethylethylenediamine (TMEDA) results in the formation of [An(C≡CH)(NR2)3] (1, An = U; 2, An = Th), which can be isolated in good yields after workup. Similarly, the reaction of 3 equiv of NaCCH and TMEDA with [AnCl(NR2)3] results in the formation of [Na(TMEDA)][An(C≡CH)2(NR2)3] (4, An = U; 5, An = Th), which can be isolated in fair yields after workup. The reaction of 1 with 2 equiv of KC8 and 1 equiv of 2.2.2-cryptand in tetrahydrofuran results in formation of the uranium(III) acetylide complex [K(2.2.2-cryptand)][U(C≡CH)(NR2)3] (3). Thermolysis of 1 or 2 results in formation of the bimetallic dicarbide complexes [{An(NR2)3}2(µ,η1:η1-C2)] (6, An = U; 7, An = Th), whereas the reaction of 1 with [Th{N(R)(SiMe2CH2)}(NR2)2] results in the formation of [U(NR2)3(µ,η1:η1-C2)Th(NR2)3] (8). The 13C NMR chemical shifts of the α-acetylide carbon atoms in 2, 5, and 7 exhibit a characteristic spin-orbit-induced downfield shift, due to participation of the 5f orbitals in the Th-C bonds. Magnetism measurements demonstrate that 6 displays weak ferromagnetic coupling between the uranium(IV) centers (J = 1.78 cm-1).

Synthesis and Characterization of Two "Tied-Back" Lithium Ketimides and Isolation of a Ketimide-Bridged [Cr2]6+ Dimer with Strong Antiferromagnetic Coupling.

Reaction of 1 equiv of KN(SiMe3)2 with 9-fluorenone results in the formation of (Me3Si)N═C13H8 (1) in high yield after work-up. Addition of 1 equiv of phenol to 1 results in rapid desilylation and formation of 9-fluorenone imine, HN═C13H8 (2). Subsequent reaction of 2 with 1 equiv of LiNiPr2 results in deprotonation and formation of [Li(Et2O)]4[N═C13H8]4 (3) in good yield. Reaction of 1 equiv of KN(SiMe3)2 with 2-adamantanone for 7 days at room temperature results in the formation of (Me3Si)N═C10H14 (4) in good yield. Dissolution of 4 in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═C10H14 (5). Subsequent reaction of 5 with 1 equiv of LiNiPr2 results in formation of [Li(THF)]4[N═C10H14]4 (6). Both 3 and 6 were characterized by X-ray crystallography. Finally, reaction of CrCl3 with 3.5 equiv of 6 results in formation of the [Cr2]6+ dimer, [Li][Cr2(N═C10H14)7] (7), which can be isolated in modest yield after work-up. Complex 7 features a Cr-Cr bond length of 2.653(2) Å. Additionally, solid-state magnetic susceptibility measurements reveal strong antiferromagnetic coupling between the two Cr centers, with J = -200 cm-1.

Expanding the Nonaqueous Chemistry of Neptunium: Synthesis and Structural Characterization of [Np(NR2)3Cl], [Np(NR2)3Cl]-, and [Np{N(R)(SiMe2CH2)}2(NR2)]- (R = SiMe3).

Reaction of 3 equiv of NaNR2 (R = SiMe3) with NpCl4(DME)2 in THF afforded the Np(IV) silylamide complex, [Np(NR2)3Cl] (1), in good yield. Reaction of 1 with 1.5 equiv of KC8 in THF, in the presence of 1 equiv of dibenzo-18-crown-6, resulted in formation of [{K(DB-18-C-6)(THF)}3(µ3-Cl)][Np(NR2)3Cl]2 (4), also in good yield. Complex 4 represents the first structurally characterized Np(III) amide. Finally, reaction of NpCl4(DME)2 with 5 equiv of NaNR2 and 1 equiv of dibenzo-18-crown-6 afforded the Np(IV) bis(metallacycle), [{Na(DB-18-C-6)(Et2O)0.62(κ1-DME)0.38}2(µ-DME)][Np{N(R)(SiMe2CH2)}2(NR2)]2 (8), in moderate yield. Complex 8 was characterized by 1H NMR spectroscopy and X-ray crystallography and represents a rare example of a structurally characterized neptunium-hydrocarbyl complex. To support these studies, we also synthesized the uranium analogues of 4 and 8, namely, [K(2,2,2-cryptand)][U(NR2)3Cl] (2), [K(DB-18-C-6)(THF)2][U(NR2)3Cl] (3), [Na(DME)3][U{N(R)(SiMe2CH2)}2(NR2)] (6), and [{Na(DB-18-C-6)(Et2O)0.5(κ1-DME)0.5}2(µ-DME)][U{N(R)(SiMe2CH2)}2(NR2)]2 (7). Complexes 2, 3, 6, and 7 were characterized by a number of techniques, including NMR spectroscopy and X-ray crystallography.

[Ni8(CNtBu)12][Cl]: A nickel isocyanide nanocluster with a folded nanosheet structure.

The reaction of 1.75 equiv of tBuNC with Ni(1,5-COD)2, followed by crystallization from benzene/pentane, resulted in the isolation of [Ni8(CNtBu)12][Cl] (2) in low yields. Similarly, the reaction of Ni(1,5-COD)2 with 0.6 equiv of [Ni(CNtBu)4], followed by addition of 0.08 equiv of I2, resulted in the formation of [Ni8(CNtBu)12][I] (3), which could be isolated in 52% yield after work-up. Both 2 and 3 adopt folded nanosheet structures in the solid state, characterized by two symmetry-related planar Ni4 arrays, six terminally bound tBuNC ligands, and six tBuNC ligands that adopt bridging coordination modes. The metrical parameters of the six bridging tBuNC ligands suggest that they have been reduced to their [tBuNC]2- form. In contrast to the nanosheet structures observed for 2 and 3, gas phase Ni8 is predicted to feature a compact bisdisphenoid ground state structure. The strikingly different structural outcomes reveal the profound structural changes that can occur upon addition of ligands to bare metal clusters. Ultimately, the characterization of 2 and 3 will enable more accurate structural predictions of ligand-protected nanoclusters in the future.

Uranyl Oxo Silylation Promoted by Silsesquioxane Coordination.

The reaction of [UO2(N(SiMe3)2)2(THF)2] with 1 equiv of Cy7Si7O9(OH)3 in THF affords [U(OSiMe3)3(Cy7Si7O12)] (1) as orange plates in 24% isolated yield. Its X-ray crystal structure reveals three silylated Oyl ligands, confirming the unprecedented conversion of the uranyl ion to a U(VI) silyloxide. We propose that the formation of 1 proceeds through a transient uranyl silsesquioxide intermediate, [{Cy7Si7O11(OH)}UO2], which undergoes rapid oxo silylation by HN(SiMe3)2, followed by silyloxy ligand scrambling, to form 1 and the U(VI) bis(silsesquioxane) complex, [U(Cy7Si7O12)2] (3), among other products. The formation of 3 was confirmed by its independent synthesis and comparison of its 29Si{1H} NMR spectrum with that of the in situ reaction mixture. In contrast to the reaction in THF, the reaction of [UO2(N(SiMe3)2)2(THF)2] with Cy7Si7O9(OH)3 in hexanes, followed by recrystallization from Et2O/MeCN, results in the formation of the uranyl cluster, [(UO2)3(Cy7Si7O12)2(Et2O)(MeCN)2] (2), as yellow rods in 42% isolated yield. Complex 2 features two Oyl···U dative interactions, but in contrast to 1, none of its three uranyl fragments are silylated. Overall, the conversion of [UO2(N(SiMe3)2)2(THF)2] to 1 and 3 is likely promoted by the strong electron donor ability of the silsesquioxane ligand and suggests that the actinide coordination chemistry of mineral surface mimics, such as silsesquioxane, is a fruitful arena for the discovery of new reactivity.