Synthesis of a terminal Ce(iv) oxo complex by photolysis of a Ce(iii) nitrate complex.

Reaction of [Ce(NR2)3] (R = SiMe3) with LiNO3 in THF, in the presence of 2,2,2-cryptand, results in the formation of the Ce(iii) "ate" complex, [Li(2,2,2-cryptand)][Ce(κ2-O2NO)(NR2)3] (1) in 38% yield. Photolysis of 1 at 380 nm affords [Li(2,2,2-cryptand)][Ce(O)(NR2)3] (2), in 33% isolated yield after reaction work-up. Complex 2 is the first reported example of a Ce(iv) oxo complex where the oxo ligand is not supported by hydrogen bonding or alkali metal coordination. Also formed during photolysis are [Li(2,2,2-cryptand)]2[(μ3-O){Ce(μ-O)(NR2)2}3] (3) and [Li(2,2,2-cryptand)][Ce(OSiMe3)(NR2)3] (4). Their identities were confirmed by X-ray crystallography. Complex 4 can also be prepared via reaction of [Ce(NR2)3] with LiOSiMe3 in THF, in the presence of 2,2,2-cryptand. When synthesized in this fashion, 4 can be isolated in 47% yield. To rationalize the presence of 2, 3, and 4 in the reaction mixture, we propose that photolysis of 1 first generates 2 and NO2, via homolytic cleavage of the N-O bond in its nitrate co-ligand. Complex 2 then undergoes decomposition via two separate routes: (1) ligand scrambling and oligomerization to form 3; and, (2) abstraction of a trimethylsilyl cation to form a transient Ce(iv) silyloxide, [CeIV(OSiMe3)(NR2)3], followed by 1e- reduction to form 4. Alternatively, complex 4 could form directly via ·SiMe3 abstraction by 2

Synthesis of a terminal Ce(iv) oxo complex by photolysis of a Ce(iii) nitrate complex.

Reaction of [Ce(NR2)3] (R = SiMe3) with LiNO3 in THF, in the presence of 2,2,2-cryptand, results in the formation of the Ce(iii) "ate" complex, [Li(2,2,2-cryptand)][Ce(κ2-O2NO)(NR2)3] (1) in 38% yield. Photolysis of 1 at 380 nm affords [Li(2,2,2-cryptand)][Ce(O)(NR2)3] (2), in 33% isolated yield after reaction work-up. Complex 2 is the first reported example of a Ce(iv) oxo complex where the oxo ligand is not supported by hydrogen bonding or alkali metal coordination. Also formed during photolysis are [Li(2,2,2-cryptand)]2[(μ3-O){Ce(μ-O)(NR2)2}3] (3) and [Li(2,2,2-cryptand)][Ce(OSiMe3)(NR2)3] (4). Their identities were confirmed by X-ray crystallography. Complex 4 can also be prepared via reaction of [Ce(NR2)3] with LiOSiMe3 in THF, in the presence of 2,2,2-cryptand. When synthesized in this fashion, 4 can be isolated in 47% yield. To rationalize the presence of 2, 3, and 4 in the reaction mixture, we propose that photolysis of 1 first generates 2 and NO2, via homolytic cleavage of the N-O bond in its nitrate co-ligand. Complex 2 then undergoes decomposition via two separate routes: (1) ligand scrambling and oligomerization to form 3; and, (2) abstraction of a trimethylsilyl cation to form a transient Ce(iv) silyloxide, [CeIV(OSiMe3)(NR2)3], followed by 1e- reduction to form 4. Alternatively, complex 4 could form directly via ·SiMe3 abstraction by 2

Synthesis, Characterization, and Electrochemistry of the Homoleptic f Element Ketimide Complexes [Li]2[M(N═CtBuPh)6] (M = Ce, Th).

Reaction of [Ce(NO3)3(THF)4] with 6 equiv of Li(N═CtBuPh), followed by addition of 0.5 equiv of I2, affords the homoleptic Ce(IV) ketimide [Li]2[Ce(N═CtBuPh)6] (1), which can be isolated in 44% yield after workup. Similarly, reaction of [ThCl4(DME)2] (DME = 1,2-dimethoxyethane) with 6 equiv of Li(N═CtBuPh) in tetrahydrofuran affords the isostructural Th(IV) ketimide [Li]2[Th(N═CtBuPh)6] (2), which can be isolated in 53% yield after workup. Both 1 and 2 were fully characterized, including analysis by X-ray crystallography, allowing for a detailed structural and spectroscopic comparison. The electronic structures of 1 and 2 were also explored with density functional theory and multiconfigurational wave function calculations. Additionally, the redox chemistry of 1 was probed by cyclic voltammetry, which revealed a highly cathodic Ce(IV)/Ce(III) reduction potential, providing evidence for the ability of the ketimide ligand to stabilize high oxidation states of the lanthanides

Oxidation of the 14-Membered Macrocycle Dibenzotetramethyltetraaza[14]annulene upon Ligation to the Uranyl Ion

Reaction of Li₂(tmtaa) (tmtaaH₂ = dibenzotetramethyltetraaza[14]­annulene) with 1 equiv of [UO₂Cl₂(THF)₃], in an attempt to form <i>cis</i>-[UO₂(tmtaa)], affords the bis­(uranyl) complex [Li­(THF)₃]­[Li­(THF)₂]­[(UO₂Cl₂)₂(tmtaa)] (<b>1</b>) as a red-brown crystalline solid in modest yield. Complex <b>1</b> can be synthesized rationally by reaction of Li₂(tmtaa) with 2 equiv of [UO₂Cl₂(THF)₃]. Under these conditions, it can be isolated in 44% yield. In the solid state, complex <b>1</b> features two [UO₂Cl₂]­ fragments that are bridged by a highly puckered (tmtaa)^2– ligand. Both uranyl fragments feature normal uranyl metrical parameters (U–O (av.) = 1.78 Å, O–U–O = 176.8(3)° and 178.0(3)°). The most notable structural feature of <b>1</b>, however, is the presence of a lithium cation that coordinates to an oxo ligand from each uranyl fragment. In contrast to the Li₂(tmtaa) reaction, addition of [K­(DME)]₂[tmtaa] to 1 equiv of [UO₂Cl₂(THF)₃] results in formation of the 2e^– oxidation products of (tmtaa)^2–. Three isomers of C₂₂H₂₂N₄ (compounds <b>2</b>, <b>3</b>, and <b>4</b>) were isolated as a mixture of orange crystals in 41% combined yield. All three isomers were characterized by X-ray crystallography. We hypothesize that these ligand oxidation products are formed upon decomposition of the unobserved cis uranyl intermediate, <i>cis</i>-[UO₂(tmtaa)], which undergoes a facile intramolecular redox reaction

Uranyl Coordination by the 14-Membered Macrocycle Dibenzotetramethyltetraaza[14]annulene

Reaction of [UO₂(N­(SiMe₃)₂)₂(THF)₂] with 1 equiv of dibenzotetramethyltetraaza[14]­annulene (tmtaaH₂) affords the uranyl complex [UO₂(tmtaaH)­(N­(SiMe₃)₂) (THF)] (<b>1</b>) (THF = tetrahydrofuran) as red blocks in 83% yield. Similarly, thermolysis of a mixture of [UO₂(N­(SiMe₃)₂)₂(THF)₂] and 2 equiv of tmtaaH₂ affords [UO₂(tmtaaH)₂] (<b>2</b>), which can be isolated as red-orange crystals in 67% yield after workup. Both <b>1</b> and <b>2</b> were fully characterized, including analysis by X-ray crystallography. The tmtaaH ligands in <b>1</b> and <b>2</b> are only coordinated to the uranium center via one β-diketiminate fragment, while the protonated β-diketimine portion of the ligand remains uncoordinated. Reaction of [UO₂(N­(SiMe₃)₂)₂(THF)₂] with 1 equiv of Li₂(tmtaa) in C₆H₆ results in the formation of [Li­(THF)]₂[UO₂­(N­(SiMe₃)₂)₂(tmtaa)] (<b>3</b>), which can be isolated in 55% yield as a red-brown crystalline solid. The tmtaa ligand in complex <b>3</b> supports a dative interaction between an oxo ligand in the uranyl fragment and a lithium cation, suggesting that tmtaa could be a useful ligand for developing the oxo ligand functionalization chemistry of the uranyl ion