Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle

U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings

Expanding yttrium Bis(trimethylsilylamide) chemistry through the reaction chemistry of (N2)2–, (N2)3–, and (NO)2–complexes

The reaction chemistry of the side-on bound (N2)2–, (N2)3–, and (NO)2– complexes of the [(R2N)2Y]+ cation (R = SiMe3), namely, [(R2N)2(THF)Y]2(μ-η2:η2-N2), 1, [(R2N)2(THF)Y]2(μ-η2:η2-N2)K, 2, and [(R2N)2(THF)Y]2(μ-η2:η2-NO), 3, with oxidizing agents has been explored to search for other (E2)n−, (E = N, O), species that can be stabilized by this cation. This has led to the first examples for the [(R2N)2Y]+ cation of two fundamental classes of [(monoanion)2Ln]+ rare earth systems (Ln = Sc, Y, lanthanides), namely, oxide complexes and the tetraphenylborate salt. In addition, an unusually high yield reaction with dioxygen was found to give a peroxide complex that completes the (N2)2–, (NO)2–, (O2)2– series with 1 and 3. Specifically, the (μ-O)2– oxide-bridged bimetallic complex, [(R2N)2(THF)Y}2(μ-O), 4, is obtained as a byproduct from reactions of either the (N2)2– complex, 1, or the (N2)3– complex, 2, with NO, while the oxide formed from 2 with N2O is a polymeric species incorporating potassium, {[(R2N)2Y]2(μ-O)2K2(μ-C7H8)}n, 5. Reaction of 1 with 1 atm of O2 generates the (O2)2– bridging side-on peroxide [(R2N)2(THF)Y]2(μ-η2:η2-O2), 6. The O–O bond in 6 is cleaved by KC8 to provide an alternative synthetic route to 5. Attempts to oxidize the (NO)2– complex, 3, with AgBPh4 led to the isolation of the tetraphenylborate complex, [(R2N)2Y(THF)3][BPh4], 7, that was also synthesized from 1 and AgBPh4. Oxidation of the (N2)2– complex, 1, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO, generates the (TEMPO)− anion complex, (R2N)2(THF)Y(η2-ONC5H6Me4), 8

Expanding Yttrium Bis(trimethylsilylamide) Chemistry Through the Reaction Chemistry of (N₂)^2–, (N₂)^3–, and (NO)^2– Complexes

The reaction chemistry of the side-on bound (N₂)^2–, (N₂)^3–, and (NO)^2– complexes of the [(R₂N)₂Y]⁺ cation (R = SiMe₃), namely, [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-N₂), <b>1</b>, [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-N₂)­K, <b>2</b>, and [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-NO), <b>3</b>, with oxidizing agents has been explored to search for other (E₂)^<i>n</i>−, (E = N, O), species that can be stabilized by this cation. This has led to the first examples for the [(R₂N)₂Y]⁺ cation of two fundamental classes of [(monoanion)₂Ln]⁺ rare earth systems (Ln = Sc, Y, lanthanides), namely, oxide complexes and the tetraphenylborate salt. In addition, an unusually high yield reaction with dioxygen was found to give a peroxide complex that completes the (N₂)^2–, (NO)^2–, (O₂)^2– series with <b>1</b> and <b>3</b>. Specifically, the (<i><i>μ</i>-</i>O)^2– oxide-bridged bimetallic complex, [(R₂N)₂(THF)­Y}₂(<i><i>μ</i>-</i>O), <b>4</b>, is obtained as a byproduct from reactions of either the (N₂)^2– complex, <b>1</b>, or the (N₂)^3– complex, <b>2</b>, with NO, while the oxide formed from <b>2</b> with N₂O is a polymeric species incorporating potassium, {[(R₂N)₂Y]₂(<i><i>μ</i>-</i>O)₂K₂(<i><i>μ</i>-</i>C₇H₈)}_<i>n</i>, <b>5</b>. Reaction of <b>1</b> with 1 atm of O₂ generates the (O₂)^2– bridging side-on peroxide [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-O₂), <b>6</b>. The O–O bond in <b>6</b> is cleaved by KC₈ to provide an alternative synthetic route to <b>5</b>. Attempts to oxidize the (NO)^2– complex, <b>3</b>, with AgBPh₄ led to the isolation of the tetraphenylborate complex, [(R₂N)₂Y­(THF)₃]­[BPh₄], <b>7</b>, that was also synthesized from <b>1</b> and AgBPh₄. Oxidation of the (N₂)^2– complex, <b>1</b>, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl, TEMPO, generates the (TEMPO)⁻ anion complex, (R₂N)₂(THF)­Y­(η²-ONC₅H₆Me₄), <b>8</b>

Isolation of (CO)1–and (CO2)1–radical complexes of rare earths via Ln(NR2)3/K reduction and [K2(18-crown-6)2]2+oligomerization

Deep-blue solutions of Y2+ formed from Y(NR2)3 (R = SiMe3) and excess potassium in the presence of 18-crown-6 at −45 °C under vacuum in diethyl ether react with CO at −78 °C to form colorless crystals of the (CO)1– radical complex, {[(R2N)3Y(μ-CO)2][K2(18-crown-6)2]}n, 1. The polymeric structure contains trigonal bipyramidal [(R2N)3Y(μ-CO)2]2– units with axial (CO)1– ligands linked by [K2(18-crown-6)2]2+ dications. Byproducts such as the ynediolate, [(R2N)3Y]2(μ-OC≡CO){[K(18-crown-6)]2(18-crown-6)}, 2, in which two (CO)1– anions are coupled to form (OC≡CO)2–, and the insertion/rearrangement product, {(R2N)2Y[OC(═CH2)Si(Me2)NSiMe3]}[K(18-crown-6)], 3, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of 2, the ynediolate [(R2N)3Y]2(μ-OC≡CO)[K(18-crown-6)(THF)2]2, 2a. CO2 reacts analogously with Y2+ to form the (CO2)1– radical complex, {[(R2N)3Y(μ-CO2)2][K2(18-crown-6)2]}n, 4, that has a structure similar to that of 1. Analogous (CO)1– and (OC≡CO)2– complexes of lutetium were isolated using Lu(NR2)3/K/18-crown-6: {[(R2N)3Lu(μ-CO)2][K2(18-crown-6)2]}n, 5, [(R2N)3Lu]2(μ-OC≡CO){[K(18-crown-6)]2(18-crown-6)}, 6, and [(R2N)3Lu]2(μ-OC≡CO)[K(18-crown-6)(Et2O)2]2, 6a

N to C aryl migration in lithiated carbamates: &#945;-arylation of benzylic alcohols

We report a new mode of reactivity displayed by lithiated O-benzyl carbamates carrying an N-aryl substituent: upon lithiation, the N-aryl group is transferred cleanly from N to C. An arylation of the carbamate results, providing a route to alpha,alpha-arylated secondary or tertiary alcohols. We also report density functional theory calculations supporting the proposal that arylation proceeds through a dearomatizing attack on the aromatic ring, a significantly lower energy pathway than the 1,2-acyl transfer observed with related N-alkyl carbamates

Varying the Lewis Base Coordination of the Y2N2Core in the reduced dinitrogen complexes {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) (L = benzonitrile, pyridines, triphenylphosphine oxide, and trimethylamine N-oxide)

The effect of the neutral donor ligand, L, on the Ln2N2 core in the (N═N)2– complexes, [A2(L)Ln]2(μ-η2:η2-N2) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2), 1, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine N-oxide were investigated. THF is displaced by all of these ligands to form {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) complexes (L = PhCN, 2; py, 3; DMAP, 4; Ph3PO, 5; Me3NO, 6) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y2N2 cores in 2–5 are similar to that in 1 with N–N bond distances between 1.255(3) Å and 1.274(3) Å, but X-ray analysis of the N–N distance in 6 shows it to be shorter: 1.198(3) Å

Isolation of (CO)^1– and (CO₂)^1– Radical Complexes of Rare Earths via Ln(NR₂)₃/K Reduction and [K₂(18-crown-6)₂]²⁺ Oligomerization

Deep-blue solutions of Y²⁺ formed from Y­(NR₂)₃ (R = SiMe₃) and excess potassium in the presence of 18-crown-6 at −45 °C under vacuum in diethyl ether react with CO at −78 °C to form colorless crystals of the (CO)^1– radical complex, {[(R₂N)₃Y­(μ-CO)₂]­[K₂(18-crown-6)₂]}_<i>n</i>, <b>1</b>. The polymeric structure contains trigonal bipyramidal [(R₂N)₃Y­(μ-CO)₂]^2– units with axial (CO)^1– ligands linked by [K₂(18-crown-6)₂]²⁺ dications. Byproducts such as the ynediolate, [(R₂N)₃Y]₂(μ-OCCO)­{[K­(18-crown-6)]₂(18-crown-6)}, <b>2</b>, in which two (CO)^1– anions are coupled to form (OCCO)^2–, and the insertion/rearrangement product, {(R₂N)₂Y­[OC­(CH₂)­Si­(Me₂)­NSiMe₃]}­[K­(18-crown-6)], <b>3</b>, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of <b>2</b>, the ynediolate [(R₂N)₃Y]₂(μ-OCCO)­[K­(18-crown-6)­(THF)₂]₂, <b>2a</b>. CO₂ reacts analogously with Y²⁺ to form the (CO₂)^1– radical complex, {[(R₂N)₃Y­(μ-CO₂)₂]­[K₂(18-crown-6)₂]}_<i>n</i>, <b>4</b>, that has a structure similar to that of <b>1</b>. Analogous (CO)^1– and (OCCO)^2– complexes of lutetium were isolated using Lu­(NR₂)₃/K/18-crown-6: {[(R₂N)₃Lu­(μ-CO)₂]­[K₂(18-crown-6)₂]}_<i>n</i>, <b>5</b>, [(R₂N)₃Lu]₂(μ-OCCO)­{[K­(18-crown-6)]₂(18-crown-6)}, <b>6</b>, and [(R₂N)₃Lu]₂(μ-OCCO)­[K­(18-crown-6)­(Et₂O)₂]₂, <b>6a</b>

Varying the Lewis Base Coordination of the Y₂N₂ Core in the Reduced Dinitrogen Complexes {[(Me₃Si)₂N]₂(L)Y}₂(μ-η²:η²-N₂) (L = Benzonitrile, Pyridines, Triphenylphosphine Oxide, and Trimethylamine <i>N</i>-Oxide)

The effect of the neutral donor ligand, L, on the Ln₂N₂ core in the (NN)^2– complexes, [A₂(L)­Ln]₂(μ-η²:η²-N₂) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me₃Si)₂N]₂(THF)­Y}₂(μ-η²:η²-N₂), <b>1</b>, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine <i>N</i>-oxide were investigated. THF is displaced by all of these ligands to form {[(Me₃Si)₂N]₂(L)­Y}₂(μ-η²:η²-N₂) complexes (L = PhCN, <b>2</b>; py, <b>3</b>; DMAP, <b>4</b>; Ph₃PO, <b>5</b>; Me₃NO, <b>6</b>) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y₂N₂ cores in <b>2</b>–<b>5</b> are similar to that in <b>1</b> with N<i>–</i>N bond distances between 1.255(3) Å and 1.274(3) Å, but X-ray analysis of the N<i>–</i>N distance in <b>6</b> shows it to be shorter: 1.198(3) Å