Thermally Stable Uranium Dinitrogen Complex with Siloxide Supporting Ligands

A new dinitrogen adduct of a homoleptic uranium tris­(siloxide) complex, [U­{OSi­(Mes)3}3]2(μ-η2:η2-N2), is reported. Synthesis of the 15N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N2 to a (N2)2– dianion. The 15N NMR shift of the 15N2-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N2)2– coordinated in either an eclipsed or staggered conformation in different crystals. The U–N2–U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 °C. The parent three-coordinate uranium­(III) [U­{OSi­(Mes)3}3] could not be isolated in our hands, with N2-free syntheses affording only uranium­(IV) compounds. The rational synthesis and full characterization of two such U­(IV) byproducts, [U­{OSi­(Mes)3}­{N­(SiMe3)2}3] and [U­{OSi­(Mes)3}4], is also reported

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>

Thermally Stable Uranium Dinitrogen Complex with Siloxide Supporting Ligands

A new dinitrogen adduct of a homoleptic uranium tris­(siloxide) complex, [U­{OSi­(Mes)₃}₃]₂(μ-η²:η²-N₂), is reported. Synthesis of the ¹⁵N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N₂ to a (N₂)^2– dianion. The ¹⁵N NMR shift of the ¹⁵N₂-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N₂)^2– coordinated in either an eclipsed or staggered conformation in different crystals. The U–N₂–U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 °C. The parent three-coordinate uranium­(III) [U­{OSi­(Mes)₃}₃] could not be isolated in our hands, with N₂-free syntheses affording only uranium­(IV) compounds. The rational synthesis and full characterization of two such U­(IV) byproducts, [U­{OSi­(Mes)₃}­{N­(SiMe₃)₂}₃] and [U­{OSi­(Mes)₃}₄], is also reported

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

Synthesis and Reactivity of Bis-tris(pyrazolyl)borate Lanthanide/Aluminum Heterobimetallic Trihydride Complexes

Molecular heterobimetallic hydride complexes of lanthanide (Ln) and main-group (MG) metals exhibit chemical properties unique from their monometallic counterparts and are highly reactive species, making their synthesis and isolation challenging. Herein, molecular Ln/Al heterobimetallic trihydrides [Ln­(Tp)2(μ-H)2Al­(H)­(N″)] [2-Ln; Ln = Y, Sm, Dy, Yb; Tp = hydrotris­(1-pyrazolyl)­borate; N″ = N­(SiMe3)2] have been synthesized by facile insertion of aminoalane [Me3N·AlH3] into the Ln–N amide bonds of [Ln­(Tp)2(N″)] (1-Ln). Thus, this is a simple synthetic strategy to access a range of Ln/Al hydrides. Reactivity studies demonstrate that 2-Ln is a heterobimetallic hydride, with evidence for the cooperative nature of 2-Ln shown by the catalytic amine–borane dehydrocoupling under ambient conditions in contrast to its monomeric counterparts

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

New Chemistry from an Old Reagent: Mono- and Dinuclear Macrocyclic Uranium(III) Complexes from [U(BH₄)₃(THF)₂]

A new robust and high-yielding synthesis of the valuable U^III synthon [U­(BH₄)₃(THF)₂] is reported. Reactivity in ligand exchange reactions is found to contrast significantly to that of uranium triiodide. This is exemplified by the synthesis and characterization of azamacrocyclic U^III complexes, including mononuclear [U­(BH₄)­(L)] and dinuclear [Li­(THF)₄]­[{U­(BH₄)}₂(μ-BH₄)­(L^Me)] and [Na­(THF)₄]­[{U­(BH₄)}₂(μ-BH₄)­(L^A)­(THF)₂]. The structures of all complexes have been determined by single-crystal X-ray diffraction and display two new U^III₂(BH₄)₃ motifs

New Bidentate <i>Trans</i>-Chelating N-Heterocyclic Carbene Ligands for Palladium

A family of imidazolium salts of the type [BnN(CH2CH2CH2RIm)2]·2[Cl] (Bn = CH2Ph; RIm = 1-methylimidazole (1a), 1-tert-butylimidazole (1b), 1-benzylimidazole (1c), 1-methylbenzimidazole (1d)), which contain a tertiary amine linking two imidazolium groups, has been synthesized. These imidazolium salts can be deprotonated with Ag2O to generate the Ag carbene complexes [{BnN(CH2CH2CH2RIm)2}Ag]·[AgCl2] (RIm = 1-methylimidazole (2a), 1-tert-butylimidazole (2b), 1-benzylimidazole (2c), 1-methylbenzimidazole (2d)). In the solid state 2d exists as an unusual tetramer, which consists of an [Ag2Cl4]2− core bridging two Ag(NHC) cations. Subsequent reaction of the Ag complexes with PdCl2(MeCN)2 generates Pd species of the type {BnN(CH2CH2CH2RIm)2}PdCl2 (RIm = 1-methylimidazole (3a), 1-tert-butylimidazole (3b), 1-benzylimidazole (3c), 1-methylbenzimidazole (3d)), which is a rare example of a family of Pd complexes that contain a bidentate trans-chelating N-heterocyclic carbene ligand. Compounds 3a and 3c were crystallographically characterized by X-ray crystallography and contain unusual 12-membered metallacycles. DFT calculations suggest that the preference for trans binding of the ligand is related to conformational effects of the linker. Compound 3b reacts with excess MeI to form {BnN(CH2CH2CH2tBuIm)2}PdI2 (5b), a reaction in which we believe a Pd(IV) intermediate is generated. Compound 5b was crystallographically characterized. Compounds 3a−d are all active catalysts for the Heck reaction, and 3a can also catalyze the Suzuki reaction

New Bidentate <i>Trans</i>-Chelating N-Heterocyclic Carbene Ligands for Palladium

A family of imidazolium salts of the type [BnN(CH2CH2CH2RIm)2]·2[Cl] (Bn = CH2Ph; RIm = 1-methylimidazole (1a), 1-tert-butylimidazole (1b), 1-benzylimidazole (1c), 1-methylbenzimidazole (1d)), which contain a tertiary amine linking two imidazolium groups, has been synthesized. These imidazolium salts can be deprotonated with Ag2O to generate the Ag carbene complexes [{BnN(CH2CH2CH2RIm)2}Ag]·[AgCl2] (RIm = 1-methylimidazole (2a), 1-tert-butylimidazole (2b), 1-benzylimidazole (2c), 1-methylbenzimidazole (2d)). In the solid state 2d exists as an unusual tetramer, which consists of an [Ag2Cl4]2− core bridging two Ag(NHC) cations. Subsequent reaction of the Ag complexes with PdCl2(MeCN)2 generates Pd species of the type {BnN(CH2CH2CH2RIm)2}PdCl2 (RIm = 1-methylimidazole (3a), 1-tert-butylimidazole (3b), 1-benzylimidazole (3c), 1-methylbenzimidazole (3d)), which is a rare example of a family of Pd complexes that contain a bidentate trans-chelating N-heterocyclic carbene ligand. Compounds 3a and 3c were crystallographically characterized by X-ray crystallography and contain unusual 12-membered metallacycles. DFT calculations suggest that the preference for trans binding of the ligand is related to conformational effects of the linker. Compound 3b reacts with excess MeI to form {BnN(CH2CH2CH2tBuIm)2}PdI2 (5b), a reaction in which we believe a Pd(IV) intermediate is generated. Compound 5b was crystallographically characterized. Compounds 3a−d are all active catalysts for the Heck reaction, and 3a can also catalyze the Suzuki reaction