24 research outputs found
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
Uranium(III) Coordination Chemistry and Oxidation in a Flexible Small-Cavity Macrocycle
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 (N<sub>2</sub>)<sup>2–</sup>, (N<sub>2</sub>)<sup>3–</sup>, and (NO)<sup>2–</sup> Complexes
The reaction chemistry of the side-on bound (N<sub>2</sub>)<sup>2–</sup>, (N<sub>2</sub>)<sup>3–</sup>, and (NO)<sup>2–</sup> complexes of the [(R<sub>2</sub>N)<sub>2</sub>Y]<sup>+</sup> cation (R = SiMe<sub>3</sub>), namely, [(R<sub>2</sub>N)<sub>2</sub>(THF)Y]<sub>2</sub>(<i>μ</i>-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>), <b>1</b>, [(R<sub>2</sub>N)<sub>2</sub>(THF)Y]<sub>2</sub>(<i>μ</i>-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>)K, <b>2</b>, and
[(R<sub>2</sub>N)<sub>2</sub>(THF)Y]<sub>2</sub>(<i>μ</i>-η<sup>2</sup>:η<sup>2</sup>-NO), <b>3</b>, with
oxidizing agents has been explored to search for other (E<sub>2</sub>)<sup><i>n</i>−</sup>, (E = N, O), species that
can be stabilized by this cation. This has led to the first examples
for the [(R<sub>2</sub>N)<sub>2</sub>Y]<sup>+</sup> cation of two
fundamental classes of [(monoanion)<sub>2</sub>Ln]<sup>+</sup> 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 (N<sub>2</sub>)<sup>2–</sup>, (NO)<sup>2–</sup>,
(O<sub>2</sub>)<sup>2–</sup> series with <b>1</b> and <b>3</b>. Specifically, the (<i><i>μ</i>-</i>O)<sup>2–</sup> oxide-bridged bimetallic complex, [(R<sub>2</sub>N)<sub>2</sub>(THF)Y}<sub>2</sub>(<i><i>μ</i>-</i>O), <b>4</b>, is obtained as a byproduct from reactions
of either the (N<sub>2</sub>)<sup>2–</sup> complex, <b>1</b>, or the (N<sub>2</sub>)<sup>3–</sup> complex, <b>2</b>, with NO, while the oxide formed from <b>2</b> with N<sub>2</sub>O is a polymeric species incorporating potassium, {[(R<sub>2</sub>N)<sub>2</sub>Y]<sub>2</sub>(<i><i>μ</i>-</i>O)<sub>2</sub>K<sub>2</sub>(<i><i>μ</i>-</i>C<sub>7</sub>H<sub>8</sub>)}<sub><i>n</i></sub>, <b>5</b>. Reaction of <b>1</b> with 1 atm of O<sub>2</sub> generates the (O<sub>2</sub>)<sup>2–</sup> bridging
side-on peroxide [(R<sub>2</sub>N)<sub>2</sub>(THF)Y]<sub>2</sub>(<i>μ</i>-η<sup>2</sup>:η<sup>2</sup>-O<sub>2</sub>), <b>6</b>. The O–O bond in <b>6</b> is cleaved
by KC<sub>8</sub> to provide an alternative synthetic route to <b>5</b>. Attempts to oxidize the (NO)<sup>2–</sup> complex, <b>3</b>, with AgBPh<sub>4</sub> led to the isolation of the tetraphenylborate
complex, [(R<sub>2</sub>N)<sub>2</sub>Y(THF)<sub>3</sub>][BPh<sub>4</sub>], <b>7</b>, that was also synthesized from <b>1</b> and AgBPh<sub>4</sub>. Oxidation of the (N<sub>2</sub>)<sup>2–</sup> complex, <b>1</b>, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl,
TEMPO, generates the (TEMPO)<sup>−</sup> anion complex, (R<sub>2</sub>N)<sub>2</sub>(THF)Y(η<sup>2</sup>-ONC<sub>5</sub>H<sub>6</sub>Me<sub>4</sub>), <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: α-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)<sup>1–</sup> and (CO<sub>2</sub>)<sup>1–</sup> Radical Complexes of Rare Earths via Ln(NR<sub>2</sub>)<sub>3</sub>/K Reduction and [K<sub>2</sub>(18-crown-6)<sub>2</sub>]<sup>2+</sup> Oligomerization
Deep-blue solutions of Y<sup>2+</sup> formed from Y(NR<sub>2</sub>)<sub>3</sub> (R = SiMe<sub>3</sub>) 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)<sup>1–</sup> radical complex, {[(R<sub>2</sub>N)<sub>3</sub>Y(μ-CO)<sub>2</sub>][K<sub>2</sub>(18-crown-6)<sub>2</sub>]}<sub><i>n</i></sub>, <b>1</b>. The polymeric structure
contains trigonal bipyramidal [(R<sub>2</sub>N)<sub>3</sub>Y(μ-CO)<sub>2</sub>]<sup>2–</sup> units with axial (CO)<sup>1–</sup> ligands linked by [K<sub>2</sub>(18-crown-6)<sub>2</sub>]<sup>2+</sup> dications. Byproducts such as the ynediolate, [(R<sub>2</sub>N)<sub>3</sub>Y]<sub>2</sub>(μ-OCCO){[K(18-crown-6)]<sub>2</sub>(18-crown-6)}, <b>2</b>, in which two (CO)<sup>1–</sup> anions are coupled to form (OCCO)<sup>2–</sup>, and
the insertion/rearrangement product, {(R<sub>2</sub>N)<sub>2</sub>Y[OC(CH<sub>2</sub>)Si(Me<sub>2</sub>)NSiMe<sub>3</sub>]}[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 [(R<sub>2</sub>N)<sub>3</sub>Y]<sub>2</sub>(μ-OCCO)[K(18-crown-6)(THF)<sub>2</sub>]<sub>2</sub>, <b>2a</b>. CO<sub>2</sub> reacts analogously
with Y<sup>2+</sup> to form the (CO<sub>2</sub>)<sup>1–</sup> radical complex, {[(R<sub>2</sub>N)<sub>3</sub>Y(μ-CO<sub>2</sub>)<sub>2</sub>][K<sub>2</sub>(18-crown-6)<sub>2</sub>]}<sub><i>n</i></sub>, <b>4</b>, that has a structure similar
to that of <b>1</b>. Analogous (CO)<sup>1–</sup> and
(OCCO)<sup>2–</sup> complexes of lutetium were isolated
using Lu(NR<sub>2</sub>)<sub>3</sub>/K/18-crown-6: {[(R<sub>2</sub>N)<sub>3</sub>Lu(μ-CO)<sub>2</sub>][K<sub>2</sub>(18-crown-6)<sub>2</sub>]}<sub><i>n</i></sub>, <b>5</b>, [(R<sub>2</sub>N)<sub>3</sub>Lu]<sub>2</sub>(μ-OCCO){[K(18-crown-6)]<sub>2</sub>(18-crown-6)}, <b>6</b>, and [(R<sub>2</sub>N)<sub>3</sub>Lu]<sub>2</sub>(μ-OCCO)[K(18-crown-6)(Et<sub>2</sub>O)<sub>2</sub>]<sub>2</sub>, <b>6a</b>
Varying the Lewis Base Coordination of the Y<sub>2</sub>N<sub>2</sub> Core in the Reduced Dinitrogen Complexes {[(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>2</sub>(L)Y}<sub>2</sub>(μ-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>) (L = Benzonitrile, Pyridines, Triphenylphosphine Oxide, and Trimethylamine <i>N</i>-Oxide)
The effect of the neutral donor ligand, L, on the Ln<sub>2</sub>N<sub>2</sub> core in the (NN)<sup>2–</sup> complexes,
[A<sub>2</sub>(L)Ln]<sub>2</sub>(μ-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>) (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 {[(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>2</sub>(THF)Y}<sub>2</sub>(μ-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>), <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 {[(Me<sub>3</sub>Si)<sub>2</sub>N]<sub>2</sub>(L)Y}<sub>2</sub>(μ-η<sup>2</sup>:η<sup>2</sup>-N<sub>2</sub>) complexes (L = PhCN, <b>2</b>; py, <b>3</b>; DMAP, <b>4</b>; Ph<sub>3</sub>PO, <b>5</b>; Me<sub>3</sub>NO, <b>6</b>) that were fully
characterized by analytical, spectroscopic, density functional theory,
and X-ray crystallographic methods. The crystal structures of the
Y<sub>2</sub>N<sub>2</sub> 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