Synthesis and Reactivity of Trivalent Tp*U(CH₂Ph)₂(THF): Insertion vs Oxidation at Low-Valent Uranium–Carbon Bonds

The synthesis of a rare uranium­(III) bis­(benzyl), Tp*U­(CH₂Ph)₂(THF) (<b>2</b>), was achieved by salt metathesis of Tp*UI₂(THF)₂ with 2 equiv of KCH₂Ph at low temperature. This was characterized by ¹H NMR, infrared, and electronic absorption spectroscopy as well as X-ray crystallography. Addition of benzophenone to <b>2</b> forms the uranium­(IV) radical coupling product Tp*U­(CH₂Ph)₂(OC­(Ph)₂CH₂Ph) (<b>3</b>), whereas N₃Mes produces the imido derivative Tp*U­(NMes)­(CH₂Ph)­(THF) (<b>4</b>). Adding a further 1 equiv of N₃Mes to tetravalent <b>4</b> results in U–C insertion to form the U­(IV) triazenido species Tp*U­(NMes)­[(CH₂Ph)­N₃(Mes)-κ²<i>N</i>^1,2]­(THF) (<b>5</b>). Compound <b>2</b> also reacts with the redox-active 4,6-di-<i>tert</i>-butyl-2-[(2,6-diisopropylphenyl)­imino]­quinone (^DIPPiq) to form the oxidized amido­(phenolate) Tp*U­(CH₂Ph)­(^DIPPap) (<b>6</b>)

New Fe(III)(cyclam) Complexes Bearing Axially Bound <i>geminal</i>-Diethynylethenes

Reported herein are the preparation and characterization of <i>trans</i>-[Fe­(cyclam)­(X-<i>gem</i>-DEE)₂]­OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane, <i>gem</i>-DEE = σ-<i>geminal</i>-diethynylethene, and OTf = trifluoromethanesulfonate) compounds <b>2a</b>, <b>2b</b>, and <b>2c</b> (X = −Ph (<b>2a</b>), −Si^<i>i</i>Pr₃ (<b>2b</b>), and −Fc (<b>2c</b>)), which are the first examples of redox-active 3d metal complexes containing <i>gem</i>-DEE ligands. These compounds were prepared from the reaction between <i>cis</i>/<i>trans</i>-[Fe­(cyclam)­(OTf)₂]­OTf (<b>1</b>) and X-<i>gem</i>-DEE-Li. Compounds <b>2a</b>–<b>2c</b> were characterized by spectroscopic/voltammetric techniques. The <i>trans</i>-orientation of the <i>gem</i>-DEE ligands was established from the single-crystal X-ray diffraction study of <b>2a</b>. Furthermore, the electronic structures of the model compounds <b>2a</b>′⁺ and <b>2b</b>′⁺ were analyzed with density-functional-theory calculations, which revealed significant dπ­(Fe)−π­(<i>gem</i>-DEE) interactions

Volume 2

We previously communicated the preparation and characterization of two <i>trans-</i>[Fe­(cyclam)­(CCR)₂]­OTf compounds, <b>2b</b> and <b>2c</b> (where cyclam = 1,4,8,11-tetraazacyclotetradecane, R = −Si^<i>i</i>Pr₃ (<b>2b</b>) or −Ph (<b>2c</b>), and OTf = trifluoromethanesulfonate), which were the first examples of Fe­(III) bis-alkynyl complexes. In this work, the series has been expanded to include R = −H (<b>2a</b>), −C₂SiMe₃ (<b>2d</b>), −C₄SiMe₃ (<b>2e</b>), and −Fc (<b>2f</b>), which were prepared from the reaction between <i>cis</i>/<i>trans-</i>[Fe­(cyclam)­(OTf)₂]­OTf (<b>1</b>) and LiCCR (NaCCH for <b>2a</b>). Compounds <b>2a</b>–<b>2f</b> were characterized by spectroscopic/voltammetric techniques as well as high-resolution mass spectrometry (HR-MS). The <i>trans</i>-orientation of the alkynyl ligands were established from the single-crystal X-ray diffraction studies of <b>2b</b>–<b>2d</b>. Furthermore, the electronic structures of the model compounds <b>2a′</b>^<b>+</b>, <b>2d′</b>^<b>+</b>, and <b>2e′</b>^<b>+</b> were analyzed with density-functional calculations, which revealed significant dπ–π­(CC) interactions

Use of Alkylsodium Reagents for the Synthesis of Trivalent Uranium Alkyl Complexes

A family of rare uranium­(III) alkyl complexes, Tp*₂UR (R = CH₂SiMe₃ (<b>3-CH</b>_<b>2</b><b>SiMe</b>_<b>3</b>), CH₃ (<b>4-CH</b>_<b>3</b>), (CH₂)₃CH₃ (<b>5-(CH</b>_<b>2</b><b>)</b>_<b>3</b><b>CH</b>_<b>3</b>); Tp* = hydrotris­(3,5-dimethylpyrazolyl)­borate), was synthesized by salt metathesis with alkylsodium reagents and Tp*₂UI (<b>2</b>). All compounds were fully characterized using ¹H NMR, infrared, and electronic absorption spectroscopies. Compounds <b>3-CH</b>_<b>2</b><b>SiMe</b>_<b>3</b> and <b>4-CH</b>_<b>3</b> were structurally characterized using X-ray crystallography and have U–C bond distances of 2.601(9) and 2.54(3) Å, respectively

New Fe(III)(cyclam) Complexes Bearing Axially Bound <i>geminal</i>-Diethynylethenes

Reported herein are the preparation and characterization of <i>trans</i>-[Fe­(cyclam)­(X-<i>gem</i>-DEE)₂]­OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane, <i>gem</i>-DEE = σ-<i>geminal</i>-diethynylethene, and OTf = trifluoromethanesulfonate) compounds <b>2a</b>, <b>2b</b>, and <b>2c</b> (X = −Ph (<b>2a</b>), −Si^<i>i</i>Pr₃ (<b>2b</b>), and −Fc (<b>2c</b>)), which are the first examples of redox-active 3d metal complexes containing <i>gem</i>-DEE ligands. These compounds were prepared from the reaction between <i>cis</i>/<i>trans</i>-[Fe­(cyclam)­(OTf)₂]­OTf (<b>1</b>) and X-<i>gem</i>-DEE-Li. Compounds <b>2a</b>–<b>2c</b> were characterized by spectroscopic/voltammetric techniques. The <i>trans</i>-orientation of the <i>gem</i>-DEE ligands was established from the single-crystal X-ray diffraction study of <b>2a</b>. Furthermore, the electronic structures of the model compounds <b>2a</b>′⁺ and <b>2b</b>′⁺ were analyzed with density-functional-theory calculations, which revealed significant dπ­(Fe)−π­(<i>gem</i>-DEE) interactions

B(C₆F₅)₃ Activation of Oxo Tungsten Complexes That Are Relevant to Olefin Metathesis

We have found that coordination of B­(C₆F₅)₃ to an oxo ligand in tungsten oxo alkylidene bis­(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)₂C₆H₃ (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W­(O)­(C₄H₈)­(OHMT)₂, is relatively stable toward rearrangement in the presence of B­(C₆F₅)₃. A careful balance of steric factors allows a single isomer of W­(O)­(<i>trans</i>-4,4-dimethylpent-2-ene)­(dAdPO)₂ to be formed from W­(O)­(CH-<i>t</i>-Bu)­(dAdPO)₂ in the presence of both ethylene and B­(C₆F₅)₃

B(C₆F₅)₃ Activation of Oxo Tungsten Complexes That Are Relevant to Olefin Metathesis

We have found that coordination of B­(C₆F₅)₃ to an oxo ligand in tungsten oxo alkylidene bis­(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)₂C₆H₃ (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W­(O)­(C₄H₈)­(OHMT)₂, is relatively stable toward rearrangement in the presence of B­(C₆F₅)₃. A careful balance of steric factors allows a single isomer of W­(O)­(<i>trans</i>-4,4-dimethylpent-2-ene)­(dAdPO)₂ to be formed from W­(O)­(CH-<i>t</i>-Bu)­(dAdPO)₂ in the presence of both ethylene and B­(C₆F₅)₃

Synthesis of a TREN in Which the Aryl Substituents are Part of a 45 Atom Macrocycle

A substituted TREN has been prepared in which the aryl groups in (ArylNHCH₂CH₂)₃N are substituted at the 3- and 5-positions with a total of six OCH₂(CH₂)_<i>n</i>CHCH₂ groups (<i>n</i> = 1, 2, 3). Molybdenum nitride complexes, [(ArylNCH₂CH₂)₃N]­Mo­(N), have been isolated as adducts that contain B­(C₆F₅)₃ bound to the nitride. Two of these [(ArylNCH₂CH₂)₃N]­Mo­(NB­(C₆F₅)₃) complexes (<i>n</i> = 1 and 3) were crystallographically characterized. After removal of the borane from [(ArylNCH₂CH₂)₃N]­Mo­(NB­(C₆F₅)₃) with PMe₃, ring-closing olefin metathesis (RCM) was employed to join the aryl rings with OCH₂(CH₂)_<i>n</i>CHCH­(CH₂)_<i>n</i>CH₂O links (<i>n</i> = 1–3) between them. RCM worked best with a W­(O)­(CHCMe₃)­(Me₂Pyr)­(OHMT)­(PMe₂Ph) catalyst (OHMT = hexamethylterphenoxide, Me₂Pyr = 2,5-dimethylpyrrolide) and <i>n</i> = 3. The macrocyclic ligand was removed from the metal through hydrolysis and isolated in 70–75% yields relative to the borane adducts. Crystallographic characterization showed that the macrocyclic TREN ligand in which <i>n</i> = 3 contains three <i>cis</i> double bonds. Hydrogenation produced a TREN in which the three links are saturated, i.e., O­(CH₂)₁₀O

A Well-Defined Silica-Supported Tungsten Oxo Alkylidene Is a Highly Active Alkene Metathesis Catalyst

Grafting (ArO)₂W­(O)­(CHtBu) (ArO = 2,6-mesitylphenoxide) on partially dehydroxylated silica forms mostly [(SiO)­W­(O)­(CHtBu)­(OAr)] along with minor amounts of [(SiO)­W­(O)­(CH₂tBu)­(OAr)₂] (20%), both fully characterized by elemental analysis and IR and NMR spectroscopies. The well-defined oxo alkylidene surface complex [(SiO)­W­(O)­(CHtBu)­OAr] is among the most active heterogeneous metathesis catalysts reported to date in the self-metathesis of <i>cis</i>-4-nonene and ethyl oleate, in sharp contrast to the classical heterogeneous catalysts based on WO₃/SiO₂

Computational Insights into Uranium Complexes Supported by Redox-Active α-Diimine Ligands

The electronic structures of two uranium compounds supported by redox-active α-diimine ligands, (^MesDAB^Me)₂U­(THF) (<b>1</b>) and Cp₂U­(^MesDAB^Me) (<b>2</b>) (^MesDAB^Me = [ArNC­(Me)­C­(Me)NAr]; Ar = 2,4,6-trimethylphenyl (Mes)), have been investigated using both density functional theory and multiconfigurational self-consistent field methods. Results from these studies have established that both uranium centers are tetravalent, that the ligands are reduced by two electrons, and that the ground states of these molecules are triplets. Energetically low-lying singlet states are accessible, and some transitions to these states are visible in the electronic absorption spectrum