1,2-Addition of Formic or Oxalic Acid to ^–N{CH₂CH₂(PiPr₂)}₂‑Supported Mn(I) Dicarbonyl Complexes and the Manganese-Mediated Decomposition of Formic Acid

(PN^HP)­Mn­(CO)₂ (I) carboxylate complexes (PN^HP = HN­{CH₂CH₂(PiPr₂)}₂) were prepared via 1,2-addition of either formic or oxalic acid to (PNP)­Mn­(CO)₂ (PNP = the deprotonated, amide form of the ligand ^–N­{CH₂CH₂(PiPr₂)}₂). The structural and spectral properties of these complexes were compared. The manganese formate complex was found to be dimeric in the solid state and monomeric in solution. Half an equivalent of oxalic acid was employed to form the bridging oxalate dimanganese complex. The catalytic competencies of the carboxylate complexes were assessed, and the formate complex was found to decompose formic acid catalytically. Both dehydrogenation and dehydration pathways were active as assessed by the presence of H₂, CO₂, and H₂O. The addition of LiBF₄ exhibited a strong inhibitory effect on the catalysis

Reversible 1,2-Addition of Water To Form a Nucleophilic Mn(I) Hydroxide Complex: A Thermodynamic and Reactivity Study

(^iPrPN^HP)­Mn­(CO)₂(OH) (<b>2</b>; ^iPrPN^HP = HN­{CH₂CH₂(PⁱPr₂)}₂) was formed from the reversible 1,2-addition of water to (^iPrPNP)­Mn­(CO)₂ (<b>1</b>; ^iPrPNP = the deprotonated, amide form of the ligand, ^–N­{CH₂­CH₂(PⁱPr₂)}₂). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (−0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes (^iPrPN^HP)­Mn­(CO)₂(CO₂R), where R = H, methyl, phenyl. While no reaction between <b>1</b> and neat benzaldehyde was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H₂ was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised

A Tertiary Carbon–Iron Bond as an Fe^ICl Synthon and the Reductive Alkylation of Diphosphine-Supported Iron(II) Chloride Complexes to Low-Valent Iron

Ligand-induced reduction of ferrous alkyl complexes via homolytic cleavage of the alkyl fragment was explored with simple chelating diphosphines. The reactivities of the sodium salts of diphenylmethane, phenyl­(trimethylsilyl)­methane, or diphenyl­(trimethylsilyl)­methane were explored in their reactivity with (py)₄FeCl₂. A series of monoalkylated salts of the type (py)₂FeRCl were prepared and characterized from the addition of 1 equiv of the corresponding alkyl sodium species. These complexes are isostructural and have similar magnetic properties. The double alkylation of (py)₄FeCl₂ resulted in the formation of tetrahedral high-spin iron complexes with the sodium salts of diphenylmethane and phenyl­(trimethylsilyl)­methane that readily decomposed. A bis­(cyclohexadienyl) sandwich complex was formed with the addition of 2 equiv of the tertiary alkyl species sodium diphenyl­(trimethylsilyl)­methane. The addition of chelating phosphines to (py)₂FeRCl resulted in the overall transfer of Fe­(I) chloride concurrent with loss of pyridine and alkyl radical. (dmpe)₂FeCl was synthesized via addition of 1 equiv of sodium diphenyl­(trimethylsilyl)­methane, whereas the addition of 2 equiv of the sodium compound to (dmpe)₂FeCl₂ gave the reduced Fe(0) nitrogen complex (dmpe)₂Fe­(N₂). These results demonstrate that iron–alkyl homolysis can be used to afford clean, low-valent iron complexes without the use of alkali metals

A Tertiary Carbon–Iron Bond as an Fe^ICl Synthon and the Reductive Alkylation of Diphosphine-Supported Iron(II) Chloride Complexes to Low-Valent Iron

Ligand-induced reduction of ferrous alkyl complexes via homolytic cleavage of the alkyl fragment was explored with simple chelating diphosphines. The reactivities of the sodium salts of diphenylmethane, phenyl­(trimethylsilyl)­methane, or diphenyl­(trimethylsilyl)­methane were explored in their reactivity with (py)₄FeCl₂. A series of monoalkylated salts of the type (py)₂FeRCl were prepared and characterized from the addition of 1 equiv of the corresponding alkyl sodium species. These complexes are isostructural and have similar magnetic properties. The double alkylation of (py)₄FeCl₂ resulted in the formation of tetrahedral high-spin iron complexes with the sodium salts of diphenylmethane and phenyl­(trimethylsilyl)­methane that readily decomposed. A bis­(cyclohexadienyl) sandwich complex was formed with the addition of 2 equiv of the tertiary alkyl species sodium diphenyl­(trimethylsilyl)­methane. The addition of chelating phosphines to (py)₂FeRCl resulted in the overall transfer of Fe­(I) chloride concurrent with loss of pyridine and alkyl radical. (dmpe)₂FeCl was synthesized via addition of 1 equiv of sodium diphenyl­(trimethylsilyl)­methane, whereas the addition of 2 equiv of the sodium compound to (dmpe)₂FeCl₂ gave the reduced Fe(0) nitrogen complex (dmpe)₂Fe­(N₂). These results demonstrate that iron–alkyl homolysis can be used to afford clean, low-valent iron complexes without the use of alkali metals

Synthesis and Characterization of Uranium Complexes Supported by Substituted Aryldimethylsilylanilide Ligands

We report the synthesis and characterization of substituted aryldimethylsilyldiisopropylanilide ligands and their respective bisamido complexes of U(III), (3,5-R2-PhMe2SiNDipp)2UI(dioxane)x (1, R = H, x= 0; 2, R = Me, x = 0; 3, R = tBu, x = 1). We found that the steric bulk of the 3,5-R2-Ph ring affects the hapticity of the U–arene interaction. In the solid-state, 1 is a U–(η6-arene) complex, while 2 is a bis(U–(η1-arene)) complex. Theoretically calculated bond orders at PBE0 and PBE0-D3 levels of theory support these hapticity assignments. The 3,5-tBu2-Ph rings of 3 are too bulky to interact with U and solid-state metrical parameters initially suggested a U–(η1-arene) interaction with one of the Dipp rings. However, bond order calculations show that this interaction is even weaker than in the previously reported ((PhMe2Si)2N)3U complex, leading to the conclusion that 3 is best described as a U–(η0-arene) complex. Molecular orbital analyses in conjunction with electron localization methods reveal that the U–(η6-arene) bonding in 1 is primarily electrostatic in nature. Some charge transfer takes place from the arene π orbitals to the U 6d/5f hybrid orbitals in addition to subtle δ-back-bonding. In 2 and 3, both π and δ interactions are substantially weaker, in agreement with the differences in the U–arene coordination modes. Surprisingly, attempts to generate less sterically bulky (3,5-R2-PhMe2SiNPh)2UI complexes results in disproportionation to homoleptic tetraamido (3,5-R2-PhMe2SiNPh)4U(IV) (4, R = H; 5, R = Me) complexes

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Preparation and Reactivity of the Versatile Uranium(IV) Imido Complexes U(NAr)Cl₂(R₂bpy)₂ (R = Me, ^<i>t</i>Bu) and U(NAr)Cl₂(tppo)₃

Uranium tetrachloride undergoes facile reactions with 4,4′-dialkyl-2,2′-bipyridine, resulting in the generation of UCl₄(R₂bpy)₂, R = Me, ^<i>t</i>Bu. These precursors, as well as the known UCl₄(tppo)₂ (tppo = triphenylphosphine oxide), react with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide the versatile uranium­(IV) imido complexes, U­(NDipp)­Cl₂(L)_<i>n</i> (L = R₂bpy, <i>n</i> = 2; L = tppo, <i>n</i> = 3). Interestingly, U­(NDipp)­Cl₂(R₂bpy)₂ can be used to generate the uranium­(V) and uranium­(VI) bisimido compounds, U­(NDipp)₂­X­(R₂bpy)₂, X = Cl, Br, I, and U­(NDipp)_2­I₂(^<i>t</i>Bu₂bpy), which establishes these uranium­(IV) precursors as potential intermediates in the syntheses of high-valent bis­(imido) complexes from UCl₄. The monoimido species also react with 4-methylmorpholine-N-oxide to yield uranium­(VI) oxo-imido products, U­(NDipp)­(O)­Cl₂(L)_<i>n</i> (L = ^<i>t</i>Bu₂bpy, <i>n</i> = 1; L = tppo, <i>n</i> = 2). The aforementioned molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent sources of U­(IV), U­(V), and U­(VI) imido species

Preparation and Reactivity of the Versatile Uranium(IV) Imido Complexes U(NAr)Cl₂(R₂bpy)₂ (R = Me, ^<i>t</i>Bu) and U(NAr)Cl₂(tppo)₃

Uranium tetrachloride undergoes facile reactions with 4,4′-dialkyl-2,2′-bipyridine, resulting in the generation of UCl₄(R₂bpy)₂, R = Me, ^<i>t</i>Bu. These precursors, as well as the known UCl₄(tppo)₂ (tppo = triphenylphosphine oxide), react with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide the versatile uranium­(IV) imido complexes, U­(NDipp)­Cl₂(L)_<i>n</i> (L = R₂bpy, <i>n</i> = 2; L = tppo, <i>n</i> = 3). Interestingly, U­(NDipp)­Cl₂(R₂bpy)₂ can be used to generate the uranium­(V) and uranium­(VI) bisimido compounds, U­(NDipp)₂­X­(R₂bpy)₂, X = Cl, Br, I, and U­(NDipp)_2­I₂(^<i>t</i>Bu₂bpy), which establishes these uranium­(IV) precursors as potential intermediates in the syntheses of high-valent bis­(imido) complexes from UCl₄. The monoimido species also react with 4-methylmorpholine-N-oxide to yield uranium­(VI) oxo-imido products, U­(NDipp)­(O)­Cl₂(L)_<i>n</i> (L = ^<i>t</i>Bu₂bpy, <i>n</i> = 1; L = tppo, <i>n</i> = 2). The aforementioned molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent sources of U­(IV), U­(V), and U­(VI) imido species