3 research outputs found
Oxidative Stretching of MetalâMetal Bonds to Their Limits
Oxidation of quadruply bonded Cr<sub>2</sub>(dpa)<sub>4</sub>, Mo<sub>2</sub>(dpa)<sub>4</sub>, MoWÂ(dpa)<sub>4</sub>, and W<sub>2</sub>(dpa)<sub>4</sub> (dpa = 2,2âČ-dipyridylamido)
with 2 equiv of silverÂ(I) triflate or ferrocenium triflate results
in the formation of the two-electron-oxidized products [Cr<sub>2</sub>(dpa)<sub>4</sub>]<sup>2+</sup> (<b>1</b>), [Mo<sub>2</sub>(dpa)<sub>4</sub>]<sup>2+</sup> (<b>2</b>), [MoWÂ(dpa)<sub>4</sub>]<sup>2+</sup> (<b>3</b>), and [W<sub>2</sub>(dpa)<sub>4</sub>]<sup>2+</sup> (<b>4</b>). Additional two-electron oxidation
and oxygen atom transfer by <i>m</i>-chloroperoxybenzoic
acid results in the formation of the corresponding metalâoxo
compounds [Mo<sub>2</sub>OÂ(dpa)<sub>4</sub>]<sup>2+</sup> (<b>5</b>), [WMoOÂ(dpa)<sub>4</sub>]<sup>2+</sup> (<b>6</b>), and [W<sub>2</sub>OÂ(dpa)<sub>4</sub>]<sup>2+</sup> (<b>7</b>), which feature
an unusual linear M···MîŒO structure. Crystallographic
studies of the two-electron-oxidized products <b>2</b>, <b>3</b>, and <b>4</b>, which have the appropriate number of
orbitals and electrons to form metalâmetal triple bonds, show
bond distances much longer (by >0.5 Ă
) than those in established
triply bonded compounds, but these compounds are nonetheless diamagnetic.
In contrast, the CrâCr bond is completely severed in <b>1</b>, and the resulting two isolated Cr<sup>3+</sup> magnetic
centers couple antiferromagnetically with <i>J</i>/<i>k</i><sub>B</sub>= â108(3) K [â75(2) cm<sup>â1</sup>], as determined by modeling of the temperature dependence of the
magnetic susceptibility. Density functional theory (DFT) and multiconfigurational
methods (CASSCF/CASPT2) provide support for âstretchedâ
and weak metalâmetal triple bonds in <b>2</b>, <b>3</b>, and <b>4</b>. The metalâmetal distances in
the metalâoxo compounds <b>5</b>, <b>6</b>, and <b>7</b> are elongated beyond the single-bond covalent radii of the
metal atoms. DFT and CASSCF/CASPT2 calculations suggest that the metal
atoms have minimal interaction; the electronic structure of these
complexes is used to rationalize their multielectron redox reactivity
Oxidative Stretching of MetalâMetal Bonds to Their Limits
Oxidation of quadruply bonded Cr2(dpa)4, Mo2 (dpa)4, MoW(dpa)4, and W2(dpa)4 (dpa = 2,2âČ-dipyridylamido) with 2 equiv of silver(I) triflate or ferrocenium triflate results in the formation of the twoelectron-oxidized products [Cr2(dpa)4]2+ (1), [Mo2(dpa)4]2+ (2), [MoW- (dpa)4]2+ (3), and [W2(dpa)4]2+ (4). Additional two-electron oxidation and oxygen atom transfer by m-chloroperoxybenzoic acid results in the formation of the corresponding metalâoxo compounds [Mo2O(dpa)4]2+(5), [WMoO(dpa)4]2+ (6), and [W2O(dpa)4]2+ (7), which feature an unusual linear M***MO structure. Crystallographic studies of the twoelectron-oxidized products 2, 3, and 4, which have the appropriate number of orbitals and electrons to form metalâmetal triple bonds, show bond distances much longer (by >0.5 Ă
) than those in established triply bonded compounds, but these compounds are nonetheless diamagnetic. In contrast, the CrâCr bond is completely severed in 1, and the resulting two isolated Cr3+ magnetic centers couple antiferromagnetically with J/kB= â108(3) K [â75(2) cmâ1], as determined by modeling of the temperature dependence of the magnetic susceptibility. Density functional theory (DFT) and multiconfigurational methods (CASSCF/CASPT2) provide support for "stretched" and weak metalâmetal triple bonds in 2, 3, and 4. The metalâmetal distances in the metalâoxo compounds 5, 6, and 7 are elongated beyond the single-bond covalent radii of the metal atoms. DFT and CASSCF/CASPT2 calculations suggest that the metal atoms have minimal interaction; the electronic structure of these complexes is used to rationalize their multielectron redox reactivity