Hydrogen Atom and Hydride Transfer in the Reactions of Chromium(IV) and Chromium(V) Complexes with Rhodium Hydrides. Crystal Structure of a Superoxorhodium(III) Product

The aquachromyl ion, Cr^IV_aqO²⁺, reacts with the hydrides L(H₂O)RhH²⁺ (L = L¹ = [14]aneN₄ and L² = meso-Me₆-[14]aneN₄) in aqueous solutions in the presence of molecular oxygen to yield Cr_aq³⁺ and the superoxo complexes L(H₂O)RhOO²⁺. At 25 °C, the rate constants are ∼10⁴ M^-1 s^-1 (L = L¹) and 1.12 × 10³ M^-1 s^-1 (L = L²). Both reactions exhibit a moderate deuterium isotope effect, k_RhH/k_RhD = ∼3 (L¹) and 3.3 (L²), but no solvent isotope effect, k_H2O/k_D2O = 1. The proposed mechanism involves hydrogen atom abstraction followed by the capture of LRh(H₂O)²⁺ with molecular oxygen. There is no evidence for the formation of L(H₂O)Rh²⁺ in the reaction between L(H₂O)RhH²⁺ and (salen)Cr^VO⁺. The proposed hydride transfer is supported by the magnitude of the rate constants (L = L¹, k = 8800 M^-1 s^-1; (NH₃)₄, 2500; L², 1000) and isotope effects (L = L¹, kie = 5.4; L², 6.2). The superoxo complex [L¹(CH₃CN)RhOO](CF₃SO₃)₂·H₂O crystallizes with discrete anions, cations, and solvate water molecules in the lattice. All moieties are linked by a network of hydrogen bonds of nine different types. The complex crystallized in the triclinic space group P1̄ with a = 9.4257(5) Å, b = 13.4119(7) Å, c = 13.6140(7) Å, α = 72.842(1)°, β = 82.082(1)°, γ = 75.414(1)°, V = 1587.69(14) ų, and Z = 2.