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
2000-01-28T00:00:00Z (GMT) by
The aquachromyl ion, CrIVaqO2+, reacts with the hydrides L(H2O)RhH2+ (L = L1 = aneN4 and L2 = meso-Me6-aneN4) in aqueous solutions in the presence of molecular oxygen to yield Craq3+ 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, kRhH/kRhD = ∼3 (L1) and 3.3 (L2), but no solvent isotope effect, kH2O/kD2O = 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)CrVO+. 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) Å3, and Z = 2.