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

Journal Article · Mon Feb 21 04:00:00 EST 2000 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic991098p· OSTI ID:20017568

Bakac, A; Guzei, I A

This paper examines the redox reactivity of Cr(IV) and Cr(V) toward several substrates and addresses the preference for one-electron vs. two-electron pathways for these two oxidation states in well-defined systems in aqueous solutions. The aquachromyl ion, Cr{sup IV} {sub aq}O{sup 2+}, reacts with the hydrides L(H{sub 2}O)RhH{sup 2+} (L = L{sup 1} = [14]and N{sub 4} and L{sup 2} = meso-Me{sub 6}-[14]aneN{sub 4}) in aqueous solutions in the presence of molecular oxygen to yield Cr{sub aq}{sup 3+} and the superoxo complexes L (H{sub 2}O)RhOO{sup 2+}. At 25 C, the rate constants are {approximately}10{sup 4} M{sup {minus}1} s{sup {minus}1} (L = L{sup 1}) and 1.12 x 10{sup 3} M{sup {minus}1} s{sup {minus}1} (L = L{sup 2}). Both reactions exhibit a moderate deuterium isotope effect, k{sub RhH}/k{sub RhD} = {approximately} 3 (L{sup 1}) and 3.3 (L{sup 2}), but no solvent isotope effect, k{sub H{sub 2}O}/k{sub D{sub 2}O} = 1. The proposed mechanism involves hydrogen atom abstraction followed by the capture of LRh(H{sub 2}O){sup 2+} with molecular oxygen. There is no evidence for the formation of L(H{sub 2}O)Rh{sup 2+} in the reaction between L(H{sub 2}O)RhH{sup 2+} and (salen)Cr{sup V}O{sup +}. The proposed hydride transfer is supported by the magnitude of the rate constants (L = L{sup 1}, k = 8,800 M{sup {minus}1} s{sup {minus}1}; (NH{sub 3}){sub 4}, 2,500; L{sup 2}, 1,000) and isotope effects (L = L{sup 1}, kie = 5.4; L{sup 2}, 6.2). The superoxo complex [L{sup 1}(CH{sub 3}CN)RhOO](CF{sub 3}SO{sub 3}){sub 2}{sm{underscore}bullet}H{sub 2}O 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 P{single{underscore}bond} with a = 9.4257(5){angstrom}, b = 13.4119(7){angstrom}, c = 13.6140(7){angstrom}, {alpha} = 72.842(1){degree}, {beta} = 82.082(1){degree}, {gamma} = 75.414(1){degree}, V = 1,587.69(14){angstrom}{sup 3}, and Z = 2.

• Research Organization: Iowa State Univ., Ames, IA (US)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 20017568
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 4 Vol. 39; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AQUEOUS SOLUTIONS
CHROMIUM COMPLEXES
CRYSTAL STRUCTURE
REDOX REACTIONS
RHODIUM HYDRIDES