Alkyl radical colligation and release by a chromium macrocycle

Journal Article · Tue Dec 10 23:00:00 EST 1991 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00025a027· OSTI ID:7274039

Huston, P; Espenson, J H; Bakac, A ^[1]

---

1. Iowa State Univ., Ames (United States)

Alkyl radicals, generated from the photohomolysis of organocobalt complexes, were allowed react in aqueous solution with (H{sub 2}O){sub 2}CrL{sup 2+} (L = 1,4,8,12-tetraazacyclopentadecane or (15)aneN{sub 4}). The reaction rates were evaluated by laser flash photolysis, using the known reaction between R{sm bullet} and the methyl viologen radical cation as a kinetic probe. Data were obtained for reactions of 13 radicals. The rate constants span a narrow range, (6-19) {times} 10{sup 7} L mol{sup {minus} 1} s{sup {minus} 1} at 25C. The decomposition of CH{sub 3}CH-(OH)CrL(H{sub 2}O){sup 2+} takes place by concurrent homolysis and {beta}-elimination. At 25C the overall rate constant has a value (1.60 {plus minus} 0.15) {times} 10{sup {minus} 4} s{sup {minus} 1} independent of (H{sup +}). The complexes with R = CH{sub 2}OH and CH{sub 2}OCH{sub 3} undergo decomposition too slowly for detection. Equilibrium constants for radical binding calculated from forward and reverse rate constants are log K{sub 298} = 11.23 (CH(CH{sub 3}){sub 2}) and 12.19 (CH{sub 2}C{sub 6}H{sub 5}). The kinetic and equilibrium data are discussed in terms of a reaction model featuring concurrent Cr-C and Cr-OH{sub 2} bond making and bond breaking. Results for analogous reactions are compared.

• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 7274039
• Journal Information: Inorganic Chemistry; (United States), Journal Name: Inorganic Chemistry; (United States) Vol. 30:25; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKYL RADICALS
AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMATOGRAPHY
CHROMIUM COMPLEXES
COMPLEXES
DECOMPOSITION
DISPERSIONS
ELECTROMAGNETIC RADIATION
GAS CHROMATOGRAPHY
HETEROCYCLIC COMPOUNDS
KINETICS
LASER RADIATION
MIXTURES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PYRIDINES
RADIATIONS
RADICALS
REACTION KINETICS
SEPARATION PROCESSES
SOLUTIONS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES