Oxidation of alcohols aimed at power generation from chemical energy in homogeneous reactions

INOR 563

Koji Tanaka, ktanaka@ims.ac.jp, Coordination Laboratory, Institute for Molecular Science, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
An aqua Ru complex, [Ru III (OH 2 )(sq)(terpy)] 2+ (pKa = ca. 5), dissociates two aqua protons to form a neutral oxyl radical complex, [RuII (O-.)(sq)(terpy)] 0 through [RuIII (OH-)(sq)(terpy)] + (pKa > 11) under strong basic conditions due to the electron transfer from the resultant Ru-O2- to the RuIII (sq) framework. In MeOH, [RuIII (OH2 )(sq)(terpy)] 2+ is also quantitatively converted to [RuII (O-.)(sq)(terpy)] 0 with two equivs of t-BuOK. On the other hand, [RuIII (NH3 )(sq)(terpy)] 2+ is quantitatively reduced to [RuII (NH3 )(sq)(terpy)] + in the presence of one equiv of t-BuOK in MeOH. Furthermore, both [RuIII (NH3 )(sq)(terpy)] 2+ and [RuII (NH3 )(sq)(terpy)] + work as electrocatalysts in the catalytic oxidation of MeOH and i-PrOH in the presence of t-BuOK under the electrolysis at 0.3 V (vs. SCE) in MeOH. The most plausible active species for the oxidation of MeOH is an Ru-aminyl radical complex formed through deprotonation of RuIII -NH3 coupled with electron transfer from RuIII -NH2 - to the RuIII -sq core. The drastic difference in the reactivity between Ru-oxyl and Ru-aminyl radicals toward the oxidation of MeOH will be discussed in the symposium.

Catalysis Relevant to Energy and Sustainability
8:30 AM-12:15 PM, Tuesday, March 27, 2007 McCormick Place East -- Room E270, Level 2, Oral

Division of Inorganic Chemistry

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007