A series of monometallic dihydrogen complexes of the type M(OEP)(L)(H2) (M = Ru, Os; L = THF, *Im) was synthesized and characterized by 1H NMR. The H-H bond length was found to increase when Os was replaced by Ru or when *Im was replaced by THF. The bond distances (as determined by T1) range from 0.92 to 1.18 Å. The first example of a bimetallic bridging dihydrogen complex, Ru2(DPB)(*Im)2(H2), was also prepared. The H2 ligand is simultaneously bound to both Ru-metal centers. High-field 1H NMR experiments (620 MHz) revealed a -7.37 Hz dipolar splitting of the H2 ligand for this complex. Analysis of this splitting suggests that the H2 ligand is bound with the H-H axis perpendicular to the Ru-Ru axis. These complexes were examined as possible catalysts for the oxidation of dihydrogen through prior heterolytic activation of H2. Only Ru(OEP)(THF)(H2) can be conveniently deprotonated. Ru(OEP)(THF)(H2) is also implicated in the Ru-(OEP)(THF)2 catalyzed isotopic exchange between H2 and D2O in THF solution. Each step for this mechanism has been elucidated. We have also achieved catalytic dihydrogen oxidation using [Ru(OEP)]2 adsorbed onto graphite. Two mechanisms for this ruthenium porphyrin catalyzed dihydrogen oxidation are presented and compared.
|Number of pages||11|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1992|
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