Dinuclear ruthenium complexes bearing dicarboxylate and phosphine ligands. Acceptorless catalytic dehydrogenation of 1-phenylethanol

Reaction of RuH2,CO(PPh3)(3) with tetrafluorosuccinic acid at 100 degrees C gave rise to the formation of the dinuclear bis(tetrafluorosuccinate)-bridged Ru(II) complex 2, containing two water ligands. Exchange of the PPh3 in complex 2 with various diphosphine ligands afforded a series of analogous complexes 3. Reaction of the latter with I-phenylethanol at 130 degrees C or with 2-propanol/Et3N at room temperature furnished the dinuclear dihydrido-bridged Ru(II) complexes 4. Complexes 2 and 4 were characterized by X-ray diffraction analysis. Both bis(tetrafluorosuccinate)-bridged complexes 3 and dihydrido-bridged complexes 4 catalyze the acceptorless dehydrogenation of I-phenylethanol to acetophenone and dihydrogen with good yields and excellent selectivity under relatively mild conditions in the absence of acid or base. A tentative catalytic cycle for the dehydrogenation of secondary alcohols by Ru(II) complexes of type 3 is presented.