Dinuclear Ruthenium Complexes Bearing Dicarboxylate and Phosphine Ligands. Acceptorless Catalytic Dehydrogenation of 1-Phenylethanol

Reaction of RuH2CO(PPh3)3 with tetrafluorosuccinic acid at 100 °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 1-phenylethanol at 130 °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 1-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.