Trimethylsilyl-Substituted Hydroxycyclopentadienyl Ruthenium Hydrides as Benchmarks To Probe Ligand and Metal Effects on the Reactivity of Shvo Type Complexes

The bis­(trimethylsilyl)-substituted hydroxycyclopentadienyl
ruthenium
hydride [2,5-(SiMe3)2-3,4-(CH2OCH2)­(η5-C4COH)]­Ru­(CO)2H (10) is an efficient catalyst for hydrogenation of
aldehydes and ketones. Because 10 transfers hydrogen
rapidly to aldehydes and ketones and because it does not form an inactive
bridging hydride during reaction, hydrogenation of aldehydes and ketones
can be performed at room temperature under relatively low hydrogen
pressure (3 atm); this is a significant improvement in comparison
with previously developed Shvo type catalysts. Kinetic and 2H NMR spectroscopic studies of the stoichiometric reduction of aldehydes
and ketones by 10 established a two-step process for
the hydrogen transfer: (1) rapid and reversible hydrogen bond formation
between OH of 10 and the oxygen of the aldehyde or ketone
followed by (2) slow transfer of both proton and hydride from 10 to the aldehyde or ketone. The stoichiometric and catalytic
activities of complex 10 are compared to those of other
Shvo type ruthenium hydrides and related iron hydrides.