Iodide-bridged diruthenium complexes, [(η 5 -2,5-R 2 -3,4-Ph 2 C 4 COH)(CO) 2 Ru-(μ-I)-Ru(CO) 2 (η 4 -2,5-R 2 -3,4-Ph 2 C 4 CO)] (6a, R=Ph; 6b, R=Me), were formed from the reaction of (η 5 -2,5-R 2 -3,4-Ph 2 C 4 COH)(CO) 2 RuI (2c, R= Ph; 2d, R=Me) with [(2,5-R 2 -3,4-Ph 2 C 4 CO)(CO) 2 Ru] 2 (7a, R=Ph; 7b, R=Me). The complexes exhibited a high catalytic activity for the oxidation of alcohols with silver oxide at room temperature.Shvo's complex 1 exhibits intriguing catalytic activities for many hydrogen-transfer reactions such as hydrogenation of alkynes, 1,2 reduction of ketones, 3 oxidation of alcohols, 4 Tishchenko-type disproportionation of aldehydes, 5 and oxidant-free dehydrogenation of alcohols. 6 Moreover, it is also an excellent catalyst for the racemization of secondary alcohols under the conditions for the dynamic kinetic resolution (DKR) of alcohols with enzymes and acylating reagents. 7 Recently, B€ ackvall and co-workers have reported its activity also for the racemization of amines. 8 However, heating was required to activate 1 dormant under ambient conditions, and it was proposed that heating cleaves 1 into ruthenium hydride complex 2a and 16-electron ruthenium cyclopentadienone species 3 (Scheme 1). 9 Casey and coworkers observed the hydrogen-transfer reactions of ketones and imines when 2a was employed. 9,10 A closely related monoruthenium complex, (η 5 -Ph 4 C 4 COH)(CO) 2 RuCl (2b), was shown to exhibit a catalytic activity for the oxidation of alcohols with chloroform as an oxidant. 11 However, this oxidation also required the heating of 2b at 90°C and a stoichiometric amount of base under anaerobic conditions. Shvo and co-workers have reported the reaction of the hydride-bridged complex 1 with methyl iodide to give three products: the iodide-bridged diruthenium species 4, (η 5 -Ph 4 C 4 COH)(CO) 2 RuI (2c), and (η 5 -Ph 4 C 4 COMe)(CO) 2 RuI (5) (Scheme 2). Although they isolated 4 only in a trace amount, they succeeded in determining its molecular structure by X-ray diffraction analysis, with which they proposed that 4 is an unusual neutral complex containing two Ru 1/2þ and a single iodide bridge. 12 We became interested in the structure of 4 and its catalytic activity because the presence of two units of 3 may greatly enhance its catalytic activity. Another interesting point is that the structure of 4 does not obey the 18-electron rule. Herein we report the formation of iodide-bridged diruthenium complex 6a from 2c and a dimer of 3, [(Ph 4 C 4 CO) (CO) 2 Ru] 2 (7a). The structure of 6a resembles that of 4, but obeys the 18-electron rule. Furthermore, in our present study, 6a turned out to be a more efficient catalyst than Shvo's complex (1) for the oxidation of alcohols with silver oxide under mild conditions (Scheme 3). For example, 1-phenylethanol was completely oxidized within 4 h at room temperature when a catalytic amount of 6a (2 mol % of Ru) and 1 equiv of silver oxide were used.The reaction mixture of 2c and 7a in the mole ratio of 2:1 was purified by column chromatography with...

A catalyst system was developed for the highly regio- and stereoselective hydrostannation of a range of alkynes with tributylstannane under mild conditions. The active catalytic species was generated from a stable diruthenium complex by illuminating household fluorescent light (30 W) at room temperature.

Household fluorescent light activates a diruthenium complex to generate catalytic species highly active for the racemization of secondary alcohols under ambient conditions. This catalyst system is applicable for the chemoenzymatic dynamic kinetic resolution of racemic alcohols to give optically pure acetates under mild conditions.

Abstract:The highly chemoselective hydrosilylation of aldehydes was achieved using a ruthenium catalyst activated by a household fluorescent light (30 W) at or below room temperature. The hydrosilylation was almost exclusive to aldehydes over ketones and olefins.

In the presence of fluorescent light and the Ru catalyst, secondary alcohols efficiently undergo racemization.