cathodes prepared by chemical reduction of Pt salts on Cu nanoparticles for electrochemical asymmetric hydrogenation [35]. The reactions with unactivated ketones
were also performed in the presence of cinchonidine 1; however, poor yields and
moderate enantioselectivities were observed.
In 2018, Wu reported bis-cinchona alkaloid-modified Os nanoparticles catalyzed
asymmetric dihydroxylation of olefins [36]. Os nanoparticle catalysts were prepared
from a binaphthyl bis-diazonium salt as a precursor of stabilizer (Scheme 5). The
absence of the diazonium group in the prepared Os nanoparticles was confirmed by
FTIR analysis, and the formation of small nanoparticles (1.5–2.0 nm) was confirmed
by TEM analysis. Bis-cinchona alkaloid (DHQD) 2 PHAL 2 was found to be the best
chiral modifier for asymmetric dihydroxylation. The ratio of Os loading and the
amount of binaphthyl-based stabilizer were critical for both catalytic activity and
enantioselectivity. Many substrates including styrene derivatives and unsaturated
carbonyl compounds could be converted to the corresponding diols in high to
excellent enantioselectivities (Scheme 6), while nitroolefin and unsaturated nitrile
Scheme 4 Alkaloid@Cu nanoparticle composites for electrochemical asymmetric hydrogenation
of ketones
Scheme 5 Preparation of
Os nanoparticles using a
binaphthyl
bis-diazonium salt
Scheme 6 Bis-cinchona alkaloid-modified Os nanoparticles catalyzed asymmetric
dihydroxylation of olefins
Chiral Metal Nanoparticles for Asymmetric Catalysis
283
were also performed in the presence of cinchonidine 1; however, poor yields and
moderate enantioselectivities were observed.
In 2018, Wu reported bis-cinchona alkaloid-modified Os nanoparticles catalyzed
asymmetric dihydroxylation of olefins [36]. Os nanoparticle catalysts were prepared
from a binaphthyl bis-diazonium salt as a precursor of stabilizer (Scheme 5). The
absence of the diazonium group in the prepared Os nanoparticles was confirmed by
FTIR analysis, and the formation of small nanoparticles (1.5–2.0 nm) was confirmed
by TEM analysis. Bis-cinchona alkaloid (DHQD) 2 PHAL 2 was found to be the best
chiral modifier for asymmetric dihydroxylation. The ratio of Os loading and the
amount of binaphthyl-based stabilizer were critical for both catalytic activity and
enantioselectivity. Many substrates including styrene derivatives and unsaturated
carbonyl compounds could be converted to the corresponding diols in high to
excellent enantioselectivities (Scheme 6), while nitroolefin and unsaturated nitrile
Scheme 4 Alkaloid@Cu nanoparticle composites for electrochemical asymmetric hydrogenation
of ketones
Scheme 5 Preparation of
Os nanoparticles using a
binaphthyl
bis-diazonium salt
Scheme 6 Bis-cinchona alkaloid-modified Os nanoparticles catalyzed asymmetric
dihydroxylation of olefins
Chiral Metal Nanoparticles for Asymmetric Catalysis
283