Five ruthenium(ii) complexes were synthesized, including (HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)Cl2 (3), [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2Cl][PF6] (4) and [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2OH][PF6] (5) bearing an unsymmetrical pincer NNN ligand with a 2-hydroxypyridylmethylene fragment, and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][Cl]2 (6) and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][PF6]2 (7) containing 2-methoxypyridylmethylene moieties. 4 reacts with H2O at room temperature to give 5 whose crystal structure reveals the existence of intramolecular hydrogen-bonding between its two -OH groups. 3 exhibits high catalytic activity for transfer hydrogenation of ketones.
Four
Ru(II)-NC complexes were tested as catalysts for semihydrogenation
of internal alkynes to (E)-alkenes with ethanol,
and the complex {(C5H4N)(C6H4)}RuCl(CO)(PPh3)2 (1a)
showed the highest activity. The reactions proceeded well with 1 mol
% catalyst loading and 0.1 equiv of t-BuONa at 110
°C for 1 h, and 32 alkenes were synthesized with excellent E:Z selectivity. This is the first ruthenium-catalyzed
semihydrogenation of internal alkynes to (E)-alkenes
using ethanol as the hydrogen donor.
The transfer hydrogenation of azoarenes to hydrazoarenes
using
ethanol as a hydrogen source by a bidentate Ru(II)-NC complex is developed.
A weak base is crucial for this semihydrogenation that can efficiently
avoid hydrazoarene dehydrogenation under strongly basic conditions.
Control experiments and density functional theory calculations demonstrate
the mechanism via a Meerwein–Ponndorf–Verley mechanism,
and the only byproduct is ethyl acetate. This study offers a new and
simple approach for the synthesis of hydrazoarenes.
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