Ruthenium Complex Catalysts Supported by a Bis(trifluoromethyl)pyrazolyl–Pyridyl-Based NNN Ligand for Transfer
Hydrogenation of Ketones
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Abstract
Ru(III)
and Ru(II) complexes bearing a tridentate 2-(3′,5′-dimethylpyrazol-1′-yl)-6-(3″,5″-bis(trifluoromethyl)pyrazol-1″-yl)pyridine
or 2-(benzimidazol-2′-yl)-6-(3″,5″-bis(trifluoromethyl)pyrazol-1″-yl)pyridine
ligand were synthesized and applied to the transfer hydrogenation
of ketones. The Ru(II) complex was structurally confirmed by the X-ray
crystallographic analysis and achieved up to 2150 turnover numbers
and final TOFs up to 29700 h<sup>–1</sup> in the transfer hydrogenation
of ketones. The benzimidazolyl moiety with an unprotected NH functionality
in the ligand exhibited an enhancement effect on the catalytic activity
of its RuCl<sub>3</sub> complex in the ketone reduction reactions,
reaching a final TOF value up to 35640 h<sup>–1</sup>. The
controlled experiments have revealed that the compatibility of the
trifluoromethylated pyrazolyl and unprotected benzimidazolyl is crucial
for the establishment of the highly active catalytic system
