Ruthenium(II) Complexes of 4′‐(Aryl)‐2,2′:6′,2′′‐terpyridyl Ligands as Simple Catalysts for the Transfer Hydrogenation of Ketones

Abstract

A series of cationic [Ru(L)(PPh 3 ) 2 Cl] + (1-3) and neutral [Ru(L)(PPh 3 )Cl 2 ] (4-6) Ru II complexes were synthesized by reacting [RuCl 2 (PPh 3 ) 2 ] with 4′-(aryl)-2,2′:6′,2′′-terpyridyl-based ligands (L1-L3) with various aryl groups (tolyl, phenyl and 4fluorophenyl). The synthesized Ru II complexes were unambiguously characterized by various spectroscopic techniques such as FTIR and multinuclear NMR spectroscopy as well as HRMS. The neutral complexes (4-6) were also structurally characterized by single-crystal X-ray diffraction studies. Photophysical and electrochemical studies of the Ru II complexes were performed to elucidate the effects of the 4′-aryl substituents of [a] 4064 Scheme 2. Synthetic route for the cationic (1-3) and neutral (4-6) ruthenium(II) complexes.

Hydrogen Transfer Reactions of Carbonyls, Alkynes, and Alkenes with Noble Metals in the Presence of Alcohols/Ethers and Amines as Hydrogen Donors

“…A series of cationic and neutral ruthenium(II) complexes with 4'-(aryl)-2,2':6',2"-terpyridyl-based ligands with various aryl groups (tolyl, phenyl, 4-fluorophenyl) were synthesized and characterized (Scheme 17) [79]. The newly synthesized catalyst series was successfully used in the transfer hydrogenation of ketones (yield/53-84%, TON/106-172) with a wide substrate scope.…”

“…The newly synthesized catalyst series was successfully used in the transfer hydrogenation of ketones (yield/53-84%, TON/106-172) with a wide substrate scope. The neutral complexes were catalytically more active than the cationic counterparts because of their reduction potentials (E 1/2 ), which were lowered by 0.30 V, promoting the reduction of ketones [79]. Based on the experimental results, the supposed mechanism is an inner-sphere reduction pathway, including the formation of a neutral complexes were catalytically more active than the cationic counterparts because of their reduction potentials (E1/2), which were lowered by 0.30 V, promoting the reduction of ketones [79].…”

“…The neutral complexes were catalytically more active than the cationic counterparts because of their reduction potentials (E 1/2 ), which were lowered by 0.30 V, promoting the reduction of ketones [79]. Based on the experimental results, the supposed mechanism is an inner-sphere reduction pathway, including the formation of a neutral complexes were catalytically more active than the cationic counterparts because of their reduction potentials (E1/2), which were lowered by 0.30 V, promoting the reduction of ketones [79]. Based on the experimental results, the supposed mechanism is an inner-sphere reduction pathway, including the formation of a [Ru-H] intermediate in 2-propanol as the hydrogen source (Scheme 9, Scheme 17).…”

Metal‐Terpyridine Complexes in Catalytic Application – A Spotlight on the Last Decade

“…More recently, Patra et al . reported on the transfer hydrogenation of ketones using cationic and neutral Ru(II) complexes equipped with 4′‐aryl‐tpy ligands ( 14 and 15 , Figure ) . Due to their lower reduction potentials, the neutral ones were more efficient in reducing ketones.…”

“… Schematic representation of the cationic and neutral Ru(II) catalysts for the transfer hydrogenation of ketones …”