Design of Air and Moisture Stable Ruthenophane and Ruthenium(II)‐π Complexes and Study of Their Applications in Catalysis

Abstract

Herein, we report the synthesis and characterization of two ruthenophane (1) and ruthenium(II)‐π (2) complexes, and the results of their catalytic applications under different conditions. These complexes exhibited excellent air and moisture stability due to the existence of effective cation‐π interactions between the metal ion and the aromatic surface of the ligand. These complexes were tested and compared in the transfer hydrogenation of acetophenone in 2‐propanol. The ruthenophane complex 1 exhibited highest efficiency in the catalytic transfer hydrogenation reaction when compared to the complex 2. The better efficiency of the complex 1 can be ascribed to the steric and cation‐π interactions of the cyclophane ligands with the metal centre under reaction conditions. Using catalyst loading of ca. 2 mol%, the transfer hydrogenation of the aromatic ketones having different substituents was achieved. Notably, these complexes exhibited high selectivity for the aromatic ketones having electronegative substituents and showed highest efficiency of ca. 100% under moderate reaction conditions when compared to the literature known ruthenium catalysts.

Recent Advances in Ru Catalyzed Transfer Hydrogenation and Its Future Perspectives

“…Realistic relevance of the asymmetric synthesis by TH/ATH in fine chemicals, pharmaceuticals, materials and industrial use required designing and exploration of efficient catalysts. Ru with versatile oxidation states, coordination geometries offered by a variety of ligand moieties make it a good candidate for catalytic Selected asymmetric transfer hydrogenation catalyzed, tethered or non-tethered Ru(II) catalysts (7)(8)(9)(10)(11).…”

“…In search of new ligand frame-work for effective and selective TH reaction of aromatic ketones, Ramaiah and co-workers [9] have established a promising new class of airÀ/moisture-stable ruthenophane/ruthenium(II)-π complexes (19)(20) and compared their TH activity (Figure 5), for the first time with the literature reported catalysts. The structure stiffness of the ligands allows forming the complexes (19)(20) through π-interactions between the anthracene moiety and ruthenium cation instead of insertion or NHC coordinated complexes.…”

“…Figure 3.Selected asymmetric transfer hydrogenation catalyzed, tethered or non-tethered Ru(II) catalysts(7)(8)(9)(10)(11).…”