pH-Dependent Transfer Hydrogenation of Ketones with HCOONa as a Hydrogen Donor Promoted by (η⁶-C₆Me₆)Ru Complexes

Abstract

The paper reports on the development of a new class of water-soluble organometallic catalysts for pH-dependent transfer hydrogenation. An organometallic aqua complex [(η 6-C6Me6)RuII(bpy)(H2O)]2+ (1, bpy = 2,2‘-bipyridine) acts as a catalyst precursor for pH-dependent transfer hydrogenation of water-soluble and -insoluble ketones with HCOONa as a hydrogen donor in water and in biphasic media. Irrespective of the solubility of the ketones toward water, the rate of the transfer hydrogenation shows a sharp maximum around pH 4.0 (in the case of biphasic media, the pH value of the aqueous phase is adopted). In the absence of the reducible ketones, as a function of pH, complex 1 reacts with HCOONa to provide a formato complex [(η 6-C6Me6)RuII(bpy)(HCOO)]+ (2) as an intermediate of β-hydrogen elimination and a hydrido complex [(η 6-C6Me6)RuII(bpy)H]+ (3) as the catalyst for the transfer hydrogenation. The structures of 1(PF6)2, 2(HCOO)·HCOOH, and [(η 6-C6Me6)RuII(H2O)3]SO4·3H2O {4(SO4)·3H2O}, the starting material for the synthesis of 1, were unequivocally determined by X-ray analysis.

Study of complexes of platinum group metals containing nitrogen bases derived from pyridine aldehydes: Interesting molecular structures with unpredicted bonding modes of the ligands

“…Interestingly, the X-ray structure analysis of [6]PF 6 shows a chloro-bridged dinuclear complex (see Fig. 1).…”

“…The IR spectra of these complexes exhibit sharp bands due to chelated multidentate ligands between 1637 and 1437 cm À1 corresponding to the different stretching frequencies of C]O, C]C and C]N bond after coordination to the metal centers (see experimental section). In addition, the infrared spectra contain a strong band between 843 and 849 cm À1 due to the stretching frequency of the PeF bonds of PF 6 À counter ions for these complexes. Comparing the IR spectra of the free ligands to that of the metal complexes, we find that the IR spectra of the free ligands show a sharp band at around 1672 cm À1 assigned to the stretching frequencies of C]O group of the ligands, but in the case of the metal complexes the stretching frequencies of C]O group appears in the lower frequency around 1637 and 1615 cm À1 .…”

“…The dinuclear arene ruthenium complexes [(h 6 2). Cations 2, 3, 7 and 8 are yellow in color, while 1 and 6 are brown.…”

“…Crystals of complexes [4](PF 6 )$H 2 O, [6](PF 6 ) and [9](PF 6 )$H 2 O were mounted on a Stoe Image Plate Diffraction system equipped with a f circle goniometer, using Mo-Ka graphite monochromated radiation (l ¼ 0.71073 Å) with f range 0e200 . The structures were solved by direct methods using the program SHELXSe97 [44].…”

“…Such complexes have been prepared as part of studies in diverse areas such as inter-metallic communication [1], bioinorganic enzyme active site modeling [2], supramolecular approaches to chiral materials [3] and functional devices [4]. The organometallic chemistry of half sandwich complexes have been broadly developed in the past few decades, due to their wide range of potential applications as catalyst precursors for hydrogen transfer [5,6], ring opening metathesis polymerization [7,8] and olefin oxidation [9]. Arene ruthenium compounds have also been extensively investigated for their persuasive antibacterial and anticancer activity [10,11].…”