Transfer Hydrogenation of Ketones Catalyzed by Surface‐Active Ruthenium and Rhodium Complexes in Water

Abstract

An improved, high-yield, one-pot synthetic procedure for water-soluble ligands functionalized with trialkyl ammonium side groups H2 N(CH2 )2 NHSO2 -p-C6 H4 CH2 [NMe2 (Cn H2n+1 )](+) ([HL(n) ](+) ; n=8, 16) was developed. The corresponding new surface-active complexes [(p-cymene)RuCl(L(n) )] and [Cp*RhCl(L(n) )] (Cp*=η(5) -C5 Me5 ) were prepared and characterized. For n=16 micelles are formed in water at concentrations as low as 0.6 mM, as demonstrated by surface-tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C16 tails due to their ability to be adsorbed at the water/substrate interface. The scope of these catalyst systems in aqueous solutions was extended from partially water soluble aryl alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (2-dodecanone).

Cooperative effects of ruthenium micellar catalysts and added surfactants in transfer hydrogenation of ketones in water

“…The capability of mixtures of RuL 8 and S to form mixed micelles was also assessed by measuring the corresponding diffusion coefficients. As reported previously, 28 the performance of RuL 16 (initial TOF 1400 h -1 ) and RuL 8 (TOF 350 h -1 ) in the hydrogenation of 1 differs significantly: the latter is less catalytically active and its reaction profile is sigmoidal with substantial induction period. At the Transfer hydrogenation of 1 catalyzed by the S/RuL n mixtures.…”

“…28 We have shown that the most surface active RuL 16 complex is a better catalyst for hydrophobic ketones hydrogenation in aqueous media compared to the rhodium analogue RhL 16 . 28 We have shown that the most surface active RuL 16 complex is a better catalyst for hydrophobic ketones hydrogenation in aqueous media compared to the rhodium analogue RhL 16 .…”

“…28 A noticeable deflection on the profile for TH of 3 catalyzed by RuL 16 indicates insufficient micellization of 3 and the assistance of the alcohol product as co-surfactant is required (Figure 3). 28 A noticeable deflection on the profile for TH of 3 catalyzed by RuL 16 indicates insufficient micellization of 3 and the assistance of the alcohol product as co-surfactant is required (Figure 3).…”

ChemInform Abstract: Synthesis and Characterization of Rhodium(I) Complexes with P—N Donor Ligands and Their Catalytic Application in Transfer Hydrogenation of Carbonyl Group.

“…However, use of rhodium complexes with P~N donor hemilabile ligands are less studied and needs to be addressed. Kalsin et al have recently reported the hydrogenation of ketone by a rhodium complex containing P~N hemilabile ligand in water and obtained good yield. Aydemir et al have reported same type of reaction with good yield.…”

Imidazolium ion tethered TsDPENs as efficient water-soluble ligands for rhodium catalyzed asymmetric transfer hydrogenation of aromatic ketones

“…In 2001 the first example of Ru(II)-catalyzed ATH of ketones with HCO 2 Na as a hydride source in aqueous media was reported [17]. Since this discovery, a number of water-soluble ligands and catalysts have been developed for ATH in aqueous media providing the reduction products in high conversion yields and enantioselectivities [18][19][20][21][22][23][24][25][26]. However, a major problem associated with these catalytic systems is that the low substrate/catalyst (S/C) ratio (normally S/C = 100) and large excess amounts of hydride donor (≥ 5 equiv.…”