Anionic metal hydride catalysts. 2. Application to the hydrogenation of ketones, aldehydes, carboxylic acid esters, and nitriles

Abstract

The application of the potassium hydrido(ph0sphine)ruthenate complexes K+[(Ph3P)2Ph2-PC6H4RuH2]-.CloHs.(C2H~)z0 (1) and K2' [(Ph3P)3(PhzP)Ru2H4]2-.2C6H1403 (2) as catalysts for the homogeneous phasehydrogenation of a variety of unsaturated organic compounds is described. Ketones and aldehydes are catalytically hydrogenated with 1 and 2 typically at 85 OC and under 620 kPa of hydrogen, to yield the corresponding alcohols as well as minor aldol condensation byproducts. The hydrogenation of acrolein, depending on conditions, can give either propionaldehyde or mixtures of propionaldehyde and allyl alcohol. Carboxylic acid esters, which are activated by adjacent electron-withdrawing groups, e.&, CF3C02CH3, CF3C02CH2CF3, (-CO*CHJ2, can be hydrogenated, with 1 and 2, to yield, respectively, CF3CH20H and CH30H, CF3CH20H, and HOCHzCOZCH3. Methyl acetate diluted with toluene (1:lO (v/v)) in the presence of 2 is hydrogenated (at 90 OC, under 620 kPa of H,) giving methanol, ethanol, and ethyl acetate (formed by trans-esterification with the ethanol product). This represents the first instance of a homogeneous catalytic hydrogenation of a simple aliphatic ester. Nitriles are hydrogenated with 1 and 2 (at 90 OC, 620 kPa of H2) to give, selectively, primary amines. The rates and achievable conversions for these reactions are dependent upon the solvent medium used and on the nature of the cation associated with the hydridometalate catalysts. . In the previous paperlc we described the synthesis, composition, and basic chemical properties of the potassium hydrido(phosp h i n e ) r u t h e n a t e c o m p 1 e x e s , K+[(Ph3P),Ph2-I (1) (a) A'MH-t A -O T ( A+MH--A t M : o f H O T ( A+MH-A t M L O f H t H2 MH2 t dO-+H t -MHz t At . -+ A+ = cation; M = transition metal with associated ligands.

Catalytic Transfer Hydrogenation of Ketones with KHCr(CO)5/HCO2H/Et3N Systems

“…[9] This phenomenon may be ascribed to K ϩ assistance, as previously demonstrated for the hydrogenation of ketones with Secondly, the complex [PPN] ϩ [Cr(CO) 5 (OAc)] Ϫ is an active catalyst precursor for the hydrogenation of ketones in THF potassium hydrido(phosphane)ruthenate complexes. [13] From a more general point of view, and as previously obat 125°C under 40 bar of H 2 . [10] In these catalytic reactions, [HCr(CO) 5 ] Ϫ is believed to be the active species.…”

Hydrogenation of Polar Bonds Catalysed by Ruthenium-Pincer Complexes

“…While there are many examples of Ru-catalysed hydrogenations of ketones and aldehydes [7,11], and recently Fe-catalysed hydrogenation of ketones was also reported [35][36][37][38][39], including our system based on pincer-iron complexes [24,25], catalytic hydrogenation of esters, particularly non-activated ones, under mild conditions is a challenging task [6,7,9,10,40,41]. In pioneering work by Elsevier et al various aromatic and aliphatic esters were hydrogenated in fluorinated solvent using in situ prepared ruthenium complexes bearing P,P,P ligands at high pressure of dihydrogen under basic conditions [42].…”

Ruthenium-catalysed hydrogenation of esters using tripodal phosphine ligands

“…Having explored the potential and limitations of the TriPhos Ph ligand system, and noting the improvements offered by the ligand systems of Saudan and Milstein, we decided to explore tripodal phosphine ligands incorporating an additional nitrogen moiety albeit in the ligand backbone rather than as a donor atom, due to the ease of synthesis. Table 5 summarises the data from initial catalytic studies with the N--TriPhos Ph (6) and N--TriPhos Et (7) ligands for DMO reduction, and includes runs with the TriPhos Ph ligand conducted at the same time for accurate comparison. A graphic representation of the gas uptake during this catalysis can be seen in Figure 4.…”