Hydrogenation, of aldehydes

In hydrogen transfer from different organic compounds to aldehydes, excellent catalytic activity of RuH2(PPh3)4 was observed by Japanese scientists to override that of RhH(PPh3)4. 

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The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

Reduction of Aldehydes and Ketones to Hydrocarbons. Deep hydrogenation of aldehydes and ketones removes the oxygen functionahty and produces the parent hydrocarbons. 

The mechanism of catalytic hydrogenation of aldehydes and ketones is probably similar to that of Reaction 15-11, though not much is known about it. " ... 

Cyclopentadienone iron alcohol complexes like 37 were generated from the reactions of [2,5-(SiMe3)2-3,4-(CH2)4(ri -C4COH)]Fe(CO)2H (36) and aromatic aldehydes [47]. This process can be used for the iron-catalyzed hydrogenation of aldehydes (Fig. 18 and Fe-H Complexes in Catalysis ). 

Casey CP, Guan H (2009) Cyclopentadienone iron alcohol complexes synthesis, reactivity, and implications for the mechanism of iron-catalyzed hydrogenation of aldehydes. J Am Chem Soc 131 2499-2507... 

Transfer hydrogenation of aldehydes with isopropanol without addition of external base has been achieved using the electronically and coordinatively unsaturated Os complex 43 as catalyst. High turnover frequencies have been observed with aldehyde substrates, however the catalyst was very poor for the hydrogenation of ketones. The stoichiometric conversion of 43 to the spectroscopically identifiable in solution ketone complex 45, via the non-isolable complex 44 (Scheme 2.4), provides evidence for two steps of the operating mechanism (alkoxide exchange, p-hydride elimination to form ketone hydride complex) of the transfer hydrogenation reaction [43]. 

Table 13.3. Hydrogenation of Aldehydes a,p-Unsaturated at 363 K and at H2 Pressure of 0.62 MPa Over Ir Catalysts Supported on Mixed Oxides. Initial Activity and TOP at 10 % of Conversion.

During hydrogenation of aldehydes, especially over platinum oxide, catalyst deactivation occurs. The reasons for this deactivation are not well understood and several theories exist.6... 

Using functionalized polystyrenes and [Rh6(CO)16], polymer-bound Rh-cluster complexes were obtained in the presence of CO and H20, which exhibited high catalytic activities for hydrogenation of aldehydes to alcohols.407,408... 

Iridium-catalyzed transfer hydrogenation of aldehyde 73 in the presence of 1,1-dimethylallene promotes tert-prenylation [64] to form the secondary neopentyl alcohol 74. In this process, isopropanol serves as the hydrogen donor, and the isolated iridium complex prepared from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS is used as catalyst. Complete levels of catalyst-directed diastereoselectivity are observed. Exposure of neopentyl alcohol 74 to acetic anhydride followed by ozonolysis provides p-acetoxy aldehyde 75. Reductive coupling of aldehyde 75 with allyl acetate under transfer hydrogenation conditions results in the formation of homoallylic alcohol 76. As the stereochemistry of this addition is irrelevant, an achiral iridium complex derived from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and BIPHEP was employed as catalyst (Scheme 5.9). 

Molybdenum and tungsten carbonyl hydride complexes were shown (Eqs. (16), (17), (22), (23), (24) see Schemes 7.5 and 7.7) to function as hydride donors in the presence of acids. Tungsten dihydrides are capable of carrying out stoichiometric ionic hydrogenation of aldehydes and ketones (Eq. (28)). These stoichiometric reactions provided evidence that the proton and hydride transfer steps necessary for a catalytic cycle were viable, but closing of the cycle requires that the metal hydride bonds be regenerated from reaction with H2. 

Homogeneous Hydrogenation of Aldehydes, Ketones, I mines and Carboxylic Acid Derivatives ... 

This chapter aims to provide an overview of the current state of the art in homogeneous catalytic hydrogenation of C=0 and C=N bonds. Diastereoselec-tive or enantioselective processes are discussed elsewhere. The chapter is divided into sections detailing the hydrogenation of aldehydes, the hydrogenation of ketones, domino-hydroformylation-reduction, reductive amination, domino hydroformylation-reductive amination, and ester, acid and anhydride hydrogenation. 

Table 15.1 Hydrogenation of aldehydes with [IrH3(PPh3)3] in acetic acid.

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