Platinum unsaturated aldehydes

Reduction of unsaturated aldehydes seems more influenced by the catalyst than is that of unsaturated ketones, probably because of the less hindered nature of the aldehydic function. A variety of special catalysts, such as unsupported (96), or supported (SJ) platinum-iron-zinc, plalinum-nickel-iron (47), platinum-cobalt (90), nickel-cobalt-iron (42-44), osmium (<55), rhenium heptoxide (74), or iridium-on-carbon (49), have been developed for selective hydrogenation of the carbonyl group in unsaturated aldehydes. None of these catalysts appears to reduce an a,/3-unsaturated ketonic carbonyl selectively. 

As mentioned in Section 3.2, hydrogenation is by far the most investigated catalytic reaction and palladium the most commonly employed metal, followed by platinum. The most common substrates for catalytic hydrogenation tests are simple alkenes, cyclic alkenes and unsaturated carbonylic compounds. In the latter case, conjugated substrates (a,P-unsaturated aldehydes, acrylic acid) have received particular attention. 

Platinum-catalyzed allylation of aldehydes with allyltin reagents was first reported in 1995.4S7 457b,483 483a Ar0matiC) aliphatic, a,/3-unsaturated aldehydes and even cyclohexanone undergo allylation with allyltributyltins in the presence of PtClgtPP 113)2 >n THF at room temperature or higher temperature (Equations (123) and (124)). Allylplatinum species are considered to be the active intermediates on the basis of related mechanistic studies on palladium catalysis. 

Palladium catalysts are more often modified for special selectivities than platinum catalysts. Palladium prepared by reduction of palladium chloride with sodium borohydride Procedure 4, p. 205) is suitable for the reduction of unsaturated aldehydes to saturated aldehydes [i7]. Palladimn on barium sulfate deactivated with sulfur compounds, most frequently the so-called quinoline-5 obtained by boiling quinoline with sulfur [34], is suitable for the Rosenmund reduction [i5] (p. 144). Palladium on calcium carbonate deactivated by lead acetate Lindlar s catalyst) is used for partial hydrogenation of acetylenes to cw-alkenes [36] (p. 44). 

V-Acylsaccharins prepared by treatment of the sodium salt of saccharin with acyl chlorides were reduced by 0.5 molar amounts of sodium bis(2-methoxyethoxy)aluminum hydride in benzene at 0-5° to give 63-80% yields of aliphatic, aromatic and unsaturated aldehydes [1108 Fair yields (45-58%) of some aliphatic aldehydes were obtained by electrolytic reduction of tertiary and even secondary amides in undivided cells fitted with platinum electrodes and filled with solutions of lithium chloride in methylamine. However, many secondary and especially primary amides gave 51-97% yields of alcohols under the same conditions [130]. 

A mild one-pot procedure based on a platinum-catalyzed diborylation of 1,3-butadienes (see Eq. 30) gives doubly allylic boronate 144, which adds to an aldehyde to form a quaternary carbon center in the intermediate 145 (Eq. 105). The use of a tartrate auxiliary in this process leads to good levels of enantiose-lectivity in the final diol product, which is obtained after oxidation of the primary alkylboronate intermediate. Although examples of aliphatic, aromatic, and unsaturated aldehydes have been described, enantioselectivities vary widely (33 to 74% ee), and are good only for aliphatic aldehydes. An intramolecular variant of this interesting tandem reaction is also known. ... 

The activity and selectivity of a Cs unsaturated aldehyde (prenal) has been investigated in gaseous phase on a platinum polycrystalline sample. The aim of this work was the study of the respective effects of the pretreatment of the sample by oxygen and of the presence of a small partial pressure of H2S in the gas phase. The results gave us a better understanding of the surface mechanism and proved the importance of the chemisorption mode of the molecule. 

We chose the methyl-3, butenal or prenal as a-p unsaturated aldehyde and we carried out the reaction in gaseous phase on a polycrystalline sample of pure platinum in order to avoid any support effect. The objectives of this study were the following ... 

In fine chemical manufacturing, the application of promoted platinum catalysts is less known. Maxted and Akhar have reported that the addition of stannous, manganous, ceric and ferric chloride to platinum oxide (Adams catalyst) facilitates the hydrogenation of aldehydes, ketones and olefins (ref. 1). The selective hydrogenation of unsaturated aldehydes or ketones to unsaturated alcohols has been achieved by the addition of ferrous sulfate and zinc acetate to platinum catalysts (ref. 2). 

Chromium compounds increase the activity of platinum catalysts by increasing the electron densities of the active sites. jhe addition of ferrous sulfate, which promotes the hydrogenation of carbonyl groups, and zinc acetate, which inhibits the hydrogenation of double bonds, to platinum gives a catalyst system capable of effecting the selective hydrogenation of an unsaturated aldehyde to an unsaturated alcohoP - (Eqn. 11.12). ... 

Maiinelli TBLW, Nabuurs S, Ponec VJ (1995) Study of the selectivity in acrolein hydrogenation on platinum catalysts a model for hydrogenation of alpha, beta-unsaturated aldehydes. J Catal 156 51... 

The aim of this work was to develop and present a new method for the synthes selective platinum catalysts for the hydrogenation of unsaturated aldehydes to unsatui alcohols. The method of preparation presented above makes it possible to obtain cata possessing polar platinum surface, due to the presence of active centers near the intei metal - partially reduced transition metal oxide. This transition metal oxide adsorb carbonyl oxygen atom whereas adjacent platinum atom interacts with carbonyl ca atom. In such a situation, the C=C bond is quite far from the surface so its adsorption i favored. There are also some additional parameters which should be taken consideration. The first is the size of platinum crystallites located on the catalyst sur Large platinum crystallites cause planar adsorption of aldehyde molecule in such adsorption of both double bonds is highly probable. It is known that a more sur... 

Platinum catalysts deposited on the supports modified with transition metal oxide monolayers exhibited high activity and satisfactory selectivity in the hydrogenation of unsaturated aldehydes to the corresponding unsaturated alcohols. Platinum acetylacetonate was a more suitable catalyst precursor than hexachloroplatinic acid in the preparation of the transition metal-O-Pt catalytic system for the hydrogenation of cinnamaldehyde and... 

In another example, nanodustered Pt(0) catalysts based on cross-linked macro-molecular matrixes were evaluated in the hydrogenation of an a,(i-unsaturated aldehyde, citral. The monometallic catalysts exhibit remarkable selectivity for gera-niol/nerol when 2-3 nm, regularly shaped, spherical metal nanoclusters are deposited on the supports from solutions of solvated platinum atoms prepared by metal vapor synthesis (MVS). The immobilization in the polymer framework of ions of a second metal such as Fe(II), Co(II), or Zn(II) enhances the selectivity of the Pt catalysts by up to more than 90% [18],... 

B. Bachilier-Baeza, A. Guerrero-Ruiz and I. Rodrigez-Ramos, "Role of the residual chlorides in platinum and mthenium catalysts for the hydrogenation of a,p-unsaturated aldehydes" Appl. Catal. A General, 192, 289 (2000). 

Group VIII metals supported on silica are known to hydrogenate preferentially the C=C double bond of a,B-unsaturated aldehydes (as e.g. crotonaldehyde). Only for a few metals, like Os and Co, a significant activity for the hydrogenation of the C=0 group was reported [1]. Improved selectivity for carbonyl group hydrogenation was described for platinum catalysts modified by Sn [2,3,4], Fe... 

Unsaturated aldehydes and ketones can be selectively hydrogenated to the corresponding saturated carbonyl however, it is difficult to reduce the ethylenic group without also attacking the carbonyl group, although such a reduction may be achieved for certain compounds such as mesityl oxide (2-methyl-pentene-2-one-4) using a platinum catalyst at room temperature. 

It also catalyses oxidation reactions with an oxidant, e.g. the methylene group in cyclopropylmethyl-compormds to a carbonyl group in the presence of metaperiodate pTasegawa et al. Chem Lett (Jpn) 1385 1985, Carlsen et al. J Org Chem 46 3936 1981, cf Review Gore Platinum Metals Rev 27 111 1983], It catalyses the synthesis of 2-ethyl-3-methylqirinohnes from primary aromatic amines and triallylamine [Cho et al. Tetrahedron Lett 40 1499 1999], and has been used for the selective hydrogenation of unsaturated aldehydes pujita et al. J Catal 255 95 2004]. 

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