O Carbonyl Catalysts

Scheme 9.9 Oxidative carbonylation of phenol with CO/O with catalyst 39...

The square planar [NiX(bdppm)]+ complex was found to react with CO at room temperature and atmospheric pressure in EtOH—H20 solution according to equation (168). The nickel(O) carbonyl complex containing the protonated ligand Hbdppm reacts in turn with acids with evolution of H2 (equation 169). Thus the complex [NiX(bdppm)]+ acts as an effective homogeneous catalyst of the water-gas reaction.1373... 

A manganese(O) carbonyl complex, Mn2(CO)io, is found to be a fairly active catalyst for the reaction of 1-hexene with HSiEt3 or HSi(OEt)3 in toluene or THF at 40 °C55. Kinetic study suggests that HMn(CO)s is the catalytically active species. 

O Acid catalyst protonates the basic carbonyl oxygen atom, making the aldehyde or ketone a better acceptor for nucleophilic addition. 

Figure 4 Specific activities for methanol and methane formation over the catalysts prepared from Pt carbonyl clusters, supported by oxides indicated o, CHjOH, catalysts from Pt carbonyl clusters , CH3OH, catalysts from HjPtCl analogous results for CH4 (Reproduced, by permission, from ref. 51)...

Work by Wayland et aL has shown that the low-valent rhodium compounds such as [(TXP)Rh]2 (TXP = tetra-(3,5-dimethylphenyl)porphyrinato), can reduce CO to form ethane dionyl compounds of the type [(TXP)Rh-C(O)-C(0)-Rh(TXP)] [97-100]. The late transition metals prefer to bind to carbon, and therefore this is formed in preference to an ethyne diolate product. Although carbocychc products are not observed, the reactions demonstrate that reductive homologation of CO is feasible with transition metals imder mild conditions. Related are the reactions of hydrosilanes with CO using rhodium and cobalt carbonyl catalysts, which give straight-chain products containing up to two or three coupled CO imits (however, at elevated pressmes and tem-peratmes) [101,102]. 

Under carbon monoxide pressure, rhodium carbonyl catalysts such as Rh4aromatic compound to allow the interaction with isocyanates to qive the corresponding amides <220"C and 26 atm), e.g.[324]j... 

Other Rhodium Catalysts. Another type of rhodium catalyst is the rhodium(O) carbonyl cluster of Rh6(CO)i6 (27). In the cyclopropanation of 22... 

A 4 molar excess of fris-o-tolylphosphite in the presence of the supported nickel—carbonyl catalyst gave a 92% yield in cyclooctadiene, a result identical to that obtained in homogeneous catalysis. Again, the rate is three times lower than... 

XVIII) these salts act as both the carbonylation catalyst and the oxidant inactive palladium(O) is recovered at the end of the reaction ... 

The absolute configuration of the rearranged products was again ascertained by determining the sign of optical rotation of one compound previously obtained by Fu [10]. Catalyst 6 was successfully tested in the rearrangement of O-carbonylated benzofuranones (Scheme 40.11) and of O-carbonylated oxindoles (Scheme 40.12), although for this last class of compounds the enantioselectivities were lower than those recorded by Hills and Fu [12]. 

Scheme 40.11 Enantioselective rearrangement of O-carbonylated benzofuranones with catalyst (R)-6.

Scheme 40.10 Enantioselective Steglich rearrangement of O-carbonylated aziactones with Vedejs catalysts 6 and 7,...

A useful catalyst for asymmetric aldol additions is prepared in situ from mono-0> 2,6-diisopropoxybenzoyl)tartaric acid and BH3 -THF complex in propionitrile solution at 0 C. Aldol reactions of ketone enol silyl ethers with aldehydes were promoted by 20 mol % of this catalyst solution. The relative stereochemistry of the major adducts was assigned as Fischer- /ir o, and predominant /i -face attack of enol ethers at the aldehyde carbonyl carbon atom was found with the (/ ,/ ) nantiomer of the tartaric acid catalyst (K. Furuta, 1991). 

The study of the chemistry of carbonyl compounds has shown that they can act as carbon nucleophiles in the presence of acid catalysts as well as bases. The nucleophilic reactivity of carbonyl compounds in acidic solution is due to the presence of the enol tautomer. Enolization in acidic solution is catalyzed by O-protonation. Subsequent deprotonation at carbon gives the enol ... 

Complete exchange of protons in a sterically unhindered position a to a carbonyl group can be achieved by heating a solution of the ketone in O-deuterated solvents in the presence of an acid or base catalyst, the latter being the more effective. The most commonly used solvents are methanol-OD, ethanol-OD, and the aprotic solvent anhydrous tetrahydrofuran or dioxane mixed with deuterium oxide. Under alkaline conditions the exchange rate in 153 2 14,164 stcroids, for example, is usually... 

A multitude of 1,4-dicarbonyls (1) undergo the Paal-Knorr reaction with and ranging from H to alkyl, aryl, carbonyl, nitrile, and phosphonate, while R and R vary between H, alkyl, aryl, trialkylsilyl, and O-alkyl. Protic acid catalysts are typically used with sulfuric, hydrochloric, and p-toluenesulfonic acids the most popular. Conversion to the furan takes place either at room temperature or upon heating with reaction times varying from five minutes to 24 hours and yields ranging from 17-100%. 

As a catalyst sulfuric acid is most often used phosphoric acid, boron trifluoride or an acidic ion exchange resin have also found application. 1,1-disubstituted alkenes are especially suitable substrates, since these are converted to relatively stable tertiary carbenium ion species upon protonation. o ,/3-unsaturated carbonyl compounds do not react as olefinic component. 

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