Reductive carbonylation examples

It is worth mentioning that some precursors easily catalyze the reductive carbonylation of alkynes from the C0/H20 couple. Here, the main role of water is to furnish hydrogen through the water-gas-shift reaction, as evidenced by the co-production of CO2. In the presence of Pd /KI terminal alkynes have been selectively converted into furan-2-(5H)-ones or anhydrides when a high concentration in CO2 is maintained. Two CO building blocks are incorporated and the cascade reactions that occur on palladium result in a cyclization together with the formation of an oxygen-carbon bond [37,38]. Two examples are shown in Scheme 4. 

Methyl acetate probably originates from the reaction of methanol with the intermediate cobalt-acyl complex. The reaction leading to the formation of acetaldehyde is not well understood. In Equation 8, is shown as the reducing agent however, metal carbonyl hydrides are known to react with metal acyl complexes (20-22). For example, Marko et al. has recently reported on the reaction of ri-butyryl- and isobutyrylcobalt tetracarbonyl complexes with HCo(CO) and ( ). They found that at 25 °C rate constants for the reactions with HCo(CO) are about 30 times larger than those with however, they observed that under hydroformylation conditions, reaction with H is the predominant pathway because of the greater concentration of H and the stronger temperature dependence of its rate constant. The same considerations apply in the case of reductive carbonylation. Additionally, we have found that CH C(0)Co(C0) L (L r PBu, ... 

Recent attention on reactions of this type with unactivated carbonyls has focused on the possibility of using an active hydride as the attacking nucleophile. The resultant formyl species is then viewed as an intermediate on the path to CO reduction. For example, Casey and Neumann (55) have shown that trialkoxyborohydride reacts with various metal carbonyls according to... 

In 2007, Molander demonstrated that 5-exo-transannular reductive carbonyl addition to an endo- or exocyclic alkene can be highly effective for the formation of bicyclic ring systems. For example, treatment of cyclooctenone 36 with Sml2 and HMPA gave bicyclic alcohol 37 in 70% yield (Scheme 5.28).56 Transannular cyclisations have even been extended to 11-membered carbo-cyclic starting materials and give bicyclic products in good yield. 

In addition to alkenes, arenes can sometimes be used as radical acceptors in Sml2-mediated carbonyl-alkene couplings. For example, Schmalz reported extensive studies on ketyl additions to arenechromium tricarbonyl complexes 66,67 tetralin-Cr(CO)3 complex 49 underwent reductive carbonyl addition to the aromatic ring upon treatment with Sml2 to furnish the skeleton of the naturally occurring aryl glycoside pseudopterosin G (Scheme 5.37).66,67 Here, the bulky metal tricarbonyl group not only serves to control the... 

Large metal clusters have been supported on many metal oxides. For example, the carbido-cluster anion [OsioC(CO)24] has been adsorbed directly onto MgO. This cluster anion can also be prepared in situ on MgO by the Reductive Carbonylation of adsorbed H2OSCI6. The adsorbed osmium cluster anion appears to be ionically bound to the surface. 

The second inherent problem is encountered in the reduction of ketones with a proton-bearing chiral center adjacent to the carbonyl group. In this case, enolate formation may lead to equilibration before reduction. For example, reduction of a 98.6 1.4 mixture of menthone (4) and its epimer isomenthone (5) with Na or K in ethanol gave approximately 15% of a mixture of alcohols (8) and (9), in addition to 82% of menthol (6) and a small amount of neomenthol (7), because of partial isomerization. 

Reductive carbonylation reduction of a metal compound in the presence of CO and an appropriate reducing agent. Examples are... 

The transfer of an inorganic ion such as OH from one phase to another is called phase transfer, and the tetraalkylammonium salt is referred t as a phase-transfer catalyst. Many different kinds of organic reactions, includ ing oxidations, reductions, carbonyl-group alkylations, and 8 2 reaction an subject to phase-transfer catalysis, often with considerable improvements ii yield. 8 2 reactions are particularly good candidates for phase-transfi-catalysis because inorganic nucleophiles can be transferred from an aqut ous (protic) phase to an organic (aprotic) phase, where they are much mort reactive. For example ... 

Reductive carbonylation. In this procedure, a transition metal compound (with the metal in a positive oxidation state) is allowed to react with CO and a reducing agent. Examples ... 

The application of carbon monoxide as a reductant in organic synthesis is confined to relatively few examples. In the last 25 years, the catalytic reductive carbonylation of organic nitro compounds has become a very intense field of research. This is because a series of industrially important compounds can be obtained from nitro compounds and carbon monoxide in a single step. Very important chemicals such as isocyanates (Eq. 1), carbamates (Eq. 2) and ureas (Eq. 3) can be obtained by this methodology ... 

The formation of Me3NO can also be exploited in reductive carbonylation reactions for example, in the synthesis of benzotriazole photostabilizers from... 

This reaction profile, also called carbonylation, governs the reactivity of Pd-carbonyl complexes. Anionic M[Pd(CO)l3], for instance, catalyzes the reductive carbonylation of esters.f On the other hand, Pd(CO)(PPh3)3 was reported to catalyze the carboxymethy-lation of organic halides and the cyclocarbonylation of cinnamyl halides.f " However, the Pd-CO complexes are most often generated in situ from preformed alkyl -palladium complexes and CO under stoichiometric or catalytic conditions, for example, in the copolymerization of alkenes and CO. Decarbonylation reactions also involve the intermediacy of Pd-CO complexes. In this case, migratory deinsertion (Sect, n.3.1), that is, the microscopic reversal of the migratory insertion, takes place. 

The use of readily available and cheap formate salts is an economically attractive variant for performing palladium-catalyzed reductive carbonylations [22, 23]. For example, Cai and his associates developed a silica-supported phosphine palladium complex ( Si -P-Pd) for the formylation of aryl bromides and iodides with sodium formate (1 bar CO, 90-110 °C) [24]. The polymeric catalyst could be recovered afterwards and shown in simple model reactions comparable catalytic activity than homogeneous PdCl2(PPh3)2 (Table 3.3). 

Metal carbonyl complexes can be prepared in some cases from the bulk metal and from the reduction of complexes in higher oxidation states. For example, the highly toxic Ni(CO) can be prepared directly from nickel metal and carbon monoxide at one atmosphere pressure, and small amoimts of Fe(CO)j are found in carbon monoxide that has been stored under pressure in steel cylinders. However, most metal carbonyls are best made in an ordinary laboratory by reductive carbonylation, as shown in Equations 2.1 and 2,2. The reducing agents used include electropositive metals and aluminum alkyls, as well as carbon monoxide itself. 

Many examples of phosgene-free processes, mainly concerning the carbonylation of aryl nitro derivatives, have been claimed. Some of the most representative, cited in part in the Kirk-Othmer Encyclopedia of Chemical Technology (4th ed., vol. 19), are illustrated belotv. 2,4-Dinitrotoluene undergoes reductive carbonylation with CO to form 2,4-toluene diisocyanate (TDI) in the presence of palladium catalysts [209-213]. A variation on this process involves capturing the isocyanate formed with methanol, followed by thermolysis of the bis(carbamate) 326 [212]. 

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