Reversible decarbonylation

The Dotz reaction mechanism has received further support from kinetic and theoretical studies. An early kinetic investigation [37] and the observation that the reaction of the metal carbene with the alkyne is supressed in the presence of external carbon monoxide [38] indicated that the rate-determining step is a reversible decarbonylation of the original carbene complex. Additional evidence for the Dotz mechanistic hyphotesis has been provided by extended Hiickel molecular orbital [23, 24] and quantum chemical calculations [25],... 

These reactions occur readily and in good yield and are reversible for Y = CO. The reverse decarbonylation reaction is more favorable for X = I than for X = Cl . Table summarizes the reactions represented by equation (d). 

Thus, it appears that the iridium/zeolite combination in our initial example may be nearly optimal for allowing the reversible decarbonylation and recarbonylation reactions whidi retain the duster nudearity. It may also be that iridium is not so noble as to undergo agglomeration and not so oxophilic as to... 

Manganese.—Elimination of transition-metal hydride from metal alkyls and addition of metal hydrides to alkenes are usually considered to be cA-processes. Since acylmanganese compounds undergo stereospecific reversible decarbonylation, thermal decomposition of (eryrAro-2,3-dimethylpentanoyl)(pentacarbonyl)manga-nese(i) should allow the determination of the stereochemistry of elimination of [MnH(CO)8] (Scheme 4). However, both the erythro and a mixture of the erythro and threo acyl complexes decompose thermally to give the same mixture of cis- and trans-3-methylpent-2-ene and 3-methylpent-l-ene under conditions which do not isomerize these alkenes. It is suggested that the mechanism involves interconversion of... 

Campora J, Palma P, del Rio D, Alvarez E (2005) CO insertion reactions into the M — OH bonds of monomeric nickel and palladium hydroxides. Reversible decarbonylation of hydroxycarbonyl palladium complex. Organometallics 23(8) 1652-1655... 

The CC triple bond of the bridging alkyne of cluster (30) is cleaved in a reversible decarbonylation to form the bis-alkylidyne (31). Two molecules of HCCH are incorporated into a ligand in a photochemical reaction of Cp(0C)2Mo( rPPh2)( U"H)Mn(CO)4. A rare U3 ri roethylenearsanediyl complex is formed in the reaction of PPh3=CH2 with the M3-AS cluster As[Mo(CO)2Cp]3. 

Thermal decomposition of the grafted cluster (H)Os3(CO)io(OSi ) results in a total destruction of the molecular cluster frame. This destruction probably results from a multiple oxidative addition of silanol groups on 3 metal atoms with formation of (H)Os(CO)3(OSi ) which can be reversibly decarbonylated to HOs(CO)2(OSi ). These mononuclear osmium hydrido species are also catalysts for hydroformylation. 

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

Cases of the S-coordinated rhodium and iridium are quite scarce. To complete the picture, we next consider the possibilities of S-coordination using complicated derivatives of thiophene. 2,5-[Bis(2-diphenylphosphino)ethyl]thiophene is known to contain three potential donor sites, two phosphorus atoms and the sulfur heteroatom, the latter being a rather nucleophilic center (93IC5652). A more typical situation is coordination via the phosphorus sites. It is also observed in the product of the reaction of 2,5-bis[3-(diphenylphosphino)propyl]thiophene (L) with the species obtained after treatment of [(cod)Rh(acac)] with perchloric acid (95IC365). Carbonylation of [Rh(cod)L][C104]) thus prepared yields 237. Decarbonylation of 237 gives a mixture of 238 and the S-coordinated species 239. Complete decarbonylation gives 240, where the heterocycle is -coordinated. The cycle of carbonylation decarbonylation is reversible. 

The decarbonylation of aromatic aldehydes with sulfuric acid" is the reverse of the Gatterman-Koch reaction (11-16). It has been carried out with trialkyl- and trialkoxybenzaldehydes. The reaction takes place by the ordinary arenium ion mechanism the attacking species is H and the leaving group is HCO, which can lose a proton to give CO or combine with OH from the water solvent to give formic acid." Aromatic aldehydes have also been decarbonylated with basic catalysts." When basic catalysts are used, the mechanism is probably similar to the SeI process of 11-38. See also 14-39. 

The insertion of a carbonyl group into a metal-alkyl or metal-aryl bond, and the reverse reaction involving decarbonylation of an acyl complex, have been studied from both the synthetic and mechanistic points of view. The mechanism proposed for this type of reaction seems well established and is... 

One of the properties of transition metal acyl complexes is their ability to lose CO, usually on heating or photolysis. This so-called decarbonylation often represents a special case of the reverse of the CO insertion in Eq. (8), where L = CO. 

Whereas some acyl products, especially RCOMn(CO)5 and RCOCo-(CO)4, easily eliminate carbon monoxide via the reverse of the insertion, others decarbonylate through a different route. For example, the reaction... 

The carbonylation step that is involved in both hydroformylation and the Fischer-Tropsch reaction can be reversible. Under appropriate conditions, rhodium catalyst can be used for the decarbonylation of aldehydes285 and acyl chlorides.286... 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

The success of the phase space theory in fitting kinetic energy release distributions for exothermic reactions which involve no barrier for the reverse reaction have led to the use of this analysis as a tool for deriving invaluable thermochemical data from endothermic reactions. This is an important addition to the studies of endothermic reactions described above. As an example of these studies, consider the decarbonylation reaction 11 of Co+ with acetone which leads to the formation of the... 

The thermal cycloreversion of imines 268, i.e. formation of isocyanide and alkyne, which would be expected by analogy with cyclopropenone decarbonylation and in reversal of cyclopropenone imine formation (see p. 25), was found to be only a minor side-reaction203). 

As data for the rates of spin-trapping reactions are accumulated, so it becomes possible to use the competition experiment in reverse , i.e. to determine rates of rearrangement, fragmentation, atom transfer, etc. which can compete with spin trapping. An attempt to estimate rates of decarbonylation of acyl radicals depended on this approach (Perkins and Roberts, 1973). Although the results obtained were intuitively reasonable, they depended on the assumption that the rate of scavenging of acyl radicals by MNP would be no different from that measured for the butoxycarbonyl radical. This still awaits experimental verification. Another application, reported recently, was to the rates of rearrangement (23) of a series of (o-(alkoxycarbonyl)-alkyl radicals... 

Di-rm-butylphenol dealkylation, 41 161, 171 Dodecacarbonylhexarhodium, reversible catalytic decarbonylation, 35 206-207 Dodecacarbonyltriiron, reaction on catalytic surfaces, 35 192-194 on alumina, 35 192 on silica, 35 190... 

Bimetallic particles with a very narrow size distribution of circa 1.5 nm have been prepared by decarbonylation under H2 at 400 °C of the impregnated Ru5PtC(CO)i6 on carbon black. EXAFS data indicate that a surface segregation of Pt on the fee Ru structure occurs in the bimetallic nanoparticles. Moreover, they undergo reversible oxidation, forming a MO surface and a core of metal [62]. 

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