Dimeric carbonyls

Carbonyiation of butadiene gives two different products depending on the catalytic species. When PdCl is used in ethanol, ethyl 3-pentenoate (91) is obtained[87,88]. Further carbonyiation of 3-pentenoate catalyzed by cobalt carbonyl affords adipate 92[89], 3-Pentenoate is also obtained in the presence of acid. On the other hand, with catalysis by Pd(OAc)2 and Ph3P, methyl 3,8-nonadienoate (93) is obtained by dimerization-carbonylation[90,91]. The presence of chloride ion firmly attached to Pd makes the difference. The reaction is slow, and higher catalytic activity was observed by using Pd(OAc) , (/-Pr) ,P, and maleic anhydride[92]. Carbonyiation of isoprcne with either PdCi or Pd(OAc)2 and Ph,P gives only the 4-methyl-3-pentenoate 94[93]. 

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

The a-methylene-/3-lactam 103 is obtained by the carbonylation of the inethyleneaziridine 102 under mild conditions[91]. The azirine 104 undergoes an interesting dimerization-carbonylation to form the fused )3-lactam 105[92]. 

Formation of FeCp2 is also noted in neutron-irradiated [CpFe(CO)2]2, as will be described later. An important difference here is that the radioferrocene seems to be formed in the dimeric carbonyl only by very fast solid-state reactions. 

The simplest overall interpretation of these data is in terms of a rate-determining dissociation. Entropies of activation are positive and the solvent-dependence for a better leaving group (Cl) is less marked than for a worse one (Br) in the case of reaction (38) . For the dimeric carbonyls, [M(CO)4X]2, bridge-breaking, essentially the same dissociation, could result in a rapid pre-equilibrium. If this were followed by a second dissociative step, then the kinetics could be first-order (as for Mn), while a rate-determining entry of L could produce second-order kinetics (as for Re). 

Simple carbonylation and dimerization-carbonylation of butadiene take place in alcohol depending on the catalytic species of palladium. When PdCl2 is used as a catalyst with or without PPh3, 3-pentenoate (72) is the sole product (74, 75). On the other hand, when Pd(OAc)2 is used with PPh3, the dimerization-carbonylation takes place to give 3,8-nona-dienoate (73) (76, 77). 

The essential factor which differentiates the monomeric and dimeric carbonylations seems to be the presence or absence of halide ion coordinated to the palladium. The dimerization-carbonylation proceeds satisfactorily with halide-free palladium phosphine complexes. Most conveniently, Pd(OAc)2 is used with PPh3. PdCl2(PPh3)2 can be used as a catalyst with addition of an excess of bases. The reaction is carried out at 1I0°C under 50 atm of carbon monoxide pressure in alcohol. Higher... 

No dimerization-carbonylation takes place with isoprene, irrespective of the catalytic species (78). Selective formation of 4-methyl-3-pentenoate (75) was observed in alcohol by the catalysis of either PdCl2 or Pd(OAc)2 and PPh3 ... 

The hydrogen and halogen carbonyls and the nitroso carbonyls Co(NO)(CO)3, in which all bonds are covalent, are non-polar compounds with relatively low boiling points. The dimeric carbonyl, too, is non-polar, but its boiling point is much higher than that of the monomeric carbonyls because of the larger size of the molecule. 

Electro-generated chromium(II) is also very effective in the pinacolization of otherwise unsatisfactory dimerizing carbonyl compounds (Table 5, No. 13)220-222) this case the chromium(II) ion does not act as redox agent but catalyzes the formation of a chromium(III) complex of the carbonyl compound which subsequently is reduced to the pinacol directly at the cathode (Eqs. (73)-(77)). 

Because of its potential application to the synthesis of estersfor lubricating oils, the dimerization-carbonylation of butadiene has received special attention. Basic phosphines such as PBun3 and weakly basic tertiary amine solvents (quinoline, N, N-diethylaniline) were found to improve both the stability and activity of the catalyst system.S3° In a further report in which PPr 3 was used as phosphorus ligand it was found that the addition of maleic anhydride caused a marked increase in the catalytic activity. It was believed that through coordination it stabilized the palladium(O) complexes formed against precipitation as metal.s 1... 

The samarium-lV-bromosuccinimide combination reductively dimerizes carbonyl compounds.163 This pinacol-type coupling gives diols in 60-80% yield, with some diastereoselectivity the by-product from simple reduction (i.e. alcohol) is typically 5-10%. The conditions suggest a single electron transfer to give carbonyl radical anion, which then self-couples. Even congested ketones such as benzophenone and fluorenone worked well. 

The reaction of carbonylmetalates with monomeric and dimeric carbonyls has yielded many mixed-metal clusters, as illustrated by the reactions shown in Eqs. (28) (15), (29) (87), (30 (88), and (31) (88). 

The reaction of bromopentacarbonylmanganese(I) and of pentacarbonylchlororhenium(I) with bis[trimethylstannyl] tellurium produced dimeric carbonyl complexes with two trimethylstannyltelluro groups bridging the metal centers5. 

Figure 3 shows FTIR spectra of CO adsorption on nickel magnesia catalysts. On Nim Mg(,2>oO and Ni/MgO catalysts, linear (2100-2000 cm ), bridge (2000-1850 cm ) and physisorbed Ni(CO)4 (2057 cm ) were mainly observed. In contrast, on NidojMgo O nickel monomer and dimer carbonyl species which are interacted with MgO were mainly observed as previously reported[10]. These species were increased with the CO pressure, therefore they are found to be formed via CO induced structural change. On NioojMgj O solid solution, Ni metal particles seem to be highly dispersive. 

The first dimeric carbonyl complex with a heterometal bond was formed by a reaction of this typeh... 

The carbonylation of butadiene, readily available from petroleum sources, yields a dicarbonylated adduct and dimer-carbonylated product, both desirable from a commercial standpoint. Palladium-catalyzed reactions yield monocarbonylated ... 

The one-step dimerization-carbonylation utilizes a halide-free Pd complex suspended in... 

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