Alkoxycarbonyl complex

The course of the reductive carbonylation reaction is considered to involve intially the alkoxycarbonyl complex 156, which attacks 150 to form the nickel enolates 157 followed by protonation [81]. (Scheme 56)... 

As shown in Eqs. (17) and (18), the isolated formyls 19 and 24 are capable of reducing aldehydes and ketones (37, 38, 42. 47, 66). Thus there is no doubt that hydride transfer is an intrinsic chemical property of anionic formyl complexes. One reaction of a neutral formyl complex with an aldehyde has been reported addition of benzaldehyde to (i7-C5H5)Re(NO)(CO)(CHO) (38) yields the alkoxycarbonyl complex (i7-C5H5)Re(NO)(CO)(C02CH2C6Hs) (62). This transformation, which appears to require catalysis by adventitious acid, can be viewed as occurring via attack of initially formed benzyl alcohol upon the intermediate carbonyl cation [(i -C5H5)Re(NO)(CO)2]+. 

Carbamoyl or alkoxycarbonyl complexes 87 are obtained by the attack of amines or alkoxides to metal carbonyls. They are important intermediates of carbonylation reactions and undergo insertion of alkene and alkyne. 

An important reaction of the carbonyl cations of Group VII metals is their base attack by alkoxides (135, 167, 168, 175), which has already been mentioned. The product is an alkoxycarbonyl complex. 

Alkoxycarbonyl Complexes by Reaction of Metal Carbonyls with Alcohols and Alkoxides. 

Carbamoyl complexes such as M(CONHMeXCO)3(PPh3)2 (M = Mn, Re) are converted to alkoxycarbonyl complexes by reaction with xs MeOH... 

Formation of Carbon-Transition and Inner Transition Metal Bond 205 5.8.2.12. from Carbon Monoxide 5.8.2.12.5. Alkoxycarbonyl Complexes... 

Figure 18 Complexes observed in high pressure model studies of alkoxycarbonylation (complexes in square brackets not observed) [86]...

It is well known that the oxidative carbonylation of aniline and the reductive carbonylation of nitrocompounds to give DPU or MPC occur according to the stoichiometry of reactions (1-2) and (4-5). Alkoxycarbonyl complexes (M-COOR 1) and carbamoyl complexes (M-CONHR 2) which then evolve into the final products, are believed to be key intermediates for these reactions. The two accepted different mechanisms for the formation of 1 and 2 along with their catalytic cycles are illustrated in the schemes 1 and 2 for the oxidative carbonylation of amines catalyzed by noble metals. Both the cycles involve a two electron redox process. 

A related group of compounds is that of the gold(III) dimethyl(alkoxycarbonyl) complexes, accessible by the reaction of carbon monoxide with dimethyl(alkoxy)(triphenyl-phosphine)gold(III), which is prepared in situ from cw-[AuIMe2(PPli3)] and sodium alkoxide in methanol (equation 80)353,359. Thermolysis of the methoxycarbonyl complex in benzene leads to the reductive elimination of methyl acetate and ethane, indicating competition between the two modes of decomposition illustrated in Scheme 27. The reaction of the same complex with electrophiles such as hydrogen chloride proceeds with liberation of carbon monoxide and methanol, as illustrated in equation 81. 

Carbamoyl and alkoxycarbonyl complexes of transition metals. (R. Angelici, Accounts Chem. Res., 1972, 5, 335). 

The alkoxide pathway occurs by initial insertion of CO into a palladium alkoxide, followed by insertion of the alkene into the bond between the metal and the alkoxycarbonyl group to form a paUadium-alkyl complex (Scheme 17.18). Protonation of this metal alkyl by alcohol would form the free organic product and regenerate the paUadium alkoxide. This mechanism has now been ruled out for the reactions of ethylene to form methyl propanoate. Although each of these steps has precedent, the absence of reduction products from the alkoxide argues against this pathway. Moreover, the alkyl generated from insertion of ethylene into the palladium-alkoxycarbonyl complex (Scheme 17.18) is chelated to the metal, and metha-nolysis of this species is slower than the steps of the alternative hydride mechanism. ... 

Salaiin and co-workers have reported that the bis(acyl) complex Fe2(G0)6(//-0 = GMe)2 results from addition of oxalyl chloride to Z equiv. of Li[Fe(G0)4 G(0)Me ], the analogous carbamoyl complex resulting when Li[Fe(G0)4 G(0)NPry] is used. In contrast, with the alkoxycarbonyl complexes, Li[Fe(G0)4 G(0)0R ] (R = Bu GMe2GH=GH2), unbridged 184 result. Addition of PPh3 to 184 (R = Bu ) at low temperatures initially affords a monosubstituted product 185 but this slowly converts to a //-alkoxyacyl complex 186 upon standing at room temperature (Equation (20)). 

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