Rhodium-Complex-Catalyzed Carbonylation

Figure 8.7 Proposed mechanism of rhodium complex-catalyzed carbonylation of methanol (Forster, 1976).

Forster, D. On the mechanism of a rhodium-complex-catalyzed carbonylation of methanol to acetic acid. J. Am. Chem. Soc. 98, 846 (1976)... 

Forster, D. (1976) Mechanism of a rhodium-complex-catalyzed carbonylation of melhanol to acetic add. Journal of the American Chemical Society, 98, 846 Adamson, G.W., Daly, J.J. and Forster, D. (1974) Reaction of iodocarbonylrhodium ions with melhyl-iodide - structure of rhodium acetyl complex -[Me3PhN+]2[Rh2l6(MeCO)2(CO)2]2-. Journal of Organometallic Chemistry, 71, Cl7 Haynes, A., Mann, B.E., Gulliver, D.J., Morris, D.E. and Maillis, P.M. (1991) Direct observation of MeRh(CO)2l3 the key intermediate in rhodium catalyzed methanol carbonylation. Journal of the American Chemical Society 113, 8567 Haynes, A., Mann, B.E., Morris, G.E. and Maidis, P.M. (1993) Mechanistic studies on rhodium-catalyzed carbonylation reactions — spectroscopic detection and reactivity of a key intermediate, [MeRh(CO)2l3]. Journal of the American Chemical Society, 115, 4093. 

Oxidative cleavage of P-aminoacyl complexes can yield P-amino acid derivatives (320,321). The rhodium(I)-catalyzed carbonylation of substituted aziridines leads to P-lactams, presumably also via a P-aminoacyl—metal acycHc compound as intermediate. The substituent in the aziridine must have 7T or electrons for coordination with the rhodium (322,323). 

Expansion of aziridines to -lactams. This rhodium complex catalyzes a regio-specific carbonylation of N-f-butyl-2-arylaziridines (1) to form lactams (2). The reaction fails if the alkyl group on nitrogen contains acidic hydrogens adjacent to nitrogen. 

FIGURE 1 Process flow diagram for rhodium-complex-catalyzed methanol carbonylation. Adapted with permission from Figure 1 in reference [16], copyright 2006, Springer Science + Business Media. 

SCHEME 1 Catalytic cycle for the rhodium-complex-catalyzed methanol carbonylation. 

One approach that enables the use of lower water concentrations for rhodium-complex-catalyzed methanol carbonylation is the addition of iodide salts, as exemplified by the Celanese Acid Optimization (AO Plus) technology [11,33]. A lithium iodide promoter allows carbonylation rates to be achieved that are comparable with those in the conventional Monsanto process—but at significantly lower water concentrations. The AO technology has been implemented to increase productivity at the Celanese facility in Clear Lake, Texas, and in a new 500 kt/a plant in Singapore. 

It has been found that iodide salts can promote the oxidative addition of Mel to [Rh(CO)2I2], the rate-determining step in the cycle of the rhodium-complex-catalyzed methanol carbonylation reaction [20]. 

A process for the coproduction of acetic anhydride and acetic acid, which has been operated by BP Chemicals since 1988, uses a quaternary ammonium iodide salt in a role similar to that of Lil [8]. Beneficial effects on rhodium-complex-catalyzed methanol carbonylation have also been found for other additives. For example, phosphine oxides such as Ph3PO enable high catalyst rates at low water concentrations without compromising catalyst stability [40—42]. Similarly, iodocarbonyl complexes of ruthenium and osmium (as used to promote iridium systems, Section 3) are found to enhance the activity of a rhodium catalyst at low water concentrations [43,44]. Other compounds reported to have beneficial effects include phosphate salts [45], transition metal halide salts [46], and oxoacids and heteropolyacids and their salts [47]. 

Diphosphine ligands of the type Ar2P(CH2)nPAr2 (n = 2 4) were originally found by Moloy and Wegman [85,86] to be effective in the rhodium-complex-catalyzed reductive carbonylation of methanol to acetaldehyde (Equation (10)) when synthesis gas (CO + H2) was used instead of pure CO as the feed gas. With a ruthenium trichloride cocatalyst, in situ hydrogenation of the aldehyde to ethanol resulted in the overall homologation reaction shown in Equation (11). 

Adapted from Hjortkjaer, J. and Jensen, V. W., Rhodium complex catalyzed methanol carbonylation. Ind. Eng. (Jhem. Prod. Res. Dev., 15(1), 46-49 (1976). 

Palladium and rhodium complexes catalyze the carbonylation of arylmercury and aiyllead compounds to form ketones of alhydrides and esters, for example, accor ng to the scheme... 

The stereospecific polymerization of alkenes is catalyzed by coordination compounds such as Ziegler-Natta catalysts, which are heterogeneous TiCl —AI alkyl complexes. Cobalt carbonyl is a catalyst for the polymerization of monoepoxides several rhodium and iridium coordination compounds... 

Rhodium catalyzed carbonylations of olefins and methanol can be operated in the absence of an alkyl iodide or hydrogen iodide if the carbonylation is operated in the presence of iodide-based ionic liquids. In this chapter, we will describe the historical development of these non-alkyl halide containing processes beginning with the carbonylation of ethylene to propionic acid in which the omission of alkyl hahde led to an improvement in the selectivity. We will further describe extension of the nonalkyl halide based carbonylation to the carbonylation of MeOH (producing acetic acid) in both a batch and continuous mode of operation. In the continuous mode, the best ionic liquids for carbonylation of MeOH were based on pyridinium and polyalkylated pyridinium iodide derivatives. Removing the highly toxic alkyl halide represents safer, potentially lower cost, process with less complex product purification. 

Mannig and Noth reported the first example of rhodium-catalyzed hydroboration to C=C bonds in 1985.4 Catecholborane reacts at room temperature with 5-hexene-2-one at the carbonyl double bond when the reaction was run in the presence of 5mol.% Wilkinson s catalyst [Rh(PPh3)3Cl], addition of the B—H bond across the C=C double bond was observed affording the anti-Markovnikoff ketone as the major product (Scheme 2). Other rhodium complexes showed good catalytic properties ([Rh(COD)Cl2]2, [ Rh(PPh3)2(C O )C 1], where... 

THE CARBONYLATION OF METHANOL CATALYZED BY RHODIUM COMPLEXES IN SOLUTION... 

A variety of rhodium complexes also catalyze the isomerization of allylic alcohols to saturated carbonyl compounds. RhH(CO)(PPh3)3 quantitatively isomerized methallyl alcohol to isobutylaldehyde at 70°C in trifluoroethanol (Equation (11 )).42... 

Rhodium(i) complexes are excellent catalysts for the 1,4-addition of aryl- or 1-alkenylboron, -silicon, and -tin compounds to a,/3-unsaturated carbonyl compounds. In contrast, there are few reports on the palladium(n) complex-catalyzed 1,4-addition to enones126,126a for the easy formation of C-bound enolate, which will result in /3-hydride elimination product of Heck reaction. Previously, Cacchi et al. described the palladium(n)-catalyzed Michael addition of ArHgCl or SnAr4 to enones in acidic water.127 Recently, Miyaura and co-workers reported the 1,4-addition of arylboronic acids and boroxines to a,/3-unsaturated carbonyl compounds. A cationic palladium(n) complex [Pd(dppe)(PhCN)2](SbF6)2 was found to be an excellent catalyst for this reaction (dppe = l,2-bis(diphenyl-phosphine)ethane Scheme 42).128... 

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