Rhodium, carbonyl halides

Rhodium and iridium carbonyl halides are also prepared from organic compounds, for example, anhydrous HCOOH and DMF, which decompose with carbon monoxide evolution. The following rhodium carbonyl halides are known [Rh2X2(CO)4], [RhX2(CO)2] - (X = Cl, Br, I), [Rh2X4(CO)2] (X = Br, I), [RhX3(CO)],... 

A particularly interesting case is that of the platinum metal group which, in addition to platinum (Pt), comprises ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), and palladium (Pd). These carbonyl halides are usually the most practical precursors for metal deposition because of their high volatility at low temperature. Indeed two of them, palladium and platinum, do not form carbonyls but only carbonyl halides. So does gold. 

Spectroscopic investigations have shown that the carbonylation of rhodium(III) halides in alcoholic (9) and aqueous media (10) results in the formation of the dicarbonyldihalorhodate(I) anions, e.g., RhX3 + 3CO + HjjO - [Rh(CO)2X2]- + C02 + 2H+. 

The simple procedure for the carbonylation of allyl halides has been extended in the high yielding solid-liquid two-phase conversion of allyl phosphates into amides (60-80%) under the influence of a rhodium carbonyl cluster in the presence of primary or secondary amines (Scheme 8.8). A secondary product of the reaction is the allylamine, the concentration of which increases as the pressure of the carbon monoxide is reduced, such that it is the sole product (ca. 80%) in the absence of carbon monoxide [28],... 

The picture is different for the bimetallic ruthenium-rhodium systems both metals in the presence of iodide promoters and CO give anionic iodocarbonyl species, namely [Ru(C0) I ] and [Rh(CO)2l2] j but the range of I, CO concentration and temperature in which the anions exist and are catalytically active in carbonylation reactions is different. [Ru(CO)3l2] species in fact are extensively transformed at high temperature and low carbon monoxide pressure by an excess of I (i.e. I/Ru 50) into catalytically inactive [Ru(CO)2l4] (v q 2047, 1990 cm"l in THF (JJ.)) (eq. 1), whereas [Rh(CO)2l2] can work in the carbonylation process only in the presence of a large excess of I"" (I/Rh 100-1000) which prevents reduction to metal (12) (for instance at 150 C rhodium(I) carbonyl halides, [Rh(CO) X2]"", without CH3I under a CO/H2 pressure of 10 MPa are completely reduced to metal). 

These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

The compound Na2 [Rh12(CO)30] can be prepared by reaction of Rh2(CO)4-Cl2 with sodium acetate in methanol under an atmosphere of carbon monoxide.1 It contains one of the fust polynuclear anions to be formed when the rhodium carbonyls or carbonyl halides are reduced by the action of alkaline reagents in alcohols or by alkali metals in tetrahydrofuran (THF). It provides a unique example of a double octahedral cluster carbonyl anion in which the noble gas rule is not obeyed,1 2 and it is a starting material for the preparation of other polynuclear rhodium carbonyl anions.1 3"5 The synthesis reported here is a modification of the original method. The starting material is Rh4(CO)i2, now easily prepared at atmospheric pressure.6"8 The reaction is fast, and the overall procedure requires about 6-7 hours with 80-85% yields. 

Delgado, F., Cabrera, A., Gomez-Lara, J. Steric and electronic influences on the reaction mechanism of the catalytic decarbonylation of acid halides in homogeneous phase using rhodium carbonyl complexes. J. Moi. Catai. 1983, 22, 83-87. 

A-Alkylphenotellurazines form 1 1 molecular complexes with mercury(II) halides and with silver nitrate or silver perchlorate <85KGS757>. Bis(benzonitrile)palladium(II) chloride reacts to form a 2 1 adduct and rhodium carbonyls also complex with phenotellurazines <82D0K(266)1164>. 

Halogeno-carbonyl and -phosphine complexes. I.r. spectral studies at elevated CO pressures have indicated that carbon monoxide, like other Lewis bases, is capable of bridge splitting in rhodium dicarbonyl halides, as in reaction (15). ... 

Rhodium(iii) halide is used as catalyst precursor. Under the reaction conditions, it is reductively carbonylated to the active catalyst species, the anionic rhodium(i) complex [Rh(CO)2l2]. The reaction then proceeds as shown in Equation 2-92. 

Preliminary results of the reaction between vanadium(iii)-tetrasulpho-phthalocyanine complex with oxygen have been reported these data were compared with those obtained for the corresponding reaction of the hexa-aquo complex ion. The oxidation of methyl ethyl ketone by oxygen in the presence of Mn"-phenanthroline complexes has been studied Mn " complexes were detected as intermediates in the reaction and the enolic form of the ketone hydroperoxide decomposed in a free-radical mechanism. In the oxidation of 1,3,5-trimethylcyclohexane, transition-metal [Cu", Co", Ni", and Fe"] laurates act as catalysts and whereas in the absence of these complexes there is pronounced hydroperoxide formation, this falls to a low stationary concentration in the presence of these species, the assumption being made that a metal-hydroperoxide complex is the initiator in the radical reaction. In the case of nickel, the presence of such hydroperoxides is considered to stabilise the Ni"02 complex. Ruthenium(i) chloride complexes in dimethylacetamide are active hydrogenation catalysts for olefinic substrates but in the presence of oxygen, the metal ion is oxidised to ruthenium(m), the reaction proceeding stoicheiometrically. Rhodium(i) carbonyl halides have also been shown to catalyse the oxidation of carbon monoxide to carbon dioxide under acidic conditions ... 

Cobalt carbonyl halides, in contrast to rhodium and iridium carbonyl halides, are very unstable, and only few have been prepared and investigated [CoX(CO)4] is... 

Rhodium and iridium carbonyl halides are easily formed from [MX ] or MX3 by the action of CO, most commonly in solutions, although in some cases these compounds may be obtained in the solid state under atmospheric pressure of CO ... 

The following metal compounds are used for the preparation of the catalysts oxides, metal carbonyls, halides, alkyl and allyl complexes, as well as molybdenum, tungsten, and rhenium sulfides. Oxides of iridium, osmium, ruthenium, rhodium, niobium, tantalum, lanthanum, tellurium, and tin are effective promoters, although their catalytic activity is considerably lower. Oxides of aluminum, silicon, titanium, manganese, zirconium as well as silicates and phosphates of these elements are utilized as supports. Also, mixtures of oxides are used. The best supports are those of alumina oxide and silica. 

The initial step is oxidative addition of the acid chloride to the dissociated form of the complex (LVI) to form the acyl complex (LXV). Aryl migration (reverse insertion) affords a supposed intermediate (LXVI) which can eliminate CO to form (LXVII), which in turn loses aryl halide to regenerate the catalyst. Alternatively (LXVI) can lose aryl halide (reductive elimination) to form a rhodium carbonyl (LXVIIl). It is thought that this path is... 

Suitable catalysts for ring closure reactions are cobalt carbonyls [123, 280, 673, 674], rhodium carbonyls [280, 678], iron carbonyl [123] and certain palladium compounds [679]. Nickel carbonyls, the active catalysts in the Reppe syntheses, are inactive in most cases [123, 673]. A few examples in which nickel is active are the formation of phenols from allyl halides, acetylene and carbon monoxide, which is only a side reaction, and the mechanistically unclear formation of lactones from allyl carbinol and bu-tyne-l-ol-4 [438]. 

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. 

Historically, the rhodium catalyzed carbonylation of methanol to acetic acid required large quantities of methyl iodide co-catalyst (1) and the related hydrocarboxylation of olefins required the presence of an alkyl iodide or hydrogen iodide (2). Unfortunately, the alkyl halides pose several significant difficulties since they are highly toxic, lead to iodine contamination of the final product, are highly corrosive, and are expensive to purchase and handle. Attempts to eliminate alkyl halides or their precursors have proven futile to date (1). 

In this manuscript, we will chronicle the discoveiy and development of these non-alkyl halide containing processes for the rhodium catalyzed carbonylation of ethylene to propionic acid and methanol to acetic acid when using ionic liquids as solvent. 

The rhodium catalyzed carbonylation of ethylene and methanol can be conducted in the absence of added alkyl halide if the reactions are conducted in iodide based ionic liquids or molten salts. In the case of ethylene carbonylation, the imidazolium iodides appeared to perform best and operating in the absence of ethyl iodide gave improved selectivities relative to processes using ethyl iodide and ionic hquids. In the case of... 

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