Carbonylation Catalyst precursor

The active catalyst is maintained only under NO and CO gas mixtures. Under CO alone the carbonyl catalyst precursor [RhCl2(CO)2] is reformed, and under NO alone a nitrosyl complex is formed which also functions as a... 

Although we have been able to demonstrate that methyl formate is derived directly from carbon dioxide, it is possible, employing the same metal carbonyl catalyst precursors, to catalyze the production of methyl formate from the reaction of CO and methanol (Equation 9). 

An Ir11 intermediate in the carbonylation of ethanol, stabilized by the isoquinoline cation, has been isolated and characterized.496 IrCl3 31FO is the catalyst precursor and HI the promoter. The intermediate analyzes as (C9H8N)[Ir(CO)2l3(COC2H5)]. The magnetic moment is measured at 1.33 B.M., which is indicative of Ir1. 

Several nickel catalysts for the carbonylation of methanol have been reported,54"57 and an IR study has been described.58 The carbonylation of MeOH to form MeOAc and HOAc was studied using phosphine-modified Nil2 as the metal catalyst precursor. The reaction was monitored using a high-pressure, high-temperature, in situ Cylindrical Internal Reflectance FTIR reactor (CIR-REACTOR). 

The catalyst precursor generally used for the reaction is rhodium dicarbonyl acetylacetonate. However, detailed infrared studies under the reaction conditions (ca. 1000 bar CO/H2 and 200°C) have shown both the [Rh(CO)4] and the [Rh12(CO)34 36]2 anions to be present in various concentrations at different stages of the reaction (62, 63). It is suggested that rhodium carbonyl clusters, characterized as having three intense infrared absorptions at 1868 10, 1838 10, and 1785 10 cm-1, are responsible for the catalysis (62), and it is believed that the reaction is dependent upon the existence of the following equilibria ... 

Thus, two quite different forms of rhodium catalyst precursor can give the same rhodium species under the carbonylation reaction conditions. 

The reactions with ruthenium carbonyl catalysts were carried out in pressurized stainless steel reactors glass liners had little effect on the activity. When trimethylamine is used as base, Ru3(CO) 2> H Ru4(CO) 2 an< H2Ru4(CO)i3 lead to nearly identical activities if the rate is normalized to the solution concentration of ruthenium. These results suggest that the same active species is formed under operating conditions from each of these catalyst precursors. The ambient pressure infrared spectrum of a typical catalyst solution (prepared from Ru3(CO)i2> trimethylamine, water, and tetrahydrofuran and sampled from the reactor) is relatively simple (vq q 2080(w), 2020(s), 1997(s), 1965(sh) and 1958(m) cm ). However, the spectrum depends on the concentration of ruthenium in solution. The use of Na2C(>3 as base leads to comparable spectra. 

First, solvent molecules, referred to as S in the catalyst precursor, are displaced by the olefinic substrate to form a chelated Rh complex in which the olefinic bond and the amide carbonyl oxygen interact with the Rh(I) center (rate constant k ). Hydrogen then oxidatively adds to the metal, forming the Rh(III) dihydride intermediate (rate constant kj). This is the rate-limiting step under normal conditions. One hydride on the metal is then transferred to the coordinated olefinic bond to form a five-membered chelated alkyl-Rh(III) intermediate (rate constant k3). Finally, reductive elimination of the product from the complex (rate constant k4) completes the catalytic cycle. 

Pearson and Mauermann/Squires—metallocarboxylate intermediates as C02 precursor over Fe carbonyl catalysts. In 1982, Pearson and Mauermann65 studied two reaction steps of the water-gas shift mechanism involving Fe(CO)5 in basic media using the infrared cell of Ford these included (a) Fe(CO)5 + OH- <-> HFe(CO)4 + C02 and (b) H2Fe(CO)4 <-> H2 + Fe(CO)4. For reaction (a), they proposed the following mechanism, as shown in Scheme 26 ... 

Fachinetti and coworkers—acid cocatalyzed water-gas shift over Rh and Ru carbonyl catalysts. Fachinetti and coworkers133 145 published research on the acid cocatalyzed homogeneous water-gas shift reaction by Rh4(CO)12 and Ru3(CO)12 precursors in aqueous pyridine solution. For Rh carbonyl, experiments were carried out at 80 °C, PCo = 1 atm, and [Rh] = 0.02 mol/L in a solution of pyridine containing 3% H20. They observed the following reaction in anhydrous pyridine ... 

In this body of catalysts, the metal cluster is said to be formed around the carbonyl precursor. According to SEM and TEM imaging, it appears that the carbonyl clusters are on the order of 1 pm in diameter when supported on carbon.192 Analysis with FTIR has shown that the carbonyl is present.189 190 198-200 203 Non-noble metals have also been studied along side the noble-metals in this group of catalysts. Table 4 lists the non-noble metal carbonyl catalysts studied.189-192 198-200 The non-noble metal carbonyl catalysts studied produced mixed results for the ORR activity. 

The SILP carbonylation catalyst was prepared by one-step impregnation of sihca support using a methanohc solution of the ionic liquid [BMIMjl and the dimer [Rh(CO)2l]2- The use of the dimeric precursor complex allowed formation of the catalyst anion [Rh(CO)2l2] directly during catalyst preparation without formation of contaminating byproducts in the ionic hquid catalyst solution. 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

The importance of this study is given by the fact the carbonylation is mn in water with no need for co-solvents, furthermore the catalyst precursor and the intermediates do not contain other ligands than the constituents of the final product (C2H4, CO and H2O). Besides, aU elementary steps of the catalytic cycle were studied separately, and aU intermediate complexes were characterized unambiguously either in isolated form by X-ray crystallography or/and in solution by NMR techniques. 

Higher olefins have negligible solubility in water therefore their hydrocarboxylation in aqueous/organic biphasic systems needs co-solvents or phase transfer agents. With the aid of various PT catalysts 1-octene and 1-dodecene were successfully carbonylated to the corresponding carboxylic acids with good yields (< 85 %) and up to 87 % selectivity towards the formation of the linear add with a [Co2(CO)g] catalyst precursor under forcing conditions (150 °C, 200 bar CO) [57],... 

On the other hand, hi- or multi-metallic supported systems have been attracting considerable interest in research into heterogeneous catalysis as a possible way to modulate the catalytic properties of the individual monometalUc counterparts [12, 13]. These catalysts usually show new catalytic properties that are ascribed to geometric and/or electronic effects between the metalUc components. Of special interest is the preparation of supported bimetallic catalysts using metal carbonyls as precursors, since the milder conditions used, when compared with conventional methods, can render catalysts with homogeneous bimetallic entities of a size and composition not usually achieved when conventional salts are employed as precursors. The use of these catalysts as models can lead to elucidation of the relationships between the structure and catalytic behavior of bimetalUc catalysts. 

In the preparation of faujasite zeolite-supported Pt-Re catalysts, bimetallic PtRe clusters have been reported to be predominantly formed when a carbonyl rhenium precursor (Re2(CO)io) is contacted with zeolite in which platinum has been previously introduced and reduced. The preexisting Pt clusters may act as nucleation sites. After reduction, these Pt-Re systems show a high selectivity to CH4 in the hydrogenolysis of n-heptane [58]. 

Hexaruthenium carbonyl complexes have been used to prepare Ti02-supported mthenium catalysts for the sulfur dioxide reduction with hydrogen [112, 113], A catalyst derived from [Ru6C(CO)i6] showed higher activity in the production of elemental sulfur at low temperatures than that prepared from RUCI3 as precursor. This catalytic behavior is related with the formation of an amorphous ruthenium sulfide phase that takes place during the reaction over the ex-carbonyl catalyst [112]. 

In the ruthenium catalysed carbonylation of piperidine (60 °C, 10 bar CO) the catalyst precursor, [Ru3(CO)i2] was found to be converted mainly to [Ru(CO)5], although IR absorptions due to other minor species were also observed [94]. A catalytic mechanism was tentatively proposed, which involved [RuCO)4] as the active... 

An HP IR study of the platinum catalysed carbonylation of methanol to methyl formate, revealed that the catalyst precursor, ds-[Pt(PEt3)2Cl2] is converted into cis-[Pt(PEt3)2(CO)2] along with a cluster species, [Pt3(PEt3)3(CO) ] (n = 3 or 4) [95]. A mechanism involving oxidative addition of methanol to Pt(0) followed by CO insertion into the Pt-OMe bond was suggested. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

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