Synthesis of Metal Carbonyls

Considering the significant discovery of metal carbonyls and their formation in technical processes, it became my intention after our first 

The thermochemical aspects of these reactions have been discussed in terms of heats of formation of the halides of elements of the iron group, and of the acceptor metal (75). The yield of carbonyls was especially favored with the iodides and also with sulfides or sulfur-containing materials (76). With iron and cobalt iodides the reaction is facilitated by formation of the carbonyl iodide as an intermediate. 

With rhenium, however, these researches led not to the pure carbonyl but, on account of their great stability, to the carbonyl halides XRe(CO)s. To our surprise, however, we were able to obtain rhenium carbonyl by reduction of heptoxide (77). 

Studies on the carbonyl halides of the noble metals led us directly to the discovery of the pure carbonyls of these elements. Especially impressive was the formation of tetranuclear iridium tricarbonyl, [Ir(CO)3]4, via the tricarbonyl chloride Ir(CO)3Cl, as demonstrated by the simultaneous 

Manchot and Gall (81) were the first to observe the formation of Ni(CO)4 upon passing carbon monoxide through an aqueous alkaline suspension of nickel sulfide. As we later established, a similar reaction occurs also with cobalt sulfide to form the anion Co(CO)4-, the course of the reaction being explained by Behrens and Eisenmann in the Munich Institute (VII, 52). 

Both its solubility and any potential side reaction with reductant dictate the choice of precursor metal salt or complex. In many cases the reductant is an aluminium alkyl or electropositive metal (Goups 1,2, 12 or 13, possibly amalgamated with mercury), requiring the use of anhydrous metal salts or complexes. Carbonyls of higher nuclearity are 

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Abstract This review is a summary of supported metal clusters with nearly molecular properties. These clusters are formed hy adsorption or sirnface-mediated synthesis of metal carbonyl clusters, some of which may he decarhonylated with the metal frame essentially intact. The decarhonylated clusters are bonded to oxide or zeolite supports by metal-oxygen bonds, typically with distances of 2.1-2.2 A they are typically not free of ligands other than the support, and on oxide surfaces they are preferentially bonded at defect sites. The catalytic activities of supported metal clusters incorporating only a few atoms are distinct from those of larger particles that may approximate bulk metals. 

Synthesis of Metal Carbonyl Clusters and Decarbonylated Clusters... 

Supported metal carbonyl clusters are alternatively formed from mononuclear metal complexes by surface-mediated synthesis [5,13] examples are [HIr4(CO)ii] formed from Ir(CO)2(acac) on MgO and Rh CCOlie formed from Rh(CO)2(acac) on y-Al203 [5,12,13]. These syntheses are carried out in the presence of gas-phase CO and in the absence of solvents. Synthesis of metal carbonyl clusters on oxide supports apparently often involves hydroxyl groups or water on the support surface analogous chemistry occurs in solution [ 14]. A synthesis from a mononuclear metal complex precursor is usually characterized by a yield less than that attained as a result of simple adsorption of a preformed metal cluster, and consequently the latter precursors are preferred when the goal is a high yield of the cluster on the support an exception is made when the clusters do not fit into the pores of the support (e.g., a zeolite), and a smaller precursor is needed. 

Synthesis of metal carbonyl clusters on oxide surfaces (followed by extraction into a solvent and workup) is occasionally a more convenient and efficient method for preparation of a metal carbonyl cluster than conventional solution chemistry. This synthetic strategy offers the green chemistry advantage of minimizing solvent use, as the reaction often occurs in the absence of solvent. 

The field of surface-mediated synthesis of metal carbonyl clusters has developed briskly in recent years [4-6], although many organometallic chemists still seem to be unfamiliar with the methods or consider themselves ill-equipped to carry them out. In a typical synthesis, a metal salt or an organometallic precursor is brought from solution or the gas phase onto a high-area porous metal oxide, and then gas-phase reactants are brought in contact with the sample to cause conversion of the surface species into the desired products. In these syntheses, characteristics such as the acid-base properties of the support influence fhe chemisfry, much as a solvenf or coreactant influences fhe chemisfry in a convenfional synfhesis. An advanfage of... 

Figure 1. Ship-in-a-bottle synthesis of metal carbonyl clusters in NaY zeolite.

Several approaches have been used for the synthesis of metal carbonyl polychalcogenide anions.28-31... 

Hydro(solvo) thermal technique, synthesis of metal-carbonyl polychalcogenide anions, 250-252... 

Important aspects of the synthesis of metal carbonyls by reductive ligation see Reductive Ligation) are (a) the reducing agent (b) the reaction medium and (c) the pressme of CO and the temperature. 

Sonication of metal powders has proved to be a very efficient method for the direct synthesis of metal carbonyls from metals ... 

Grignard reagents have long been known to be reductants of metal halides for the synthesis of metal carbonyls in the presence of carbon monoxide [97] ... 

Caiiati E, Roberto D, Ugo R, Lucent E (2003) The surface of inorganic oxides or zeoUtes as a nonconventional reaction medium for the selective synthesis of metal carbonyl complexes and clusters. Chem Rev 103 3707... 

Only preliminary work has been carried out in these areas. Dealing first with palladium, this investigation was motivated by the fact that unsubstituted Pd carbonyls are unknown and, since the most common synthesis of metal carbonyl phosphine complexes is the reaction of a phosphine with a metal carbonyl, there are relatively few Pd carbonyl phosphine complexes in the literature. Clearly, the general method discussed earlier in this account could have considerable potential as a route to such complexes. 

J2.5 Surface organometallic chemistry new perspectives for the synthesis of metal carbonyl clusters J2.6 NMR investigations of binding of aromatics at catalytic surfaces... 

Synthesis of Metal Carbonyls in Non-Thermal Plasma Effect of Vibrational Excitation of CO Molecules on Carbonyl Synthesis... 

Synthesis of Metal Carbonyls in Non-Thermal Plasma. Based on relation (7-135), compare the contribution of vibrational temperature of CO molecules and chromium surface temperature on the rate of desorption of Cr(CO)e during its synthesis in non-equilibrium plasma. Make reasonable assumptions about values of TV and 7s (see Section 7.1.7). 

For the most part, the chemistry involved in synthesis of metal carbonyl clusters in cages is similar to that occurring in solutions and on the surfaces of amorphous metal oxides. Syntheses that take place in neutral solvents and on nearly neutral surfaces also take place within the cages of nearly neutral zeolites such as NaY. The synthesis of cluster anions like [HIr4(CO)n] takes place in basic zeolites such as NaX, in much the same way as it does in basic solutions and on basic surfaces. 

Other papers of general interest deal with several new metal carbonyl cluster complexes molecular approaches to heterogeneous catalysis and a new perspective for the synthesis of metal-carbonyl clusters the reactions of carbonyl clusters with strained ring thioethers and the use of tri(m-sulphonatophenyl)phosphine salts as water solubilizing agents for carbonyls and carbonyl hydrides 2. 

The synthesis of metal carbonyl complexes proceeds industrially. It is sometimes possible to directly use the metal, but the most frequent synthetic method consists in reducing a metal salt in the presence of CO ... 

Synthesis of metal carbonyl complexes of Cr, Mo, W, and Fe highly enriched in CO. 

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