Metal carbonyls formation

In summary, the results of this section demonstrate that by application of XPS, adsorbate structures and coverages can be obtained at pressures of the order of a millibar. Thus, the pressure range in XPS has been expanded by at least five orders of magnitude. Even at these relatively high pressures, CO structures were found to be similar to those known from UHV investigations, but obtained at low temperatures (<300 K). CO on Pd(lll) adsorbs in threefold hollow, bridge, and on-top sites. Bukhtiyarov and coworkers (Bukhtiyarov et al., 1994 Kaichev et al., 2003) did not find any indications of CO dissociation or metal carbonyl formation under the experimental conditions (Bukhtiyarov et al., 2005 Kaichev et al., 2003). 

C- and 0-Bonded Metal Carbonyls Formation, Structures, and Reactions, 23, 219... 

It is possible that a reaction similar to the 0X0 reaction occurs on the surface of catalysts during the synthesis of hydrocarbons and alcohols by the Fischer-Tropsch and the synol processes, and accounts for the small (about 10%) fraction of branched hydrocarbons and isoalcohols produced. In this coimection it is of interest to note that as Pichler (37) indicated, the optimum operating pressures for nickel, cobalt, iron, and ruthenium Fischer-Tropsch catalysts increase in the order mentioned, and the difficulty of metal carbonyl formation also increases in this order. 

Surface catalysis routes using alkaline earth oxides have yielded mixtures of various (CO) n = 2-6 ) species from CO [91]. These routes are of mechanistic interest, but are of no synthetic value as only trace amounts of product are detected. Recent work has been reported that shows the formation of the rhodizonate mono-anion from the reaction of CO with molybdenum suboxide cluster anions Mo Oy" (y < 3x), which are generated using pulsed laser ablation/molecular beam methods [92]. The results suggest that a series of reactions occur involving the oxidation of CO until the oxygen content of the clusters is depleted, followed by metal carbonyl formation and, ultimately, free C Oe" formation. 

The sonochemistry of solutes dissolved in organic Hquids also remains largely unexplored. The sonochemistry of metal carbonyl compounds is an exception (57). Detailed studies of these systems led to important mechanistic understandings of the nature of sonochemistry. A variety of unusual reactivity patterns have been observed during ultrasonic irradiation, including multiple ligand dissociation, novel metal cluster formation, and the initiation of homogeneous catalysis at low ambient temperature (57). 

Table 3. Heats of Combustion and Formation for Metal Carbonyls...

Syntheses from Dry Metals and Salts. Only metaUic nickel and iron react direcdy with CO at moderate pressure and temperatures to form metal carbonyls. A report has claimed the synthesis of Co2(CO)g in 99% yield from cobalt metal and CO at high temperatures and pressures (91,92). The CO has to be absolutely free of oxygen and carbon dioxide or the yield is drastically reduced. Two patents report the formation of carbonyls from molybdenum and tungsten metal (93,94). Ruthenium and osmium do not react with CO even under drastic conditions (95,96). 

Condensation of Simple Metal Carbonyls. Some metal carbonyls of lower molecular weight lose CO on heating or uv irradiation leading to the formation of higher molecular weight species. In some cases this method is a useful preparative tool (112,113). 

Garbonylation of Olefins. The carbonylation of olefins is a process of immense industrial importance. The process includes hydroformylation and hydrosdylation of an olefin. The hydroformylation reaction, or oxo process (qv), leads to the formation of aldehydes (qv) from olefins, carbon monoxide, hydrogen, and a transition-metal carbonyl. The hydro sdylation reaction involves addition of a sdane to an olefin (126,127). One of the most important processes in the carbonylation of olefins uses Co2(CO)g or its derivatives with phosphoms ligands as a catalyst. Propionaldehyde (128) and butyraldehyde (qv) (129) are synthesized industrially according to the following equation ... 

Formation of Functional Groups. Metal carbonyls have been used in a number of cases to synthesize organic molecules containing particular functional groups (147—149). A synthesis of olefins from -dihahdes has been reported (148) ... 

L oss of Catalyst by Vapor Transport. The direct volatilisation of catalytic metals is generally not a factor in catalytic processes, but catalytic metal can be lost through formation of metal carbonyl oxides, sulfides, and hahdes in environments containing CO, NO, O2 and H2S, and halogens (24). 

Metal carbonyls react with diazirines with complex formation at one or both N atoms (75JOM(94)75). The 1 2 complex (187) is converted to (188) by N —N cleavage in acidic media. 

The nature of the bonding, particularly in CO, has excited much attention because of the unusual coordination number (1) and oxidation state (-f2) of carbon it is discussed on p. 926 in connection with the formation of metal-carbonyl complexes. 

Bis ( -arene) metal complexes have been made for many transition metals by the AI/AICI3 reduction method and cationic species [M( j -Ar)2]"" " are also well established for n = 1, 2, and 3. Numerous arenas besides benzene have been used, the next most common being l,3,5-Mc3C6H3 (mesitylene) and CeMce. Reaction of arenas with metal carbonyls in high-boiling solvents or under the influence of ultraviolet light results in the displacement of 3CO and the formation of arena-metal carbonyls ... 

The most satisfactory route to the synthesis of the ri -borole complexes is the reaction of dihydroboroles (2-borolenes and 3-borolenes) with metal carbonyls. An alternative method of synthesis includes formation of the borole adducts with ammonia, 320 (R = Me, Ph) [87JOM(336)29]. Thermal reaction of 320 (R = Me, Ph) with M(C0)6 (M = Cr, Mo, W) gives 321 (M = Cr, R = Me, Ph M = Mo, W, R = Ph). There are data in favor of the Tr-electron delocalization over the borole... 

The primary photochemical of transition metal carbonyls [Me(CO)n] involves the scission of carbon monoxide (CO) and the formation of coordinated unsaturated species ... 

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

The lobes of electron density outside the C-O vector thus offer cr-donor lone-pair character. Surprisingly, carbon monoxide does not form particularly stable complexes with BF3 or with main group metals such as potassium or magnesium. Yet transition-metal complexes with carbon monoxide are known by the thousand. In all cases, the CO ligands are bound to the metal through the carbon atom and the complexes are called carbonyls. Furthermore, the metals occur most usually in low formal oxidation states. Dewar, Chatt and Duncanson have described a bonding scheme for the metal - CO interaction that successfully accounts for the formation and properties of these transition-metal carbonyls. 

Reactions of metal carbonyls with alkyllithium reagents to give the corresponding acyls, e.g., conversion of W(CO)g to Li[PhCOW(CO)5] with LiPh (90), undoubtedly involve attack of LiR upon coordinated CO. Another carbanion-like interaction with a bonded CO is thought to be responsible for the formation of... 

Recent work on [CpFe(CO)2]2 was intended to test whether once again a complex molecule could be found to have a high yield and also to test a possible preferential formation of metal carbonyls over metal sandwich compounds. In this compound, thermal decomposition of the starting compound gives rise predominantly to ferrocene (28, 68). The data (50) given in Table VIII show that indeed the carbonyl is preferentially formed... 

Although knowledge on the biodegradation of these compounds is sparse, a number of them are important in industrial processes. Formation of methylated derivatives may take place in metals and metalloids belonging to groups 15 and 16 of the periodic table, and a few of group 14. These have been discussed in a critical review (Thayer 2002) and in Chapter 3, Part 4, and they have been noted in the context of the bacterial resistance to metals and metalloids. Since carbon monoxide has been considered as an organic compound (Chapter 7, Part 1), it is consistent to make brief comments on metal carbonyls. 

Some data on the adsorption stoichiometry of various gases on relevant transition metals have been collected in Table 3.7, which illustrates the usefulness of certain molecules for catalyst characterization by chemisorption. Note that Cu as active phase can be measured well with N2O and CO, but not with H2. It is not wise to determine Ni dispersion with CO, due to the possibility of carbonyl formation Ni carbonyls are volatile and poisonous. Note that in Table 3.7, for Rh the H/Me ratio is size dependent. This phenomenon is not restricted to Rh it is common in the chemisorption of metals. 

Heteronuclear compounds containing gold(I) and other metal atoms which present Au -M interactions are well represented in the area of metal carbonyl clusters. The addition of a AuPR3+ or Au2(/u-P-P)2+ fragment to a metal cluster results in the formation of Au—M bonds often with retention of the cluster framework. Several reviews have been reported recently,3153-3155 and so it will not be treated here. Some representative examples are found in Figure 26. 

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