Iron and nickel carbonyls

The decomposition of Fe(CO)5 by photolysis15 and 60Co-y radiolysis16 have been reported. The mechanism of the photolysis is adequately represented by reactions (1) and (2) 

Reaction (6) is a complex process which has been partially resolved by flash photolysis experiments18. At low conversion the rate of reaction was proportional to the square of the flash energy. This was taken as evidence that reaction (7) 

With19 D(Ni-Ni) = 55 kcal.mole-1 and assuming the average Ni-CO bond dissociation energy in Ni(CO)2 is the same (35.2 kcal.mole-1)20 as in Ni(CO)4, reaction (8) would be endothermic by approximately 85 kcal.mole-1. It is therefore unlikely that this reaction occurs by a single homogeneous step. It might proceed by reaction (9) 

The thermal decomposition of Ni(CO)4 has been extensively investigated by Chan and McIntosh21. They assume a mechanism for the homogeneous portion of the reaction based on reactions (5) and (6). This gives 

The heterogeneous reaction is assumed to depend on the surface area and fraction of the surface covered. Allowing for the competition between Ni(CO)4 and CO for adsorption sites 

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Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

When heated to about 60°C, nickel carbonyl explodes. Eor both iron and nickel carbonyl, suitable fire extinguishers are water, foam, carbon dioxide, or dry chemical. Large amounts of iron pentacarbonyl also have been reported to ignite spontaneously (189). Solutions of molybdenum carbonyl have been reported to be capable of spontaneous detonation (190). The toxicity of industrial chemicals including metal carbonyls may be found in references 191-194. 

The work cited in sections 2.4 and 2.5 is representative of the SN1 substitution reactions of metal carbonyls. However, a much more extensive and detailed account has recently been published covering similar reactions of vanadium, chromium, molybdenum, tungsten, rhenium, iron and nickel carbonyls in addition to those of manganese and cobalt2 9a. 

It has been claimed that attempts to prepare iron and nickel carbonyl complexes of 1,2-and 1,4-dihydropyridines resulted in reduction of the metal (67AG(E)988). This problem has been avoided by using dihydropyridines with electron withdrawing groups on the nitrogen... 

The gas phase homogeneous catalysis of the CO + O2 reaction in shock waves by addition of chromium, iron and nickel carbonyls has been described by Izod et al. [507], and Matsuda [508, 509]. It will not be discussed further here. 

Other metal compounds that are capable of decomposing at end gas temperatures to produce oxide smokes also can act as anti-knocks. These include iron and nickel carbonyls, trimethyl bismuth and methyl cyclopen-tadienyl manganese tricarbonyl [6]. The last has been used commercially for some years in Canada. Its anti-knock properties also can be amplified by organic co-anti-knocks (diketones in this case) [47]. Concerns over the possible toxicity of fine aerosols which are emitted in the exhaust will limit the acceptability of these metal containing materials in the future. 

The process is also able to remove HCN, NH3, and iron and nickel carbonyls. 

The results of Sims and Mardle s work indicate that iron and nickel carbonyl are more efficient than lead tetraethyl. A comparison of the three compounds on the basis of equal amounts of metal per unit of fuel... 

What formulas would you expect for the metal carbonyls of (a) molybdenum, (b) osmium (c) rhenium Note that the simple carbonyls shown in Figure 23-15 have one metal atom per molecule. Some metal carbonyls are hinuclear that is, they have two metal atoms bonded together in the carbonyl structure. Also, (d) explain why iron and nickel carbonyls are liquids at room temperature, whereas that of cobalt is a solid, and (e) describe the probable nature of the bonding in the compound Na[V(CO)g]. 

Earlier catalysts were based on cobalt, iron, and nickel. However, recent catalytic systems involve rhodium compounds promoted by methyl iodide and lithium iodide (48,49). Higher mol wt alkyl esters do not show any particular abiUty to undergo carbonylation to anhydrides. 

What is the composition of iron, cobalt, and nickel carbonyls Consider the structure of the carbonyls of these elements from the standpoint of the valence bond theory. 

A more favorable synthesis of salts of the iron, cobalt and nickel carbonyl anions, which were initially prepared by disproportionation reactions of Fe(CO)5, Co2(CO)8, and Ni(CO)4 with pyridine and other amines, was found by treatment of the neutral carbonyls with alkali in aqueous or alcoholic solutions. Careful studies by Hieber revealed that Fe(CO)5 as well as Fe3(CO)12 reacted with exactly four equivalents of hydroxide ions to give the corresponding dianionic iron carbonylates (Scheme 4.4). These dianions are relatively strong bases and readily accept a proton from a water molecule to give the monoanionic hydrido carbonylates [I IFe(CO)4] and [HFe3(CO)n], respectively [36]. The related carbonylates of cobalt and manganese, [Co(CO)4] and [Mn(CO)5], were obtained by a similar way as [Fe(CO)4]2 [25]. With regard to the mechanism of Hieber s Basenreaktion , the most plausible explanation is based on an initial nucleophilic attack by the hydroxide ion at the carbon atom of a CO... 

Some iron and nickel cyanide and carbonyl complexes have been reported as models of the [FeNi]-hydrogenase enzymes. The preparation and structures of the trigonal bipyramidal nickel and iron complexes with the tetradentate ligands tris(2-phenylthiol)phosphine (PS3) and tris(3-phenyl-2-thiophenyl)phosphine (PS3 ) have been reported [70, 71]. The nickel carbonyl complex [Ni(PS3 )(CO)] exhibits vco at 2029 cm compared with the value of 1940 em" for the iron earbonyl complex [Fe(PS3 )(CO)]. Both of these complexes lose CO upon oxidation. The use of cyanide in place of carbon monoxide allows for the preparation of both [Fe (PS3)(CN)] and [Fe (PS3 )(CN)] eomplexes. The IR properties of... 

The catalyst deactivation studies described here were carried out in 300 cm.. gas-sparged, stirred autoclaves and in a nominal 10 ton (CH30H)/day pilot-plant, bubble-column reactor. The details of the design and operation of these reactor systems have been reported elsewhere [refs. 4,5]. AH of the present studies were carried out with a feed gas that is referred to as "CO-Rich Gas , with a molar composition of H2 35%, CO-51 %, C02-13% and N2 1%- Its stoichiometric ratio, defined as H2/(CO+1.5002), is 0.5. A typical stoichiometric ratio for the feed to a conventional methanol reactor Is about 2.6, well on the H2-rich side of 2.0, the ratio tor exact stoichiometric equivalence. The feed concentrations of known poisons such as hydrogen sulfide, carbonyl sulfide, chlorine compounds, iron carbonyl and nickel carbonyl were below the limits of detection, 50 ppb, 50 ppb, 10 ppb, 50 ppb and 50 ppb, respectively. 

Alkyne cyclotrimerization occurs at various homogeneous and heterogeneous transition metal and Ziegler-type catalysts [7], Substituted benzenes have been prepared in the presence of iron, cobalt, and nickel carbonyls [8] as well as trialkyl- and triarylchromium compounds [9]. Bis(acrylonitrile)nickel [10] and bis(benzonitrile)palladium chloride [11] catalyze the cyclotrimerization of tolane to hexaphenylbenzene. NiCl2 reduced by NaBH4 has been utilized for the trimer-ization of 3-hexyne to hexaethylbenzene [12]. Ta2Cl6(tetrahydrothiophene)3 and Nb2Cl6(tetrahydrothiophene)3 as well as 7 -Ind-, and 77 -Ru-rhodium... 

Fig. 15.2 Structures of the simple carbonyl complexes of chromium, iron, and nickel.

Upon heating to — 30 "C, metal insertion occurred yielding metallacyclobutenone 5. Similar reactions had earlier been observed with carbonyl complexes of cobalt, iron, and nickel. 

Thomas succeeded in forming 2-30nm particles of cobalt with a narrow size distribution by decomposing cobalt carbonyl compounds in the presence of suitable surface-active reagents [50]. By the same procedure, iron and nickel particles were prepared. Papirer et al. studied the decomposition of a toluene solution of Co2(CO)8 in the presence of a surface-active reagent and found that at least two factors are responsible for the formation of particles with an extremely narrow size distribution the division of the system into microreactors and a diffusion-controlled growth mechanism of the individual particles [51]. 

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