Reactions of metal carbonyls

Metal carbonyls undergo reactions with a great many compounds to produce mixed carbonyl complexes. A large number of these reactions involve the replacement of one or more carbonyl groups by a substitution reaction. Such reactions have also been studied kinetically in some cases. 

Many substitution reactions occur between metal carbonyls and other potential ligands. For example, 

Substitution reactions of metal carbonyls frequently indicate differences in bonding characteristics of 

Reactions of metal carbonyls with halogens lead to the formation of carbonyl halide complexes by substitution reactions or breaking metal-metal bonds. The reaction 

The reaction of CO with some metal halides results in the formation of metal carbonyl halides directly, as illustrated in the following examples  

It is useful to consider the reactions of carbonyl metallates separately, since their reactivity is generally concerned with the nucleophilic metal centre and will be discussed below. Simple ligand substitution reactions have already been discussed above, as have redox processes that provide access to carbonyl metallates through reduction of the metal centre. These redox or ligand addition/elimination processes are in principle no different from those encountered for classical ligands. We will now consider reactions in which the carbonyl ligand itself enters directly into the reaction and emerges transformed. 

Although free CO is attacked by very strong nucleophiles (e.g. Bu Li), the resulting acyl anions are generally unstable. In contrast, coordinat- 

Controlled, and ideally catalytic, C-C bond formation in its many and various forms is the crowning achievement of modem organometallic chemistry, and its continuing preoccupation. 

Because metal carbonyls are reactive compounds, it is possible to carry out a large number of reactions that lead to useful derivatives. A few of the more general and important types of reactions are described in this section. 

The structure of Mn(CO)3(py)3 has all three CO ligands trans to pyridine ligands, so the resulting structure is 

The structure shown for Mn(CO)3(py)3 is the result of the difference in the ability of CO and py to accept back donation from the metal. In the case where good n acceptors are the entering ligands, all of the CO groups may be replaced as shown in case of the reaction of Ni(CO)4 with PF3. These substitution reactions show that the electron acceptor properties of CO influence the replacement reactions. 

Tracer studies using isotopically labeled CO have shown that four CO ligands in Mn(CO)5Br undergo exchange with 14CO, but the fifth (bonded trans to Br) does not  

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Reagent and catalyst induced substitution reactions of metal carbonyl complexes. M. O. Albers and N. J. Coville, Coord. Chem. Rev., 1984, 53, 227-259 (153). 

Substitution reactions of metal carbonyl compounds. D. A. Brown, Inorg. Chim. Acta, Rev., 1967, 1,35-47 (76). 

Novel reactions of metal carbonyl cluster compounds, R. D. Adams and 1. T. Horvarth, Prog. Inorg. Chem., 1985, 33,127 (200). 

Solvent effects on the rate of the decarbonylation of MeCOMn(CO)5 were examined by Calderazzo and Cotton (50) and are presented in part in Table IV. In general they are very small, and no regular trends can be discerned. This virtual lack of dependence of the rate on the nature of the solvent and very little correlation between the rate and the dielectric constant of the solvent are typical of substitution reactions of metal carbonyls (J). In the light of the foregoing, a qualitative observation that CpFe(CO)2-COMe decarbonylates much more readily on treatment at reflux in nonpolar heptane or cyclohexane than in polar dioxane is somewhat intriguing 219). 

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... 

A second type of reaction leading to the formation of carbonylate anions is the reaction of metal carbonyls with strong bases. For example,... 

Some reactions of carbonyl hydrides will be illustrated in Chapter 22. Such species are involved in catalytic processes in which metal carbonyls function as hydrogenation catalysts. Generally carbonyl hydrides are obtained by acidifying solutions containing the corresponding carbonylate anion or by the reactions of metal carbonyls with hydrogen. The following reactions illustrate these processes ... 

The very large perturbing influence of C and 0 bonding on the CO bond order led us to explore the influence of Lewis acid and proton acid promoted reactions of metal carbonyl complexes. 

Adams, Richard D. and Horvath, Istvan T., Novel Reactions of Metal Carbonyl... 

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. 

Successive reactions of metal carbonyl monoanions with EX3 can lead to structure types III through VIII in Scheme 1, although these compounds may also be obtained from other, less obvious routes. Further options include replacing the X units with alkyl or aryl functions, which is usually achieved by starting with EX3 xRx. 

The dominant photochemical reaction of metal carbonyl compounds is loss of carbon monoxide, which is usually followed by substitution of another ligand to replace the expelled carbon monoxide. 

Caution. Due to the toxic nature of CO, which may be released in reactions of metal carbonyls, and due to the toxic nature of B2H6 and flammable nature of B2H6 and H2, this reaction must be carried out in a well-ventilated hood. 

Oligo- and polymethylene-bridged complexes can be prepared by reaction of metal carbonyl anions with w.w -dihaloalkanes. This method proved to be a simple entry to the iron series /j,-(CH2)j.][(t75-C5H5) Fe(CO)2]2 (x s 3) (283), but yielded quite different products in the case of Na[(T 5-C5H5)Mo(CO)3] (283) and Na[Mn(CO)s] (284). An alternative two-step synthesis of the iron compounds involves the preparation of the mononuclear w-haloalkyls LXM—(CH2)X—X, and a subsequent... 

F. Basolo, Mechanisms of Substitution Reactions of Metal Carbonyls , Chem. Br., 1969, 5, 505 and refs, therein. 

Photochemical Reactions of Metal Carbonyls with Dihydrogen... 

The carbonylchloroiridium(III) porphyrins can be transformed into a variety of other carbonyl complexes by chloride exchange with acids or salts (path e). Concentrated sodium hydroxide in ethanol appears to destroy the carbonyl ligand in these compounds (path — d, a) in a manner similar to the alkoxide addition to RhCl(TPP) CO (path f) here, this should give a carboxylic acid RhCOOH(P) which is decarboxylated to a hydride RhH(P) according to the typical base reaction of metal carbonyls. The hydride may then be autoxidized to the hydroxide. 

There are no known metallacyclohexanes of Fe, although the Ru and Os compounds (CO)4M(C5Hio) (M — Ru 99, Os 100) have been prepared and characterised.56 The synthetic protocol followed that developed for the corresponding metallacyclopentanes [Eqs. (21) and (22)], via the reactions of metal carbonylates with 1,5-ditriflates (Scheme 32). The X-ray crystal structure of 100 has been determined (Fig. 30).56... 

The reactions of metal carbonyl complexes, containing more than one coordinated TFIF molecule, in a series of cases lead to incomplete exchange of these ligands. In this respect, the following synthesis (3.100) of the radical complex of fluorene 691 is representative [274,275] ... 

IV. Reactions of Metal Carbonyls and Metal Carbonyl Derivatives with... 

With respect to the derivatives of metal carbonyls, the substituted metal carbonyls of the VIB Group (e.g., Mo(CO)apya), the halogenocar-bonyls of iron, ruthenium, iridium, and platinum, the hydridocarbonyls H2Fe(CO)4 and HCo(CO)4 discovered in 1931 and 1934, and the nitrosyl carbonyls FelCOj NOjg and Co(CO)3NO were the most important (/). The known anionic CO complexes were limited to [HFe(CO)J and [Co(CO)J-. For studies of substitution reactions of metal carbonyls at this time, work was almost totally limited to reactions involving the classical N ligands such as NH3, en, py, bipy, and phen. 

REACTIONS OF METAL CARBONYLS AND METAL CARBONYL DERIVATIVES WITH LIQUID AMMONIA... 

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