Metal carbonyl hydrides and halides

Hydrido ligands can be introduced by various routes including protonation (equations 23.2 and 23.46), reaction with H2 (reactions 23.47 and 23.48) and action of [BH4] (reactions 23.49 and 23.50). 

Reactions 23.51-23.53 illustrate preparations of selected metal carbonyl halides (see Section 23.9) from binary carbonyls. 

Large numbers of derivatives are formed by displacement of CO by other ligands (see equations 23.25-23.28 and discussion). Whereas substitution by tertiary phosphine ligands gives terminal ligands, the introduction of a secondary or primary phosphine into a multinuclear carbonyl complex creates the possibility of oxidative addition of a P—H bond to a second metal centre and the formation of a bridging phosphido ligand (reaction 23.54). 

We saw earlier that CO displacement can be carried out photolyticaUy or thermally, and that activation of the starting compound (as in reaction 23.25) may be necessary. In multinuclear compounds, activation of one site can control the degree of substitution, e.g. Os3(CO)n(NCMe) is used as an in situ intermediate during the formation of monosubstituted derivatives (equation 23.55). 

In the first step of the reaction, Me3NO oxidizes CO to CO2, liberation of which leaves a vacant coordination site that is occupied temporarily by the labile MeCN ligand. This method can be applied to higher nuclearity clusters to achieve control over otherwise complex reactions. 

Displacement of CO by a nitrosyl ligand alters the electron count and, for an 18-electron centre to be retained, one-for-one ligand substitution cannot occur. Reaction 24.62 shows the conversion of octahedral Cr(CO)g to tetrahedral Cr(NO)4, in which NO is a 3-electron donor. 

Reactions of metal carbonyls with unsaturated organic ligands are discussed in later sections. 

Mononuclear hydrido carbonyl anions include [HFe(CO)4] and [HCr(CO)5], both of which can be made by the acticm of hydroxide on the parent metal carbonyl (eqs. 24.51 and 24.64). Selected reactions of [HCr(CO)5] are shown in Fig. 24.16.  

Methods of forming carbonyl halides include starting from binary metal carbonyls (eqs. 24.57-24.59) or metal halides (eqs. 24.65-24.67). 

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Ligands bonding and spectroscopy Metal carbonyl hydrides and halides... 

This report deals with the chemistry of the metal carbonyls, metal carbonyl hydrides and metal carbonyl halides. Infrequently, complexes which are ostensibly outside the scope of this chapter are included for their importance and relevance to metal carbonyl chemistry. Ref.36 is a good example of this type of work. The general format remains similar to the 1991 report. Apart from the first and second sections, concerned with General Studies and Reviews and Theoretical and Spectroscopic Studies, the chapter is divided into sections for the transition metals of each group. A handful of references that appeared late in 1990 and were omitted from last year s report are included here. 

Darensbourg et al. have conducted extensive studies of the nucleophilic reactivity of a series of anionic metal carbonyl hydrides [24], which have been used for the reduction of alkyl halides [25], acyl chlorides [26], and ketones [27]. The... 

G. Mass Spectra of Metal Carbonyl Halides and Metal Carbonyl Hydrides. . 107... 

Anionic metal carbonyl hydrides, such as (CO)5MH (M = W or Cr) have been studied in detail by Darensbourg and coworkers [25]. Alkyl halides are readily converted to alkanes through reaction with anionic metal carbonyl hydrides (3.4) [26]. 

Ligand substitutions of 18-electron complexes can also occur by radical-chain processes initiated by atom abstraction. These radical chains occur through 17-electron intermediates that imdei o facile associative substitutions. Substitutions of metal carbonyl hydrides, halides, and stannyl complexes by this mechanism are all known. These reactions are particularly prevalent in first-row metal hydrides because the M-H bond is weaker than the M-H bond in second- and third-row metal complexes, and hydrogen atom abstraction is one step of the radical chain. However, they have also been proposed to occiu with third-row metal-hydride complexes... 

This report deals widi those puUicalioiis desaiUiig advances in the chonistiy of the metal carbon and metal carbonyl hydrides, halides and pseudohalides fiar 1994. Activity in dus area continues to run at a high level... 

Most reactions of bromine are highly exothermic which can cause incandescence or sudden increase in pressure and rupture of reaction flasks. There are a number of cases of explosions documented in the literature. (NFPA. 1986. Fire Protection Guide on Hazardous Materials, 9th ed. Quincy, MA National Fire Protection Association) Reactions of liquid bromine with most metals (or any metal in finely divided state), metal hydrides, carbonyls and nitrides can be explosive. Many oxides and halides of nonmetals, such as nitrogen triiodide or phosphorus trioxide, react explosively or burst into flame in contact with liquid bromine. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

GC has been used extensively for the separation and determination of volatile organic molecules, and most aspects of this application area are fully documented in monographs on this technique. In the inorganic trace analysis area, however, fewer species possess the required volatility, and applications tend to be limited to the separation of volatile species of low molecular weight (such as methyl derivatives of As, Se, Sn, Hg) and the separation of semi-volatile organo-metals, metal halides, metal hydrides, metal carbonyls and metal chelates. For organo-metal species, the type of detection system required varies with the nature of the analyte, and the options include electron capture detection, flame photometric detection (sometimes ICP), AAS and MS. 

The mercury compounds HgFe(CO)4 and Fe(CO)4(HgX)2 (X = C1, Br, I), which were the first representatives of non-ionic metal derivatives of iron carbonyl hydrides, were discovered by Hock and Stuhlmann (V, 36). During investigations into the preparation of cobalt carbonyls from cobalt halides under CO pressure, in the presence of another metal as a halogen acceptor, we discovered the mixed metal carbonyls M[Co(CO)4]2 (M = Zn, Cd, Hg, Sn) and M[Co(CO)4]3 (M = In, Tl) (44), e.g.,... 

What is especially intriguing is the reverse behavior exhibited by the use of ruthenium carbonyl as the metal carbonyl. This reaction, which is catalytic in both Ru3(CO)2 and quaternary ammonium halide (which accelerates the rate of formation of the hydride intermediate), occurs in much higher yield under a carbon monoxide than a nitrogen atmosphere (22). The reaction conditions used for the Ru3(CO)12-catalyzed reaction are much milder than those reported using the water gas shift reaction [100°C, 500 psi] (25). 

Elimination of hydrogen halides, particularly in the presence of base, is also a common reachon (equation 54). The actual mechanism of these reactions could involve nucleophihc displacement of halide by the metal carbonyl halide that is formed in situ from the hydride (equations 55 and 56). 

These carbonyl anions are strong nucleophiles (see Nucleophile) and can be used to form a diverse range of new compounds. Protonation gives the /t-hydride (see Bridging Ligand) [(/u.-H) Mo(CO)5 ]. Reactions with other metal carbonyls lead to CO substitution and the formation of metal metal-bonded heteronuclear anions, for example, [Mo(CO)s Fe(CO)4] and [Mo(CO)5-Co(CO)4] . Reaction with main group halides is shown in Scheme 1. The dianion reacts similarly. 

Deviating from the route via nucleophilic attack of the carbanion at the carbon atom of a CO ligand and then reaction of the acylmetallate with an electrophile are those methods which involve (a) addition of the carbanion to the carbon atom of a carbyne ligand, (b) displacement of halides from transition-metal carbonyl halides by cyclohepta-trienyllithium, or derivatives thereof, followed by hydride abstraction or (c) substitution of a coordinated solvent from a metal-carbonyl complex (see also reaction of LiR with carbene complexes). 

The intermediate metal hydride has been isolated on occasion for Co and Mn , and Eq. (b) has actually been used to prepare silicon-metal bonds (see 5.2.3.2.2.). Inspection of Table 1 reveals the ease of reaction of Co2(CO)g compared with the other carbonyls. Normally this reaction is performed simply by condensing volatile silane onto the carbonyl in the absence of solvent and then allowing rapid reaction in the liquid phase at room temperature, but for the remaining carbonyls it is necessary to use elevated temperatures and sealed, evacuated tubes. The products are volatile and readily purified by vacuum fractionation or sublimation, but are often oxygen and moisture sensitive. The route is most efficient for RjSi derivatives of Co, Mn and Re, which are not generally obtainable by the reactions of silicon halides with metal carbonyl anions (see S.8.3.3.I.). In this way lCo(SiR,)(CO -] = Et, Phj, Clj -, (OEt)j, F/, ... 

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