Binary metal carbonyl compound

For binary metal carbonyl compounds, the 18-electron mle is a very useful concept. Stable metal complexes will be formed when the metal has 18 electrons in its valence shell (metal valence electrons -H 2 electrons from each CO ligand). Since Tc(0) has 7 valence electrons, the neutral monomeric species Tc(CO) cannot be stable, but ions like [Tc(CO)6]" or [Tc(CO)5] attain a total of 18 electrons. In the neutral molecule, it will dimerize to Tc2(CO)io in order to obey the 18-electron rule. The formation of a Tc-Tc bond adds an electron on each Tc atom. This 18-electron mle is quite useful to predict the stmctures of the metal binary carbonyl compounds. 

Complexes terminal carbonyl ligands found in all binary metal carbonyl compounds. The —CsO... 

Because Ni(CO)4 is volatile (b.p. 43 °C) and cobalt will not react under these conditions, this process afforded a method for separating Ni from Co by the process now known as the Mond process. Although there are many complexes known that contain both carbonyl and other ligands (mixed carbonyl complexes), the number containing only a metal and carbonyl ligands is small. They are known as binary metal carbonyls, and they are listed in Table 21.1. The structures of most of these compounds are shown later in Figures 21.1 through 21.3. 

The organometallic chemistry of the first-row transition metals generally starts with the binary metal carbonyl organometallic complexes. Noncarbonyl organometallic complexes starting with other easily accessible binary compounds provide entries to a broader spectrum of complexes. In this context, we describe the synthesis of the mixed sandwich complex (tj5-pentamethylcyclopentadienyl) ( j5-cyclopentadienyl) iron as an example of the synthetic utility of the solution-stable derivative (>j5-pentamethyl-cyclopentadienyl) (2,4-pentanedionate) iron. 

While Schiitzenberger had intended to study the action of CO on platinum and its compounds, the discovery of the first binary metal carbonyl Ni(CO)4... 

Apart from the work on binary metal carbonyls and metal carbonyl hydrides, Flieber and his school also greatly extended the field of carbonyl(ni-trosyl) metal complexes. The first compound of the general composition M(CO)x(NO)- was obtained by Robert L. Mond and Albert Wallis as early as in 1922 [67]. While studying the reactivity of Co2(CO)8 toward various substrates, they observed that slowly at room temperature, but almost instantaneously at 40°C, nitric oxide gas reacts with cobalt tetracarbonyl to form a cherry-red liquid, with the evolution of carbon monoxide . This liquid was... 

For metal carbonyls, redox reactions (see Redox Properties Processes) have been studied in a smaller number of cases, relative to substitution reactions. The simplicity of binary metal carbonyls and the possibility for these compounds to undergo electron transfers make them excellent substrates for studying redox processes in nonaqueous media. Convenient organometallic one-electron oxidants or reductants (number of valence electrons in parenthesis) are " V(CO)e... 

For M(V) and M(VI), no binary compounds with the heavier halogens and no oxides are known. Iridium(VI) fluoride is the precursor to [Ir(CO)g] +, the only example to date of a tripositive, binary metal carbonyl cation. Compare reaction... 

Metal clusters" are compounds containing a metal skeleton in which three or more metal atoms are joined by metal-metal bonds. They may be characterized by the geometry of their metal skeletons. Some examples of neutral binary metal carbonyl cluster skeletons are given in Figure 9. The transition metal vertices in metal carbonyl... 

Binary metal carbonyls These compounds, also called homoleptic carbonyls, have the general formula M(CO)n. 

On the descriptive side, previously known binary carbonyl cations are usually of the [M(C0)6] type with M = Mn, Tc or Re (82), The oxidation state of the metal in these or other ternary cations is 0 or +1, and the ionic charge of the complex does not exceed +1. In addition, far more basic anions are used as counter ions. The effective atomic number rule, which plays an important role in judging stability, structure and reactivity of transition-metal carbonyls, is not valid for the noble-metal carbonyl compounds reported so far. The silver(I) and gold(I) carbonyl derivatives have 14, and the Pt(II) carbonyls have 16 electrons in the metal valence shell. 

Perhaps because of inadequate or non-existent back-bonding (p. 923), the only neutral, binary carbonyl so far reported is Ti(CO)g which has been produced by condensation of titanium metal vapour with CO in a matrix of inert gases at 10-15 K, and identified spectroscopically. By contrast, if MCI4 (M = Ti, Zr) in dimethoxy-ethane is reduced with potassium naphthalenide in the presence of a crown ether (to complex the K+) under an atmosphere of CO, [M(CO)g] salts are produced. These not only involve the metals in the exceptionally low formal oxidation state of —2 but are thermally stable up to 200 and 130°C respectively. However, the majority of their carbonyl compounds are stabilized by n-bonded ligands, usually cyclopentadienyl, as in [M(/j5-C5H5)2(CO)2] (Fig. 21.8). 

C. H. Langford and M. Parris Reactions of Inert Complexes and Metal Organic Compounds, pp. 1-52 (170) see especially sections 6 and 7, complexes with B class ligands the binary carbonyls, and the substituted carbonyls. 

Table 8.1 compiles the most common stable homonuclear neutral binary carbonyls. They can be prepared by direct carbonylation of pure metals or made from available metallic precursors by reductive carbonylation. However, most of them are commercially available. Moreover, heteronuclear carbonyl compounds are known, and they are usually prepared by reaction between homonuclear binary carbonyls or carbonyl-derivative complexes. 

Reasons for the Use of Metal Binary Carbonyl Compounds as Precursors in the Preparation of Tailored Supported Catalysts... 

Catalysts prepared from iridium neutral binary carbonyl compounds and several supports have been studied extensively. Small Ir (x = 4, 6) clusters supported on several oxides and caged in zeolite, and their characterization by EXAFS, have been prepared [159, 179, 180, 194-196]. The nuclearity of the resulting metallic clusters has been related with their catalytic behavior in olefin hydrogenation reactions [197]. This reaction is structure insensitive, which means that the rate of the reac-hon does not depend on the size of the metallic particle. Usually, the metallic parhcles are larger than 1 nm and consequently they have bulk-like metallic behavior. However, if the size of the particles is small enough to lose their bulk-like metallic behavior, the rate of the catalytic reaction can depend on the size of the metal cluster frame used as catalyst. 

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