Metal carbonyls substitution reactions

A trans effect see Trans Effect) in octahedral metal-carbonyl substitution reactions was observed in the reactions of Cr(CO)4TU with CO ... 

Reactions with metal carbonyls Substitution reactions Ring expansion reactions... 

The isonitrile metal complexes can be synthesized by reactions of isonitriles with metal carbonyls (substitution reactions) or, more rarely, by alkylation of metal-... 

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. 

The reaction of the transition-metal fragments with main group 15 elements directly has proven a very fruitful field for exploration. The methodology has been successful for a wide range of metal complexes. These fall generally into three basic types (1) reactions with cyclopentadienyl metal carbonyls, (2) reactions with homoleptic metal carbonyls and substituted derivatives, and (3) reactions with metal cations in the presence of a multi-dentate chelating ligand. 

Now for some of the reactions you have seen in the last few chapters. Starting with carbonyl substitution reactions, the first example is the conversion of acid chlorides into esters. The simplest mechanism to understand is that involved when the anion of an alcohol (a metal alkoxide RO ) reacts with an acid chloride. The kinetics are bimolecular rate = fc[MeCOCl] [RO ]. The mechanism is the simple addition elimination process with a tetrahedral intermediate. 

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... 

As seen from Table III, iron pentacarbonyl reacts satisfactorily in spite of its inertness towards carbon monoxide substitution under the normal conditions 189). In benzene at 80° C, however, Fe(CO)5 dissociates rapidly (190). The Fe(CO)4 generated displays a nucleophilic reactivity which should promote an A-type mechanism. In spite of the specificities discussed, Maitlis et al. 177) have proposed the following mechanism for the metal carbonyl exchange reactions. 

Metallated spirobicyclicphosphoranes 96a-c were found to undergo carbonyl substitution reactions with triphenylphosphine in toluene to form (97a-c) and the isolated products were characterised by IR, H nmr, elemental analysis and thermo-gravimeteric studies. There was no evidence for insertion of CO into the pentaco-ordinate P -Mn bond. 

A carbonyl substitution reaction accompanied by a ligand hydrogenation has been observed in the reaction of HRu3(CO)9C2- Bu with cy-clopentadiene, to yield, among other products, the complex (ir-CjHslRusCCOlgCCCHjCMea), in which the ruthenium metal triangle is capped by the C-CHjCMes group (127). 

These complexes are prepared by substitution reactions between the B9Hi4 anion and metal carbonyl halides (Reaction 4) (14). Oxidation... 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bis(trimethylsilyl)amine (ii) insertion reactions with CO2, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate and (iii) addition reactions with metal carbonyls. These reactions are summarized with reference to Zr(NMc2)4 in Scheme 1. 

Dinuclear Carbonyls.—Substitution reactions of [Mn2(CO)io] do not occur by CO dissociation or by associative reaction with incoming ligand, but by thermal or photochemical formation of [Mn(CO)5 ]. Rapid substitution of metal carbonyl radicals has been frequently noted but the mechanisms of these substitutions are... 

Substitution of CO ligands in clusters is most commonly realized in the same way as in the case of mononuclear metal carbonyls. Substitution may be induced by one of the following, most frequently utilized methods thermal, electrochemical, chemical (reactions with N-oxide of trimethylamine or Bu"PO), photochemical, catalysis by radicals, catalysis by transition metal compounds, etc. ... 

As mentioned in the chapter on the reaction mechanism, the anion, especially of Ni-salts, is important in affecting the reaction course. The catalytic efficiency of the nickel halides strongly increases in the series fluoride, chloride, bromide, iodide [374—376]. The molar ratio of cobalt or nickel to iodine is also very important [414]. As in the hydroformylation reaction, metal carbonyls substituted by phosphine ligands are very reactive [377, 1009], and especially modified rhodium and palladium catalysts [1021, 1045] allow reactions under mild conditions. Thus, the nickel bromide triphenylphosphine allyl bromide complex shows an increased reactivity in the carbonylation of acetylenes. On the other hand, carbonyls substituted by phosphine ligands are also readily soluble in the reaction mixture [345, 377]. 

Silylene 59 also behaves somewhat like a phosphine in its interactions with metal carbonyls Typical reactions involve substitution of silylene for CO, to give a silylene-metal complex. Three examples are shown in Scheme 20, and the structure of the nickel complex 75 is displayed in Figure This complex is both the first silylene-nickel complex, and the first example of a bis-silylene-metal complex free of stabilization by Lewis base donors. 

Utilizing the method just described, higher metal-carbonyl-substituted 1,3,5-trisilacyclohexanes can be achieved, as the reactions of compounds 3, 379 and 376 with Co2(CO)8 show [163]. 

The hydroformylation reaction is carried out in the Hquid phase using a metal carbonyl catalyst such as HCo(CO)4 (36), HCo(CO)2[P( -C4H2)] (37), or HRh(CO)2[P(CgH3)2]2 (38,39). The phosphine-substituted rhodium compound is the catalyst of choice for new commercial plants that can operate at 353—383 K and 0.7—2 MPa (7—20 atm) (39). The differences among the catalysts are found in their intrinsic activity, their selectivity to straight-chain product, their abiHty to isomerize the olefin feedstock and hydrogenate the product aldehyde to alcohol, and the ease with which they are separated from the reaction medium (36). 

Bimolecular substitution and oxidation reactions of 17-electron pentacoordinate metal carbonyl radicals. A. Poe, Transition Met. Chem. (Weinheim, Ger.), 1982,7, 65-69 (41). 

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). 

Kinetic studies on substitution reactions of carbonyl metal complexes. H. Werner, Angew. Chem., Int. Ed. Engl., 1968, 7,930-941 (106). 

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

The reactions of nucleophilic reagents with cationic and uncharged metal carbonyl complexes have received much attention in the past, and it is not surprising that these studies have now been extended to isocyanide metal complexes. Different products in these reactions can arise by three general routes these include ligand substitution, reactions involving attack at a ligand, and reduction of the metal complex. All have been observed in reactions with metal isocyanide complexes. 

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). 

Nucleophilic substitution reactions, to which the aromatic rings are activated by the presence of the carbonyl groups, are commonly used in the elaboration of the anthraquinone nucleus, particularly for the introduction of hydroxy and amino groups. Commonly these substitution reactions are catalysed by either boric acid or by transition metal ions. As an example, amino and hydroxy groups may be introduced into the anthraquinone system by nucleophilic displacement of sulfonic acid groups. Another example of an industrially useful nucleophilic substitution is the reaction of l-amino-4-bromoanthraquinone-2-sulfonic acid (bromamine acid) (76) with aromatic amines, as shown in Scheme 4.5, to give a series of useful water-soluble blue dyes. The displacement of bromine in these reactions is catalysed markedly by the presence of copper(n) ions. 

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