Carbonyls, metal substitution

One of the most remarkable recent advances in metal carbonyl substitution chemistry has been the discovery by Coville and co-workers of the homogeneous and heterogeneous catalytic labilization of the metal-carbon bond in metal-carbonyl complexes (26-31). Considering that restrictions to catalysis involving metal carbonyl species can, in some instances, be related to the strength of the metal-carbon bond, these discoveries could have far-reaching implications. To exemplify these catalytic substitution processes, comparisons in the systems M(CO)6(M = Cr, Mo, W), CpMoI(CO)3, CpFeI(CO)2, Fe(CO)5, Fe(CO)4(olefin), and Ir4(CO)12 will be made. 

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... 

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]. 

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

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). 

Amines react with CO in the presence of metal carbonyls forming /V-formyl derivatives or substituted ureas (152,153). 

Several 3-substituted 6-methylmercuriothiopyridazines and complexes of perfluoro-pyridazine with metal carbonyl anions have been prepared <67MI21200). 

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). 

Photochemical substitutions on metal carbonyls and their derivatives. W. Strohmeier, Angew. Chem., Int. Ed. Engl., 1964, 3, 730-737 (68). 

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

Advances in platinum metal carbonyls and their substituted derivatives, I. Ruthenium and osmium carbonyls. S. C. Tripathi, S. C. Srivastava, R. P. Mani and A. K. Shrimal, Inorg. Chim. Acta, 1975, 15,249-290 (327). 

With respect to CO complexes, the luminescence spectra of a series of Group VI metal carbonyls and substituted carbonyls were obtained in frozen gas matrices at 12K. In addition, the IR spectra of HCo(CO>4 and HCo(CO)3 (proposed as an intermediate in hydroformylation) were observed in an argon matrix. ... 

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. 

Several papers have appeared recently comparing various properties of carbonyl metal complexes substituted by various phosphines or phosphite ligands or isocyanides. Angelici and Ingemanson (4) studied the equilibrium... 

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). 

In addition to clusterification, ligand substitution also occurs for Fe(CO)5, and in fact for most metal carbonyls. This has proved useful as a mechanistic probe of the reactive species formed during cavitation. Sonica-tion of Fe(CO)5 in the presence of phosphines or phosphites produces Fe(CO)5 L (n = 1,2, and 3). The ratio of these products is independent of length of sonication the multiply substituted products increase with increasing initial [L] Fe(CO)4L is not sonochemically converted to Fe(CO)3L2 on the timescale of its production from Fe(CO)5. These observations are consistent with the same primary sonochemical event... 

Sonochemical ligand substitution readily occurs with a variety of other metal carbonyls, as shown in Table IV. In all cases, multiple ligand substitution originates directly from the parent carbonyl. The rates of sonochemical ligand substitution of the various metal carbonyls follow their relative volatilities, as predicted from the nature of the cavitational collapse. 

While the replacement of carbon monoxide by a tertiary phosphine ligand represents one of the most fundamental substitution reactions in metal carbonyl chemistry, it was not until 1975, some 16 years after the... 

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