Metal-carbonyl complexes, substitution

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). 

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. 

Keto Derivatives of Group IV Organometalloids, 7, 95 Lewis Base-Metal Carbonyl Complexes, 3, 181 Ligand Substitution in Transition Metal ir-Complexes, 10, 347 Literature of Organo-Transition Metal Chemistry 1950-1970, 10, 273 Literature of Organo-Transition Metal Chemistry 1971,11, 447 Literature of Organo-Transition Metal Chemistry 1972, 12, 379 Mass Spectra of Metallocenes and Related Compounds, 8, 211 Mass Spectra of Organometallic Compounds, 6, 273... 

Base catalysis of ligand substitutional processes of metal carbonyl complexes in the presence of oxygen donor bases may be apportioned into two distinct classifications. The first category of reactions involves nucleophilic addition of oxygen bases at the carbon center in metal carbonyls with subsequent oxidation of CO to C02, eqns. 1 and 2 (l, 2). Secondly, there are... 

Y. Harel, A. W. Adamson. Photocalorimetry. 2. Enthalpies of Ligand Substitution Reactions of Some Group 6 Metal Carbonyl Complexes in Solution. J. Phys. Chem. 1982, 86, 2905-2909. 

Reaction of (butadiene)ZrCp2 (31/32), and substituted Cp variants, with a wide range of metal-carbonyl complexes, generates the chelated metal-carbene complexes 163 (equation 22)163. The crystal structure of a number of these complexes has been determined... 

Nucleophilic substitutions of simple aromatic compounds which formally involve a hydride displacement are difficult to achieve because of the poor leaving group and the high electron density of the aromatic nucleus which repels approach of a nucleophile. However, rc-electron deficient aromatic compounds such as metal carbonyl complexes are susceptible to attack by certain carbon nucleophiles. Studies of this chemistry have shown [16] an opposite jegioselectivity to the corresponding electrophilic substitutions, in agreement with the polarity alternation rule. 

Phosphorus trifluoride is a ligand that is used extensively in coordination chemistry. It substitutes readily into various metal carbonyl complexes using either thermal or photochemical techniques. As a ligand, it is unique in its similarity to carbon monoxide in lower-valent organometallic compounds. In its role as a model for CO, a number of studies are possible that cannot be done on the carbonyls themselves.1 The name normally used for PF3 in complexes is trifluorophosphine. 

A recent review has highlighted the extensive and interesting chemistry of metal isocyanide complexes.1 Although synthetic procedures are varied, a vast number are based on substitution in metal carbonyl complexes by isocyanides. Such procedures are, however, not always successful. This is especially so in cases where multiple substitution of CO is required, as in the syntheses of homoleptic isocyanide complexes. Many of the inherent difficulties are illustrated by the reaction of iron pentacarbonyl with isocyanides. 

Naturally, the ideal source of starting materials for homoleptic metal isocyanide compounds is via metal carbonyl complexes, but previously only with the two carbonyls Ni(CO)4 (24) and Co2(CO)g (25) has direct substitution of all carbonyl groups been effected. Recently, however, remarkable discoveries by Coville and co-workers (26-31) on the transition-metal-catalyzed substitution of carbonyl groups in monomeric and cluster compounds have shown that Fe(CNR)s, Mo(CNR)6, and Ir4(CO)5(CNR)7 (32) can be prepared in high yield by stepwise substitution from the parent carbonyl. 

There are few other examples of complete substitution of carbonyl groups from a homoleptic metal-carbonyl complex by isocyanide ligands [cf. Ni(CO)4 (24), Fe(CO)s (26), and Mo(CO)6 (124)]. The corresponding butyl isocyanide derivative Co CNBuOg was formed by reduction of [Co(CNBu )5]PF6 with potassium amalgam (19). 

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. 

P. Vogel s group studied exhaustively the 5,6,7,8-tetramethylidenebicyclo[2.2.2]octane system and its metal carbonyl complexes. The preparation and CD spectra of tricarbonyl-iron complexes (144-147) were reported333. The chirality of complexes 144 and 146 is due uniquely to the coordination of Fe(CO)3 moieties. The signs of the Cotton effects for (+)-144 and (+)-146 obey the octant rule, as the endo-Ft(CO)j, of 144 and 146 fall in a positive octant, while the second exo-Fe(CO)3 (syn to the carbonyl) lies almost on the XY nodal plane, and thus its contribution is expected to be small. The deuterium-substituted free tetraenone 148, however, showed an anti-octant behavior. The CD spectra of 144 and 146 are strongly temperature and solvent dependent. 

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. 

The substitution of a neutral ligand, including carbon monoxide, attached to a metal carbonyl complex by the nitrosyl cation, produces a cationic metal carbonyl nitrosyl. 

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. 

Carbohydrate, synthesis of substituted al-kenylcarbene complexes, 216-218 Chalcogen-bridged metal-carbonyl complexes... 

Carbonyl precursors of the type [R3MM (CO)5] (M = group IV metal M = transition metal) react readily with PF3 either thermally or under the influence of UV irradiation (method D), and PF5 has also been utilized in the case of silyl-substituted metal carbonyl complexes (method E). 

Phosphonium salts of anionic trihydridogermyl metal carbonyl complexes for V, Nb, Cr, Mo, W, Mn, Re, Co and Ni have been synthesized by substitution of carbonyl group with trihydrido germane, —GeH3 " (equation 9). Hydridogermyl metal complexes are the precursors for metal germylenes and polynuclear metal germyl complexes . 

Substitution of several metal-carbonyl complexes Cr(CO)6 and Mn(CO)5 (amine) show a small dependence on the nature and concentration of the entering hgand. Under pseudo-first-order conditions, the rate laws for these substitutions have two terms, as shown for Cr(CO)6 (as for some substitution reactions with 16e complexes, see equation 5). The second-order term was always much smaller than the first-order term. A mechanism that ascribes the second-order term to dissociative interchange (U) has been suggested for the Mo(CO)5Am system (Am = amine) and involves a solvent-encased substrate and a species occupying a favorable site for exchange. Thus, the body of evidence for the simple metal carbonyls indicates that CO dissociation and is the mechanism of ligand substitution reactions. 

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