Disproportionation, of metal carbonyls

Ligand functional groups on the polymer first form a soluble macromolecular complex. The loss of CO transforms complexes into polymer-immobilized cluster particles M . The subsequent growth of these particles leads to the formation of a nanoparticle. Initiation, growth of particles, and termination by simple disproportionation of metal carbonyl on the particle surface all occur. 

Photochemical disproportionation of metal-metal bonded carbonyl dimers. A. E. Stiegman and D. R. Tyler, Coord. Chem. Rev., 1985, 63, 217 (59). 

A number of metal carbonyls undergo disproportionation reactions in the presence of other coordinating ligands. For example, in the presence of amines, Fe(CO)5 reacts as follows ... 

Although the reaction responsible for the generation of the hydride is not specified, it is assumed that it arises from a disproportionation of iron carbonyl complexes. The hydride presumably adds after ir-complexing to form the c-bonded complex which then splits out the metal hydride in either direction. The ir-complexed olefin may then be displaced by another olefin or undergo another hydride addition-elimination sequence. The second path involves olefin complexing with the deficient Fe(CO)3 species and formation of a jr-allyliron hydride intermediate ... 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Based on the foregoing experimental results, the versatility of metal carbonyls and their derivatives in their reactions with liquid NH3 may be summarized as follows (/) substitution of CO or other ligands by NH3 without change in the oxidation number of the transition metal in question (2) conversion of covalent carbonyl complexes into ionic compounds by addition of NH3 molecules (3) base reactions" in which the transition metal is reduced to a carbonyl metalate with complementary oxidation of a CO ligand to CO(NH2)2 (4) valence disproportionations with... 

Since 1948-50, by using as reactants isonitriles, phosphorus trihalides, and tertiary phosphines, we have gained important insight into the dependence of reactions of metal carbonyls with bases upon the nature of the ligand. Organophosphines were introduced into carbonyl chemistry even prior to 1948 by Reppe and Schweckendiek (7). In general, these ligands react only by substitution of CO, and do not cause disproportionation. Thus nickel carbonyl frequently reacts with complete displacement of carbon monoxide, as we were first able to demonstrate in the reaction with phenyl isonitrile (8). 

In the presence of excess base, a number of metal carbonyl complexes disproportionate (equations 73 and 74). 

The course of the reactions of metal carbonyls with nitrogen bases leading either to disproportionation or to carbonyl substitution has been recognized since the very early work on metal carbonyls Since that... 

Reviews have appeared of photochemical disproportionation of metal-metal bonded carbonyl dimersphotofragmentation of transition metal cluster carbonyls in the gas phase, and f-element photochemistry. ... 

Tl derivatives of metal carbonyl anions are generally stable when the anion is weakly basic, e.g. Co(CO)3[P(OPh)3] , whereas disproportionation to Tl derivatives and Tl° occur when it is more strongly basic, e.g. Mn(CO)i. ... 

Polynuclear anionic metal carbonyl compounds are usually prepared by reduction reactions of metal carbonyls M(CO) with such reducing agents as the alkali metals, NaBH4 in ethers, hydrocarbons, liquid ammonia, and similar solvents [see, for example, reactions (2.54), (2.55), (2.84), (2.89), (2.95>-(2.102), and (2.108)-(2.113)]. In alkali medium the metal carbonyls may be reduced by certain solvents (e.g., alcohols) or by the CO ligand itself, and in the presence of Lewis bases the carbonyls disproportionate to give anionic clusters. The mixed metal clusters containing platinum and rhodium are formed by reduction reactions of chloro complexes... 

Two major pathways in the thermolysis of metal carbonyls in polar media are realized. First, the disproportionation products react with the polymeric chain and initiate the side reactions of crosslinking, destruction, and isomerisation of the chain as well as the immobilization of mononuclear carbonyl complexes. For example, the polybutadiene containing 92% cis-, A- 4% trans-1,4- and4% 1,2-units (M= 246 000) undergoes isomerization when reacted with Fe3(CO)i2 for 2 h at 350K. This increases the trans-1,4 content to 76%. Simultaneously, significant particle enlargement occurs as the hot metal atoms form 1-10-nm nanoparticles (scheme 14). 

The preparation of metal carbonyl anions from Lewis bases and certain neutral metal carbonyl derivatives was described above. In general, such reactions involve disproportionation of the zero-valent metal atom in the metal carbonyl to a cation, with coordination of the base to the metal atom, and to the metal carbonyl anion. A different t3rpe of reaction between Lewis bases and metal carbonyls involves displacement of carbonyl groups in the metal carbonyl by the Lewis base without change in the oxidation state of the central metal atom, e.g.,... 

Lees, A. J. Luminescence Properties of Organometallic Complexes, Chem. Revs. 1987, 87,711-743. Stiegman, A. E. lyier, D. R. "Photochemical Disproportionation of Metal>Metal Bonded Carbonyl Dimers, Coord. Chem. Revs. 1985,63, 217-240. 

Similarly, treatment of a hexane solution of (77-C5Me5)2TiCl with CO at room temperature gave the thermally unstable adduct (17-C5Me5)2Ti(CO)(Cl) (52) as evidenced by again a high energy metal carbonyl band at 2000 cm-1 (98). Complex 52 slowly disproportionated at... 

Not all reactions leading to carbonylate anions require strong reducing agents. Some involve reduction of the meta by carbon monoxide already present in the metal carbonyl or disproportionation of the complex In fact, the first synthesis of u metal carbonylate involved the former procedure ... 

There have been several recent reports of the reduction of carbon dioxide to carbon monoxide by transition metal complexes. Maher and Cooper (2/) have reported that several metal carbonyl dianions can effect the disproportionation of C02 to metal bound carbon monoxide [Eq. (37)] with Li2C03... 

For several decades after this, the metal alkoxides remained objects of interest only for organic chemists, who applied them for reduction of carbonyl compounds and as catalysts for disproportionation of aldehydes, condensation and polymerization. Among these works, of special interest is the work of Meerwein and Bersin [1101], who were the first to prepare the bimetallic alkoxides that were then called Meerwein alkoxosalts in analogy... 

The method is limited by the tendency of some T1(I) metal carbonylates to disproportionate, even at low temperatures, e.g. (79),... 

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