Reactions of Carbon Monoxide with Transition Metals

Reactions of Carbon Monoxide with Transition Metals... 

Henrici-Olive G, Olive S Reactions of carbon monoxide with transition metal-carbon bonds, Transition Met Chem l(2) 77-93, 1976. 

Moulton and Shaw were the first to report direct reactions of carbon monoxide with transition metal pincer complexes in their seminal work in 1976 [4]. In this paper, the... 

Transition-metal organometallic catalysts in solution are more effective for hydrogenation than are metals such as platinum. They are used for reactions of carbon monoxide with olefins (hydroformyla-tion) and for some ohgomerizations. They are sometimes immobihzed on polymer supports with phosphine groups. 

The bonding between carbon monoxide and transition-metal atoms is particularly important because transition metals, whether deposited on soHd supports or present as discrete complexes, are required as catalysts for the reaction between carbon monoxide and most organic molecules. A metal—carbon ( -bond forms by overlapping of metal orbitals with orbitals on carbon. Multiple-bond character between the metal and carbon occurs through formation of a metal-to-CO TT-bond by overlap of metal-i -TT orbitals with empty antibonding orbitals of carbon monoxide (Fig. 1). 

Figure C shows carbon monoxide insertion reactions. There are a number of reduction reactions of carbon monoxide catalyzed by transition metals, and these, I believe, all involve an insertion of carbon monoxide into a metal hydride as an initial step. Cobalt hydrocarbonyl reacts with carbon monoxide to give formate derivatives. This is probably an insertion reaction also.

Some small changes in rate with changes in the dielectric constant of the solvent have been used to infer the changes in polarity of the reactant complex upon activation. The substitution reactions of metal carbonyl halides show a decrease in rate with increasing dielectric constant, which correlates with an expected decrease in polarity on going to the transition state. On the other hand, the insertion reactions of carbon monoxide into methyl manganese pentacarbonyl show an increase in rate, which suggests a transition state more polar than the reactant. 

There exist obvious cases where relativistic methods are mandatory such as reactions in which the educts and products feature electronic ground states of different spin. This implies that the spin symmetry is changed on the reaction path (mediated by spin-orbit coupling). Such events occur fairly often in transition metal chemistry (for an example see the recombination of carbon monoxide with iron tetra-carbonyl [1013,1014]), so often that even a new... 

In the absence of hydrogen, a catalytic reaction of carbon monoxide and an alcohol produces alkyl formate (Eq. 7.7). The catalyst involved is an alkali metal alkoxide alone or together with a transition metal carbonyl cluster, e.g. Ru3(CO)i2. ° ... 

The most appealing and promising strategy, however, is the carhonylation of amines and/or nitro compounds with carbon monoxide over transition metal complexes, which permits the use of safer raw materials. These reactions are catalytic and do not produce large amounts of saline by-products [34, 35]. 

Homogeneous catalysts based on complexes of low-valence transition metals favor the reactions of carbon monoxide and formate with molecular hydrogen,... 

The reaction of alkenes with alkenes or alkynes does not always produce an aromatic ring. An important variation of this reaction reacts dienes, diynes, or en-ynes with transition metals to form organometallic coordination complexes. In the presence of carbon monoxide, cyclopentenone derivatives are formed in what is known as the Pauson-Khand reaction The reaction involves (1) formation of a hexacarbonyldicobalt-alkyne complex and (2) decomposition of the complex in the presence of an alkene. A typical example Rhodium and tungsten ... 

The purpose of this article is to review the results of transient low pressure studies of carbon monoxide oxidation over transition metal substrates. Particular emphasis is given to the use of in-situ electron spectroscopy, flash desorption, modulated beam and titration techniques. The strengths and weaknesses of these will be assessed with regard to kinetic insight and quantification. An attempt will be made to identify questions that are ripe for investigation. Although not limited to it, the presentation emphasizes our own work. A very recent review of the carbon monoxide oxidation reaction C l) will be useful to readers who are interested in a more comprehensive view. 

During the last few years, the PKR has been developed as a straightforward and practicable method for the synthesis of highly substituted cyclopentenones. But for many synthetic chemists, the employment of poisonous CO still represents a disadvantage. Hence, different strategies focused on the replacement of carbon monoxide within the reaction sequence. Recent successful examples are based on results from the early 1960s, which dealt with the transition metal catalyzed decarbonylation of organic oxo compounds [67]. 

Cobalt, as its CpCo(CO)2 complex, has proven to be especially suited to catalyze [2 + 2 + 2] cycloadditions of two alkyne units with an alkyne or alkene. These cobalt-mediated [2 + 2 + 2] cycloaddition reactions have been studied in great detail by Vollhardt337. The generally accepted mechanism for these cobalt mediated cycloadditions, and similar transition metal mediated cycloadditions in general, has been depicted in equation 166. Consecutive co-ordination of two triple bonds to CpCo(CO)2 with concomitant extrusion of two molecules of carbon monoxide leads to intermediates 578 and 579 via monoalkyne complex 577. These react with another multiple bond to form intermediate 580. The conversion of 578 to 580 is said to be kinetically favored over that of 579 to 580. Because intermediates like 580 have never been isolated, it is still unclear whether the next step is a Diels-Alder reaction to form the final product or an insertion to form 581. The exact circumstances might determine which pathway is followed. 

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

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