Types of organometallic reactions

These are but three examples of the limitations of electron-counting schemes. As more clusters are structurally characterized, further exceptions arise providing yet more challenges for the theorist. 

In this section, we introduce the main types of ligand transformations that take place at metal centres in organometallic compounds  

X-ray crystallography confirms that IRh fP PrsIsHnl possesses an octahedral Rhg-cage. Show that this cluster is 10 electrons short of the expected electron count. 

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In the examples of catalysis that follow, the reader will find it useful to identify the catalysts, the species regenerated in each complete reaction cycle. In addition, the individual steps in these cycles will provide examples of the various types of organometallic reactions introduced earlier in this chapter. In each case, the proposed mechanisms presented in this section should be viewed as subject to modification as additional research is conducted. 

For a good discussion of a number of common types of organometallic reactions, see C. A. Tolman, Chem. Soc. Rev., 1972,1, 337. 

The mechanism of hydrocyanation turns out to be another classic example of a set of catalytic cycles that use many of the fundamental types of organometallic reactions that we have already encountered. In fact, the investigation of the details of this mechanism went hand in hand with the advancement of important general... 

On the next page is the catalytic cycle associated with the Heck olefina-tion reaction. For each step marked with a letter, attach the name of one of the fundamental types of organometallic reactions (e.g., nucleophilic abstraction or ligand substitution). 

A plausible mechanism for this reaction is shown in Scheme 10.2, which consists of a stepwise sequence of several fundamental types of organometallic reactions. 

Types of organometallic reactions Complexes containing p - and p -ligands... 

These exercises review types of organometallic reactions and the 18-electron rule. 

Each step of the hydroformylation cycle may be categorized according to its characteristic type of organometallic reaction. The cobalt-containing intermediates in this cycle alternate between 18- and 16-electron species. The 18-electron species react to formally reduce their electron count by 2 (by ligand dissociation, 1,2 insertion of coordinated alkene, alkyl migration, or reductive elimination), whereas the 16-electron species can increase their formal electron count (by coordination of alkene or CO or by oxidative addition). The catalytic activity is in large part a consequence of the capability of the metal to react by way of a variety of 18- and 16-electron intermediates. 

The synthesis of acetic acid from methanol and CO is a process that has been used with commercial success by Monsanto. The mechanism of this process is complex a proposed outline is in Figure 14.20. The individual steps are the characteristic types of organometallic reactions described previously the intermediates are 18- or 16-electron species having the capability to lose or gain, respectively, 2 electrons. Solvent molecules may occupy empty coordination sites in the 4- and 5-coordinate 16-electron intermediates. The first step, oxidative addition of CH3I to [Rhl2(CO)2] , is rate determining. ... 

J. F. Hartwig, Organotransition Metal Chemistry, From Bonding to Catalysis, University Science Books, Mill Valley, CA, 2010, provides a detailed discussion, with numerous references, of many of the reactions and catalytic processes described in this chapter, as well as a variety of other types of organometallic reactions. In addition to providing extensive information on the structural and bonding properties of organometallic compounds, G. Wilkinson,... 

The hallmark of any chemical transformation is the bond-breaking and bond-making that occur in reaction coordinate diagrams. One of the most important types of organometallic reactions involves C-H or C-C bond activation. We have already shown how C—H bonds can be activated through a combination of OA through a nonpolar agnostic intermediate, followed by RE. This process is reviewed in... 

A summary of the most common types of organometallic reactions and the conditions that favor each mechanism is listed in Table 19.2. 

TABLE 19.2 Summary of the different types of organometallic reactions covered in this textbook. 

Ligands Bonding and spectroscopy 18-electron rule Metal carbonyls Isolobal principle Electron counting schemes Types of organometallic reactions... 

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