Organometallic Substitution Reactions

1 Carbon Monoxide Replacement in Mononuclear Metal Carbonyls 

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Most studies of organometallic substitution reactions have been accomplished on transition metal-carbonyl complexes (see Carbonyl Complexes of the Transition Metal. These complexes are readily prepared and purified, are stable, and have very characteristic IR spectra that allow quantitative analysis. The reactions can be represented by... 

The reactions of phosphines with metal carbonyls, investigated by Basolo, form the basis for our understanding of organometallic substitution reactions in general. The phosphine is usually refluxed with the carbonyl in an organic solvent, such as ethanol or toluene. One can distinguish two extreme mechanisms for substitution, one dissociativelabeled D, and the other associative, labeled A. Intermediate cases are often labeled I I, if closer to A and Id if closer to D. ... 

Atwood, J.D. (1983) Ligand effects on organometallic substitution reactions. Acc. Chem. Res., 16, 350. 

A rather comprehensive review of the ligand substitution reactions of low-valent organometallic complexes has appeared and is a most welcome addition to the literature. Another useful review deals with ligand substitution processes in metal carbonyls. Brief accounts of ligand effects on organometallic substitution reactions and of the mechanistic behavior of metal-metal bonded carbonyls " have also been published. 

Carbanions are very useful intermediates in the formation of carbon-carbon bonds. This is true both for unstabilized structures found in organometallic reagents and stabilized structures such as enolates. Carbanions can participate as nucleophiles both in addition and in substitution reactions. At this point, we will discuss aspects of the reactions of carbanions as nucleophiles in reactions that proceed by the 8 2 mechanism. Other synthetic aj lications of carbanions will be discussed more completely in Part B. 

Mechanistically the reaction can be divided into two steps. Initially the alkyl halide 1 reacts with sodium to give an organometallic species 3, that can be isolated in many cases. In a second step the carbanionic R of the organometallic compound 3 acts as nucleophile in a substitution reaction with alkyl halide 1 to replace the halide ... 

Reutov, O. A., The mechanisms of the substitution reactions of non-transition metal organometallic compounds, J. Organomet. Chem. 100, 219 (1975). 

In addition to trialkylboranes, various alkoxyboron compounds have prominent roles in synthesis. Some of these, such as catecholboranes (see. p. 340) can be made by hydroboration. Others are made by organometallic or related substitution reactions. Alkoxyboron compounds are usually named as esters. Compounds with one alkoxy group are esters of borinic acids and are called borinates. Compounds with two alkoxy groups are called boronates. Trialkoxyboron compounds are borates. 

Substitution reactions on phosphorus-halogen compounds using organometallics and related reagents... 

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