The synthesis and applications of phosphines

In addition to having access to a variety of phosphine sizes, it is straightforward to synthesize phosphines of varying electron donor properties. The ability of a ligand to donate or receive electrons from a metal is a crucial factor in determining the relative stabilities of metal oxidation states and also the strength of other bonds within the complex. These two factors are of fundamental importance in the reactivity of homogeneous catalysts. 

There are many phosphines which are commercially available. It is possible to buy triaryl phosphines with many different aromatic substituents, and phosphines containing a variety of alkyl chains are also easily available. There are about 20 different chiral phosphines commercially available. In addition, there are commercially available phosphines that are useful as synthons. A few examples are given in Table 2.1. 

5Many of these phosphines are available from several suppliers. 

There are three general methods for the synthesis of phosphines. 

Reaction of an organometallic reagent with a phosphorus halide (or any phosphine with a good leaving group) (see Protocol 1). 

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M. Shi and Y.-L. Shi reported the synthesis and application of new bifunctional axially chiral (thio) urea-phosphine organocatalysts in the asymmetric aza-Morita-Baylis-Hillman (MBH) reaction [176, 177] of N-sulfonated imines with methyl vinyl ketone (MVK), phenyl vinyl ketone (PVK), ethyl vinyl ketone (EVK) or acrolein [316]. The design of the catalyst structure is based on axially chiral BINOL-derived phosphines [317, 318] that have already been successfully utilized as bifunctional catalysts in asymmetric aza-MBH reactions. The formal replacement of the hydrogen-bonding phenol group with a (thio)urea functionality led to catalysts 166-168 (Figure 6.51). 

Most syntheses continue to use the chiral-directing group approach or the use of chiral-protecting groups for metallation. The synthesis and application of a new family of air-stable, highly unsymmetrical ferrocene-based phosphine-phosphoramidites, exemplified by 37, has been described, and their use in Rh-catalyzed asymmetric... 

Relatively few applications of optically active tertiary arsines to asymmetric synthesis have been reported by comparison with the extensive work with phosphines . Authoritative accounts of the synthesis and stereochemistry of compounds of Group V elements are available other reviews cover the subject up until 1979 . For general treatments of organoarsenic chemistry up until 1976, including optically active compounds, two important works are available . Of related interest is an article on stereochemical aspects of phosphorus chemistry and another published in this series on optically active phosphines preparation, uses and chiroptical properties . On matters concerning the intricacies of resolutions work, the reader should consult Reference 21, especially Chapter 7, which is entitled Experimental Aspects and Art of Resolutions. 

As in recent years, the synthesis of new chiral phosphines and related chiral tervalent phosphorus esters and amides continues to be a major preoccupation, being driven by the need for improved performance in metal-catalysed processes. It is very pleasing to note that two of the recipients of the 2001 Nobel Prize for Chemistry, William S. Knowles, and Ryoji Noyori, are honoured for their work in the synthesis and application in catalysis of chiral phosphine ligands. Interest in the structures of metallo-organophosphide systems, noted in the previous volume, has continued to develop. The chemistry of heteroaromatic ring systems, notably that of phospholes, and of low coordination number p -bonded compounds, also remain active areas. 

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