Metallophosphorus Coordination Complexes

Metal-phosphorus coordination complexes provide many elegant illustrations of the varied stereochemical requirements of the different metallic elements. Known compounds number many thousands, and a considerable number of these have had their detailed crystal structures determined by x-ray diffraction methods. In addition there is a vast literature of infra-red and NMR data on these complexes. 

In addition to metallophosphines (8.52), there are also many phosphite (8.53a), phosphonite (8.53b), phosphinite (8.53c) and other complexes which have been studied. Phosphite, phosphonito and phosphinito complexes, which contain M-O-P as well as M-P linkages have also been prepared (Table 8.16). 

Compounds of types (8.52) and (8.53) belong to the class of compounds now termed P-donor ligands . Earliest examples of these were discovered in the nineteenth century by Rose [5], Hoffmann [6] and Cahors [7]. 

Phosphine complexes are generally stable, non-ionic, soluble in organic solvents, and obtainable as pure highly crystalline (often highly coloured) compounds. Some of these compounds have important catalytic properties, which can be compared with the action of metal/enzyme/substrate complexes in which the bonding is of the type M-O-P (Chapter 11.4). 

Asymmetric phosphines are currently of much interest as catalysts, particularly for the production of single optical isomers (Chapter 12.18). 

---

Whilst almost all metals are included here in the treatment of metal phosphides (Sections 8.1 through 8.7), the treatment of metallophosphorus coordination complexes (Sections 8.9 through 8.20) deals mostly with transition metals. The discussion of metal phosphines and metal phosphites (Section 8.8) is largely confined to metals from Groups I through in while compounds with p-block metals are dealt with in Chapter 9 (Eigure 8.1). 

Early studies of metal phosphides were carried out by Pelletier [1] in 1789, and the first metallq)hospho-rus coordination complex (M-P-E type with E=H), was reported by Rose [2] in 1832. The first M-P-E type with E=C was a tertiary phosphine complex made by Hoffmann [3] in 1857. Although this was followed by the synthesis of a few other complexes of this type by Cahors and Gal in 1870, it was not until after the pioneering work of Mann, Chatt [4] and Jensen [5] in the field of organometallic chemistry during the 1930-1960, that the exponential rise of metallophosphorus chemistry was to begin. 

Whereas most compounds in the latter class (2) are covalent, with P often exhibiting not more than 3 or 4 coordination, the bonding in metal phosphides of class (1) may be of various kinds and is not always satisfactorily explained in terms of any one of them. In addition, the P atom adopts a much wider variety of coordination schemes (up to nine-fold or more) than are usually found amongst metallophosphorus complexes or coordination compounds. 

---