Complexes with P Units Bonded to M Atoms

This branch of metallophosphorus chemistry has expanded particularly rapidly over the past two decades. It includes single P atoms encapsulated in cages of metal atoms (cf. metal phosphides (Sections 8.1 through 8.7), and various P groups where n = 2 to at least 8. These P groups can be chains, rings or fragments which are structurally related to the crystalline forms of the element itself The element is in fact used in many cases for the preparation of these compounds. 

The P units act as electron donors and the structures have been described in terms of covalent a P-M, o-donor P — M, and various sideways n bonding schemes. Ring P units are capable of forming both a- and Jt-type complexes as indicated below. 

Complexes in which a single P atom is linked to three metal atoms only, are represented by tetrahe-dranes such as (8.242a) and cubanes (8.242b) [8,9]. 

Double tetrahedranes such as (8.243) contain P atoms tetrahedrally linked to four metal atoms. 

When higher coordination is present the schemes often resemble those found in simple metal phosphides. Thus trigonal prismatic coordination is found in Os6(CO)jg(pg-P) (8.244b) (cf. FCjP) and octahedral coordination is found in Cso 35Zr6( ag-P)l,4 (cf. SnP) [10,11]. 

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