Metal boron single bonds

Presumably these processes also involve transient formation of boron-metal single bonds. Recently it was reported that oxidative addition of (1- or 2-)BrB5H8 to IrCl(CO) (PMe3)2 formed cis-dihromo-trans-his-(trimethylphosphine) (2-pentaboranyl) carbonyliridium (III) (29). 

The values of f (l) given in the table for electronegative atoms are their normal covalent single-bond radii28 (except for boron, discussed below). The possibility that the radius 0.74 A. of Schomaker and Stevenson29 should be used for nitrogen in the metallic nitrides should be borne in mind. 

A large number of metal borides have been prepared and characterized. Several hundred binary metal borides M Bj, are known. With increasing boron content, the number of B-B bonds increases. In this manner, isolated B atoms, B-B pairs, fragments of boron chains, single chains, double chains, branched chains, and hexagonal networks are formed, as illustrated in Fig. 13.3.1. Table 13.3.1 summarizes the stoichiometric formulas and structures of metal borides. 

Another route to metalloborane derivatives with metal-boron single bonds is the reaction of certain cationic transition metal compounds with borane anions (20). Addition of solid [(C5H5)Fe(CO)2(cyclohexene)]-PFe to an ether solution of NaBioHia at room temperature formed yellow 6-[(C5Hr>)Fe(CO)2]BioHi3 in 50% yield. The pattern of the B NMR spectrum of this derivative was very similar to other 6-substituted deca-borane derivatives, and on this basis it was proposed that an iron-boron single bond had been formed at B(6) of the decaborane cage as illus-... 

What type of compounds will be covered in this overview. Strictly, only compounds which have at least one metal-carbon bond (with the exception of metal carbides) are called organometaiiic. However, this definition was not adopted in this chapter because many families of compounds that are relevant in organometaiiic chemistry would not be included (e.g., alkoxides). By metal we mean any element from groups 1 (except hydrogen), 2, 3 (including lanthanides and actinides), 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 (except boron), 14 (except carbon and silicon), and 15 (antimony and bismuth only). Most of the available thermochemical data for all these species are freely available in a single on-line database the NIST Chemistry WebBook Unless stated otherwise, all the data included in this chapter were quoted from that reference. 

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