The Carbaborane Group as a Spectator Ligand

Treatment of the salts 5 with [AuCl(PPh3)], in the presence of KPF6, affords the complexes [WAu(/i-CR)(CO)2(PPh3)(f/6-C2BloH10Me2)] (7a, R = C6H4Me-4 7b, R = C6H3Me2-2,6) (14). The species 7 are formed as mixtures of two isomers, with each isomer undergoing fluxional behavior of the kind discussed above for the anions 5. The isomerism may be the result of 

The structure of 11a has been established by X-ray diffraction. The compounds 11 are 30-cluster valence-electron (CVE) dimetal species, and are therefore electronically unsaturated. The electron distribution within the W(fi-C)fth rings may be represented by various canonical forms. However, that shown, which implies that the W=C bond in the ( 5-C2B9H9R 2)(OC)2-W=CC6H4Me-4 moiety formally contributes three electrons to the rhodium center (16-electron valence shell), accords with other results from our laboratory involving electronically unsaturated dimetal compounds with bridging alkylidyne ligands 18). 

Treatment of [Mo(NCMe)(CO)2(ij7-C7H7)][BF4] with 2c in THF affords the dimetal compound [MoW(/i-CC6H4Me-4)(CO)2(f/7-C7H7)(f/5-C2B9H9-Me2)] (17). The latter species, like complex 15a, contains a B—H —Mo three-center two-electron bond (22). 

Compounds 15 and 16 are electronically unsaturated 32-CVE species. This unsaturation is reflected in the dimensions of the W( -CC6H4Me-4)M rings and in the relatively deshielded resonances (5 364-382 ppm) of the n-C nuclei in the NMR spectra (18). The compounds 15a and 15b 

In both series of compounds, 15 and 18, exopolyhedral B—H — M (M = Mo or W) bonds are present. However, in certain circumstances this interaction may be lifted. Thus treatment of 15a or 15b with PMe3 affords, respectively, the complexes [MW( -CC6H4Me-4)(CO)3(PMe3)( 5-C9H7)-(f/5-C2B9H9Me2)] (19a, M = Mo 19b, M = W). In contrast, the reaction 

---