Dicarbollide

Even the addition of 4 equiv. of dimethylzinc to a bis(dicarbollide)tantalum dichloride, Scheme 23, produced only the monomethyl complex 26 in an isolated yield of 75%.63 In these reactions, the oxidation state of the transition metal and the steric bulk of its ligands obviously play a role in the degree of alkylation. 

Incorporation of rhodium triphenylphosphine moieties into carboranes has led to HRh(C2B9Hn)(PPh3)2 complexes, which are formally hydri-dorhodium(III) dicarbollides and which catalyze olefin hydrogenation under mild conditions (527). Iridium and ruthenium analogs are also known, including complexes with carboranylphosphine ligands, e.g., HRuCl(PPh3)(l-P(CH3)2-l,2-C2B, Hn]2 (,527-530). 

As a second illustrative aspect of the boron/carbon connection, we consider the dicarbollide ion, C2B9H112-, which can be pictured as derived from Bi2Hi22- by removing one BH(t) vertex and replacing two adjacent borons of the exposed pentagonal face by carbon atoms, as shown in Fig. 3.116. This ion exhibits remarkable electronic mimicry of the cyclopentadienyl ion (C5H5-, Section 3.3.2), forming similar coordination and sandwich complexes with many metallic species.162... 

Figure 3.116 The optimized structure of the dicarbollide anion, C2B9Hn2, with the atom numbering employed herein.

Figure 3.117 The bent ctbc ( ttbc ) rim bond (see Eq. (3.269) in the text) in the dicarbollide anion, C2B9H112-.

The carbonylation of (Cp )(77S-C2B9H11)TiMe resulted in an unusual B-H activation, generating novel complexes containing linked carborane-alkoxide ligands.30 However, dicarbollide analogs of the constrained-geometry complex,... 

Reactions between salts of [m Jo-7-CBioHi3] and [Fc3(CO)i2] afford the mononuclear anionic iron compound [2,2,2-(CO)3-c/o5o-2,l-FeCBioHn], typically isolated as its [N(PPh3)2] salt (11) (Chart 4). No anionic triiron complex analogous to 5 and 7 is formed in this reaction. The anionic mononuclear iron, ruthenium and osmium complexes and the previously mentioned neutral mononuclear ruthenium dicarbollide complex 4, obtained from [Ru3(CO)i2] and /Jo-7,8-C2BgHi3, are iso-lobal with the cyclopentadienide species [Mn(CO)3(ri-C5H5)] and [Fe(CO)3 (il-CsHs)]. ... 

Wade points out that Wing s slipped dicarbollide species 176) such as Cu(C2B0Hii)2 could be considered as a dinido species, each CUC2B9H11 unit filling twelve of the vertices of the thirteen-vertex polyhedron typified by IV-24. 

Aside from their extensive use in metaUacarborane chemistry, the dicarbollide anions are important intermediates in the synthesis of other carborane compounds. For example, aqueous ferric chloride oxidation of the [7,8-C2B9H1 L] anion results in the 10-vertex cage nido-5,6-C2BgH12 (118) and the aqueous chromic acid oxidation of [7,9-C2B9H1J yields rcz //0-l,3-C2B7H13 [17653-38-2] (29). 

In the early 1960s it was recognized (6,187) that there were bonding similarities between the pentagonal face of the isomeric [nirio-(y HjJ2- ions and the well-known cyclopentadienide ion (Cp ) [CydJ- (Fig. 16). The isomeric nido-C2B9H1 J2- ions, which are commonly known as dicarbollide ions, and many other carborane anions, form stable complexes with most of the metallic elements. Indeed nearly all metals can be combined with polyborane hydride clusters to produce an apparently limitless variety of cluster compounds. 

Fig. 16. Structural analogy between the [7,8-C2B9H1J2 dicarbollide dianion and the [C5HJ cyclopentadienide anion (6) where O represents BH , CH ...

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