Metallacarborane clusters

Serendipitous insertion of CsHs- into the metallaborane Cp 2Cr2B4Fl8 gave the triple-decker sandwich 122 in low yield.140 This compound can be described as an eight-vertex Cr2C2B4 c/ara-metallacarborane cluster, and its preparation is notable as one of the few examples of metallacarborane synthesis from a metallaborane precursor (rather than by the usual metal insertion into a carborane), an approach first demonstrated by Grimes and co-workers in the 1970s.34,141,141a... 

In this chapter, we report herein on large high-boron-content molecules that contain several icosahedral borane, carborane, and metallacarborane clusters either as part of the scaffolds or as decorating the periphery of platforms. On purpose, we will not deal with in this chapter on polymers containing boranes, carboranes, and metallacarboranes. 

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

More remarkably, the reaction forming the Mn-Pt species is unique among the compounds 144-149 in that three other metallacarborane products were also isolated from this system alone. These are two 12-vertex species, [l-Ph-2,2,2-(CO)3-7-X-8,8-dppe-/iyperc/oAo-8,2,l-PtMnCBgHg] pC = H (150), OEt (151)], and the complex [3,6,7- Mn(CO)3 -3,7-(p-H)2-l-Ph-6,6-dppe-c/oio-6,l-PtCBgH6] (152) formed by cluster contraction. Subsequent studies confirmed that the ethoxylated compound 151 is formed by reaction of 146 with adventitious EtOH present in the precursor 129. Indeed, treatment of 146 with other alcohols ROH afforded similar species [l-Ph-2,2,2-(CO)3-7-OR-8,8-dppe-/z3y crc/oA o-8,2,l-PtMnCBgHg] [R = Me (153), (CH2)20H (154), (CH2)40H (155)] with, surprisingly, only mono-cage products observed when diols were used as substrates. All of the alkoxy-substituted compounds 151 and 153-155 are relatively stable and do not react further, whereas... 

Application of the polyhedral expansion methodology to C2B10H12 leads to supraicosahedral metallacarboranes such as closo-(t C HB) Co C2B1 -H 12 [33340-90-8] (194—199). Further expansion of 13-vertex species or thermal metal transfer reactions leads to the 14-vertex cluster [(T C H )Co]2C2B1 ( H 12 [52649-56-6] and [52649-57-7] (199). Similar 14-vertex species have been obtained from tetracarbaboranes (203) and show unusual structures. The isomeric bimetallic cobaltacarborane complexes c/oso-(r 3 -CpCo)2C2BgH10 (cp = C H ) can be formed by either polyhedral expansion or contraction reactions. Six isomers of this cluster are formed in the thermally-induced intermolecular metal transfer and polyhedral expansion of the 11-vertex Ao-(t b-CbHb)CoC2B8H10. 

Cobaltocenium calix[4]arene receptors, characteristics, 12,475 Cobaltocenium-metallacarborane salts, preparation, 3, 23 Cobaltocenium receptors, characteristics, 12, 474 Cobalt phosphines, as supports, 12, 683 Cobalt-platinum nanoparticles, preparation, 12, 74 Cobalt-ruthenium clusters, as heterogeneous catalyst precursors, 12, 768... 

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