Metal Complexes with Non-Icosahedral Core Frameworks

MONOCARBOLLIDE-METAL COMPLEXES WITH NON-ICOSAHEDRAL CORE FRAMEWORKS 

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. 

As with the icosahedral monocarbollide-metal species reviewed in the preceding sections, the boron-bound hydrides of 129 and 130 may be abstracted by Me and 

The neutral double zwitterions 139-142 are also susceptible to oxidation and treatment of 141 with I2 (1 equiv) gave a surprising result.In the product, [3,4-(OEt)2-l,l,l-(CO)3-2-Ph-/zy crc/oA o-l,2-ReCB8H6] (143), the rhenium center may be considered to be in the -I- III oxidation state, as in 132-138, but the cluster in 143 has also lost one BH vertex. It is known that oxidation of [6-Ph- /Jo-6-CB9H11], the 10-vertex carborane parent of 129 and 130, with FeCls affords 9-vertex [4-Ph-arac/z o-4-CBgHi3] and indeed the carborane subunit of 143 also has the arachno-A-CB geometry. In addition, two I ions would be liberated following the oxidation reaction and nucleophilic attack of these upon the positively 

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 

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IV. Monocarbollide-Metal Complexes with Non-Icosahedral Core Frameworks.. 28... 

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