Cluster compounds 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) ... 

Metallacarboranes are cluster compounds in which the cluster vertices comprise one or more metal atoms (main group metal, transition metal or rare earth [lanthanide or actinide] metal), one or more (most often two) carbon atoms, and boron atoms, the last usually in the majority. The total number of cluster vertices may vary but the vast majority of metallacarboranes have between 6 and 14 vertices moreover, the cluster may be either open or closed. However, the single largest group of metallacarboranes has 12 vertices and is structurally based on the closed icosahedron, 1. 

STRUCTURE-ACTIVITY ANALYSIS OF SELECTED METALLACARBORANES DOUBLE (TRIPLE)-CLUSTER COMPOUNDS... 

In our preliminary unpublished experiments, we noticed that some proteins, for example, HIV PR, can precipitate on addition of the parent metallacarborane GB-18 at elevated concentrations. On the other hand, in the case of dansyl and fluorescein moieties attached to one cobaltacarborane cluster, we observed almost quantitative solubilization of the probes in the presence of serum albumin with no traces of secondary aggregates. It was further estimated that approximately three fluorescein-metal-lacarborane conjugate (single-cluster compound) molecules are bound to one human serum albumin molecule. Interestingly, no such binding was observed for the double-cluster fluorescein conjugate (GB-179, see Table 3.1), representing the model compound of potent HIV protease inhibitors. 

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... 

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... 

Metallacarbaborane (also called metallacarborane) an electron-deficient compound, usually a polyhedral cluster comprising an array of boron-hydride (BH), carbon-hydride (CH), and metal (ML, where L = ligand) fragments the inclusion of a substituted carbon fragment CR (R = alkyl, aryl, or trimethylsilyl) in place of a CH unit is common... 

Metallacarbaboranes (or metallacarboranes) are compounds that contain cluster polyhedra comprising carbon, boron, and metal atoms in various combinations. The first metallacarbaborane clusters were prepared by Hawthorne in 1965, and were derived from the icosahedral closo-carbaborane l,2-C2BioHi2 see Boron Polyhedral Carbo-ranes) by the replacement of one BH vertex with a metal center. Compounds such as [Fe(C2B9Hn)2]" (n = 1 or 2) can be represented as the commo-metallacarbaborane (1) or as... 

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