Borane cluster compounds reactions

Another complex hydride, A1(BH4)3 (9), a colorless liqnid (mp -64.5 °C, bp 44.6 °C), was the first componnd demonstrated to be flnxional (see Fluxional Molecule). Its thermal decomposition also led to the first componnd to be discovered and structurally characterized by NMR spectroscopy, AI2B4H18 (10). Reaction of A1(BH4)3 with a variety of boranes produces compounds analogous to boron hydride clusters such as AIB4H u, AIB5 H11, AIB5 H12, A1B6Hi2, and AlBeHn (seeBoron Hydrides) ... 

This novel reaction paves the way towards the synthesis of polyfunctionalized borane clusters (closomers) bearing large organic groups attached to the B12 core. With diameters greater than 1 nm, these novel compounds can be considered true molecular nanoparticles. We discuss them in detail later on in this chapter. Further information on the preparation and reactivity of borane compounds can be found in the more specialized chemistry literature [6]. 

Insertion and rearrangement steps were also observed in the reaction of 1 with B2C1443 (Scheme 14). Compounds 52 and 53 were characterized by NMR spectroscopic or mass-spectrometric data, compound 54 by an X-ray crystal structure analysis. 54 may be regarded as a borane-stabilized boranediyl, consisting of a Me5C5B nido-cluster unit (Fig. 8). 

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. 

Photochemical transformations are widely employed in both organic and organoinetallic chemistry and have been extensively used as synthetic strategies for the formation of a variety of new compounds.1 Part of our recent research has focused upon an exploration of the photochemical reactions of borane and metallaborane clusters. As a contextual setting for these photochemical studies, we have also explored several aspects of the thermal and redox chemistry of these clusters. In this paper, we present a summary of our recent work on the thermal, photochemical, and redox reactions of borane and metallaborane clusters. In addition, recent work directed toward the application of these clusters to several aspects of molecular electronics will be presented. 

This compound is prepared by reaction of AuCl[P(C6Hj)3] with BjHg in warm benzene. Besides the cluster itself, only (CeHj)3P—BH3 has been identified as a product. The formation of chlorinated boranes is assumed but not proven. A stoichiometrically correct equation for the reaction cannot be given. The three-necked flask B in Fig. 1 is charged with 3.94g of AuC1[P(C6H5)3] (see Section. 42.A) and ISOmL of benzene. 

Like the double bond, the carbon-carbon triple bond is susceptible to many of the common addition reactions. In some cases, such as reduction, hydroboration and acid-catalyzed hydration, it is even more reactive. A very efficient method for the protection of the triple bond is found in the alkynedicobalt hexacarbonyl complexes (.e.g. 117 and 118), readily formed by the reaction of the respective alkyne with dicobalt octacarbonyl. In eneynes this complexation is specific for the triple bond. The remaining alkenes can be reduced with diimide or borane as is illustrated for the ethynylation product (116) of 5-dehydro androsterone in Scheme 107. Alkynic alkenes and alcohols complexed in this way show an increased structural stability. This has been used for the construction of a variety of substituted alkynic compounds uncontaminated by allenic isomers (Scheme 107) and in syntheses of insect pheromones. From the protecting cobalt clusters, the parent alkynes can easily be regenerated by treatment with iron(III) nitrate, ammonium cerium nitrate or trimethylamine A -oxide. ° ... 

The adherence to close-packed structural arrangements lends support to the idea that these compounds can be used as models for metal surface chemistry—with respect to chemisorbed species and their mobility and reactions of substrates on these surfaces. It also indicates a marked deviation from the behavior of boranes and their derivatives. Structures based upon some polyhedra favored by boron, such as the pentagonal bipyramid, triangulated dodecahedron, and especially the icosahedron, are absent so far in metal-carbonyl cluster chemistry. In this connection, it has been mentioned that [M(CO)3],g compounds should be the closest analogs to On skeletal electron counting... 

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