Metallaborane synthesis

Metal-vapor synthesis also prepares metallaboranes and metallacarboranes with oxidation of the metal. Thermally generated Ni, Co and Fe atoms react with the nido-carborane 2,6-C2B7H, and either cyclopentadiene, toluene, mesitylene, or... 

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... 

An important method for the synthesis of carbaboranes is the reaction of a borane cluster with an alkyne. However, an analogous reaction of a metallaborane cluster with an alkyne is not commonly used to prepare metallacarbaborane clusters. Equation (21) illustrates one example. 

The synthesis of metallaboranes in quantity permits the examination of reaction chemistry and we have already described a considerable number of reactions of chroma-,27, 281 29, 30 molybda-,20 ruthena-,15, cobalta-,31 and rhodaboranes.13 This work constitutes a true study of the effects of the transition metal on chemistry as the metal ancillary ligand (Cp ) is unchanged. Space does not permit more than a single example that serves to illustrate the type of new chemistry that has been revealed by these new metallaboranes. 

Contemporary Boron Chemistry contains 80 reports in nine chapters. Clearly, since much research is interdisciplinary in nature, our decision to include a report in one particular section rather than another was sometimes an arbitrary one. With this caveat in mind, the sections are as follows Applications to Polyolefin Catalysis Materials and Polymers Medicinal Applications Cluster Synthesis Carboranes Metallaboranes Metallaheteroboranes Organic and Inorganic Chemistry of Mono- and Di-boron Systems and Theoretical and Computational Studies. 

The structures of a representative cross-section of known carboranes are shown in Figures 3.2-3.6. Though many new carboranes have been synthesized and characterized since the borane/carborane structural pattern was hrst described,these have tended to consolidate rather than greatly extend the picture. A little progress has been made with the synthesis of macropoly-hedral borane clusters in which fused smaller polyhedra share edges or faces.This area need not concern us here, as it almost exclusively involves boranes and metallaboranes rather than carboranes and metallacarboranes. 

In the area of synthesis, the structural and theoretical framework contributed by Lipscomb provided a foundation for the monumental synthetic work of M. F. Hawthorne and his students, who transformed boron cluster chemistry first by their synthesis of the polyhedral borane anions BioHio and Bi2Hi2 (30) and later by the synthesis of metallacarboranes (31). In our own laboratory, considerations of charge distribution in borane anions (14) prompted us to explore reactions of transition metal ions with small borane and carborane anions (32). This, in turn, led to a number of advances including the first closed polyhedral metallaboranes (33), the discovery of metal-induced oxidative cage fusion (34), and the synthesis of B12H16, the only neutral Bi2 hydride, via metal-promoted fusion of BeHQ (35)... 

Several metallaboranes containing the Cp Ru moiety have been synthesized. The reaction of dimeric dichloride 1 with LiBH4 affords trinuclear ruthenaborane (Cp Ru)3(/ -H)2B3H6 21 as a byproduct of the synthesis of (Cp Ru)2(/U-H)2B3H7 20 (Equation (4)). ... 

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