Metallacarborane isomerization

Whilst it is very encouraging that our recent work with metallacarborane isomerization has provided experimental support for the conclusions of previous theoretical studies on carborane isomerization, the inclusion of metal vertices can clearly have a moderating effect. This is dramatically demonstrated by examples of metal-dependency. Thus, reaction of 3 with Pt(PR3)2 " instantaneously produces a 1,2 1,7 Ccage isomerization, whereas reaction with Ni(PR3)2 " results in one... 

Metallacarboranes. These are used in homogeneous catalysis (222), including hydrogenation, hydrosilylation, isomerization, hydrosilanolysis, phase transfer, bum rate modifiers in gun and rocket propellants, neutron capture therapy (254), medical imaging (255), processing of radioactive waste (192), analytical reagents, and as ceramic precursors. 

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. 

Linear polarization, and NLO properties, 12, 102 Linear polymers, siloxanes, synthesis, 3, 660 Linkage isomerism, for photochromic behavior, 1, 245 Linked cages, metallacarboranes, 3, 245 Linkers, traceless, chromium carbonyls as, 5, 251 Lipids, in bioorganometallic chemistry, 1, 904 Liquefied noble gases, in low-temperature infrared studies, 1, 264... 

It is tempting to suggest that such low-temperature isomerization is driven by the relief of steric crowding in the pre-isomerized molecule, but whilst overcrowding is likely to be an important contributory factor there are several clues that it is not solely responsible metallacarborane 19 does not appear to be particularly over-... 

Pre-organizing for metallacarboranes to be deliberately overcrowded can have significant structural effects. Work in our group has focused on polyhedral deformation and on low-temperature isomerization. 

---