Icosahedral Carborane Derivatives

Icosahedral Carborane Derivatives

New carborane monomers generated from the carborane icosahedra ortho-1,2-C₂B₁₀H₁₂, meta 1,7-C₂B₁₀H₁₂  and para-1,12-C₂B₁₀H₁₂  were synthesized and characterized for high temperature polymers. This project led to the development of a general route to C-aryl carboranes which is currently exploited by several research groups working in liquid crystals (e.g. Kaszynski of Nashville) and drug designs (e.g. Endo of Tokyo). Using the excellent copper-coupling route to aryl-carboranes, many carborane assemblies were synthesized, as potential precursors to useful high temperature ceramics (such as boron carbide, B₄C). The diethynyl-para-carborane, an analogue to the well known organic precursor to molecular rods, 1,4-(HCC)₂C₆H₄ was also made.

Nitrogen, oxygen or sulfur atoms attached to the cage carbon in these icosahedra revealed that the cage acts as a viable electron acceptor of pi-bonding electrons. However with ethynyl, aryl or ethenyl substituents at the cage carbons the electronic interaction between the cage and the substituents is purely inductive.

Evidence for electronic transmission through the cage have been demonstrated by carbon NMR spectroscopy on ‘push-pull’ diaryl-para-carboranes and by cyclic voltammetry on a three-cage system containing two cobalt-ethyne clusters and a para-carborane linker. These studies indicate that the carborane clusters may be incorporated in oligomeric or polymeric electronically unsaturated and/or thermally stable substances for use in electronic device technology.

24. Transmission of electronic effects by icosahedral carboranes; skeletal ¹³C chemical shifts and ultraviolet – visible spectra of substituted aryl-para-carboranes.

     M. A. Fox, R.J. Peace, J.A.H. MacBride and K. Wade,

      J. Chem. Soc., Dalton Trans., 1998, 401-411.

31. Synthesis and structure of 1,12-diethynyl-para-carborane

      A.S. Batsanov, M. A. Fox, J.A.K. Howard, J.A.H. MacBride and K. Wade,

      J. Organomet. Chem., 2000, 610, 20-24.

55. Big Macrocyclic Assemblies of Carboranes (Big MACs): Synthesis and Crystal Structure of a Macrocyclic Assembly of four Carboranes containing alternate ortho– and meta-Carborane Icosahedra linked by para-phenylene units

M. A. Fox, J. A. K. Howard, J. A. H. MacBride, A. Mackinnon and K. Wade,

J. Organomet. Chem., 2003, 680, 155-164.

72. Synthetic and Structural Studies on C-Ethynyl- and C-Bromo-Carboranes. Gas Phase Electron Diffraction Studies of C-Ethynyl– and C-Trimethylsilylethynyl-para-carboranes

      M. A. Fox, A. M. Cameron, P.J. Low, M.A.J. Paterson, A.S. Batsanov, A.E. Goeta, D.W.H. Rankin, H.E. Robertson and J.T. Schirlin,

      Dalton Trans., 2006, 3544-3560.

73. Improved syntheses of bis(ethynyl)-para-carboranes, 1,12-(RC≡C)₂-1,12-C₂B₁₀H₁₀ and 1,10-(RC≡C)₂-1,10-C₂B₈H₈ (R = H or Me₃Si)

      M.A. Fox, T.E. Baines, D. Albesa-Jové, J.A.K. Howard and P.J. Low,

      J. Organomet. Chem., 2006, 691, 3889-3894.