DERIVATIVE CHEMISTRY OF NINE-BORON CLUSTERS

The synthesis of perhalogenated nonahydrononaborates B(,9)X(,9)(\u272-) (X = Cl,Br,I) from B(,9)H(,9)(\u272-) is described. Oxidations of the perchloro, perbromo, and periodo dianions gave the corresponding novel and highly colored borane radicals. Further oxidations gave the corresponding neutral clusters B(,9)X(,9). The redox sequence B(,9)X(,9)(\u272-) (DBLHARR) B(,9)X(,9)(\u27-) (DBLHARR) B(,9)X(,9) has been established. The stability of the oxidation products has been ascribed to the extensive involvement of the halogen substituents in the cage. The Synthesis of B(,9)H(,8)S(Me)(,2)(\u27-) and B(,9)H(,7)(S(Me)(,2))(,2) from B(,9)H(,9)(\u272-) and DMSO/acetic anhydride is also described. Variable temperature (\u271)H nmr and (\u2713)C nmr studies revealed the first intramolecular rearrangement of a nine-boron cluster. The disubstituted product exists as the 1,5- isomer in the solid state and in low temperature solutions (0(DEGREES)C). The nmr results suggested that above ambient temperature the 1,5- isomer is in equilibrium with the 1,7(8)- and 4,5- isomers. Coalescence occurs at 130(DEGREES)C indicating rapid cage rearrangement. The structural nonrigidity of the nine boron cluster is discussed in the light of known dynamic processes in boron cluster chemistry. X-ray structure analysis of B(,9)H(,7)(SMe(,2))(,2) showed that this compound crystallizes in the orthorhombic space group P2(,1)2(,1)2(,1). Unit cell parameters are a = 7.879(2), b = 9.014(2), c = 19.436(4) (ANGSTROM), V = 1379.4 (ANGSTROM)(\u273), Z = 4, and D(,x) = 1.101 g/cm(\u273). The structure was solved by conventional heavy atom methods, resulting in a final R factor of 7.9% for 1538 independent reflections. Substitution occurs at two different boron sites yielding the 1,5-isomer. Bonds joining capping boron atoms (a) to prismatic boron atoms (e) are shorter than those joining two prismatic boron atoms as is expected. The long bond distances of the B(2)-B(3) and B(8)-B(9) support the fact that these are involved in the pairwise interconversion of the five- and six-coordinate vertices