REACTIVITY OF DECABORANE(14) WITH PYRIDINE - SYNTHESIS AND CHARACTERIZATION OF THE FIRST 6,6-SUBSTITUTED ISOMER OF NIDO-B10H14, 6,6-(C5H5N)(2)B10H12, AND APPLICATION OF B-11-B-11 DOUBLE-QUANTUM NMR-SPECTROSCOPY

In the low-temperature reaction of B10H14 with C5H5N, a new product, i dentified as arachno-6,6-(C5H5N)(2)B10H12, was formed in high yield an d purity. The proposed 6,6-L(2)B(10)H(12) compound represents the firs t known report of this decaborane substitution pattern. The formation of an asymmetric 6,5-(C5H5N)(2)B10H12 isomer was unexpected on the bas is of literature precedent describing the synthesis and structural elu cidation of numerous 6,9-L(2)B(10)H(12) species (where L = Lewis base) . The observed reaction sequence in the formation of the 6,6-(C5H5N)(2 )B10H12 compound proceeded through an initially observed [H . C5H5N]()[B10H13](-) intermediate. In addition to the formation of the 6,6-iso mer, the synthesis of the 6,9-(C5H5N)(2)B10H12 isomer is also reported from the reflux of nido-B10H14 in pyridine. Refluxing the 6,6-(pyridi ne)(2)B10H12 isomer in pyridine was also found to convert this isomer into the 6,9-isomer. Both isomers were characterized by B-11 NMR, FTIR , UV-vis, mass spectroscopic, and elemental analyses. The structure of the 6,6-isomer was established by 2D B-11-B-11 COSY NMR data and by t he first application of a pure phase B-11-B-11 2Q correlation NMR (dou ble-quantum) experiment to the elucidation of a borane cluster framewo rk. This latter NMR technique was very successful in greatly simplifyi ng the NMR assignments of the 6,6-substituted decaborane cluster speci es and should be a very powerful tool in cluster structure elucidation in general.