Polyhedral monocarbaborane chemistry. Functionality and isomerism: Reactions of the [6-Ph-nido-6-CB9H11](-) anion with aminopyridines NC5H4NH2 to yield neutral arachno and closo ten-vertex monocarbaborane derivatives

Reaction of NC5H4-2-NH2 with the [6-Ph-nido-6-CB9H11] - anion ( 1) in the presence of hydrated FeCl3 gives [6-Ph-9-((NCH4)-H-5-2-NH2)- arachno-6-(CBH12)-H-9] (4) and thence [1-Ph-2( NC5H4-2-NH2)- closo-1-CB9H8] (5), in which the pyridine substituent is on a boron atom a to the cluster carbon atom. This behaviour contrasts to the reactions of organyl-substituted pyridines NC5H4R to yield neutral 9-pyridine arachno species [6-Ph-9-(NC5H4R)- arachno-6- CB9H12] and thence neutral 6-pyridine closo species [1-Ph-6-(NC5H4R)-closo-1-CB9H8], in which the pyridine substituent is on a boron atom beta to the cluster carbon atom. The chlorinated analogue [1-Ph-2-(NC5H4-2-NH2)-4-Cl- closo-1-CB9H7] (7) is also identified as a minor by-product from the reaction system. Reaction of anion 1 with NC5H4-4-NH2 does not proceed further than [6-Ph-9-(NC5H4-4-NH2)- arachno-6- CB9H12] ( 8). The 2-NH2 compounds 4, 5 and 7 exhibit intramolecular BH-HN dihydrogen bonding, whereas the 4-NH2 compound 8 exhibits an intermolecular BH-HN dihydrogen-bonded network that involves inversion-related pairs of dihydrogen-bonded chains.