Syntheses and Characterization of o ‐Carboranes Containing Fused exo ‐Polyhedral Di‐ and Triboraheterocycles

Reaction of dilithio‐ o ‐carborane Li 2 C 2 B 10 H 10 (generated in situ from o ‐carborane 1 and butyllithium) with the 1, 2‐diborylbenzene derivative 1, 2‐C 6 H 4 ( i Pr 2 NBCl) 2 yielded the o ‐carborane compound 3 having the fused exo ‐polyhedral C 2 B 2 C 2 heterocycle. The analogous reactions with 1, 1‐bis(dimethylaminochloroboryl)ethane and with 1, 3‐dichloro‐1, 2,3‐tris(dimethylamino)triborane(5) afforded the o ‐carborane compounds 5 and 7 containing the fused exo ‐polyhedral five‐membered C 2 B 2 C and C 2 B 3 rings, respectively. Attempts to use 1, 2‐dichloro‐1, 2‐bis(dimethylamino)diborane(4) for the synthesis of the o ‐carborane compound 10 with a fused exo ‐polyhedral C 2 B 2 ring instead led to the diborane(4)yl‐ o ‐carborane species 9c and 9d (the latter in trace amount), which contain a diborane(4)yl moiety bonded to the o ‐carborane. The molecular compositions of the new o ‐carborane derivatives follow from NMR spectroscopic and mass spectrometric data as well as from X‐ray diffraction analyses of 3 , 7 and 9c . The structures exhibit weak intramolecular C–H ··· H–B hydrogen‐hydrogen interactions.