Reduction of 1,2-(CH₂)<i>_n</i>-1,2-C₂B₁₀H₁₀ by Group 1 Metals. Effects of Bridge Length/Rigidity on the Formation of Carborane Anions

The effects of bridge length and rigidity on the formation of C,C‘-linked carborane anions were studied. Reaction of 1,2-(CH2)3-1,2-C2B10H10 (1), 1,2-(CH2CHCHCH2)-1,2-C2B10H10 (2), or 1,2-(CH2)4-1,2-C2B10H10 (3) with excess Li metal in THF gave “carbon-atoms-adjacent” (CAd) arachno-carborane salt [{1,2-(CH2)3-1,2-C2B10H10}{Li4(THF)5}]2 (6), [{1,2-(CH2CHCHCH2)-1,2-C2B10H10}{Li4(THF)5}]2 (7), or [{1,2-(CH2)4-1,2-C2B10H10}{Li4(THF)5}]2 (8), respectively. On the other hand, reduction of 1,2-(CH2)5-1,2-C2B10H10 (4) or 1,2-(CH2)6-1,2-C2B10H10 (5) with excess Li metal followed by cation exchange of NaI, or directly with excess Na metal, afforded “carbon-atoms-apart” (CAp) nido-carborane salt [{1,3-(CH2)5-1,3-C2B10H10}{Na2(THF)4}]n (9) or [{1,4-(CH2)6-1,4-C2B10H10}{Na2(THF)4}]n (10). All complexes were fully characterized by various spectroscopic techniques and elemental analyses as well as single-crystal X-ray diffraction studies. The results showed that although both the bridge length and rigidity of C,C‘-linked o-carboranes have significant effects on the formation of carborane anions, the former plays a more important role than the latter in controlling the relative positions of the two cage carbon atoms during the reductive process.