Reduction of 1,2-(CH2)n-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'-Iinked 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}{Li-4(THF)(5)}] (6), [{1,2-(CH2CH= CHCH2)-1,2-C2B10H10}{Li-4(THF)(5)}](2) (7), or [{1,2-(CH2)(4)-1,2-C2B10H2O}{Li-4(THF)(5)}](2) (8), respectively. On the other hand, reduction of 1,2-(CH2)(5)-1,2-C2B10H10 (4) or 1,2-(CH2)6-1,2C(2)B(10)H(10) (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}- {Na-2(THF)(4)}](n) (9) or [{1,4-(CH2)6-1,4-C2B10H10}{Na-2(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.