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‘-linked carborane anions were studied. Reaction of 1,2-(CH 2 ) 3 -1,2-C 2 B 10 H 10 ( 1 ), 1,2-(CH 2 CH CHCH 2 )-1,2-C 2 B 10 H 10 ( 2 ), or 1,2-(CH 2 ) 4 -1,2-C 2 B 10 H 10 ( 3 ) with excess Li metal in THF gave “carbon-atoms-adjacent” (CAd) arachno -carborane salt [{1,2-(CH 2 ) 3 -1,2-C 2 B 10 H 10 }{Li 4 (THF) 5 }] 2 ( 6 ), [{1,2-(CH 2 CH CHCH 2 )-1,2-C 2 B 10 H 10 }{Li 4 (THF) 5 }] 2 ( 7 ), or [{1,2-(CH 2 ) 4 -1,2-C 2 B 10 H 10 }{Li 4 (THF) 5 }] 2 ( 8 ), respectively. On the other hand, reduction of 1,2-(CH 2 ) 5 -1,2-C 2 B 10 H 10 ( 4 ) or 1,2-(CH 2 ) 6 -1,2-C 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-(CH 2 ) 5 -1,3-C 2 B 10 H 10 }{Na 2 (THF) 4 }] n ( 9 ) or [{1,4-(CH 2 ) 6 -1,4-C 2 B 10 H 10 }{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.