Deuteration of closo-1,2- and 1,7-C2B10H12 using C6D6/AlCl3: Mechanistic considerations

✍ Scribed by Hans Lee; Thomas Onak; Jojo Jaballas; Uyen Tran

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 261 KB
• Volume: 9
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1998)9:1<95::aid-hc12>3.0.co;2-y

✦ Synopsis

Regioselective deuteration of 1-X-C 2 B 10 H 12 (X ‫ס‬ 2, 7) cage systems with C 6 D 6 /AlCl 3 is correlated to ab initio calculational results on a [C 2 B 10 H 13 ] ‫ם‬ intermediate. Full geometry optimizations of pertinent [C 2 B 10 H 13 ] ‫ם‬ isomers, derived from each of the two 1-X-C 2 B 10 H 12 carborane isomers, result in cage geometries not unlike the (nearly) icosahedral starting carborane. Each isomer contains a BH 2 group having an acute H-B-H angle, long B-H bonds, and a very short H • • • H distance, hinting that the pertinent boron shares the electrons of a hydrogen molecule r pair. It is suggested that the structural differences between the BH 2 group of [C 2 B 10 H 13 ] ‫ם‬ and the CH 2 group of the benzenium ion, [C 6 H 7 ] ‫ם‬ (the intermediate strongly intimated upon protonation of benzene), can be explained, in part, by (a) the availability of the p-ring electrons for bonding to the (extra) proton in the latter and (b) the unavailability of p electrons from the carborane. Thus, the C 2 B 10 H 12 cage is most probably very reluctant to give up a cage electron pair in order to assist in bonding to an (externally bound) proton. Instead, it is more probable that "hydridic" B-H sigma electrons could very well play the important role in providing bonding to the attacking proton.