Steric Effects in Heteroboranes. V. 1-Ph-2-Me3Si-1,2-closo-C2B10H10

The structure of 1-phenyl-2-trimethylsilyl-1,2-dicarba-closo-dodecaborane(12), C 11 H 24 B 10 Si, has been determined crystallographically. The C cage -C cage distance is 1.708 (4) A, only slightly longer than in the 2-methyl analogue. However, in contrast to the 2-methyl and 2-bromo analogues, relief from steric congestion is afforded by a mutual'bend back'of both the phenyl and trimethylsilyl groups, the latter involving deformation of valency angles both at Si and the C cage atom to which it is attached