BORON CAGE EXPANSION STUDIES - CONVERSION OF NIDO-2,3-DICARBAHEXABORANE(8) TO B-METHYL DERIVATIVES OF CLOSO-1,7-DICARBAOCTABORANE(8) AND CLOSO-2,4-DICARBAHEPTABORANE(7) AND FORMATION OF B-DIMETHYL-CLOSO-2,4-DICARBAHEPTABORANE(7) FROM CLOSO-1,6-DICARBAHEXABORANE(6)

A two-boron cage expansion to give 2,3,4,5,6,8-Me6-closo-1,7-C2B6H2, as well as a previously observed one-boron expansion to give l,3,5,6,7-Me5-closo-2,4-C2B5H2, is observed upon reacting trimethylborane with nido-2,3-C2B4H8 at 220-230 °C. closo-2,4-C2B5H7 and its B-methyl derivatives do not undergo B-methyl exchange with trimethylborane at the temperatures used for the cage expansion reaction which, along with the results from 10B/11B isotope studies on the cage expansion reaction, suggests that the per-B-methyl five-boron closo product from the reaction of 2,3-C2B4H8 with trimethylborane may be produced via a six-boron intermediate. closo-1,6-C2B4H6 reacts with excess trimethylborane in the temperature region 550-600 °C to give the cage expansion product 5-Me2-closo-2,4-C2B5H5 along with minor amounts of mono- and trimethyl derivatives of this closo carborane. © 1979, American Chemical Society. All rights reserved.