Isomeric Borabicyclo[4.3.0]nonanes from Bis(9‐borabicyclo[3.3.1]nonane) by Gas‐Phase Pyrolysis

Abstract

Abstract The gas‐phase pyrolysis of bis(9‐borabicyclo[3.3.1]nonane) ( 1 ) 2 has been studied in the range of 400 −620°C. At 490°C approximately equal amounts of 1‐borabicyclo[4.3.0]nonane ( 2 ) and 8‐borabicyclo[4.3.0]nonane ( 3 ) are formed (yield > 95%). Heating of 3 which persumably exists as the oligomer with mixed 1,1:2,2‐ and 1,2:1,2‐diborane(6) structure 4 , in the condensed phase to above 100°C results in the formation of the air and hydrolysis stable 5 with a 1,2:1,2‐diborane(6) structure. The structure of 5 has been determined by X‐ray analysis. The pyrolysis of 9‐alkyl‐9‐borabicyclo[3.3.1]nonanes 6 [alkylethyl ( 6a ), 1,2‐dimethylpropyl ( 6b ), and isopinocampheyl ( 6c ) gives 2 and small amounts of ( 1 ) 2 . The formation of 2 ( 1 ) 2 as well as 2 and ( 1 ) 2 from 6 indicate that monomeric 9‐borabicyclo[3.3.1]nonane 1 is an intermediate.