Bicyclic medium-ring diphosphines: contrasting behaviour in the bicyclo[3.3.3]undecane and bicyclo[4.4.4]tetradecane series

Abstract

Reaction of cis-1,5-dibenzyl-1,5-diphosphacyclooctane 9 with CH₂(CH₂OTf)₂ gives 1,5-dibenzyl-1,5-diphosphoniabicyclo[3.3.3] undecanediium bistriflate 10 which is debenzylated with LiAlH₄ to 1,5-diphosphabicyclo[3.3.3]undecane 11, but attempts to prepare 1,6-diphosphabicyclo[4.4.4]tetradecane 7 lead to oligomerisation and rearrangement reactions; 1,5-diphosphoniatricyclo[3.3.3.0]undecanediium bistriflate 8 is slowly formed by reaction of 1,5-diphosphabicyclo[3.3.0] octane with CH₂(CH₂OTf)₂ in nitromethane, but is hydrolysed much more rapidly than its [4.4.4.0] counterpart.