BRIDGEHEAD DIPHOSPHINES IN THE BICYCLO[3.3.3]UNDECANE AND BICYCLO[4.4.4]TETRADECANE SERIES - SYNTHESIS, STRUCTURE AND PROPERTIES

Several propellane diphosphonium salts 8 are prepared by the reaction of 1,k + 2-diphosphabicyclo[k.l.0]alkanes 6 with alpha,omega-alkanedio l bis-triflates [bis(trifluoromethanesurfonates)]; their properties ar e strongly dependent on ring size. 1,6-Diphosphoniatricyclo[4.4.4.0]te tradecane bis-triflate 8d is stable in acidic aqueous solution, and re acts with nucleophiles [X = F-, MeO-, H- (from BH4-) and R- (from Grig nard and alkyllithium reagents)] to give products 13-18 with partial X -P-P+ bonding, hydroxide ion gives the diphosphine monooxide 12b but e ven this may retain some P-P bonding. However 1,5-diphosphoniatricyclo [3.3.3.0]undecane bis-triflate 8a is hydrolysed irreversibly and much more rapidly than its [4.4.4.0] counterpart, 1,6-Diphosphoniatricyclo[ 4.4.3.0]tridecane bis-triflate 8c reacts with NaBH4 to give a hydride adduct 15a which is deprotonated by Bu '' Li to give 1,6-diphosphabicy clo[4.4.3]tridecane 9c. However several attempts to prepare 1,6-diphos phabicyclo[4.4.4]tetradecane 9d led to a deep-seated rearrangement to give 1,4-bis(1-phospholan-1-yl)butane. These included reaction of hydr ide adduct 15b with Bu '' Li, and debenzylations of yl-1-phosphonia-6- phosphabicyclo[4,4,4]tetradecane trifluoromethanesulfonate 16b and dib enzyl-1,6-diphosphoniabicyclo[4.4.4]tetradecane bromide triflate 21 wi th LiAlH4. Reaction of cis-1,5-dibenzyl-1,5-diphosphacyclooctane with CH2(CH2OTf)(2) gives ,5-dibenzyl-1,5-diphosphoniabicyclo[3.3.3]undecan e bis-triflate which is debenzylated with LiAlH4 to 1,5-diphosphabicyc lo[3.3.3]undecane 9a. Attempts to prepare 1,6-diphosphabicyclo[4.4.4]t etradecane by related methods lead to oligomerisation reactions. The s tructure of 1,5-diphosphabicyclo[3.3.3]undecane is reported; its He(I) photoelectron spectrum shows two well separated bands at 7.58 and 8.1 4 eV, and RHF/6-31G ab initio calculations indicating that this is du e to through-bond interactions.