MEDIUM-RING DIPHOSPHINES FROM DIPHOSPHABICYCLO[K.L.0]ALKANES - STEREOSELECTIVE SYNTHESES, STRUCTURE AND PROPERTIES

A series of 1,k + 2-diphosphabicyclo[k.l.0]alkanes 2b-e are prepared b y Bu '' Li-promoted cyclisation of 1,omega-diphosphinoalkanes, followe d by alkylation and cycloalkylation with 1,omega-dihaloalkanes. These compounds appear to be exclusively cis-isomers except 1,6-diphosphabic yclo[5.4.0]undecane 2e which is a 3:1 cis/trans mixture. Mono-quaterni sation of cis-1,k + 2-diphosphabicyclo[k.l.0]alkanes, followed by trea tment of the mono-quaternary salts with alkyllithium or Grignard reage nts produces cis-1,n-disubstituted-1,n-diphosphacycloalkanes 4 exclusi vely; examples containing 8-, 9- and 10-membered rings and a range of substituents on phosphorus are described. Di-quaternisation of 1,k + 2 -diphosphabicyclo[k.l.0]alkanes, followed by hydrolysis, yields the tr ans-isomers of 1,n-disubstituted-1,n-diphosphacycloalkane monooxides 6 exclusively; reduction of these with LiAlH4 in benzene gives largely trans-1,n-disubstituted-1,n-diphosphacycloalkanes 7, but is not comple tely stereoselective. The structure and properties of these diphosphac ycloalkanes are discussed. He(I) photoelectron spectra of 1,5-diphosph abicyclo[3.3.0]octane, 1,6-diphosphabicyclo[4.3.0]nonane and 1,6-dipho sphabicyclo[4.4.0]decane show little evidence of interaction between p hosphorus lone pairs, unlike the corresponding hydrazines. The medium- ring diphosphacycloalkanes, 1,5-dimethyl-1,5-diphosphacyclooctane and 1,6-dimethyl-1,6-diphosphacyclodecane also show little evidence of int eraction between phosphorus lone pairs.