Intramolecular nucleophilic substitution by phosphinate and thiophosphinate anions: relative rates of formation of five- and six-membered rings

In CH2Cl2 solution the phosphinate anion BrCH2CH2(CH2)nCH2(Ph)P(O)O– cyclises only 4,3 times faster when n= 0 (five-membered ring product) than when n= 1; for the thiophosphinate anion ClCH2CH2(CH2)nCH2(Ph)P(S)O– cyclisation (via sulfur) is still only 30 times faster when n= 0 than when n= 1.