Previously, we demostrated that TMSP reacts with (I) p-tolyl and (II)benzyl chloroformates, followed by hydrolysis, forming the corresponding acyl phosphonates.Now, in a similar reaction performed with (III)p-nitro and (IV)p-fluorocholroformates, we have identified the products as the corresponding bis-phosphonates derivatives. The effect of electron-withdrawing groups in the formation of the products will be discussed.