Concerted Pathway to the Mechanism of the Anilinolysis of Bis(N,N-diethylamino)phosphinic Chloride in Acetonitrile

The kinetics of the nucleophilic substitution reactions of bis(N,N-diethylamino)phosphinic chloride with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated in MeCN at 65.0 degrees C. The deuterium kinetic isotope effects (DKIEs) are secondary inverse (k(H)/k(D)<1: 0.706-0.947) and the magnitudes of the secondary inverse DKIEs (k(H)/k(D)) increase constantly as the nucleophiles are changed from weakly basic to strongly basic anilines. The magnitudes of the selectivity parameters are (X(H))=-6.34, and (X(H))=2.24 with substituted anilines and (X(D))=-6.13 and (X(D))=2.17 with deuterated anilines. A concerted S(N)2 mechanism involving predominant backside attack is proposed based on the k(H)/k(D) values with substituent X.