Kinetics and Mechanism of the Aminolysis of Dimethyl Thiophosphinic Chloride with Anilines

Abstract

The second-order rate constants (kH and kD) for the reactions were obtained as the slope of k obsd (pseudofirst-order rate constant) against at least five concentrations of aniline nucleophiles [XC6H4NH2(D2)] in eq 1.The intercept (k 0 ) was negligible in all cases. No third-order kinetics was observed and no complications were found in the determination of kobsd. The kH values are summarized in Table 1, together with kD values involving deuterated anilines. The rate increases with a more electron-donating substituent X in the nucleophile which is consistent with a typical nucleophilic substitution reaction with negative charge development at the reaction center P in the transition state (TS).As shown in Figure 1, the reactivity of the P=O system is greater than that of its P=S counterpart [kH(2)/kH(1) ≈ 800 and kH(4)/kH(3) ≈ 3]. It is well known that the P=O systems are generally more reactive than their P=S counterparts for several reasons, the so-called "thio effect", which is mainly the electronegativity difference between O and S and favors O over S. 3 The natural bond order (NBO) charges 4 of the reaction center P in the gas phase are 1.180 (1), 1.793 (2), ligands. Solely considering the positive charge of the reaction center P atom in the P=S (and P=O) system, the anilinolysis rate of 1 (and 2) should be slower than that of 3 (and 4), i.e., kH(1)/kH(3) < 1 [and kH(2)/kH(4) < 1]. However, the observed rate ratios of kH(1)/kH(3) = 16 and kH(2)/kH(4) = 4,520 are completely opposite to expectations from the inductive effects of the ligands, strongly suggesting that the inductive effects of the ligands do not play an important role to decide the reactivity in each reaction system, P=S or P=O system. 6The values of second-order rate constants (kH), selectivity parameters (ρX and βX 9 : see Figure 2), and DKIEs (kH/kD) of