Pyridinolysis of Bis(N,N-dimethylamino) Phosphinic Chloride in Acetonitrile

The kinetic studies on the pyridinolysis of bis(N,N-dimethylamino) phosphinic chloride have been carried out in acetonitrile at 55.0 .deg. C. The free energy correlations for substituent X variations in the X-pyridines are biphasic concave upwards with a break point at X = H. A concerted SN2 mechanism is proposed with a change of the attacking direction of the X-pyridine from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines on the basis of greater βX value with more basic pyridines than with less basic pyridines. The kinetic studies of the pyridinolyses of tetracoordinated phosphorus have been studied extensively by this lab. In the present work, the nucleophilic substitution reactions of bis(N,N-dimethylamino) phosphinic chloride with substituted X-pyridines are investigated kinetically in acetonitrile (MeCN) at 55.0 ± 0.1 .deg. C (Scheme 1) to gain further systematic information into the reactivity and mechanism depending on the variation of the two ligands, as well as to compare with the relevant phosphinic chloride systems: dimethyl, diethyl, methyl phenyl, and diphenyl phosphinic chlorides on the basis of the magnitude of positive charge of the reaction center P atom, steric effects of the two ligands, and selectivity parameters. The numbering of the substrates follows the sequence of the summations of the Taft's steric constants of the two ligands