On the Facile P-C Bond Break

Associative vs. dissociative mechanism of P-C bond breaking in α-aminophosphonates leading to phosphoric acid [P(V)] derivatives.

“…This study confirmed that a three-step process including amino-group protonation, proton transfer through a hydrogen-oxygen bond NH•••O(P), 43 and P-C bond cleavage, leading to a protonated imine and derivatives of H-phosphonate is the most probable mechanism. 6,27,28,43,44 It should be noted that for N-alkyl aminophosphonates the decomposition is not observed as the amine nitrogen in this case is protonated and formation of imine (leaving group) is prevented. Lowering the basicity of the amine as is the case in the N-benzhydryl derivative, again facilitates the elimination process 47 Decomposition to P V .…”

“…For decomposition of aminophosphonate to P III derivatives. 6,24,27,35,36,43 we have proposed the retro Kabachnik elimination mechanism. In this mechanism we assumed that in aminophosphonate (N-aromatic, or with bulky groups) the presence of a nitrogen of relatively low basicity causes the equilibrium between species protonated on nitrogen and phosphoryl oxygen to be significantly shifted toward the latter.…”

“…[1][2][3] Many efforts have been made to uncover the pathways by which the P=O centre can react with nucleophiles. In general, two mechanisms have been proposed: S N 1@P, in which pentavalent three-coordinated species would be intermediates (Scheme 1a) 4,5 (in some papers it is described as EA -elimination-addition) and S N 2@P, which proceeds via a pentavalent pentacoordinated transition state or intermediate (Scheme 1b) 4,6 (in some papers denoted by AE -addition-elimination). The metaphosphate monoanion as a possible reaction intermediate has been discussed since 1955.…”