Geminal systems Communication 20. Structure and properties of aminomethylphosphonium salts

1. The arguments for the phosphonium-phosphorane equilibrium involving the formation of a tricyclic phosphorane previously proposed for phosphonium salt cations R3\(\mathop P\limits^ +\)CH2X (X=R2N, RO, HO, RS), were examined. This proposal was rejected in light of a) the observed nonequivalence of the isopropyl group methyl protons of [i-Pr2(Me)\(\mathop P\limits^ +\)CH2N(CH2CH2)2O] I− in its PMR spectrum in C5D5N solution, b) x-ray structural analysis of this salt (N⋯P distance 2.69(2) A), and c) the configurational stability of [o-MeOC6H4\(\mathop P\limits^ \oplus\)(Me)Pr2-i] I⊖ Up to 190°C. 2. Aminomethylphosphonium salts have aminomethylating action relative to MeO⊖, while phosphineomethylammonium salts do not react with Me.