Ethylenediamine (en) solutions of E-7(3-), where E = P (1) or As (2), react with excess (PhCH2)Me3NBr to give NMe3 and a single diastereomer of the (PhCH2)(2)E-7(-) ions, when E = P (3) or As (4), in good yields. X-ray crystal structures of the [PPh4]3 and [K(2,2,2-crypt)]4 salts showed that both anions adopt the sterically favored symmetrical structure. DMF solutions of 1 also react with ethyl esters of N-methylated amino acids, (EtOCOCHR)Me3N+, where R = H (glycine) or Me (alanine), to give (EtOCOCHR)(2)P-7(-) ions where R = H (7) or Me (8). The transfer of Me+ to give the known Me2P7- ion (5) is competitive with (EtOCOCHR)(+) transfer when R is not a proton such that 5 is favored over the formation of 8 (5:8 = 2.5:1), but 5 is only a trace impurity for R = H (5:7 approximate to 1:48). Reactions of R and S enantiomers of the alanine esters were conducted to probe the stereochemistry at carbon in these reactions, but the three different diastereomers of 8 (i.e., (R,R)- or (S,S)-, (R,S)-, and (S,R)(EtOCOCHR)(2)P-7(-)) were indistinguishable by NMR spectroscopy. These studies advance the alkylation chemistry of the polypnictides by (1) unequivocally showing which isomer is formed in the alkyl transfer reaction, (2) showing that the alkylammonium alkylations proceed with As-7(3-) With the same stereospecificity, and (3) demonstrating that the chemistry can be extended to N-methylated amino acid esters. Crystallographic data for [PPh4]3 : orthorhombic, space group Pbca, a = 17.6049(13) Angstrom, b = 17.1910(12) Angstrom, c = 23.798(2) Angstrom, V = 7202.4(9) Angstrom(3), Z = 8, R(F)= 4.03%, R(wF(2))= 10.41% (F-o > 4 sigma F-o). For [K(2,2,2-crypt)]4 : monoclinic, space group I2/a, a = 25.527(2) Angstrom, b = 13.292(2) Angstrom, c = 24.687(2) Angstrom, beta = 96.836(11)degrees, V = 8317(2) Angstrom(3), Z = 8, R(F) = 6.47%, R(wF(2)) = 15.85% (F-o > 4 sigma F-o).