Room temperature reactions of S4N4 with (amino) diphenylphosphines, (R)Ph2P, have basically yielded two different types of SN heterocycles under two different stoichiometric conditions. Phosphiniminocyclotrithiatriazenes, (R)Ph2PNS3N3 (R = C4H8N, C5H10N, C6H12N, CH3NC4H8N, (C6H11)2 N, and (C6H5CH2)2N) have been obtained (yield 45–76%) from a 1:2 mole ratio (S4N4:(R)Ph2P) reaction, while the disubstituted S4N4 derivatives, 1,5‐[Ph2(R)PN]2S4N4 (R = C4N8N, C5H10N, and C6H12N) have been obtained (yield 30–45%) only from a 1:3.5–4 mole ratio reaction. All the 1,5‐[Ph2(R)PN]2S4N4 derivatives prepared in this study undergo a room temperature solution phase transformation to the corresponding (R)Ph2PNS3N3 heterocycles. Copyright © 1992 VCH Publishers, Inc.