Reactions of the ring system trans-NPCl₂(NSOPh)₂(1) with MgMeCl and an excess of propan-2-ol in tetrahydrofuran show that chlorine substitution occurs both along a nucleophilic substitution pattern and a metal–halogen exchange process, the latter giving rise to the formation of bicyclic compounds. For reactions of this ring system with MgBu^tCl or the organosilyl Grignard reagents Mg(CH₂SiMe₃)Cl and Mg[CH(SiMe₃)₂]Cl nucleophilic substitution appears to be the preferential process. Application of the copper-assisted Grignard reagents MgRCl–[{Cul(PBu₃ⁿ)}₄](R = alkyl) and alkyl iodides, allyl bromide, or propan-2-ol leads to the formation of dialkyl, alkylallyl, or alkylhydrido derivatives, according to an initial metal–halogen exchange process. The crystal and molecular structure of the bicyclic compound [NPMe(NSOPh)₂]₂·C₆H₆ has been determined. Crystals are triclinic, space group P, a= 8.063(1), b= 8.979(1), c= 12.712(3)Å, α= 71.38(1), β= 74.13(1), γ= 86.57(1)°, and Z= 1. The basic structure consists of two six-membered N₃PS₂ rings coupled by a P–P bond [2.211 6(9)Å] with the methyl groups in trans position. Mean bond lengths are N–P 1.614(2), N–S 1.565(5), 1.585(1), S–0 1.436(1 ), S–C 1.768(1), and C–C (phenyl) 1.388(1)Å. The endocyclic angles at P and S are 114.6(1) and 113.3(4)°(average), respectively, and those at N range from 121.3(1) to 124.8(1)°.