Inhaltsu È bersicht. Isocyanacetonitril (1 a), Pentacarbonyl(diisocyanmethan)chrom (1 b) und 2,2,2-Trifluorethylisocyanid (1 c) bilden mit dem Diphosphen R±P=P±R (R = C[Si(CH 3 ) 3 ]) (2) in einer [2 + 1]-Cycloadditonsreaktion die Diphosphiranimine 3 a±c. Alle drei Verbindungen sind sehr stabil und es ist keine Ru È ckbildung des Diphosphens zu beobachten. Einkristallro È ntgenstrukturanalysen von 3 a: triklin, P 1, a = 918.0(2), b = 1174.7(4), c = 1821.9(5) pm, a = 93.83(2), b = 97. 22(2),c = 97.08(2)°,Z = 2,R 1 = 0.069;3 c: monoklin,P2 1 ,a = 928.6(2),b = 1659.8(3),c = 1261.2(3) pm,b = 107.65(2)°,Z = 2,R 1 = 0.073 und 1,[tris(trimethylsilyl)]methyl-N-trifluormethyl-3-diphosphiranimin: monoklin, P2 1 /n, a = 1374.6(3), b = 1685.9(1), c = 1658.6(5) pm, b = 108.99(9)°, Z = 4, R 1 = 0.092 zeigen in allen Verbindungen ein gleichartiges dreigliedriges PCP Ringsystem mit exocyclischer C±N-Doppelbindung. Cycloaddition Reactions of Isocyanides with Bis[tris(trimethylsilyl)methyl]diphosphene Abstract. The [2 + 1] cycloaddition reactions of isocyanoacetonitrile (1 a), pentacarbonyl(diisocyanomethane)chromium (1 b), and 2,2,2-trifluoroethylisocyanide (1 c) with the diphosphene R±P=P±R (R = C[Si(CH 3 ) 3 ]) (2) yield the expected diphosphirane imines 3 a±c. All compounds are thermally very stable and show no evidence for a [2 + 1] cycloreversion reaction. The structures of 3 a: triclinic, P 1, a = 918.0(2), b = 1174.7(4), c = 1821.9(5) pm, a = 93.83(2), b = 97.22(2)°, c = 97.08(2)°, Z = 2, R 1 = 0.069; 3 c: monoclinic, P2 1 , a = 928.6(2), b = 1659.8(3), c = 1261.2(3) pm, b = 107.65(2)°, Z = 2, R 1 = 0.073, and 1,2-Bis[tris(trimethylsilyl)]methyl-Ntrifluormethyl-3-diphosphiranimin: monoclinic, P2 1 /n, a = 1374.6(3), b = 1685.9(1), c = 1658.6(5) pm, b = 108.99(9)°, Z = 4, R 1 = 0.092, were elucidated by X-ray crystallography. All three compounds possess a similar three membered PCP ring system with an exocyclic C±N double bond.