A set of lithium phosphonium diylides Li[CH2-PR2-CpX] (9–12; CpX = C5Me4, C5H3 tBu, R = Ph, Me) is presented. Two of the lithium complexes were characterized by means of single-crystal X-ray analysis, revealing a dimeric head-to-tail arrangement in the solid state. The coordination behavior of 9–12 in the liquid phase is solvent dependent. These lithium phosphonium diylides exist as contact ion pairs in benzene and as solvent-separated ion pairs in THF solutions. Phosphonium salts [H3C-PR2-CpXH)]+I– (1–4) are starting materials for the syntheses of the title compounds and exist as mixtures of isomers due to [1,5]-prototropic rearrangements. The dynamic behavior in solution has been investigated. Two different routes allow access to title compounds 9–12. Reactions of 1–4 with 2 equiv of nBuLi give 9–12 in a one-pot synthesis. In an alternative two-step route, dehydrodehalogenation of 1–4 with KH gives the corresponding phosphonium ylides 5–8. Two of these phosphonium ylides were characterized by single-crystal X-ray analysis. In one case two different conformers were obtained.

We report the investigation of four new monoanionic cyclopentadienyl‐N‐silylphosphazene ligands [C5R4‐SiMe2‐NPR′3]– (CpSiNP–) 1–4. In this system the amido moiety of the classical dianionic chelate ligand (CpSiN2–) is displaced by an isoelectronic phosphazene donor function (CpSiNP–). The iminophosphorane‐functionalized tetramethylcyclopentadiene ligands have been prepared by the reaction of two equivalents of tris(tert‐butyl)iminophosphorane or tris(dimethylamino)iminophosphorane with tetramethyl or tert‐butyl‐substituted chlorodimethylsilyl‐1,3‐cyclopentadiene. The molecular structures of the protonated species of two representatives 1‐H and 2‐H were established by X‐ray diffraction analysis. Furthermore the metallation of the ligand [C5R4‐SiMe2‐NPtBu3]H (2‐H) was explored by the aryl elimination pathway using chelate stabilized arene complexes of rare‐earth metals (RE) [RE(dmba)3][RE = Y, Lu; (dmba–) = ortho‐metalated N,N‐dimethylbenzylamine]. The resulting cyclopentadienyl diaryl complexes of the type [(η5‐C5Me4‐SiMe2‐NPtBu3)RE(dmba)2] [RE = Y (5); Lu(6)] were completely characterized by NMR spectroscopy, elemental analysis and X‐ray diffraction analysis. The coordination number of the central atom in each case is nine. Five RE–C bonds to the Cp fragment, two RE–C bonds to the aryl‐carbon atom and two RE–N bonds to the chelating amino function are realized. The phosphazene unit with uncommonly large Si–N–P angles of 173° (5) and 166° (6) do not form a bond in terms of the Constrained‐Geometry ligand concept at least in these complexes. It seems that on the one hand the high coordination number and on the other hand the stable chelate structure of the coordinated amino‐aryl ligand is responsible for this result.