Syntheses, structures and flexible coordination of sterically demanding di- and "tri"-lithiated methandiides.

Lithiation of the sterically demanding bis(iminophosphoranyl)methane H2C{Ph2P(=NDip)}2 (Dip = 2,6-iPr2C6H3), H2L, with alkyllithium reagents afforded the methandiide complexes [(LLi2)2] 2, [LLi2(OEt2)2] 4, [LLi2(THF)3] 5, [LLi2(THF)2] 6, and [LLi2(PMDTA)] 7 (PMDTA = N,N,N',N'',N''-pentamethyldiethylenetriamine), from various solvents or after the addition of donor molecules. The complex [HC(Ph2PNDip)(Ph2P)Li(THF)2] 3 was further identified as a by-product under certain conditions. Further lithiation of the methandiide in ortho-position of one P-bound phenyl group affords complexes of the trianionic ligand L'(3-), and the complexes [(L'Li3)2] 8 and [L'Li3(THF)4] 9 were obtained. Different isomeric forms for the methandiide units investigated in solution and in the solid state are described, and the crystal structures of complexes 2, 3, and 5-9 are reported.