Ylide and zwitterionic complexes

It is known that REM trimethylsilylmethyl derivatives are stable and this ligand is isoelectronic to trimethylmethylenephosphorane. On diis base Schumann and coworkers have supposed that the lanthanoid complexes with phosphoric ylides ligands should be also stable and have realized their synthesis [54, 234-238, 240-243]. It was found that the direct reaction of Me3P-CH2 with REM chlorides in the pentane or hexane medium leads to the formation of insoluble pyrophoric phosphonium salts with a high yield  

The decomposition temperatures of phosphonium salts are given below  

The interaction of these products with butyllithium in the ether/hexane mixture gives ylide complexes (Table 1.17) along with LiCl and butane  

With Lu and Tm derivatives as an example it was established, that triphenylmethylene-phosphorane also forms the adducts Ln[(CH2-PPh3)Cl]3 (Ln = Tm, Lu) with chlorides of these metals. These products melt at 166° and 183°C, respectively, without decomposition. However, the attempt to transform these compounds into ylide form by the treatment with an excess of phosphorane, MeLi or BuLi has been unsuccessful. 

Cp2Lu(CH2SiMe3)CH2PPh3 103 THF, toluene, methylenechlori- de,ether,benzene [241] 

---