Diylides, phosphonium

At last, barium and calcium complexes of phosphonium bifluorenylide 19 was obtained from the corresponding phosphonium iodide (Scheme 12). The anion displays weak nucleophilicity toward both cations which prefer to coordinate with neutral oxygen of THF and with iodide. Located outside the coordination sphere of the metals, it represents thus the first example of uncomplexed phosphonium diylide [59]. 

As the phosphonium diylides, lithium phosphonium yldiides, first described by Schlosser and Corey (Ph3P=CR-Li R=H, C3H7) [60-62], have a high nucleophilicity and reactivity. Recently, the a-silylated lithium phosphonium yldiide 20 has been prepared from the stable phosphanyl-(silyl)carbene 19 and alkyl-lithium (Scheme 13). The first crystal X-ray diffraction study of such a reagent was proposed for 20 and its reaction with methyl iodide or phosphorus elec-... 

Particular highlights include the first structurally authenticated example of a phosphonium diylide and the use of ionic liquids as a novel medium for performing Wittig reactions. Ylides, particularly their iminophosphorane counterparts, continue to provide a strikingly rich avenue of coordination chemistry research. A useful study by Pandolfo et al. reports the solid state NMR spectra of several ylides and their complexes, showing that this technique can provide valuable structural information in situations where it is difiicult to obtain solution data due to solubility problems or decomposition. 

Keywords. Phosphonium, Ylide, Diylide, Wittig, Coordination, Reactivity... 

H.J. Cristau, C. Garcia, J. Kadoura u. E. Torreilles, Phosphorus, Sulfur, Silicon Relat. Elem. 49/50,151-154 (1990). Phosphonium Diaza-diylids and Aza-yldiid as New and Efficient Reagents for Primary and Secondary Amine Synthesis". 

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