The First Unambiguous Characterization of a Neutral Phosphorus Ylide-Lithium Complex: Isolation, Structure, and Ab Initio Investigations of [(PhCH_2)_2NLi centre dot CH_2PPh_3]_2

摘要

The Nobel Prize-winning discovery by Wittig of the reaction that bears his name signaled the beginning of interest in phosphorus ylides. Though this interest was then in the realm of organic synthesis. the mid-1960s saw the advent of the inorganic chemistry of these compounds. The isolation and characterization of (initially) silicon derivatives led rapidly to the development of an extensive literature of p-block and transition metal chemistry associated with both stabilized and nonstabilized ylides.However, the isolation and structural characterization of adducts of inorganic alkali metal salts and yiides. and of alkali metalated organic complexes with neutral phosphorus ylides has remained an unexplored area. This is surprising on two counts. Firstly, alkali metals are intimately associated with the generation of ylides from phosphonium halides. Secondly, the use of phosphorus-carbon ylides (1. where X = CH:) as neutral donors to early main group metals is only a small conceptual step from the use of isoelectronic phosphune oxide donors (1. where X = O) such as hexamethylphosphoramide [HMPA. I a]. This is a common Lewis base in the chemistry of alkali metal species, and its phosphorus-oxygen bond has been shown by ab initio calculations to possess ylidic charac-ter. We now report the crystal structure, solution behavior, and MO calculations for a simple, nonstabilized ylide complex of a lithium amide, the first neutral ylide complex of an alkali metal compound to be characterized in the solidstate.