Synthesis, properties, and molecular structures of 2,3,4,5-tetraethylphospholides of the alkali metals sodium, potassium, rubidium, and cesium as well as metathesis reactions of the potassium derivatives with tin(II) chloride and gallium(III) chloride

The reduction of chloro-2,3,4,5-tetraethylphosphole with sodium, potassium, rubidium, and cesium in THF or 1,2-dimethoxyethane (DME) yields nearly quantitatively after recrystallization from a DME solution the corresponding alkali metal 2,3,4,5-tetraethylphospholides (DME)Na(PC4Et4) (1), K(PC4Et4) (2), (DME)Rb(PC4Et4) (3), and (DME)Cs(PC4Et4) (4). If the chloro-2,3,4,5-tetraethylphosphole still contains zirconocene dichloride from its preparation heteroleptic (THF)CsC5H5.Cs(PC4Et4) (5) precipitates. Whereas the sodium derivative 1 crystallizes as a dimer, the phospholides 2 to 4 of the heavier alkali metals crystallize as one-dimensional polymers. Due to the size of the potassium cation no additional ether ligands are coordinated to this metal atom and a linear column precipitates, whereas for the Rb and Cs compounds the DME complexes are formed thus leading to a zig-zag chain. The substitution of half of the phospholide anions by cyclopentadienide ligands in 5 leads to a three-dimensional network in the crystalline state. The metathesis reaction of the potassium derivative 2 with GaCl3 and SnCl2 yields dimeric (DME)K[(mu-Cl)(4)Ga-2(PC4Et4)(3)] (6) and monomeric Sn(PC4Et4)(2) (7), respectively. Whereas in the alkali metal phospholides 1 to 5 a high degree of delocalization of the anionic charge within the five-membered ring and a eta(5)-coordination are realized, the 2,3,4,5-tetraethylphospholide anion is sigma-bonded to gallium(III) in 6 and to tin(II) in 7.