Molekulare Aggregate von donorsolvensfreien Lithiumsilylphosphaniden mit dem Triphenylsilyl- und Triisopropylsilyl-Substituenten am Phosphor

Molecular Aggregates of Donorsolvent-Free Lithiumsilylphosphanides with the Triphenylsilyl- and Triisopropylsilyl-Substituent at Phosphorus The lithiumphosphanides 6 and 7 were formed by lithiation of the bulky disilylphosphanes 1 a and 1 b with nBuLi in toluene as solvent. 1 a and 1 b are accessible in high yield by simple salt-elimination reactions, following a one-pot procedure. X-ray crystal structure determinations revealed that 6 exists as an donorsolvent-free dimer, whereas, surprisingly, 7 is a mixed tetrameric aggregate bearing three molecules LiP(SiiPr₃)₂ and one molecule LiPH(SiiPr₃). The aggregate building block LiPH(SiiPr₃) is obviously formed upon a nucleophilic Si? P bond cleavage in 1 b under the reaction conditions used for the lithiation. The tetramer 7 shows a unprecedented structure of a lithiumphosphanide: The lithium atoms are twofold-coordinated and exhibit extremely large endocyclic angles (153.4–164.5°). Furthermore the P₄Li₄ heterocyclooctane framework ist strongly flattened and the bulky silyl groups obviously suppress a rearrangement to a normal ladder-like structure. The flattened pyramidal coordination of the P atom, which bears one SiiPr₃ group and one H atom, is probably due to steric effects.