MOLECULAR AGGREGATES OF DONORSOLVENT-FREE LITHIUMSILYLPHOSPHANIDES WITH THE TRIPHENYLSILYL-SUBSTITUENT AND TRIISOPROPYLSILYL-SUBSTITUENT ATPHOSPHORUS

The lithiumphosphanides 6 and 7 were formed by lithiation of the bulky disilylphosphanes la and Ib with nBuLi in toluene as solvent. la and Ib are accessible in high yield by simple salt-elimination reactions, following a one-pot procedu re. X-ray crystal structure determinations revealed that 6 exists as an donorsolvent-free dimer, whereas, surpri singly, 7 is a mixed tetrameric aggregate bearing three molecules LiP( SiiPr(3))(2) and one molecule LiPH(SiiPr(3)). The aggregate building b lock LiPH(SiiPr(3)) is obviously formed upon a nucleophilic Si-P bond cleavage in Ib 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 larg e endocyclic angles (153.4-164.5 degrees). Furthermore the P4Li4 heter ocyclooctane framework ist strongly flattened and the bulky silyl grou ps obviously suppress a rearrangement to a normal ladder-like structur e. The flattened pyramidal coordination of the P atom, which bears one SiiPr(3), group and one H atom, is probably due to steric effects.