Bestimmung der Struktur von Phenyläthinyllithium in Lösung mittels Tieftemperatur‐NMR‐Spektroskopie

Abstract

The dimeric and tetrametic structures of complexes of phenylethinyllithium, as recently discovered by X‐ray analysis in the solid state, were also found to be present in solution. Tetrahydrofuran solutions of 1‐( 6 Li)‐[1‐ 13 C]‐2‐phenylethyne in the presence or absence of N , N , N ′, N ′‐tetramethylpolymethylenediamines show a pentuplett 13 C‐NMR signal [δ=140 ppm, J (C,Li)=8.2 Hz] from the labelled C‐atom at low temperatures (−95 to −110°). This proves the dimeric structure. When ( 6 Li)BuLi is added, a mixed dimer [(C 6 H 5 CCLi)(C 4 H 9 Li)] is formed [δ=142 ppm, J (C,Li) = 7.8 Hz]. This is converted to a mixed tetramer [(C 6 H 5 CCLi)(C 4 H 9 Li) 3 ] upon addition of larger amounts of ( 6 Li)BuLi, as concluded from a signal at δ = 133.5 ppm, J (C,Li) = 5.6 Hz. The multiplicity of this signal suggests that a static tetramer is present, in which the C‐atoms couple only with three next Li‐neighbors.