Synthesis and dynamic nuclear magnetic resonance studies of co-ordinatively unsaturated alkyne complexes of tungsten(II)

Abstract

Complexes [{WBr₂(CO)(RCCR′)₂}₂] react with NaS₂PMe₂, NaS₂CNMe₂, or Tl(2-SC₅H₄N) to give monoalkyne [W(LL′)₂(CO)(RCCR′)](R = R′= Me, LL′= S₂CNMe₂ or 2-SC₅H₄N; R = Ph, R′= Me, LL′= S₂CNMe₂ or S₂PMe₂; R = R′= Ph, LL′= S₂PMe₂) or bis-alkyne derivatives [W(2-SC₅H₄N)₂(PhCCPh)₂]. Dynamic n.m.r. studies of the monoalkyne complexes reveal fluxional behaviour due to propeller rotation of the co-ordinated alkyne (R = R′= Me, LL′= S₂CNMe₂ or 2-SC₅H₄N) whereas with R = Ph, R′= Me or Ph, LL′= S₂PMe₂ an alternative process attributed to dechelation of the chelate ligand is also observed. The S₂PMe₂ derivatives react with ligands L = CNBu^t, PMe₂Ph, or P(OMe)₃ to give 1 : 1 adducts [W(S₂PMe₂)₂(CO)(PhCCR)(L)][R = Me, L = CNBu^t, PMe₂Ph, or P(OMe)₃; R = Ph, L = PMe₂Ph or P(OMe)₃] some of which, L = P(OMe)₃, dissociate in solution to give the equilibrium (i). ¹³C N.m.r. studies of [W(S₂PMe₂)₂(CO)(PhCCMe){P(OMe)₃}] are [W(S₂PMe₂)₂(CO)(PhCCR)(L)]⇌[W(S₂PMe₂)₂(CO)(PhCCR)]+ L (i) interpreted in terms of a six-co-ordinate structure containing one monodentate and one bidentate S₂PMe₂ ligand, rather than a seven-co-ordinate bis-chelate structure.