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 = CNBut, PMe2Ph, or P(OMe)3 to give 1 : 1 adducts [W(S2PMe2)2(CO)(PhCCR)(L)][R = Me, L = CNBut, 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.