Diphenylacetylene complexes of tungsten containing π-acceptor ligands

Abstract

Reaction of PhC₂Ph with [WCl₂(PhC₂Ph)(PMe₃)₃] gave [WCl₂(PhC₂Ph)₂(PMe₃)₂]1 for which IR and NMR spectral data indicated cis-chloro ligands. trans phosphines and mutually-cis diphenylacetylene ligands. This geometry was confirmed by X-ray crystallography. The average W–C bond lengths are 2.071 (3)Å. The ¹³C NMR spectrum showed the acetylenic carbon resonance at δ 185.45. The alkynes HC₂H and PhC₂H reacted with [WCl₂(PhC₂Ph)(PMe₃)₃] giving [WCl₂(PhC₂Ph)(HC₂H)(PMe₃)₂]2 and [WCl₂(PhC₂Ph)(PhC₂H)(PMe₃)₂]3. The phenylacetylene ligand gave rise to asymmetry in complex 3 leading to an AB system ³¹P-{¹H} NMR spectrum. Different values of ¹J(PW) indicated small differences in the W–P bonding. Alkyl-substituted acetylenes did not react cleanly with [WCl₂(PhC₂Ph)(PMe₃)₃]. The complexes [WCl₂(PhC₂Ph)(PrⁿC₂Me)(PMe₃)₂]4 and [WCl₂(PhC₂Ph)(MeC₂Me)(PMe₃)₂]5 were prepared by sodium–mercury amalgam reduction of [WCl₃(PhC₂Ph)(PMe₃)₂] with hex-2-yne or but-2-yne present but were not particularly stable in solution. Sodium-mercury amalgam reduction of [WCl₃(PhC₂Ph)(PMe₃)₂] under ethylene or propene gave [WCl₂(PhC₂Ph)(CH₂CH₂)(PMe₃)₂]6 or [WCl₂(PhC₂Ph)(MeCHCH₂)(PMe₃)₂]9. Complex 9 was unstable in solution and was characterised by NMR spectroscopy. The ¹³C NMR acetylenic carbon resonances in complexes 6 and 9 are at δ 218.11 and 218.82. Reduction of [WCl₃(PhC₂Ph)(PMe₃)₂] under cis- or trans-but-2-ene or 2-methylpropene afforded [WCl₂(PhC₂Ph)(PMe₃)₃] and [WCl₂(PhC₂Ph)(PMe₃)₂]_x10 as characterised by NMR spectroscopy. Reduction of [WCl₃(PhC₂Ph)L₂](L = PMe₃or PMePh₂) under CO gave [WCl₂(PhC₂Ph)(CO)(PMe₃)₂]11 and [WCl₂(PhC₂Ph)(CO)(PMePh₂)₂]12 for which X-ray crystal structure determinations showed cis-chloro ligands, trans phosphines and mutually-cis PhC₂Ph and CO ligands. The W–C and C–C bond lengths for complex 11 are 2.009(5), 2.024(5) and 1.341 (6)Å, respectively. Overall the reactions showed that the diphenylacetylene ligand in these complexes acts like an organoimido or oxo ligand.