Evaluation of the 2,6-diisopropylphenylimido ligand as a steric force in d1 and d2 monomeric octahedral complexes of tungsten

Abstract

Reduction of [{WCl₄(NC₆H₃Prⁱ₂-2,6)}₂] with 2 equivalents of Na–Hg amalgam in the presence of phosphines gave the d¹ complexes [WCl₃(NC₆H₃Prⁱ₂-2,6)L₂](L = PMe₃, PMe₂Ph or PMePh₂). The crystal structure of [WCl₃(NC₆H₃Prⁱ₂-2,6)(PMe₃)₂]1 shows the 2,6-diisopropylphenylimido ligand exerts a greater trans influence than a phenylimido ligand but only slightly more steric pressure. Solutions of complex 1 react with air to give [WCl₃(NC₆H₃Prⁱ₂-2,6)(PMe₃)(OPMe₃)]2 for which the crystal structure shows the OPMe₃ ligand lying trans to the imido ligand. Reduction of [{WCl₄(NC₆H₃Prⁱ₂-2,6)}₂] with 4 equivalents of Na–Hg amalgam in the presence of phosphines gave the d² complexes [WCl₂(NC₆H₃Prⁱ₂-2,6) L₃](L = PMe₃ or PMe₂Ph). Complex [WCl₂(NC₆H₃Prⁱ₂-2,6)(PMe₃)₃]3 reacts with alkynes L′ to give the complexes [WCl₂(NC₆H₃Prⁱ₂-2,6) L′(PMe₃)₂](L′= PhC₂Ph, MeC₂Me or PhC₂H) for which ¹H and ¹³C-{¹H} NMR spectral data were obtained. The crystal structure of [WCl₂(NC₆H₃Prⁱ₂-2,6)(PhC₂H)(PMe₃)₂]6 shows cis-chloro ligands, trans-phosphines and mutually cis-imido and alkyne ligands. The C(6) isopropyl group rotates to minimise the isopropyl group and PhC₂H interaction. The complex [WCl₂(NC₆H₃Prⁱ₂-2,6)(PhC₂Ph)(PMe₂Ph)₂] can be prepared but not [WCl₂(NC₆H₃Prⁱ₂-2,6)(PhC₂Ph)(PMePh₂)₂]. Reduction of [WCl₃(NC₆H₃Prⁱ₂-2,6)(PMe₃)₂](L′= CH₂CH₂ or CH₂CHMe). A more bulky organoimido ligand or a large phosphine is needed to exert steric pressure in all the complexes prepared.