2,6-Diisopropylphenylimido and diphenylacetylene complexes of tungsten containing the bidentate ligands 4,4′-dimethyl-2,2′-bipyridine and 1,2-bis(diphenylphosphino)ethane

Abstract

Sodium–mercury amalgam reduction of [{WCl₄(NC₆H₃Prⁱ₂-2,6)}₂] in the presence of 4,4′-dimethyl-2,2′-bipyridine (dmbipy) or 1,2-bis(diphenylphosphino)ethane (dppe) gave the d¹ complexes [WCl₃(NC₆H₃Prⁱ₂-2,6)(dmbipy)]1 and [WCl₃(NC₆H₃Prⁱ₂-2,6)(dppe)]2. A crystal-structure determination of complex 2 shows the three chloro ligands in a mer arrangement and the dppe ligand phosphorus atoms lying trans to one chloro ligand and also the imido ligand. The W–P bond trans to the chloro ligand is normal [2.550(2)Å] whereas the W–P bond trans to the imido ligand is very long [2.765(2)Å]. One phenyl group of dppe rotates to accommodate an isopropyl group of the imido ligand. Sodium–mercury amalgam reduction of [{WCl₄(PhC₂Ph)}₂] in the presence of dmbipy gave [WCl₃(PhC₂Ph)(dmbipy)] which the W–Cl stretches suggest is the mer trichloride. However, an IR spectrum of the product of standing [{WCl₄(PhC₂Ph)}₂] and dmbipy in tetrahydrofuran indicates the fac isomer. A reduction of [{WCl₄(PhC₂Ph)}₂] in the presence of dppe gave [WCl₃(PhC₂Ph)(dppe)] for which the mer isomer is preferred. The dppe complexes do not give characterisable complexes on further reduction in the presence of diphenylacetylene, ethylene or CO. Sodium mercury amalgam reduction of 1 in the presence of diphenylacetylene gave [WCl₂(NC₆H₃Prⁱ₂-2,6)(PhC₂Ph)(dmbipy)] which IR and NMR spectra indicate has an asymmetric structure where the alkyne ligand is a two-electron donor. Reductions of complex 1 under ethylene or CO gave [WCl₂(NC₆H₃Prⁱ₂-2,6)(CH₂CH₂)(dmbipy)] and [WCl₂(NC₆H₃Prⁱ₂-2,6)(CO)(dmbipy)] both of which consist of several isomers.