Chemistry Surrounding Chiral Tungsten(II) η¹-Imine Complexes

Chiral tungsten(II) η¹-imine complexes [Tp‘(CO)(PhC⋮CMe)W(NHCRR‘)]⁺ (Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) have been prepared by oxidation of the corresponding amido complexes Tp‘(CO)(PhC⋮CMe)W(NHCHRR‘) (R/R‘ = Ph/Ph, Ph/Me, Me/Et, and H/CHMePh) with elemental iodine. These oxidations also result in formation of amine complexes which have been independently synthesized. Oxidation in the presence of a weak base suppresses amine formation. However, when R = Ph, deprotonation of the imine product forms the neutral azavinylidene complex Tp‘(CO)(PhC⋮CMe)W(NCRR‘). Protonation of the azavinylidene complex provides a clean route to the desired imine complex. Crystal structures of a representative complex from each category of nitrogen donor ligand have been determined:  cationic imine complex [Tp‘(CO)(PhC⋮CMe)W(NHCMeEt)][BAr‘₄] (2a), cationic amine complex [Tp‘(CO)(PhC⋮CMe)W(NH₂CH₂CHMePh)][I₃] (4d), neutral amido complex Tp‘(CO)(PhC⋮CMe)W(NHCHMeEt) (1a), and neutral azavinylidene complex Tp‘(CO)(PhC⋮CMe)W(NCMePh) (3b).