Chemistry surrounding chiral tungsten(II) eta(1)-imine complexes

Chiral tungsten(II) eta(1)-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(NH(2)CH(2)CHMePh)][I-3] (4d), neutral amido complex Tp'(CO)(PhC=CMe)W(NHCHMeEt) (1a), and neutral azavinylidene complex Tp'(Co)(PhC=CMe)W(N=CMePh) (3b).