A Search for π/σ Equilibria in Chiral Rhenium Imine Complexes of the Formula [(η5-C5H5)Re(NO)(PPh 3)(N(H)=C(CF3)X)]+TfO-: Investigation of Electronic Effects upon the Binding Mode Academic Article uri icon

abstract

  • Reaction of the amido complex (η5-C5H5)Re(NO)(PPh 3)(N̈H2) (2) and hexafluoroacetone gives the methyleneamido complex (η5-C5H5)Re(NO)(PPh 3)(N̈=C(CF3)2) (3, 58%). Addition of TfOH to 3 yields the σ-imine complex [(η5-C5H5)Re(NO)(PPh 3)(η1-N(H)=C(CF3)2)] +TfO- (4, 96%). Similar reactions of 2 with trifluoroacetaldehyde and then TfOH give the σ-imine complex [(η5-C5H5)Re(NO)(PPh 3)(η1-N(H)==C(CF3)H)]+TfO - (5, 78%) and sometimes small amounts of the corresponding π-trifluoroacetaldehyde complex. Reaction of 5 and t-BuO-K+ gives the methyleneamido complex (η5-C5H5)Re(NO)(PPh 3)(N̈=C(CF3)H) (6, 82%). The IR and NMR properties of 3-6 are studied in detail. The 13C NMR spectra show C=N signals (157-142 ppm) diagnostic of σ-binding modes. No evidence is observed for π isomers of 4 or 5. Analogous O=C(CF3)X complexes give exclusively π isomers, and rationales are discussed. Reactions of 3 or 6 with MeOTf and heteroatom electrophiles are also described.

author list (cited authors)

  • Stark, G. A., & Gladysz, J. A.

publication date

  • December 1996