A Search for / Equilibria in Chiral Rhenium Imine Complexes of the Formula [(5-C5H5)Re(NO)(PPh 3)(N(H)=C(CF3)X)]+TfO-: Investigation of Electronic Effects upon the Binding Mode
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abstract
Reaction of the amido complex (5-C5H5)Re(NO)(PPh 3)(NH2) (2) and hexafluoroacetone gives the methyleneamido complex (5-C5H5)Re(NO)(PPh 3)(N=C(CF3)2) (3, 58%). Addition of TfOH to 3 yields the -imine complex [(5-C5H5)Re(NO)(PPh 3)(1-N(H)=C(CF3)2)] +TfO- (4, 96%). Similar reactions of 2 with trifluoroacetaldehyde and then TfOH give the -imine complex [(5-C5H5)Re(NO)(PPh 3)(1-N(H)==C(CF3)H)]+TfO - (5, 78%) and sometimes small amounts of the corresponding -trifluoroacetaldehyde complex. Reaction of 5 and t-BuO-K+ gives the methyleneamido complex (5-C5H5)Re(NO)(PPh 3)(N=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 -binding modes. No evidence is observed for isomers of 4 or 5. Analogous O=C(CF3)X complexes give exclusively isomers, and rationales are discussed. Reactions of 3 or 6 with MeOTf and heteroatom electrophiles are also described.
