A Search for π/σ Equilibria in Chiral Rhenium Imine Complexes of the Formula [(η⁵-C₅H₅)Re(NO)(PPh₃)(N(H)C(CF₃)X)]⁺TfO^-:  Investigation of Electronic Effects upon the Binding Mode

Abstract

Reaction of the amido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;H(2)) (2) and hexafluoroacetone gives the methyleneamido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;=C(CF(3))(2)) (3, 58%). Addition of TfOH to 3 yields the sigma-imine complex [(eta(5)-C(5)H(5))Re(NO)(PPh(3))(eta(1)-N(H)=C(CF(3))(2))](+)TfO(-) (4, 96%). Similar reactions of 2 with trifluoroacetaldehyde and then TfOH give the sigma-imine complex [(eta(5)-C(5)H(5))Re(NO)(PPh(3))(eta(1)-N(H)=C(CF(3))H)](+)TfO(-) (5, 78%) and sometimes small amounts of the corresponding pi-trifluoroacetaldehyde complex. Reaction of 5 and t-BuO(-)K(+) gives the methyleneamido complex (eta(5)-C(5)H(5))Re(NO)(PPh(3))(&Numl;=C(CF(3))H) (6, 82%). The IR and NMR properties of 3-6 are studied in detail. The (13)C NMR spectra show C=N signals (157-142 ppm) diagnostic of sigma-binding modes. No evidence is observed for pi isomers of 4 or 5. Analogous O=C(CF(3))X complexes give exclusively pi isomers, and rationales are discussed. Reactions of 3or 6 with MeOTf and heteroatom electrophiles are also described.

Synthesis of Rhenium Complexes That Contain the [(C6F5NCH2CH2)3N]3- Ligand

“…We conclude that [N 3 N F ]Re complexes that contain rhenium in the “mid” oxidation states (Re(III), Re(IV), and Re(V)) are viable. This finding is somewhat surprising in view of the rarity of monomeric rhenium complexes that contain more than one amido ligand. − There appears to be some preference for Re(III) complexes that contain η 2 -bound ligands over Re(V) tautomers, perhaps in part as a consequence of the ability of the d 4 metal for back-bonding, balanced with a steric pressure to maintain the trigonal coordination pocket. The current entry into [N 3 N F ]Re chemistry relies on an indirect synthesis of a low-spin d 3 starting material ( 2 ) that appears to be easily reduced.…”

Synthesis, Characterization and Reactivity of New (μ‐Aminocarbyne)diruthenium Complexes Containing Alkynylimino Ligands

“…[4] Among the latter, some interesting examples are: a) oxidation of coordinated amines; [5] b) condensation of coordinated amines with free aldehydes and ketones; [6] c) reduction of coordinated nitriles. [7,8] Only in a limited number of cases the imino ligands have been obtained via addition of a carbon nucleophile to coordinated nitriles.…”

Formation of Imine−Vinylidene−Osmium(II) Derivatives by Hydrogen Transfer from Alkenyl Ligands to Azavinylidene Groups in Alkenyl−Azavinylidene−Osmium(IV) Complexes

“…The benzophenone imine derivatives M(CO) 5 (NHCPh 2 ) (M = Cr, W) have been synthesized by reaction of M(CO) 5 (CPh 2 ) with trimethylsilyl azide . Gladysz and co-workers have reported imine complexes of the type [Re(η 5 -C 5 H 5 )(NO)(NHCRR‘)(PPh 3 )][CF 3 SO 3 ], which are obtained by displacement of triflate by the free imine or by addition of nucleophiles to cationic nitrile complexes followed by protonation . Complexes Os(C 2 Ph) 2 (CO)(NHCPh 2 )(P i Pr 3 ) 2 and MHCl(CO)(NHCPh 2 )(P i Pr 3 ) 2 (M = Ru,19a Os 19b ) have been obtained by addition of benzophenone imine to the corresponding five-coordinate precursors.…”