SYNTHESIS, STRUCTURE, AND REACTIVITY OF CHIRAL RHENIUM IMINE AND METHYLENEAMIDO COMPLEXES OF THE FORMULAS [(ETA-5-C5H5)RE(NO)(PPH3)(ETA-1-N(R'')=C(R)R']+TFO- AND (ETA-5-C5H5)RE(NO)(PPH3)(N=C(R)R')

Three syntheses of sigma-imine complexes [(eta5-C5H5)Re(NO)(PPh3)(eta1-N(R'')=C(R)R')]+TfO-(2) have been developed. Reactions of (eta5-C5H5)Re(NO)(PPh3)(OTf) (1) and R'(R)C=NR'' (R/R'/R''=Ph/Ph/H(a), Me/Ph/H(b), H/Ph/Me(c); 25-110-degrees-C) give 2a-c(79-88%). Reactions of [(eta5-C5H5)Re(NO)(PPh3)(NH3)]+TfO- with n-BuLi and then R'(R)C=O give 2d-h (R/R'/R'' = Me/Me/H (d), Me/Et/H (e), (-CH2-)5/H (f), H/Ph/H (g), H/CH=CHMe/H (h; after TfOH addition); 56-87 %). Reactions of [(eta5-C5H5)Re(NO)(PPh3)(N=CR')]+TfO- with R- and then TfOH give 2b,i,j (R/R'/R'' = p-tol/p-tol/H (i), H/Me/H (j); 78-98%). Reaction of (+)-(S)-1 (98% ee) and c gives (+)-(S)-2c (98% ee; retention). Complexes 2b,c,e,g,h,j are obtained as (90-81):(10-19), 95:5, 68:32, >99:<1, >99:<1, and >99:<1 mixtures of E/Z N=C geometric isomers, which do not readily interconvert. Crystallization gives pure(E)-2b,c. Crystal structures of 2a and (E)-2c show identical N=C bond lengths (1.272(5)-1.275(5) angstrom) but opposite Re-N=conformations. Methyleneamido complexes (eta5-C5H5)Re(NO)(PPh3)(N=C(R)R') are isolated from reactions of 2a,b and t-BuO-K+ (R/R' = Ph/Ph, Me/Ph; 76-77%) or [(eta5-C5H5)Re(NO)(PPh3)(N=CR')]+TfO- and R-(R/R'=Me/Ph, p-tol/p-tol(8);55-61%). These undergo facile exchange of E/Z N=C substituents (8, DELTAG(double dagger)(181.4 K) = 8.9 kcal/mol) and N-methylation.