SYNTHESIS, STRUCTURE, AND REACTIVITY OF CHIRAL RHENIUM N-PYRROLYL COMPLEXES [(ETA(5)-C5H5)RE(NO)(PPH(3))(NCR=CR'CH=CH)] - REGIOCHEMISTRY OF ELECTROPHILIC ADDITION AND UNPRECEDENTED REARRANGEMENTS TO CARBON-LIGATED SPECIES

Reaction of [{Re}(OTf)] (1; {Re}=(eta(5)-C5H5)Re(NO)(PPh(3))) and potassium pyrrolide gives the N-pyrrolyl complex [{Re}(NCH=CHCH=CH)] (2, 88%). Reactions of 2 with (CF3CO)(2)O/N(C2H5)(3) and CH3O2CC=CCO2CH3 give 3- and 2-substituted pyrrolyl complexes [{Re}(NCR=CR'CH=CH)], respectively (3, R/R'=H/COCF3, 77%; 5, R/R'=C(CO2CH3)=CHCO2CH3/H, 69-87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF4. OEt(2) give the 2H-pyrrole adducts [{Re}(N=CHCH=CHCH2)](+)X(-) (7(+)X(-); 89-83%). At 0-25 degrees C in CH2Cl2, these rearrange to the carbon-ligated tautomers [{Re}(C=NHCH=CHCH2)](+)X(-) (8(+)X(-)) and then [{Re}-(C=NHCH2CH=CH)](+)X(-) (9(+)X(-); 72-96 h, 90-96%). Reaction of 1 and pyrrole in refluxing toluene gives 8(+)TfO(-) and then 9(+)TfO(-) (92%). However, 1 and pyrrole react too slowly in CH2Cl2 to be intermediates in the conversion of 7(+)TfO(-) to 9'TFO-. Reaction of 9(+)TfO(-) and KH gives the C-pyrrolyl complex [{Re}(C=CHCH=HNCH)] (68%), which adds TfOH to give 9(+)TfO(-). Mechanistic aspects of the preceding reactions are discussed. The crystal structures of 2 and 9(+)TfO(-) are determined, and the NC4Hx ligand conformations analyzed with extended Huckel MO calculations.