Synthesis, Structure, and Reactivity of Chiral Rhenium <i>N</i>‐Pyrrolyl Complexes Regiochemistry of Electrophilic Addition and Unprecedented Rearrangements to Carbon‐Ligated Species

Abstract

Abstract Reaction of [{Re}(OTf)] ( 1 ; {Re} — (η 5 ‐C 5 H 5 )Re(NO)(PPh 3 ) and potassium pyrrolide gives the N ‐pyrrolyl complex magnified image 2 , 88%). Reactions of 2 with (CF 3 CO) 2 O/N(C 2 H 5 ) 3 and CH 3 O 2 CC=CCO 2 CH 3 give 3‐ and 2‐substituted pyrrolyl complexes magnified image respectively (3, R/R′ = H/COCF 3 , 77%; 5, R/R′ = C(CO 2 CH 3 )=CHCO 2 CH 3 /H, 69–87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF 4 ·OEt 2 give the 2 H ‐pyrrole adducts magnified image + X − (7 + X − ; 89–83%). At 0–25°C in CH 2 Cl 2 , these rearrange to the carbon‐ligated tautomers magnified image + X − (8 + X − ) and then magnified image + 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 CH 2 Cl 2 to be intermediates in the conversion of 7 + TfO − to 9 + TfO − . Reaction of 9 + TfO − and KH gives the C ‐pyrrolyl complex magnified image (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 NC 4 H x ligand conformations analyzed with extended Hückel MO calculations.