Synthesis, Structure, and Reactivity of Chiral Rhenium Cycloalkene Complexes of the Formula ; Facile Vinylic Deprotonation of a Coordinated Alkene

Abstract

Abstract Reactions of [(η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(ClC 6 H 5 )] + BF − 4 and ( n = 5, a ; 6, b ; 7, c ; 8, d ) give cycloalkene complexes ( 6a – d , 94 to 79%). A crystal structure of the methylcyclopentadienyl analog of 6a shows the Re – plane and Re – PPh 3 bond to be coplanar, with the vinyl protons syn to the cyclopentadienyl ligand. Reaction of 6a and t BuO − K + leads to the vinyl complex ( 9a , 90%) instead of expected allyl complex ( 10a ) Analogous reactions of 6b – d give varying mixtures of 9b – d/10b – d . HBF 4 · OEt 2 and 9a react to form the cyclopentylidene complex ( 10 + BF − 4 , 96%), the stability of which precludes any intermediacy in the deprotonation of 6a . A crystal structure of 11 + PF − 6 shows the ReCC planes to be perpendicular to the Re – P bond. Spectroscopic features of compounds 6 are analyzed in detail, and NMR data show a high barrier to cyclopentylidene ligand rotation in 11 + BF − 4 (ΔG≢ (110°C) ≥ 19 kcal/mol).