SYNTHESIS, STRUCTURE, AND REACTIVITY OF CHIRAL RHENIUM CYCLOALKENE COMPLEXES OF THE FORMULA [(ETA-5-C5H5)RE(NO)(PPH3)(CH = CH(CH2)N-2)]+BF4- - FACILE VINYLIC DEPROTONATION OF A COORDINATED ALKENE

Reactions of [(eta-5-C5H5)Re(NO)(PPh3)(ClC6H5)]+BF4- and activated CH = CH(CH2)n-2(n = 5, a; 6, b; 7, c; 8, d) give cycloalkene complexes [(eta-5-C5H5)Re(NO)(PPh3)(activated CH = CH(CH2)n-2)]+ BF4- (6a - d, 94 to 79%). A crystal structure of the methylcyclopentadienyl analog of 6a shows the [GRAPHICS] plane and Re - PPh3 bond to be coplanar, with the vinyl protons syn to the cyclopentadienyl ligand. Reaction of 6a and tBuO-K+ leads to the vinyl complex (eta-5-C5H5)Re(NO)(PPh3)(activated C = CH(CH2)3) (9a, 90%) instead of expected allyl complex (eta-5-C5H5)Re(NO)(PPh3)(activated CH-CH = CH(CH2)2) (10a). Analogous reactions of 6b - d give varying mixtures of 9b - d/10b - d. HBF4 . OEt2 and 9a react to form the cyclopentylidene complex [(eta-5-C5H5)Re(NO)(PPh3)(= activated C(CH2)4)]+BF4- (11+ BF4-, 96%), the stability of which precludes any intermediacy in the deprotonation of 6a. A crystal structure of 11+ PF6- 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+ BF4- (DELTA-G] (110-degrees-C) greater-than-or-equal-to 19 kcal/mol).