SYNTHESIS, STRUCTURE, AND REACTIVITY OF CHIRAL RHENIUM ALKENE COMPLEXES OF THE FORMULA [(ETA-5-C5H5)RE(NO)(PPH3)(H2C=CHR)]+X-

Reaction of the dichloromethane complex [(η-C5H5)Re(NO)(PPh3)(ClCH2Cl)]+BF4-and monosubstituted alkenes gives [(η5-C5H5)Re(NO)(PPh3)(H2C=CHR)]+BF4-(3+BF4-, 89-91%; R = CH3 (a), n-C3H7 (b), CH2C6H5 (c), C6H5 (d)) as (73-62):(27-38) mixtures of (RS,SR)/(RR,SS) diastereomers. Reactions of η1-allyl complexes (E)-(η5-C5H5)Re(NO)(PPh3)(CH2CH=CHR’) (4; R’ = H (a), C6H5 (c)) and electrophiles E+X-(E+ = H+, D+, R+) give alkene complexes [(η5-C5H5)Re(NO)(PPh3)(H2C=CHCHER’)]+X- (79-92%) as (75-60):(25-40) mixtures of diastereomers. When (RS,SR)/(RR,SS)-3a-c+BF4- are heated (C6H5Cl, 95-100 °C), they equilibrate to ≃95:5 mixtures of diastereomers. Rationales are given for the modest kinetic and high thermodynamic stereoselectivities. The crystal structure of independently synthesized (RR,SS)-3c+PF6- shows the =CHR alkene terminus to be approximately anti to the PPh3 ligand, with R syn to the C5H5 ligand. NOE experiments show that the =CHR terminus is anti to the PPh3 ligand in both diastereomers of 3+X- in solution. Variable-temperature13C NMR spectroscopy gives ΔG‡369K = 16.4 kcal/mol for Re-(C-C) rotation in the ethylene complex [(η5-C5H5)Re(NO)(PPh3)(H2C=CH2)]+PF6-. Also described are substitution reactions of 3+X-, a detailed analysis of the spectroscopic properties of 3+X-, and high 1,4-asymmetric induction in the reaction of 4c and CF3SO3D to give 3c-d1+CF3S03-. © 1990, American Chemical Society. All rights reserved.