Nucleophilic additions to the chiral rhenium alkene complexes [Re(η5-C5H5)(NO)(PPh3)(H2CCHR)]BF4(R = H, Me, CH2CH2Me, Ph or CH2Ph): regio-, diastereo- and enantio-selectivities

Abstract

Reactions of alkene complexes [Re(η⁵-C₅H₅)(NO)(PPh₃)(H₂CCHR)]BF₄1(R = H a, Me b, CH₂CH₂Me c, Ph d or CH₂Ph e) and LiCuMe₂ in tetrahydrofuran (thf) at –80 °C gave the primary, β-branched alkyl complexes [Re(η⁵-C₅H₅)(NO)(PPh₃)(CH₂CHMeR)]2(79–99%). No secondary alkyl complexes derived from additions to the unsubstituted CH₂ termini were detected. Product diastereomer and enantiomer ratios matched those of the reactants. Thus, the additions are regiospecific, diastereospecific and enantiospecific. A chemical correlation involving [Re(η⁵-C₅H₅)(NO)(PPh₃){CH₂CH(CD₃)Me}] and a crystal structure determination [(SR,RS)-2e·0.5C₆H₁₄] show that attack occurs on the CC face anti to the rhenium. Reactions of 1a or 1b(in thf) with NaOMe–MeOH gave predominantly the 2-methoxyalkyl complexes [Re(η⁵-C₅H₅)(NO)(PPh₃){CH₂CH(OMe)R}](R = H 4a or Me 4b)(92–97%). Analogous reactions of 1c or 1d gave 81–77:19–23 mixtures of 4c or 4d and the alkenyl complexes (E)-[Re(η⁵-C₅H₅)(NO)(PPh₃)(CHCHR)](85–71%). A similar reaction of 1e gave mainly the allyl complex [Re(η⁵-C₅H₅)(NO)(PPh₃)(CH₂CHCHPh)].