Nucleophilic additions to the chiral rhenium alkene complexes [Re(η5-C5H5)(NO)(PPh3)(H2CCHR)]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)].