Anionic manganese tricarbonyl complexes of C7 and C8 cyclic dienes and polyenes: Synthesis and reactions with electrophiles

Article abstract of DOI:10.1021/om00102a005

Reduction of (methallyl)Mn(CO)₄ with bis(2-methoxyethoxy)AlH₂^- in the presence of 1,3-cycloheptadiene, 1,3-cyclooctadiene, 1,3,5-cycloheptatriene, or 1,3,5,7-cyclooctatetraene yields (η⁴-cycloheptadiene)Mn(CO)₃^- (1a), (η⁴-cyclooctadiene)Mn(CO)₃^- (1b), (η⁴-cycloheptatriene)Mn(CO)₃^- (1c), and (η⁴-cyclooctatetraene)-Mn(CO)₃^- (1d), which were isolated as their PPN⁺ salts. Protonation of 1a and 1b gives the agostic complexes (cycloheptenyl)Mn(CO)₃ (2a) and (cyclooctenyl)Mn(CO)₃ (2b) whose dynamic behavior and CO trapping reactions are reported. Protonation or methylation of 1c gives (cycloheptadienyl)Mn(CO)₃ or (6-exo-methylcycloheptadienyl)Mn(CO)₃, respectively. Protonation of Id gives the monocyclic complex (η⁵-cyclooctatrienyl)Mn(CO)₃ (8) which is in equilibrium at 25°C via electrocyclic ring closure with (η⁵-bicyclo[5.1.0]octadienyl)Mn(CO)₃ (10). Monocyclic 8 is fluxional and exhibits a degenerate 1,3-Mn shift, ΔG? = 12.6 kcal/mol. Addition of D⁺ to Id established exo D⁺ (H⁺) attack. Methylation of 1d gives (7-exo-methylcyclooctatrienyl)Mn(CO)₃ (9) for which an X-ray structural analysis is reported.