Synthesis of Optically Active Tetrahedral Clusters through Ester Exchange Catalyzed by Lipase

Reactions of the monoanions [(η⁵-C₅H₄R)M₂(CO)₃]^- with ArCH(Me)COOCH₂C₂H(μ₃-C)Co₂(CO)₆ (4) in THF at 60 °C gave the functional cluster derivatives ArCH(Me)COOCH₂C₂H(μ₃-C)CoM₂(CO)₅(η⁵-C₅H₄R) (1a−d:  M₂ = Mo, W; R = CO₂Me, C(O)Me). Similarly, reactions of {[(η⁵-C₅H₄)C(O)OCH₂(OH)CH₃]M₂(CO)₃}^- (M₂ = Mo, W) with (μ₃-S)M₁Co₂(CO)₉ (M₁ = Fe, Ru) gave the tetrahedral metal clusters (μ₃-S)CoM₂M₁(CO)₈[(η⁵-C₅H₄)C(O)OCH₂(OH)CH₃] (8a−d:  M₁ = Fe, Ru; M₂ = Mo, W). Treatment of the two metal clusters 1a−d and three metal clusters 8a−d with methanol respectively in the presence of lipase at 50 °C for 1 h afforded the optically active cluster derivatives HOCH₂C₂H(μ₃-C)CoM₂(CO)₅(η⁵-C₅H₄R) (6a−d:  M₂ = Mo, W; R = CO₂Me, C(O)Me) and (μ₃-S)CoM₂M₁(CO)₈[(η⁵-C₅H₄)C(O)OCH₃] (9a−d: M₁ = Fe, Ru; M₂ = Mo, W). The products were separated by silica gel chromatography. The conditions of the lipase reactions were discussed. All the compounds in the global process were characterized by element analysis, and IR and ¹H NMR spectroscopy. The structures of clusters 8c and 9c have been determined by single-crystal X-ray diffraction.