Synthesis of Ortho- and Meta-Re(I)-Metallocarboranes in Water

A series of metallocarboranes of the types rac-[M(CO)₃(η⁵-7-R-7,8-C₂B₉H₁₁)]^-, rac-[M(CO)₃(η⁵-7-R-8-R‘-7,8-C₂B₉H₁₁)]^-, and rac-[M(CO)₃(η⁵-7-R-7,9-C₂B₉H₁₁)]^- (M = Re) were prepared by reacting [NEt₄]₂[Re(CO)₃Br₃] or [Re(CO)₃(OH₂)₃]Br with the corresponding carboranes in the presence of aqueous solutions of either alkali metal or tetraalkylammonium fluoride salts. Carborane derivatives that were investigated included those containing pyridine, amino, carboxylic acid, carbohydrate, and aryl substituents. During the course of the research, it was discovered that Re metallocarboranes can be prepared directly from the respective closo-clusters under similar reaction conditions used with nido-carboranes. Reaction yields ranged from modest to excellent depending on the carborane isomer and the nature of the cage substituent(s). A crystal structure of an amine-substituted Re metallocarborane was obtained where the complex crystallized in the orthorhombic space group P2₁2₁2₁ with a = 8.982(2) Å, b = 11.563(3) Å, c = 16.811(4) Å, α = β = γ = 90°, V = 1746.1(7) ų, Z = 4, and R1 = 0.0684.