Reactions of the Re(CO)₃(H₂O)₃⁺ synthon with monodentate ligands under aqueous conditions

The reactions of ammonia, pyridine (py), N-methyl imidazole (N-Melm), tetrahydrothiophene (tht), and piperidine (pip) with Re(CO)₃(H ₂O)₃⁺, 1⁺, were investigated employing aqueous conditions under atmospheric dioxygen. The reaction of [1]Br in aqueous ammonia led to [Re(CO)₃(NH₃)₃]Br ([2]Br) as the only product isolated. For the aqueous reactions of [1]Br with py, N-Melm, and tht, mixtures of products are formed because of competition between the bromide and added ligand, even when the ligand is present in excess. Substitution of the PF₆^- anion for Br^- leads to the clean formation of [Re(CO)₃L₃][PF₆] ([3][PF₆]-[5][PF₆]) for py, N-Melm, and tht, respectively, as the only products observed. Reaction of [1][PF₆] with pip produces the dimeric species, (pip)(CO)₃Re(μ-OH) ₂Re(CO)₃(pip), 6. Reactions of [1]Br were also performed in methanol for comparison purposes. The reaction with pip in this solvent led to the analogous dimer, (pip)(CO)₃Re(μ-OMe)₂Re(CO) ₃(pip), 7; however, reactions with py, N-Melm, and tht gave Re(CO)₃L₂Br, 8-10, respectively, as the only products. The crystal structures of compounds [2]Br-10 are reported.