Ligand substitution reactions of the [ReX6]2− (X = Cl, Br) anions. Synthesis and crystal structure of novel oxalato complexes of rhenium(IV)

The reaction of K2[ReX6] (X = Cl, Br) with oxalic acid and triethylamine in dimethylformamide solution yields the substituted complexes [ReX4(ox)]2− and cis-[ReX2(ox)2]2−, which can be obtained separately depending on the amount of added amine. The crystal structures of (PPh4)2[ReBr4(ox)], cis-(PPh4)2[ReBr2(ox)2] and cis-(AsPh4)2[ReCl2(ox)2] have been determined by single-crystal X-ray diffraction. The anionic complexes are octahedral with only slight distortions. The direct isolation of the pure complexes as well as the formation of only the cis isomers – without the presence of trans isomers and/or [Re(ox)3]2− – is probably due to the kinetic inertness of Re(IV)–X bonds, which increases with the number of oxalato ligands bound to the metal ion.