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 K-2[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.