Ligand substitution reactions of the [ReX 6] 2− (X = Cl, Br) anions. Synthesis and crystal structure of novel oxalato complexes of rhenium(IV)

Abstract

The reaction of K 2[ReX 6] (X = Cl, Br) with oxalic acid and triethylamine in dimethylformamide solution yields the substituted complexes [ReX 4(ox)] 2− and cis-[ReX 2(ox) 2] 2−, which can be obtained separately depending on the amount of added amine. The crystal structures of (PPh 4) 2[ReBr 4(ox)], cis-(PPh 4) 2[ReBr 2(ox) 2] and cis-(AsPh 4) 2[ReCl 2(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.