The Synthesis, Stereochemistry and Properties of Linear and Branched Chain Tetraethylenepentaamine Cobalt(III) Complexes

Abstract

Described are the syntheses, isolation and resolution of many diastereoisomers of pentaaminecobalt(III) complexes obtained from commercial-grade tetraethylenepentaamine. They contain both linear (tetraen; 3,6,9-triazaundecane-1,11-diamine) and branched chain (trenen; 3-(2-aminoethyl)-3,6-diazaoctane-1,8- diamine) isomers of C₈H₂₃N₅ and are free of the many other amines present in the original (crude) pentaamine mixture. A dimeric bridging peroxocobalt(III) complex [Co₂(C₈H₂₃N₅)₂O₂] (ClO₄)₄ has been isolated and converted into a mixture of s-[Co(trenen)X]ⁿ⁺ and α-anti β-, α-syn β- and α-α-[Co(tetraen)X]²⁺ complexes (X = Cl¯, Br¯, N₃¯), and the various isomers have been separated by a combination of fractional crystallization and ion-exchange chromatography. In addition, some X = NO₃¯ and OH₂ derivatives have been made by a kinetic route, including the unstable α-syn β isomers. Many of the complexes have been resolved into their enantiomers, and visible, o.r.d. and c.d. spectra are reported. An X-ray crystallographic analysis of a prototype of each of the four isomeric complexes (X = Cl¯ or N₃¯) has been determined previously, thereby establishing the identity of many related complexes. Stereoretentive reactions are used to correlate these related isomers, and ¹³ C and ¹ H n.m.r. spectra are reported. The pure trenen and tetraen ligands have been recovered from the Co^III complexes and can be distinguished by ¹³ C n.m.r. spectroscopy