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] (C1O4)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, and13C and1H n.m.r. spectra are reported. The pure trenen and tetraen ligands have been recovered from the CoIII complexes and can be distinguished by13C n.m.r. spectroscopy.