Metal Complexes of Dissymmetric Arsines. Stereochemistry, Topological Stability, and Spectra of Cobalt(III) Complexes Containing a Linear Quadridenate Tetra(tert-arsine) Ligand

Abstract

The stable racemic and meso isomers of the arsine [(CH3)2As(CH2)3As(C6H5)CH2]2, tetars, have been separated via their Co(III) complexes and then obtained in their pure forms free of their complexes. Complexes of the racemic ligand are stereospecifically formed because of the steric constraints of the chiral inner arsenic atoms. All five possible dichloro isomers, cis-α, cis-β, and trans of the racemic ligand and cis-β and trans of the meso ligand, have been isolated and their topological equilibria have been investigated. It is found that the racemic ligand does not impose strong topological preferences but the meso ligand prefers the trans topology. Two trans-chloronitro isomers of the meso ligand have been isolated, thus establishing the identity of the meso ligand. All the complexes of the racemic ligand have been obtained in pure optical forms from which the free pure optically active arsine has been obtained, thus establishing the identity of the racemic ligand. From an analysis of their nmr the topologies of the complexes have been established and their conformations have been inferred from both the nmr and exciton circular dichroism spectra. The absorption and circular dichroism spectra reveal a collapse of interelectronic repulsion and extensive mixing within the d-electron manifold which may correlate with the organometallic reactivity of these arsine complexes. A hitherto unknown method of inverting coordinated arsenic atoms has been discovered. Show more