Redox behaviour of imino-β-diketonato ligands and their rhodium(I) complexes

Abstract

The redox behaviour of bidentate (BID) ligands containing either two O donor atoms (O,O’-BID ligand), a N and an O donor atom (N,O-BID ligand) or two N donor atoms (N,N’-BID ligand), and their rhodium complexes, are presented. The experimental reduction potential of the L,L’-BID ligands (L,L’ = N and O) and the experimental oxidation potential of [Rh(L,L’-BID)(CO)(PPh₃)] complexes relate linearly. Though, complexes with an aromatic substituent group on the L,L’-BID ligand deviate slightly from the trend, due to the resonance effect through the extended π-system of the latter complexes. The experimental reduction potential of the L,L’-BID ligands relate linearly to the computational chemistry calculated energies of their lowest unoccupied molecular orbitals (LUMOs), whereas the experimental oxidation potential of the [Rh(L,L’-BID)(CO)(PPh₃)] complexes related linearly to the computational chemistry calculated energies of their highest occupied molecular orbitals (HOMOs). In the latter relationship it is found that the data points cluster in four groups depending on both the donor atoms (N and O) and the substituent groups (amount of CF₃ groups) on the coordinating L,L’-BID ligand.