Synthesis and electronic characterization of mixed diimine ligand rhodium(III) complexes using a versatile triflate precursor

Thirteen mixed diimine ligand complexes of the form [Rh(bpy)2(NN)](PF6)3 where bpy=2,2′–bipyridine, NN=various substituted 2,2′-bipyridines and 1,10-phenanthrolines, were synthesized from cis-[Rh(bpy)2(OTf)2](OTf) under mild reaction conditions in high (82–95% overall) yield and high purity. [Display omitted] •13 mixed diimine ligand complexes were synthesized using cis-[Rh(bpy)2(OTf)2](OTf).•Electronic spectropscopy indicate that substituents subtly affect the properties.•19F NMR characterized the bound and unbound triflate in cis-[Rh(bpy)2(OTf)2](OTf).•19F NMR showed a slow ligand exchange of the triflate with the deuterated solvent. We report here the first general, high purity, high yield synthesis of thirteen mixed diimine ligand complexes of rhodium(III), nine of which are new and four which are known and were made as controls. We utilized a bis–triflate intermediate because the more labile triflate ligands were easily displaced by incoming diimine ligands and allowed these syntheses to proceed in high yields (84–97%) under relatively mild reaction conditions. The purity of the products was determined by elemental analysis and 1H NMR. Electronic characterization was done on the compounds and we examined the effect of various electron donating and electron withdrawing substituents on the ground and excited state properties of the complexes. We observed that substitution on the 2,2′-bipyridine ligands causes only small changes in the redox potentials and the electronic spectra, while substitution on the 1,10-phenanthroline ligands causes more pronounced effects on the electronic properties, presumably due to the more rigid π system.