Structural diversity and solution behavior of low-valent iridium complexes bearing 1,4-diazabutadiene ligands

Three types of 1,4-diazabutadiene stabilized low-valent iridium complexes, namely [IrCl(cod)(MesDAB)] (1), [IrCl(coe)(MesDAB)] (2) and [IrCl(MesDAB)2] (3), have been prepared from 1,4-bis(2,4,6-trimethylphenyl)-1,4-diaza-1,3-butadiene (MesDAB) and [IrCl(cod)]2 or [IrCl(coe)2]2, respectively. The complexes have been investigated by NMR spectroscopy and X-ray diffraction experiments. While tetra-coordinated 2 and penta-coordinated 3 maintain their solid state structure in solution, penta-coordinated 1 shows fluxional behavior. The crystal structures determined indicate strong π-backbonding towards the MesDAB ligand in all cases.

Graphical abstractThree different low-valent iridium complexes containing 1,4-bis(2,4,6-trimethylphenyl)-1,4-diaza-1,3-butadiene (MesDAB) as ligand have been synthesized and characterized. The influence of the metal to ligand ratio as well as the effect of the olefinic co-ligand on the coordination number and the behavior in solution has been studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Straightforward strategy for the synthesis of three types of low-valent iridium complexes bearing 1,4-diazadienes. ► Rare example of a low-valent iridium compound containing four neutral nitrogen donor atoms. ► Iridium(I) complexes containing 1,4-diazadiene ligands prefer different structures than diphosphane stabilized compounds.