Formazanate Complexes of Bis-Cyclometalated Iridium

In this work we describe a series of bis-cyclometalated iridium(III) formazanate complexes, expanding the coordination chemistry of the redox-active formazanate class to iridium. A total of 18 new complexes are described, varying the substituent pattern on the formazanate and the identity of the cyclometalating ligand on iridium. Eight of the new compounds are structurally characterized by single-crystal X-ray diffraction, which along with NMR spectroscopy evinces two binding modes of the formazanate. Two of the compounds are isolated in a C₂-symmetric geometry where the formazanate is bound in a six-member chelate "closed" conformation, involving the 1- and 5-positions of the 1,2,4,5-tetraazapentadienyl formazanate core. In most of the examples, the major isomer that forms and is exclusively isolated involves the formazanate bound in a five-member chelate "open" form, coordinating through the 1- and 4-positions of the formazanate core and resulting in C₁ point-group symmetry. All complexes are characterized by UV-vis absorption spectroscopy and cyclic voltammetry, with these features depending primarily on the substitution pattern on the formazanate, and to a lesser extent on the identity of the cyclometalating ligand and formazanate binding mode.