Pulse radiolysis studies of aqueous [Ir(C³,N′Hbpy)(bpy)₂]³⁺ and its basic form. Mechanism of H₂ formation

The decay of iridium species produced by reduction of [Ir(C³,N′Hbpy)(bpy)₂]³⁺ (hereafter referred to as Ir(III)³⁺) and [Ir(C³,N′bpy)(bpy)₂]²⁺ (Ir(III)²⁺ hereafter) is reported. At strongly acidic pH (<1.7), the species produced by one-electron reduction (Ir(II)²⁺) react with H⁺ by a pseudo-first-order reaction. Hydrogen is the final product. At higher pH's, such as about 4, Ir(II)²⁺ disproportionates, and the product Ir(I) (presumably in the protonated form [Ir(I)H]²⁺) produces Ir(III)²⁺ and hydrogen. The mechanism of these processes is discussed, and equilibrium as well as reaction rate constants are reported. Ir(III)³⁺, Ir(II)²⁺, etc. represent the appropriate formal oxidation states. The reduction site in Ir(II) is not necessarily at the Ir.