Protonation of Metal−Metal Bonds in Dinuclear Iridium Complexes: Consequences for Structure and Reactivity

Abstract

Protonation of the carbonyl-bridged dimer [Cp*Ir(μ-CO)]2 (Cp* = η5-C5Me5) (1) with 1 equiv of the strong acid HBAr‘4·2Et2O (Ar‘= 3,5-(CF3)2C6H3) generates the hydride- bridged species {[Cp*Ir(CO)]2(μ-H)}BAr‘4 (2). Addition of excess acid to 1 results in the formation of the dihydride dication [Cp*Ir(CO)]2(μ-H)22+ (3). The monoprotonated cation, 2, reacts rapidly with CO or H2 to afford [Cp*Ir(CO)]2(μ-CO)(μ-H)+ (4) and [Cp*Ir(CO)H]2(μ-H)+ (5), respectively. The structures of the cationic dimers 4 and 5 have been confirmed by X-ray diffraction studies. Deprotonation of complex 5 generates the neutral dihydride dimer [Cp*Ir(CO)H]2 (6), a compound with an unsupported Ir−Ir bond. An X-ray diffraction analysis of 6 reveals an Ir−Ir bond length of 2.730(1) Å. Formal protonation of the Ir−Ir bond of 6 to give 5 results in an increase of approximately 0.198 Å in the length of that bond.