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

Protonation of the carbonyl-bridged dimer [Cp*Ir(μ-CO)] 2 (Cp* = η 5 -C 5 Me 5 ) ( 1 ) with 1 equiv of the strong acid HBAr‘ 4 ·2Et 2 O (Ar‘= 3,5-(CF 3 ) 2 C 6 H 3 ) 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) 2 2+ ( 3 ). The monoprotonated cation, 2, reacts rapidly with CO or H 2 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.