Protonation of metal-metal bonds in dinuclear iridium complexes: Consequences for structure and reactivity

Protonation of the carbonyl-bridged dimer [Cp*Ir(mu-CO)](2) (Cp* = eta(5)-C5Me5) (1) with 1 equiv of the strong acid HBAr'(4) . 2Et(2)O (Ar'= 3,5-(CF3)(2)C6H3) generates the hydride- bridged species {[Cp*Ir(CO)](2)(mu-H)}BAr'(4) (2). Addition of excess acid to 1 results in the formation of the dihydride dication [Cp*Ir(CO)](2)(mu-H)(2)(2+) (3). The monoprotonated cation, 2, reacts rapidly with CO or H-2 to afford [Cp*Ir(CO)](2)(mu-CO)(mu-H)(+) (4) and [Cp*Ir(CO)H](2)(mu-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) Angstrom. Formal protonation of the Ir-Ir bond of 6 to give 5 results in an increase of approximately 0.198 Angstrom in the length of that bond.