PROTONATION OF METAL-METAL BONDS IN DINUCLEAR IRIDIUM COMPLEXES - CONSEQUENCES FOR STRUCTURE AND REACTIVITY

Protonation of the carbonyl-bridged dimer [CpIr(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 {[CpIr(CO) ](2)(mu-H)}BAr'(4) (2). Addition of excess acid to 1 results in the fo rmation of the dihydride dication [CpIr(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), resp ectively. The structures of the cationic dimers 4 and 5 have been conf irmed by X-ray diffraction studies. Deprotonation of complex 5 generat es the neutral dihydride dimer [CpIr(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 A ngstrom in the length of that bond.