Heterobimetallic (Ferrocenyl)Indenyl Iridium Complexes. Synthesis, Crystal Structure, Reactivity and Oxidative Activation

The reaction of (1-ferrocenyl)indenyl lithium, generated from (3-ferrocenyl)-indene (1) and n-butyl lithium in THF, with the dimers [Ir( m-Cl)(cod)]2 and [Ir( m-Cl)(coe)2]2 afforded the heterobimetallic [ h5-(1-ferrocenyl)indenyl]–Ir(cod) (2) and [ h5-(1-ferrocenyl)indenyl]–Ir(coe)2 (3) (cod=cycloocta-1,5-diene; COE=cyclooctene). The complex [ h5-(1-ferrocenyl)indenyl]–Ir(CO)2 (4) was obtained from 3 by exchange reaction with CO at room temperature. In contrast, the carbonylation of 2 at low temperature produces the h1-(1-ferrocenyl)indenyl]–Ir(cod)(CO)2 intermediate stable up to room temperature. The elimination of COD to give 4 occurs at higher temperature than in the corresponding monometallic h1-indenyl–Ir(cod)(CO)2. The crystal structure of 4 showed that iron and iridium are disposed in a cisoid configuration favoured by a stabilising weak bond interaction between the hydrogens of the cyclopentadienyl (Cp) ring and iridium and its carbonyls. The results of the electrochemical oxidation of 4 support the existence of a significant chemical interaction between the two metals. The comparison with the voltammetric results of the isomorphous rhodium complex 6 evidences for 4 a slowing down of the kinetic of the metal–metal interaction, and the absence of the radical cation oxidation even at high potential.