Heterobimetallic (ferrocenyl)-indenyl iridium complexes. Synthesis, Crystal Structure 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(mu-Cl)(cod)](2) and [Ir(mu-Cl)(coe)(2)](2) afforded the heterobimetallic [eta(5)-(1-ferrocenyl)indenyl]-Ir(cod) (2) and [eta(5)-(1-ferrocenyl)indenyl]-Ir(coe)(2) (3) (cod=cycloocta-1,5-diene; coe=cyclooctene). The complex [eta(5)-(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 eta(1)-(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 eta(1)-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.