Heterobimetallic indenyl complexes.: Synthesis and carbonylation reaction of anti-[Cr(CO)3-μ,η:η-indenyl-Ir(COD)]

The reaction of the anti-[Cr(CO)(3)-mu,eta:eta-indenyl-Ir(COD)] (I) complex with an excess of CO in CH2Cl2 at 203 K produces quantitatively the eta(1)-[eta(6)-Cr(CO)(3)-indenyl]-Ir(COD)(CO)(2) intermediate which above 273 K converts into the fully carbonylated complex eta(1)-[eta(6)-Cr(CO)(3)-indenyl]Ir(CO)(4); this in turn is stable up to 313 K. Carbonylation of the anti-[Cr(CO)(3)-mu,eta:eta-indenyl-Ir(COE)(2)] analogue (II) gives the eta(1)-[eta(6)-Cr(CO)(3)-indenyl]-Ir(CO)(4) (VII) species in a single fast step. In contrast to the behavior of the corresponding rhodium complexes, for which eta(1) intermediates have never been observed and the aromatized substitution product is the stable product, the rearomatization of the cyclopentadienyl ring in iridium complexes to give the "normal" substitution product, viz., anti-[Cr(CO)(3)-mu,eta:eta-indenyl-Ir(CO)(2)] (III) is a difficult process which takes place only on bubbling argon through the solution. The final product III is barely stable in solution. If the carbonylation is carried out using a blanket of CO over the solution of complexes I and II, viz., failing CO, the scarcely soluble iridium dimer [eta(6)-Cr(CO)(3)-indenyl-eta(3)-Ir(CO)(3)](2) (IX) Stable in the solid state is obtained, probably by dimerization of the unstable intermediate anti-[eta(6)-Cr(CO)(3)-indenyl-eta(3)-Ir(CO)(3)] (X).