Indenyl hapticity in (η-indenyl-RhL2) and Cr(CO)3(μ-η:η-indenyl-RhL2) complexes. A 1H, 13C and 103Rh NMR spectroscopic study

A series of indenyl- and (Cr(CO)3)indenyl-RhL2 complexes (L2 = COD, (CO)2) bearing substituents on both the six- and five-membered ring have been synthesized and fully characterized, and their H-1, C-13 and Rh-103 NMR spectra recorded. The changes of the spectral parameters caused by the introduction of the Cr(CO)3 unit suggest significant modifications of the electronic distribution in the indenyl moiety induced in the ground state. The increased reactivity in the ligand exchange reactions ('extra-indenyl effect') and the strong modifications of the catalytic and spectroscopic properties of the Rh center itself indicate a substantial weakening of the coordinative bond between rhodium and the indenyl moiety in the heterobimetallic species as expected on going from an eta5 towards a more pronounced eta3 coordination mode.