Bonding and structural preferences of indenyl complexes:: MInd2Ln (n=0-3)

A search of bis(indenyl) derivatives available in the Cambridge Crystallographic Data Centre was performed and the two main families, MInd(2) and MInd(2)L(n) (n = 1-3), were structurally analyzed in detail. DFT calculations were performed for some relevant compounds in order to understand their electronic structure and interpret the experimental data. For MInd(2) complexes, the rotation angles between the rings show a wide range of values, depending both on the electron count and on the steric effects of the ring substituents. Hapticity change toward eta(3) is induced by extra electrons, but a perfect eta(3) coordination is never observed. For the electron deficient Cr(II) complexes, two isomers having two and four impaired electrons are known for different substituents, and the calculated energies in models are very close, as expected. The MInd(2)L(2) family is the largest one and examples of eta(3) coordination can be found. Both electronic and steric effects play a major role in determining the structural parameters of these species, but in the absence of bulky ring substituents, the rings are fluxional. (C) 2002 Elsevier Science B.V. All rights reserved.