Bis(indenyl) complexes of Fe, Co, and Ni: electronic structure and preferences

The bis(indenyl) derivatives of Fe, Co, and Ni were studied by means of DFT calculations (ADF program). The calculated structures were compared with the experimental ones and a good agreement was observed. While bis(indenyl)iron is an 18-electron compound, exhibiting an almost perfect eta (5) coordination of the indenyl ring, the cobalt complex is a paramagnetic species, owing to the presence of an extra electron and structural distortions start to be detected. More interesting is the nickel complex, where the ring exhibits a coordination between eta (2) + eta (3) and eta (3), and is definitely slipped and folded. On the other hand, nickelocene chooses a distorted q1 coordination with long Ni-C bonds and two unpaired electrons. This different behavior is related to the tendency of the indenyl to slip, compared to cyclopentadienyl. The geometry of the indenyl ring in bis(indenyl)nickel is useful to compare with that of non-isolable intermediates and transition states. (C) 2001 Elsevier Science BN. All rights reserved.