Cerium(III) and Cerium(IV) Bis(η⁸-pentalene) Sandwich Complexes:  Synthetic, Structural, Spectroscopic, and Theoretical Studies

The Ce(III) anionic bis(pentalene) sandwich complex K[Ce{C 8 H 4 (Si i Pr 3 -1,4) 2 } 2 ] ( 1 ) has been prepared by treatment of CeCl 3 with K 2 [C 8 H 4 (Si i Pr 3 -1,4) 2 ] and crystallographically characterized as its 18-crown-6 complex. Oxidation of 1 with Ag[BPh 4 ] affords the neutral, formally Ce(IV) sandwich complex [Ce{C 8 H 4 (Si i Pr 3 -1,4) 2 } 2 ] ( 2 ), whose molecular structure has also been determined. The electronic structure of 2 has been investigated in detail by a combination of magnetic studies, K-edge XANES measurements, gas-phase photoelectron spectroscopy, and density functional calculations.