Reduktion von (Cyclobutadien)(cyclopentadienyl)‐ und (1,5‐Cyclooctadien)‐ (cyclopentadienyl)nickel‐Kationen

Reduction of (Cyclobutadiene)(cyclopentadienyl)‐ and (1,5‐Cyclooctadiene)(cyclopentadienyl)nickel Cations Cyclic voltammetry of the four cationic Ni sandwich complexes [Ni(C 5 R 5 )(C 4 R 4 ')] + ( 2 : R = H, R' = Ph; 3 : R = H, R' = Me; 4 ; R = Me, R' = Ph; 5 : R = R' = Me) shows reversible one‐electron reductions for the phenyl derivatives 2 and 4 and a peak pattern characteristic of reductive dimerization/oxidative monomerization for the methyl derivatives 3 and 5 . The product of the reduction of 3 was isolated and characterized analytically and by an X‐ray structure determination as the dimer 6 of 3 , linked through cyclobutenyl rings, the first example for a dimerization of an electron‐rich sandwich complex at a substituted C atom. EPR spectra of the neutral complexes 2 and 4 are compared to those of (1,5‐cyclooctadiene)(cyclopentadienyl)nickel ( 7 ) and are interpreted in terms of a substantial static Jahn‐Teller distortion.