Redox Chemistry of Heterobimetallic Polypnictogen Triple-Decker Complexes - Rearrangement, Fragmentation and Transfer

The redox chemistry of the heterobimetallic triple-decker complexes [(Cp*Fe)(Cp'''Co)(μ,η⁵ :η⁴ -E₅ )] (E=P (1), As (2), Cp*=1,2,3,4,5-pentamethyl-cyclopentadienyl, Cp'''=1,2,4-tri-tertbutyl-cyclopentadienyl) and [(Cp'''Co)(Cp'''Ni)(μ,η³ :η³ -E₃ )] (E=P (10), As (11)) was investigated. Compound 1 and 2 could be oxidized to the monocations 3 and 4 and further to the dications 5 and 6, while the initially folded cyclo-E₅ ligand planarizes upon oxidation. The reduction leads to an opposite change in the geometry of the middle deck, which is now folded stronger into the direction of the other metal fragment (formation of monoanions 7 and 8). For the arsenic compound 8, a different behavior is found since a fragmentation into an As₆ (9) and As₃ ligand complex occurs. The Co and Ni triple-decker complexes 10 and 11 can be oxidized initially to the heterometallic monocations 12 and 13, which are not stable in solution and convert selectively into the homometallic nickel complexes 14 and 15 and the cobalt complexes 16 and 17. This behavior was further proven by the oxidation of [(Cp'''Co)(Cp''Ni)(μ,η³ :η² -P₃ )] (19, Cp''=1,3-di-tertbutyl-cyclopentadienyl) comprising two different Cp ligands. The transfer of {Cp^R M} fragments can be suppressed when a {W(CO)₅ } unit is coordinated to the P₃ ligand (20) prior to the oxidation and the mixed cobalt and nickel cation 21 can be isolated. The reduction of 10 and 11 yields the heterometallic monoanions 22 and 23, where no transfer of the {Cp^R M} fragments is observed.