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

Abstract

The redox chemistry of the heterobimetallic tripledecker complexes [(Cp*Fe)(Cp'''Co)(μ,η 5 :η 4 -E 5 )] (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,η 3 :η 3 -E 3 )] (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-E 5 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 As 6 (9) and As 3 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,η 3 :η 2 -P 3 )] (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 P 3 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.

Synthesis and Multiple Subsequent Reactivity of Anionic cyclo‐E3 Ligand Complexes (E=P, As)

“…(12). All mentioned distances are in the range between single and double bonds, confirmed by the calculated WBIs in the range of 1.01 and 1.08 (11)a nd 0.98 and 1.09 (12), respectively.C ompound 11 and 12 represent the first complexes including af our-membered cycle consisting of three pnictogen atoms and one silicon atom and add to the row of pnictogen silicon heterocycles,f or example,[ (LSi) 2 P 2 ] [28] reported by the groups of H. W. Roesky and Driess in 2011 and its heavier analogue [(LSi) 2 As 2 ]reported 2016 by our group. [29] Thelatter synthetic approach gave also access to the inorganic benzene derivatives [(LSi) 3 E 3 ](E= P, As).…”

“…[12,13] [Cp'''Ni(h 3 -E 3 )] (E = P, As) can be reacted with the cobalt toluene complex [(Cp'''Co) 2 (m,h 4 :h 4 -C 7 H 8 )] to yield the heterobimetallic triple-decker complexes [(Cp'''Co)-(Cp'''Ni)(m,h 3 :h 3 -E 3 )] (E = P( 3), As (4)) in gram scale. [12,14] Thei nvestigation of their redox chemistry reveals an interesting fact, namely that in the monocations [(Cp'''Co)-(Cp'''Ni)(m,h 3 :h 3 -E 3 )][FAl] (E = P, As;[ FAl] = FAl{OC 6 F 10 -(C 6 F 5 )} 3 )the {Cp'''M} fragments are not strongly bound to the E 3 ligand and ar earrangement process takes place under formation of the homometallic species [(Cp'''Co) 2 (m,h 3 :h 3 -E 3 )][FAl] and [(Cp'''Ni) 2 (m,h 3 :h 3 -E 3 )][FAl]. [12] On the other hand, the reduction of 3 and 4 yields the monoanionic tripledecker complexes [K(thf) n ][(Cp'''Co)(Cp'''Ni)(m,h 3 :h 3 -E 3 )] (E = P, As), which retain their heterobimetallic character.…”

“…[12,14] Thei nvestigation of their redox chemistry reveals an interesting fact, namely that in the monocations [(Cp'''Co)-(Cp'''Ni)(m,h 3 :h 3 -E 3 )][FAl] (E = P, As;[ FAl] = FAl{OC 6 F 10 -(C 6 F 5 )} 3 )the {Cp'''M} fragments are not strongly bound to the E 3 ligand and ar earrangement process takes place under formation of the homometallic species [(Cp'''Co) 2 (m,h 3 :h 3 -E 3 )][FAl] and [(Cp'''Ni) 2 (m,h 3 :h 3 -E 3 )][FAl]. [12] On the other hand, the reduction of 3 and 4 yields the monoanionic tripledecker complexes [K(thf) n ][(Cp'''Co)(Cp'''Ni)(m,h 3 :h 3 -E 3 )] (E = P, As), which retain their heterobimetallic character. Herein we report the reaction of 3 and 4 with an excess of potassium leading to [Cp'''Co(h 3 -E 3 )] À (E = P( [ 5]), As ( [6])) in high yields,t he latter being the first anionic cyclo-As 3 ligand complex, and their reactivity towards chlorophosphanes and chlorosilylene to obtain first cyclo-E 4 heteroelement ligands with P/As/Si sequences.…”

“…(11)and 2.2775(14) (12), the E1 À E2 bond to 2.2283(19) (11)and 2.4417(8)(12), and the E2 À E3 bond to 2.2032(18) (11)a nd 2.4243(8) …”

Halogenation and Nucleophilic Quenching: Two Routes to E−X Bond Formation in Cobalt Triple‐Decker Complexes (E=As, P; X=F, Cl, Br, I)

“…Therefore, the redox‐active compounds [(Cp’’’Co) 2 (μ,η 2 : η 2 ‐E 2 ) 2 ] (E=As ( 1 ), P ( 2 ); Cp’’’=1,2,4‐tri( tert ‐butyl)cyclopentadienyl) [14] came into the focus of our research. A former investigation of these complexes showed that they exhibit a unique redox chemistry different from the usual behaviour observed for triple‐decker complexes such as [(CpMo) 2 (μ,η 6 : η 6 ‐P 6 )] [15] or for heterobimetallic triple‐decker complexes [16] . The oxidation and reduction of 1 and 2 both lead to the formation of two additional E−E bonds, highlighting a way to obtain the corresponding dications [(Cp’’’Co) 2 (μ,η 4 : η 4 ‐E 4 )][TEF] 2 (E=As ( 8 ), P ( 9 ), [TEF]=[Al{OC(CF 3 ) 3 } 4 ] in good yields [17] .…”