Oxidation Chemistry of Inorganic Benzene Complexes

Abstract

The oxidation of the 28 VE cyclo-E triple-decker complexes [(Cp Mo) (μ,η :η -E )] (E=P, Cp =Cp(2 a), Cp*(2 b), Cp (2 c)=C (CH Ph) ; E=As, Cp =Cp*(3)) by Cu or Ag leads to cationic 27 VE complexes that retain their general triple-decker geometry in the solid state. The obtained products have been characterized by cyclic voltammetry (CV), EPR, Evans NMR, multinuclear NMR spectroscopy, MS, and structural analysis by single-crystal X-ray diffraction. The cyclo-E middle decks of the oxidized complexes are distorted to a quinoid (2 a) or bisallylic (2 b, 2 c, 3) geometry. DFT calculations of 2 a, 2 b, and 3 persistently result in the bisallylic distortion as the minimum geometry and show that the oxidation leads to a depopulation of the σ-system of the cyclo-E ligands in 2 a-3. Among the starting complexes, 2 c is reported for the first time including its preparation and full characterization.

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

“…On the other hand, going from sandwich complexes to homometallic polypnictogen triple-decker complexes, a fully reversible redox chemistry over two oxidation states as e. g. in [(Cp R Mo) 2 (μ,η 6 :η 6 -E 6 )] (E = P, As) [18] or even over four and five redox stages takes place, which was found for the cobalt complex [(Cp'''Co) 2 (μ,η 2 :η 2 -E 2 )] (E = P, As). [19] Oxidation and reduction of the latter two induce a cyclization of the initially separated E 2 units to form a cyclo-E 4 ligand in [(Cp'''Co) 2 (μ,η 4 :η 4 -E 4 )] + /2 + /À (C, Scheme 1).…”

Element–Element Bond Formation upon Oxidation and Reduction

“…By reduction and oxidation, the two separate E 2 2À units in 1 and 2,respectively,can be transformed into cyclobutadienelike E 4 3À moieties (3a, 3b, 4a, 4b)a nd E 4 5À moieties (7,8), respectively,o rf inally into cyclo-E 4 2À ligands in 5 and 6. Further reduction of the monoanions 7 und 8 leads either to the cleavage of aP ÀPb ond followed by rearrangement into aC o 2 P 4 scaffold or, in the case of an (As 2 ) 2 unit, to the abstraction of one arsenic atom to yield ab ent triple-decker complex with an allylic As 3 ligand as am iddle deck (10), which represents the first example of atriple-decker complex with such al igand. All redox processes (except for the formation of 10)a re fully reversible and can be selectively reversed when stoichiometric amounts of KC 8 or AgBF 4 , respectively,are added.…”

“…[(Cp R Mo) 2 (m,h 6 :h 6 -P 6 )],for example, can be easily oxidized to [(Cp R Mo) 2 (m,h 6 :h 6 -P 6 )] + (E), retaining its initial triple-decker geometry in the solid state,whereas the cyclo-P 6 ligand in E tends to slightly distort in abis-allylic manner. [10] Therefore,i nc ontrast to the usual polypnictogen complexes,here,oxidations have the opposite effect, namely of elongating P À Pb onds,b ut of also strengthening Mo À Mo bonds.…”

“…Not only sandwich complexes with an E n ligand as a lower deck show an instructive redox chemistry, but also homometallic triple‐decker complexes with the corresponding E n ligand as a middle deck. [(Cp R Mo) 2 (μ,η 6 :η 6 ‐P 6 )], for example, can be easily oxidized to [(Cp R Mo) 2 (μ,η 6 :η 6 ‐P 6 )] + ( E ), retaining its initial triple‐decker geometry in the solid state, whereas the cyclo ‐P 6 ligand in E tends to slightly distort in a bis‐allylic manner . Therefore, in contrast to the usual polypnictogen complexes, here, oxidations have the opposite effect, namely of elongating P−P bonds, but of also strengthening Mo−Mo bonds.…”

Element‐Element‐Bindungsbildung durch Oxidation und Reduktion

“…Nicht nur Sandwich‐Komplexe mit einem E n ‐Liganden als Enddeck zeigen eine aufschlussreiche Redoxchemie, sondern auch homometallische Tripeldecker‐Komplexe mit dem entsprechenden E n ‐Liganden als Mitteldeck. Beispielsweise kann [(Cp R Mo) 2 (μ,η 6 :η 6 ‐P 6 )] leicht zu [(Cp R Mo) 2 (μ,η 6 :η 6 ‐P 6 )] + ( E ) oxidiert werden und behält dabei im Festkörper seine anfängliche Tripeldecker‐Geometrie bei, während der cyclo ‐P 6 ‐Ligand in E dazu neigt, sich etwas in bis‐allylischer Weise zu verformen . Daher haben Oxidationen, verglichen mit den üblichen Polypniktogen‐Komplexen, hier den gegensätzlichen Effekt, nämlich die P‐P‐Bindungen zu verlängern, aber auch die Mo‐Mo‐Bindungen zu verkürzen.…”