Dibora[2]ferrocenophan: ein carbenstabilisiertes Diboren in einer gespannten cis‐Konfiguration

Abstract

Ungesättigte Brücken, die in gespannten ansa-Metallocenen zwei Cyclopentadienyl-Einheiten miteinander verbinden, sind äußerst selten und auf Kohlenstoff-Kohlenstoff-Doppelbindungen beschränkt. Die Synthese und Isolierung eines gespannten Ferrocenophans mit einer ungesättigten Brückea us zwei Boratomen, die isoelektronischm it einer C=C-Doppelbindung ist, wurde durch Reduktion eines carbenstabilisierten 1,1'-Bis(dihalogenboryl)ferrocens erstmals verwirklicht. Spektroskopische und elektrochemischeM essmethoden sowie DFT-Rechnungen wurden angewendet, um den Einfluss der beispiellosen, gespannten cis-Konfiguration auf die optischen und elektrochemischen Eigenschaften der carbenstabilisierten Diboren-Einheit zu untersuchen. Erste Reaktivitätsstudien zeigen, dass das Dibora[2]ferrocenophan anfällig fürdie Spaltung der Bor-Bor-Doppelbindung ist.Abbildung 1. Beispielev on Ferrocenophanen mit einer ungesättigten, zweiatomigen Brücke (R 1 ,R 2 = Ph oder CO 2 CH 3 ,L= Lewis-Base).

Access to NHC–Boryl Mono‐ and Bis‐Selenide and Utility as Mild Selenium Transfer Reagent Including to the C−F Bond

“…The boron atom lies in the plane of the imidazolin ring for 2 and the B−Se bond is not orthogonal to the plane [torsion angle (°) N1−C2−B1−Se1: 62.6(3), N2−C2−B1−Se1: 117.6(2)]. The B−Se bond length is 2.065(3) Å, which is in good agreement with the B−Se bond lengths (1.960–2.13 Å) reported for a small number of structurally characterized compounds featuring a B−Se bond [14a,19] . The B−C bond distance in 2 [1.615(4) Å] is marginally longer than that in 1 [1.602(3) Å] due to enhanced steric crowding around the central boron atom.…”

“…However, there are examples of carbene supported boryl selenium compounds, but they were not prepared from carbene ⋅ BH 3 . For example, Braunschweig and coworkers studied the reactivity of an NHC stabilized dibora[2]ferrocenophane with excess diphenyldiselenide resulting in the cleavage of the B=B double bond and installation of two −SePh moieties on each boron atom [14a] . The same group later demonstrated the reduction of diphenyldiselenide by PMe 3 stabilized borylene leading to the formation of a cyclic alkyl amino carbene (cAAC) stabilized selenoborane radical [14b] .…”

Stepwise reduction of a base-stabilised ferrocenyl aluminium(iii) dihalide for the synthesis of structurally-diverse dialane species

“…16 In the case of group 13, in 1996 Wagner and co-workers investigated the geometry and electronic structure of borylferrocenes, FcBR 2 , revealing that there is an interaction between lled d-type orbitals at iron and the empty p orbital of boron, which causes bending of the BR 2 substituent toward the central iron atom. 17 In 2017, our group reported an NHC-stabilised dibora [2]ferrocenophane (VII, in Scheme 1) 18 that showed a strained cis conguration. Electrochemical measurements revealed that dibora [2]ferrocenophane has a remarkably low oxidation potential of E pa ¼ À1.56 V vs. the ferrocene/ferrocenium couple, corresponding to the oneelectron oxidation of the diborene unit, suggesting that the iron centre has an effect on the electrochemical properties of the compound.…”

“…Electrochemical measurements revealed that dibora [2]ferrocenophane has a remarkably low oxidation potential of E pa ¼ À1.56 V vs. the ferrocene/ferrocenium couple, corresponding to the oneelectron oxidation of the diborene unit, suggesting that the iron centre has an effect on the electrochemical properties of the compound. 18 However, there remains no report on lowvalent aluminium compounds bearing redox-active ferrocenyl units.…”