Einfach‐, Doppel‐, Dreifachbindungen und Ketten: Knüpfung elektronenpräziser B‐B‐Bindungen

Abstract

Trotz des großen präparativen Interesses an Diboranen und der hohen B‐B‐Bindungsenthalpie ist die Knüpfung von Bor‐Bor‐Bindungen immer noch schwierig, kaum zu kontrollieren und schlecht vorhersagbar. Methoden zur Herstellung von B‐B‐Mehrfachbindungen sind sogar noch seltener. In den letzten Jahren gab es nun einige Fortschritte zur Lösung dieser Probleme, und dieser Kurzaufsatz unternimmt den Versuch, einen Überblick über die Geschichte der B‐B‐Bindungsbildung zu geben und neue Ergebnisse auf diesem Gebiet zusammenzufassen.

Uncatalyzed Hydrogenation of First‐Row Main Group Multiple Bonds

“…[14] The last decade has seen rapid advances in the synthesis and chemistry of reactive boron-boron bonded compounds. [15] Recent efforts in our group have focused on the uncatalyzed activation of small molecules by boron-boron multiple bonds, including the direct hydroboration of N-heterocyclic carbene (NHC) stabilized 1,2-diaryldiborenes, [16] the reductive insertion of elemental chalcogens by NHC-supported diborynes, [17] the activation of tert-butylisocyanide and CO by a cAAC-supported diboracumulene [18] , the reductive coupling of four CO molecules by NHC-supported diborynes [18] and, most recently, the cycloaddition of apolar alkynes to boron-boron multiple bonds. [20] In this contribution we now report the facile and selective hydrogenation of B-B multiple bonds to the corresponding 1,2-dihydrodiborenes, making these the first examples of spontaneous H2 activation by lighter alkene and alkyne analogues.…”

Direct Hydroboration of BB Bonds: A Mild Strategy for the Proliferation of BB Bonds

“…However, it is notoriously difficult to selectively form such B À B bonds, despite their apparent stability. [5] It is clear that the barrier preventing the preparation of long chains of "BR" (R = amino, aryl) repeat units is less the stability of the electron-precise BÀB bonds but rather a distinct lack of mild, functional-group-tolerant synthetic methods for their preparation.Haloborane reduction is the classical method of B À B bond creation, [6][7][8] and forms the basis of the industrial synthesis of commercially available diboranes(4) (Scheme 1). However, these reactions often proceed in low yields, produce a number of byproducts stemming from overreduction and radical reactivity, and require very strong reductants, thus limiting their functional group tolerance.…”

“…However, it is notoriously difficult to selectively form such B À B bonds, despite their apparent stability. [5] It is clear that the barrier preventing the preparation of long chains of "BR" (R = amino, aryl) repeat units is less the stability of the electron-precise BÀB bonds but rather a distinct lack of mild, functional-group-tolerant synthetic methods for their preparation.…”

“…Recently, Sekiguchi and co-workers have also presented the hydroboration of the silicon-silicon triple bond of a disilyne compound. [23] With a documented desire to develop mild B À B coupling strategies, [5] we envisaged the extension of hydroboration to B = B bonds to create a new boron-boron bond and a chain of three boron atoms. Work on the synthesis of diborene molecules from Robinson et al and our laboratories has so far yielded a few stable examples (I-IV; Scheme 2).…”

Aufbau einer B‐C‐Doppelbindung in der Koordinationssphäre des Platins: ein Alkylidenborylligand, der isoelektronisch zu neutralen Aminoborylenen ist

“…[1] Darunter sind Verbindungen mit B-C-Doppelbindungen von besonderem Interesse, da sie elektronisch verwandt sind mit Vinylkationen sowie Schrock-Alkylidenkomplexen.…”