An Acid-Free Anionic Oxoborane Isoelectronic with Carbonyl: Facile Access and Transfer of a Terminal B═O Double Bond

Abstract

We disclose the synthesis and structural characterization of the first acid-free anionic oxoborane, [K(2.2.2-crypt)][(HCDippN) 2 BO] (1), which is isoelectronic with classical carbonyl compounds. 1 can readily be accessed from its borinic acid by a simple deprotonation/sequestration sequence. Crystallographic and DFT analyses support the presence of a polarized terminal B=O double bond. Subsequent π bond metathesis converts the B=O bond to a heavier B=S containing system, affording the first anionic thioxoborane [K(2.2.2-crypt)] [(HCDippN) 2 BS] (2), isoelectronic with thiocarbonyls. Facile B=O bond cleavage can also be achieved to access B−H and B−Cl bonds, and via a remarkable oxide (O 2− ) ion abstraction to generate a borenium cation [(HCDippN) 2 B(NC 5 H 5 )][OTf] (4). By extension, 1 can act as an oxide transfer agent to organic substrates, a synthetic role traditionally associated with transition metal compounds. Hence we show that B−O linkages, which are often considered to be thermodynamic sinks, can be activated under mild conditions towards bond cleavage and transfer, by exploiting the higher reactivity inherent in the B=O double bond.

Ligand Effects on the Electronic Structure of Heteroleptic Antimony‐Centered Radicals

“…This is remarkable, because more electronegative substituents (−I effect) typically lead to a stronger stabilization of the frontier orbitals, hence the opposite trend would be expected based on the electronegativities of the Sb‐bound atoms in R (B: 2.04, C: 2.55, N: 3.04 by Pauling's scale) . However, in 2‐B , the unique π‐acceptor properties (−M effect) of the boryl ligand, which allowed for the stabilization of unusual B−O and B−S double bonds, stabilizes the SOMO in 2‐B . The π‐donating amido substituent (+M effect) in 2‐N destabilizes the SOMO level due to an interaction comparable to the α‐effect .…”

Isoelectronic Aluminium Analogues of Carbonyl and Dioxirane Moieties

“…The corresponding X 13 = E functional groups for the Group 13 elements ( X 13 =B, Al, Ga, In, Tl) have, until very recently, been restricted to neutral (i.e., non‐isoelectronic) examples . Most pertinent to this study are compounds containing the Al= E functional group, which have been isolated for E =O, S, and Te (Figure ).…”

Oxoborane Formation Turns on Formazanate‐Based Photoluminescence

“…Despite significant progress, the possibility that the formation of such bonds can turn on photoluminescence hasr eceivedminimal attention. [7] Thioxoborane 6 is the first cationic, electron-precise species containing aB =Sb ond. The latter propertyw as rationalized throughd ensity-functional calculations whichi ndicated that the B=Ob ond enhances photoluminescence by drastically reducing differences between the ligand's geometries in the ground and excited states.…”

“…[1,2] In this context, the preparation of stablec ompounds containing multiple bonds to boron presentsaparticular challenged ue to the electron-deficient character and compactness of the valence orbitals of the Ba tom. [7] Thioxoborane 6 is the first cationic, electron-precise species containing aB =Sb ond. [3] More recent strategies of stabilizing double and triple bonds to boron have relied upon Lewis bases and/ors terically bulky substituents, as exemplified by compounds 1-7.…”