Electron transfer in complexes of B^IIcations with organic π-acceptors: a combined experimental and quantum-chemical study

Abstract

The complexation and reduction of a series of diones with different redox-potentials in a dicationic diborane are analysed.

Chemistry of Dicationic Diboranes

“…[59] By increasing the π-acceptor character of the organic σ-basic reaction partner, first reactions were investigated in which both the Lewis acidity and electron-donor propensity of the B-B bond in boron(II) cations became clear and were applied for the reduction of organic substrates. [59,61] The following section deals with this interesting dual reactivity pattern, commonly associated with catalytically active late-transition-metal complexes.…”

“…Owing to the complexity of the reaction mechanism we focused in our current work on strongly π-acidic, oxygen-based ligands, that do not give oligomers, such as diones. [59,61] Reaction of the diborane 15 with a range of diones (3,5 . [61] An interesting crystal structure peculiarity of these cations is a tilted orientation of the aromatic π-system and the plane that includes the B•••B axis and bisects the BN 2 angles which is supposed to allow electron transfer from the intact B-B bond to the π Lewis acid during the reaction.…”

“…[59,61] Reaction of the diborane 15 with a range of diones (3,5 . [61] An interesting crystal structure peculiarity of these cations is a tilted orientation of the aromatic π-system and the plane that includes the B•••B axis and bisects the BN 2 angles which is supposed to allow electron transfer from the intact B-B bond to the π Lewis acid during the reaction. Hence, the initial formation of a Lewis-acid-base adduct between [B 2 (hpp) 2 ] 2+ and the dione is considered as a possible trigger for the electron transfer.…”

“…Further calculations demonstrated that the energies between the lowest triplet state (obtained by one-electron transfer) and the initial diborane-substrate complex with an intact B-B bond are quite similar. [61] Since there is a significant barrier for the simultaneous two-electron transfer along the singlet potential energy curve, the system may change to a radical path with stepwise transfer of the two electrons.…”

Silicon Carbamates by CO2 Fixation: Brønsted Acid Labile Precursor of a Lewis Superacid

“…Subsequent ligand scrambling between silicon and boron gives rise to [TMPH 2 ···Cl···H 2 TMP]­[B­(cat Cl ) 2 ] and [H 2 TMP] 2 [Si­(cat Cl )­F 4 ] as further byproducts of this reaction, identified by single-crystal structural analysis (see section 4 of the Supporting Information). The appearance of a Cl – anion in the solid-state structure of bis­(catecholato)­borate further suggests that Lewis superacid 1 (in combination with a suitable Lewis base) is capable of abstracting chloride ions from the solvent DCM.…”