Gas-phase SN2 reactivity of dicoordinated borinium cations using pentaquadrupole mass spectrometry

A chelated borinium cation

Two coordinate boron cations are rare. Herein we report the synthesis of [RNSiMe2CH2]2BF (R = Dipp 3, 1-Ad 5) (Dipp = C6H3(iPr)2, Ad = C10H15) via the reaction of BF3 with the corresponding dilithiated diamides. Subsequent abstraction of fluoride provided the corresponding borinium salts, [(RNSiMe2CH2)2B][B(C6F5)4] (R = Dipp 6, 1-Ad 8). While the former was generated, the latter proved isolable and was crystallographically characterized.

The Non-Ancillary Nature of Trimethylsilylamide Substituents in Boranes and Borinium Cations

The known boranes (R(Me₃Si)N)₂BF (R=Me₃Si 1, tBu 2, C₆F₅3, o‐tol 4, Mes 5, Dipp 6) and borinium salts (R(Me₃Si)N)₂B][B(C₆F₅)₄] (R=Me₃Si 7, tBu 8) are prepared and fully characterized. Compound 7 is shown to react with phosphines to generate [R₃PSiMe₃]⁺ and [R₃PH]⁺ (R=Me, tBu). Efforts to generate related borinium cations via fluoride abstraction from (R(Me₃Si)N)₂BF (R=C₆F₅3, o‐tol 4, Mes 5) gave complex mixtures suggesting multiple reaction pathways. However for R=Dipp 6, the species [(μ‐F)(SiMe₂N(Dipp))₂BMe][B(C₆F₅)₄] was isolated as the major product, indicating methyl abstraction from silicon and F/Me exchange on boron. These observations together with state‐of‐the‐art DFT mechanistic studies reveal that the trimethylsilyl‐substituents do not behave as ancillary subsitutents but rather act as sources of proton, SiMe₃ and methyl groups.

Insertion reactions of the C-B-N-substituted borinium cation [MesBNiPr2]. Dalton Trans 2020;49:17571-17577. [PMID: 33231245 DOI: 10.1039/d0dt03665j]

The synthesis and isolation of the first stable C-B-N-substituted borinium [MesBNiPr2][B(C6F5)4] (2) is described. Compound 2 was shown to react with isothiocyanate and carbodiimides, effecting B-C insertion to afford nitrilium (4) and borenium amidinate salts, respectively. The borinium cation [MesBNiPr2]+ (2+) was also generated from reactions of MesB(Cl)NiPr2 (1) and GaCl3, and used to prepare stable borenium amidinate salts (5-6), while the triflate borane MesB(OTf)NiPr2 (7) reacts with carbodiimide to give the bis(amidinate) boronium salt [MesC(NiPr)2B((NiPr)2C)NiPr2][OTf] (8).

Quantitative Theoretical Predictions and Qualitative Bonding Analysis of the Divinylborinium System and Its Al, Ga, In, and Tl Congeners

A substituted divinylborinium cation was synthesized recently and characterized crystallographically as a gauche structure with a 153° C1-C2-C3-C4 dihedral angle. A full theoretical geometrical optimization of the bis(2-mesityl-1,2-diphenylvinyl)-borane cation shows excellent agreement with the crystal structure. However, for the parent unsubstituted divinylborinium cation, we predict a nearly 90° C1-C2-C3-C4 dihedral angle using the CCSD(T)/cc-pVTZ coupled cluster method. The cis and trans planar geometries (0° and 180° for the C1-C2-C3-C4 dihedral angle) proved to be transition states with energy barriers of 2.8 and 2.3 kcal/mol, respectively, with respect to unimolecular conversion to the gauche equilibrium. The structures of the heavier boron group cations (Al, Ga, In, and Tl) have also been investigated here, finding even lower energy barriers (0.3-0.7 kcal/mol). After the ZPVE corrections, the barriers are further decreased. The torsional angles for the unknown Al, Ga, In, and Tl dimesityl substituted compounds should be somewhat less than 153°. Many of these findings may be understood in terms of qualitative electronic structure theory. The torsional folding of borane complex, including cationic divinylborinium and elementary vinylborane (C₂H₃BH₂) or chlorovinylborane (C₂H₃BHCl) precursors, are investigated with natural bond orbital (NBO) analysis to unveil the electronic origins of the torsional properties. The NBO-based descriptors are employed to systematically deconstruct complex torsional dependence into a balanced portrayal of hyperconjugative and steric effects.

Electrochemical Reduction of Quinones in Different Media: A Review

The electron transfer reactions involving quinones, hydroquinones, and catechols are very important in many areas of chemistry, especially in biological systems. The therapeutic efficiency as well as toxicity of anthracycline anticancer drugs, a class of anthraquinones, is governed by their electrochemical properties. Other quinones serve as important functional moiety in various biological systems like electron-proton carriers in the respiratory chain and their involvement in photosynthetic electron flow systems. The present paper summarizes literatures on the reduction of quinones in different solvents under various conditions using different electrochemical methods. The influence of different reaction conditions including pH of the media, nature of supporting electrolytes, nature of other additives, intramolecular or intermolecular hydrogen bonding, ion pair formation, polarity of the solvents, stabilization of the semiquinone and quinone dianion, catalytic property, and adsorption at the electrode surface, are discussed and relationships between reaction conditions and products formed have been presented.

Borinium, Borenium, and Boronium Ions: Synthesis, Reactivity, and Applications

Boron cations are elusive and highly electrophilic species that play a key role in the chemistry of boron. Despite early interest in the chemistry of boron cations, until recently they have largely remained chemical curiosities. However, hints at harnessing their potential as potent electrophiles have begun to appear and developments in weakly coordinating anion technology suggest that this is an area of research that is ripe for exploration. It has been nearly 20 years since the last major review on boron cations; herein we summarize the progress in the area since that time.