Activation of H₂ and Et₃SiH by the Borinium Cation [Mes₂B]⁺: Avenues to Cations [MesB(μ-H)₂(μ-Mes)BMes]⁺ and [H₂B(μ-H)(μ-Mes)B(μ-Mes)(μ-H)BH₂]⁺

Abstract

Reaction of dihydrogen and the borinium cation salt [Mes2B]­[B­(C6F5)4] gave an arene-stabilized mesityl-borenium cation, which isotopically scrambles HD. Similarly, reaction with triethylsilane gave the diboranium cation [MesB­(μ-H)2(μ-Mes)­BMes]+ featuring three bridge-bonds between two boron centers. Reaction of same (Mes2BH)2 with Brønsted acid also afforded the same diboranium whereas the corresponding reaction with (MesBH2)2 yielded the triboron cation [H2B­(μ-H)­(μ-Mes)­B­(μ-Mes)­(μ-H)­BH2]+.

Computational Investigation of the Mechanism of FLP Catalyzed H2Activation and Lewis Base Assisted Proton Transfer

“…[27] Interestingly, a recent report by Stephan and co-workers explored the reactivity of H 2 with an electrophilic borinium cation, [Mes 2 B] + affording an unprecedented diboranium cation synthetic product. [33] We have also identified a H 2 capture transition state in absence of any Lewis bases, TS H2 (ΔG � = 31.6 kcal/mol), which is predicted to take place at a comparable free energetic cost as TS1 Im . A high-energy intermediate, 2 H2 (ΔG = 28.8 kcal/mol) is located where H 2 is bound to BAr 3 in absence of any Lewis base.…”

Reactions of B2(o‐tolyl)4 with Boranes: Assembly of the Pentaborane(9), HB[B(o‐tolyl)(μ‐H)]4

“…For example, we used the borinium cation [Mes 2 B][B-(C 6 F 5 ) 4 ], originally described by Shoji and co-workers, [10] in reactions with H 2 , hydridoborane and silane, leading to the first diboranium cation [B 2 (m-H) 2 (m-Mes)Mes 3 ][B(C 6 F 5 ) 4 ]. [11] This species was also derived from Mes 2 BH and Brønsted acid. Interestingly, the corresponding protonation of Targeting new avenues to unique boron reagents, our interest focuses on the potential of diboranes (4).…”

“…After 16 h, 1 was consumed and major 11 B signals at 72.4, 3.0, À0.3, À4.6, À8.3 and À46.8 ppm were observed. While the first of these resonances arises from 2, workup afforded the isolation of a product 8 in 24 % relative yield, [29] which accounts for the 11 B NMR signals at À4.6 and À46.8 (d, 1 J BH = 167 Hz) ppm.…”

“…[16] In contrast, repeating the reaction of 1 with neat BH 3 •SMe 2 , in the total absence of THF, afforded no trace of 8. Instead, 11 B NMR data reveal a mixture of 2 in addition to two new strong signals at 2.3 and À22.6 ppm (see Supporting Information). Interestingly, addition of THF to this mixture reduces the intensity of these peaks and affords 8 after 24 h, suggesting the unassigned signals arise from species that act as precursor(s) to 8.…”

B−B Bond Nucleophilicity in a Tetraaryl μ‐Hydridodiborane(4) Anion

“…Our group has recently gathered evidence for the transient occurrence of [FluBÀBFlu(R)] À (HBFlu = 9-H-9borafluorene) intermediates, which are capable of releasing a 9-borafluorenyl anion [:BFlu] À that subsequently undergoes either carbene-type C À H bond activation or nucleophilic substitution reactions (A; Figure 1). [10,11] If we consider [FluBÀBFlu(R)] À as containing a [:BFlu] À moiety stabilized via formation of an adduct through its lone pair of electrons with a Lewis acidic 9-R-9-borafluorene molecule, it would be justified to regard the entire electron density between the two boron atoms as the actual nucleophilic entity (cf. the related idea of nucleophilic B À H bonds [12] ).…”