2014
DOI: 10.1021/om500348u
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Formation, Stability, and Structures of Borenium and Boronium Cations Derived from Pentamethylazaferrocene–Boranes by Hydride or Chloride Abstraction Reactions

Abstract: Hydride abstraction reactions from 1′,2′,3′,4′,5′-pentamethylazaferrocene−boranes (PMAF-boranes, where borane = BH 3 , 9-bora[3.3.1]bicyclononane) using trityl cation in CH 2 Cl 2 yielded the corresponding borenium cations, whose stability depends on the counteranion of the trityl salt. If the [BF 4 ] − salt was employed, then fluoride abstraction from the anion occurred immediately, yielding PMAF-BF 3 and other identifiable byproducts. If the [B(C 6 F 5 ) 4 ] − salt was employed, then the borenium ions were s… Show more

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Cited by 21 publications
(18 citation statements)
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References 51 publications
(111 reference statements)
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“…6 compared to that of À12. 3 for Cp*Fe(C 5 H 4 BBr 2 ), indicating a greater interaction between Fe and boron for the neutral borane [14]. These results again suggest an enhanced hard Lewis acidity for borocations due to the unit positive charge.…”
Section: Electrophilicity Of Borocationsmentioning
confidence: 75%
See 2 more Smart Citations
“…6 compared to that of À12. 3 for Cp*Fe(C 5 H 4 BBr 2 ), indicating a greater interaction between Fe and boron for the neutral borane [14]. These results again suggest an enhanced hard Lewis acidity for borocations due to the unit positive charge.…”
Section: Electrophilicity Of Borocationsmentioning
confidence: 75%
“…This result can again be attributed to the large degree of positive charge localised at boron in 1, which is generated by the bonding of boron to three highly electronegative atoms. Finally, Brunker and co-workers used the Gutmann-Beckett method to probe the Lewis acidity of a number of pentamethylazaferrocene ligated borenium cations including 4 and 5 [14]. Cation 4 was found to be more Lewis acidic towards Et 3 PO than 5, consistent with the reduced electronic stabilisation of boron bonded to two hydride substituents relative to two chloride π donor substituents.…”
Section: Electrophilicity Of Borocationsmentioning
confidence: 99%
See 1 more Smart Citation
“…Boronium macrocycle 4a was unambiguously characterized by using spectroscopicm ethods.I n particular, 1 HNMR spectroscopy revealed the highly symmetrical structure, andt he chemical shift of the boron atom in the 11 BNMR spectrum is consistent with ab oronium speciesi n [D 6 ]DMSO. [10,12,13] High-resolutionm asss pectrometry (HRMS) confirmed the dimeric macrocyclic structure with only two species detected after positive-mode electrosprayi onization (ESI): the bis-cation without bromide counterions ([4aÀ2Br] 2 + : m/z exptl 330.7102; m/z calcd 330.7109) and the monocation-bromide complex ([4aÀBr] + : m/z exptl 740.3409; m/z calcd 740.3406). In our hands, no suitable crystalsw ere obtained to determine the spatial arrangement of the imidazolyl units.…”
Section: Synthesis and Characterizationmentioning
confidence: 99%
“…Interestingly,d ue to the bulky 9-BBN group,t he two imidazolyl moieties of boronium 2b adoptapincer-like shape in which the bromide counterion displays an umber of close contacts with the cation.I nt his case, the bromine counterionf orms noncovalent hydrogen-bonding interactions with the electropositive (C2ÀH) + of the imidazolyl moieties (Figure 1, left). [12] In contrast with other known imidazoliumr eceptors, both imidazolyl cores in 2b are facing each other and conjointly bind the same bromide anion.I np articular,t he cationic charge is delocalized between the boron-centered cation [13] and the imidazolyl moieties, which confers am ore electropositive( C ÀH) + interaction.…”
Section: Introductionmentioning
confidence: 98%