ChemInform Abstract: B(C6F5)3‐Catalyzed Hydrosilation of Imines via Silyliminium Intermediates.

Blackwell, James M.; Sonmor, Eric R.; Scoccitti, Tiziana; Piers, Warren E.

doi:10.1002/chin.200115090

Cited by 7 publications

(13 citation statements)

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“…56,57 It is also of note that base capture of a silylium cation is a critical step in the proposed mechanism of catalytic hydrosilylation of imines with B(C 6 F 5 ) 3 . 58 Phosphine/Borane Addition Reactions with Alkynes. The mechanism of the deprotonation reactions described above has not been probed via kinetic study; however it is reasonable to suggest that alkyne electrophilic attack of the Lewis acid affords a transient carbocation, which in the presence of a bulky, basic phosphine such as tBu 3 P affords the phosphonium alkynyl borates (Scheme 4).…”

Section: Resultsmentioning

confidence: 99%

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

2010

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Deprotonation of terminal alkynes is effected by the treatment with tBu3P and B(C6F5)3 to give [tBu3PH][PhCCB(C6F5)3] (1a) and [tBu3PH][RCCB(C6F5)3] (R = nBu 2, tBu 3, Me3Si 4, and CpFe(C5H4) 5). In a similar fashion, FLP deprotonation of 1,4-diethynylbenzene was employed to prepare the salt [tBu3PH]2[(C6F5)3BCC(C6H4)CCB(C6F5)3] (6). As well, use of differing Lewis acids afforded the species [tBu3PH][PhCCEAr3] (EAr3 = Al(C6F5)3 7, PhB(C6F5)2 8, BPh3 9). The corresponding reaction of Me3SiCCSiMe3 afforded [tBu3PSiMe3][Me3SiCCB(C6F5)3] (10). For less basic phosphines, phosphine/borane addition reactions were observed with alkynes. Thus the species E-R3P(Ph)CC(H)B(C6F5)3 (R = o-tol 11, Ph 12) were prepared. In the latter case, Ph3P·B(C6F5)3 was employed. Similarly, E-Ph3P(CpFe(C5H4))CC(H)B(C6F5)3 (13), E-Ph3P(Ph)CC(Me)B(C6F5)3 (14), E-R2PH(Ph)CC(H)B(C6F5)3 (R = Ph 15, C6H2Me3 16), and E-(C6H2 tBu3)PH2(Ph)CC(H)B(C6F5)3 (17) were prepared. Again, variation in the Lewis acid afforded E-Ph3P(Ph)CC(H)EAr3 (EAr3 = PhB(C6F5)2 18, Al(C6F5)3 19), E-Ph3P(nBu)CC(H)Al(C6F5)3 (20), and E-(o-tol)3P(Ph)CC(H)Al(C6F5)3 (21). The macrocyclic [(H)CC(Ph)Mes2PC6F4B(C6F5)2]2 (22) was prepared from the analogous alkyne addition to Mes2PC6F4B(C6F5)2, while E-Ph2PCH2CH2PPh2(Ph)CC(H)B(C6F5)3 (23) and E-(CH2PPh2(Ph)CC(H)B(C6F5)3)2 (24) were derived from the reactions of Ph2PCH2CH2PPh2. The related addition reaction involving 1,4-diethynylbenzene gave E-HCCC6H4C(PPh3)C(H)B(C6F5)3 (25), while subsequent reaction with tBu3P and B(C6F5)3 yielded the unusual salt/zwitterion [tBu3PH][(C6F5)3BCCC6H4C(PPh3)C(H)-B(C6F5)3] (26). Reaction of PhCH2NMe2 with PhCCH and B(C6F5)3 gave give a 84:16 mixture of [PhCH2NMe2H][PhCCB(C6F5)3] (27a) and PhCH2NMe2(Ph)CC(H)B(C6F5)3 (27b), while imines were used to prepare [(tBu)HNCHPh][PhCCB(C6F5)3] (28) and [(tBu)HNCPh2][PhCCB(C6F5)3] (29). The corresponding reaction of tBuNCNtBu, B(C6F5)3, and two equivalents of PhCCH led to the unusual product [tBuNCN(H)C(Ph)C(H)tBu][PhCCB(C6F5)3] (30). Finally, non-pnictogen Lewis bases were explored. The reaction of the N-heterocyclic carbene ItBu with B(C6F5)3 and PhCCH was shown to yield the deprotonation product [ItBuH][PhCCB(C6F5)3] (31), while the sulfides R2S gave E-R2S(Ph)CC(H)B(C6F5)3 (R = Me 32, PhCH2 33). The formation of these latter sulfide zwitterions was demonstrated to be reversible.

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Section: Resultsmentioning

confidence: 99%

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

2010

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“…Solvent corrections have also been included, using the COSMO model, 45 in the ΔG calculations for the energy of separation of the different ion-pairs. For the reactions done by Oestreich and co-workers, 26,75 Piers, Tuononen, and co-workers, 70 Piers and co-workers, 74 and Stephan and coworkers, 73,76 we have employed toluene with ε = 2.38, in order to model the solvent (toluene) that was employed in these reactions. For the reactions done by Chang and co-workers, 72 we have employed ε = 4.81 to model chloroform.…”

Section: ■ Computational Detailsmentioning

confidence: 99%

B(C₆F₅)₃: Catalyst or Initiator? Insights from Computational Studies into Surrogate Silicon Chemistry

Banerjee

Vanka

2018

ACS Catal.

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One of the most promising recent developments in catalysis has been the use of the metal-free Lewis acid B(C6F5)3 as a catalyst for a range of different chemical transformations. Perhaps the most impressive achievement in this regard is the recently accomplished in situ generation of SiH4 from surrogates (Simonneau and Oestreich, Nat. Chem., 2015, 7, 816). However, what the current computational work, with density functional theory, reveals is that this process, in addition to being catalyzed by B(C6F5)3, is also significantly dominated by a series of autocatalytic reactions. The results are further corroborated by the use of the energetic span model, which shows that the turnover frequency is higher for the newly proposed autocatalytic pathway in comparison to the conventional B(C6F5)3-catalyzed pathway. The current work therefore provides interesting new insights into surrogate silicon chemistry. But, more importantly, the current studies indicate that B(C6F5)3 is likely to function more as an initiator rather than a pure catalyst in many metal-free transformations that have been reported to date.

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“…tris(pentafluorophenyl)borane B(C6F5)3 can efficiently catalyze the hydrosilylation of carbonyl functions 10 and imines. 11 Therefore, we assumed that conceptually new and more acidic triazinium ions are required to facilitate the catalysis of reactions, which proved challenging with N,N-dialkyl substituted counterparts.…”

Section: Introductionmentioning

confidence: 99%

New generation of nitrenium salts: catalytic hydrosilylation of imines and a mechanism of action of nitrogen Lewis acids

Singh

Avigdori

Kaushansky

et al. 2022

Preprint

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Nitrogen Lewis acids (NLAs) are emerging as a powerful tool in strong bond activation and catalysis. Till now, N,N-dialkyl-nitrenium salts were known and utilized in chemical transformations. In this article, we report on the synthesis and characterization of a new generation of nitrenium-based Lewis acids – N,N-diaryl-substituted naphthotriazinium salts, which open a door to libraries of stereoelectronically modifiable catalysts. We exemplify the potency of these new Lewis acidic catalysts in a gram-scale hydrosilylation of various ketimines and aldimines in yields up to 99% and a catalyst loading as low as 0.1mol%. Notably, dialkyl-nitrenium salts proved inefficient in this reaction. Based on our experimental and theoretical studies, we elucidated, for the first time, the mechanistic action of nitrenium Lewis acids in such reduction-type reactions, demonstrating a unique hydridic behavior of N-H bonds in triazanes.

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ChemInform Abstract: B(C₆F₅)₃‐Catalyzed Hydrosilation of Imines via Silyliminium Intermediates.

Cited by 7 publications

References 1 publication

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

B(C₆F₅)₃: Catalyst or Initiator? Insights from Computational Studies into Surrogate Silicon Chemistry

New generation of nitrenium salts: catalytic hydrosilylation of imines and a mechanism of action of nitrogen Lewis acids

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ChemInform Abstract: B(C6F5)3‐Catalyzed Hydrosilation of Imines via Silyliminium Intermediates.

Cited by 7 publications

References 1 publication

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

B(C6F5)3: Catalyst or Initiator? Insights from Computational Studies into Surrogate Silicon Chemistry

New generation of nitrenium salts: catalytic hydrosilylation of imines and a mechanism of action of nitrogen Lewis acids

Contact Info

Product

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ChemInform Abstract: B(C₆F₅)₃‐Catalyzed Hydrosilation of Imines via Silyliminium Intermediates.

B(C₆F₅)₃: Catalyst or Initiator? Insights from Computational Studies into Surrogate Silicon Chemistry