Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

Abstract

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.

Frustrated Lewis Pair Chemistry: Development and Perspectives

“…Thus contrasting reactivity is seen for 3 ] (318; Scheme 99), which illustrates both reaction pathways in a single molecule. [164] A related application of such P/B additions has been described by Yamaguchi and co-workers [165] who used the intramolecular addition of phosphines and boranes to make species including 319 that are of interest for electronic materials (Scheme 100).…”

“…This species also results from both addition and deprotonation reactions. [164] Similar to pendant olefins, alkyne fragments on an aniline ring have been exploited for intramolecular cyclizations. [162] Thus reaction of o-(pentynyl)-N,N-dimethyl toluidine or o- 3 yielded the cyclized products 328 and 329 (Scheme 103).…”

“…[163] Sulfur donors have also been employed in such FLP addition reactions. The sulfides R 2 S gave E-R 2 S(Ph)C = C(H)B(C 6 F 5 ) 3 (R = Me (334), PhCH 2 (335; Scheme 104) [164] which exist in equilibria with the alkyne and thioether borane adduct. The related dimeric intramolecular FLP, (PhSCH 2 B-(C 6 F 5 ) 2 ) 2 also reacts with the terminal and internal alkynes to give the species (PhSCH 2 B(C 6 F 5 ) 2 )(R'C=CR) (R = H, R' = Ph (336), R = H, R' = C 4 H 9 (337), R = Ph, R' = C 4 H 9 (338), R = R' = C 2 H 5 (339), R = R' = Ph (340)).…”

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

“…It is known from previous publications that FLPs react with terminal alkynes via deprotonative borylation pathway, producing the respective onium alkynylborates 41,42,43,44,45,46 . Indeed, 6 reacts with hex-1-yne giving the respective adduct 31 (Scheme 6).…”

Ammonium Chloride/B(C6F5)3System Catalyzed Selective Addition of Acids to Alkynes

“…FLPs 与醛酮和炔 烃的反应都是计量的化学反应. 如图 1 所示, 羰基类化 合物与氢化后的 FLPs 反应时, 会形成较强的 B-O 键化 合物 a [4] ; 而当受限路易斯酸碱对 FLPs 与端基炔烃反应 时, 因路易斯碱(LB)结构的不同反应会形成去质子产物 b 或 1,2-加成产物 c [5] ; 当路易斯酸三(五氟苯基)硼烷 (BCF)单独与炔烃反应时, 反应产物主要以 1,1-碳硼烷 化产物 d 为主 [6] . …”