Deprotonation and Addition Reactions of Frustrated Lewis Pairs with Alkynes

Deprotonation of terminal alkynes is effected by the treatment with tBu(3)P and B(C6F5)(3) to give [tBu(3)PH][PhCCB(C6F5)(3)] (la) and [tBu(3)PH][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 [tBu(3)PH](2)[(C6F5)(3)BCC(C6H4)CCB(C6F5)(3)](6). As well, use of differing Lewis acids afforded the species [tBu(3)PH][PhCCEAr3] (EAr3 = Al(C6F5)(3) 7, PhB(C6F5)(2) 8, BPh3 9). The corresponding reaction of Me3SiCCSiMe3 afforded [tBu(3)PSiMe(3)][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 center dot 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-(C(6)H(2)tEu(3))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-(otol)(3)P(Ph)C= C(H)Al(C6F5)(3) (21). The macrocyclic [(H)C=C(Ph)Mes(2)PC(6)F(4)B(C6F5)(2)](2) (22) was prepared from the analogous alkyne addition to Mes(2)PC(6)F(4)B(C6F5)(2), while E-Ph2PCH2CH7PPh2-(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 tBu(3)P and B(C6F5)(3) yielded the unusual salt/zwitterion [tBu(3)PH][(C6F5)(3)BCC C6H4C(PPh3)=C(H)-B(C(6)Fs)(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][PhCC(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 [ItBuFl][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.