Frustrated Lewis PairBehavior of Intermolecular Amine/B(C6F5)3Pairs.

Reactions of N,N-dimethylaniline, N-isopropylaniline, 1,4-C6H4(CH2NHtBu)2,and benzyldimethylamine with the Lewis acid B(C6F5)3have been studied. In the case of N,N-dimethylaniline the combination of the Lewisacid and base forms an almost completely noninteracting frustratedLewis pair, while the corresponding reactions of N-isopropylaniline and benzyldimethylamine with B(C6F5)3afford the adducts (PhNHiPr)B(C6F5)3(1) and PhCH2NMe2B(C6F5)3(2), respectively. 1,4-C6H4(CH2NHtBu)2reacts with 2 equiv of B(C6F5)3to give rise to an inseparablemixture of the mono- and bis-amine–borane adducts as well asan iminium salt derived from hydride abstraction from a benzylic carbonof the diamine. Subsequent selected reactions of the Lewis acid/basecombinations with H2afforded [PhNMe2H][HB(C6F5)3] (3), [PhCH2NMe2H][HB(C6F5)3] (4), and [1,4-C6H4(CH2NH2tBu)2][HB(C6F5)3]2(5). Reactions with CO2gave PhCH2NMe2CO2B(C6F5)3(6), [PhNiPrH2][PhNiPrCO2B(C6F5)3] (8), [1,4-C6H4(CH2NH2tBu)(CH2NtBuCO2B(C6F5)3] (9), and [C5H6Me4NMeH]2[1,4-C6H4(CH2NtBuCO2B(C6F5)3)2] (10). Interestingly, the species 4also reacts with CO2to give [PhCH2NMe2H][HCO2B(C6F5)3] (7). Species 8reacts with HSiEt3to yield [PhNiPrC(OSiEt3)OB(C6F5)3] (11). The adduct 2also reacts with ethene, 2,4-hexadiyne, and the alkynesHCCR (R = n-Bu, Ph, tBu,SiMe3) to give the 1,2- addition products PhCH2NMe2CH2CH2B(C6F5)3(12), PhCH2NMe2C(CCMe)=CMeB(C6F5)3(13), and the ammoniumalkynylborate salts [PhCH2NMe2H][RCCB(C6F5)3] (R = n-Bu (14a), Ph (14b), tBu (14c), SiMe3(14d)). In contrast, the reactionof 1-hexyne with the Lewis pair PhNMe2and B(C6F5)3affords the trans-1,2-addition productPhNMe2C(C4H9)=CH(B(C6F5)3) (15). This chemistry demonstratesthe generality of such FLP chemistry, extending it to N-based Lewisbases and thereby expanding the scope for applications of FLP chemistry. [ABSTRACT FROM AUTHOR]