Addition of Enamines or Pyrroles and B(C6F5)3 "Frustrated Lewis Pairs" to Alkynes

Reaction of 1-morpholinocyclohexene with B(C6F5)(3) and phenylacetylene gave a mixture of two compounds, [C6H10N(CH2CH2)(2)O][PhCCB(C6F5)(3)] (1a) and C6H9(2-PhC=C(H)B(C6F5)(3))-(N(CH2CH2)(2)O (1b). The analogous reaction with ethynylferrocene resulted in only the deprotonation product, the alkynyl-borate salt [C6H10N(CH2CH2)(2)O][CpFe(C5H4)CCB(C6F5)(3)] (2). The related reactions of pyrrole, phenylacetylene, and B(C6F5)3 led to the vinyl-borate addition product, HNC4H4(2-PhC=C(H)B(C6F5)(3)) (3). In a similar fashion, reaction of N-methylpyrrole, phenylacetylene, and B(C6F5)(3) gave a 3:2 ratio of the products MeNC4H4(2-PhC=C(H)B(C6F5)(3)) (4a) and MeNC4H4(3-PhC=C(H)B(C6F5)(3)) (4b), while the corresponding reaction of N-tert-butylpyrrole with phenylacetylene and B(C6F5)(3) provided a single product, tBuNC(4)H(4)(3-PhC=C(H)B(C6F5)(3)) (5a). Variations in the aryl alkynes produced the corresponding addition complexes, tBuNC(4)H(4)-(3-ArC=C(H)B(C6F5)(3)) (Ar = P-C6H4Br 5b, m-C6H4Cl 5c, p-C6H4CF3 5d, CpFe(C5H4) 5e). Similarly MeNC4H2(2,5-Me-2)(3-ArC=C(H)B(C6F5)(3)) (Ar = Ph 6a, p-C6H4Br 6h, m-C6H4Cl 6c, p-C6H4CF3 6d, CpFe(C5H4) 6e) were derived from 1,2,5-trimethylpyrrole. The species 5a and 5b were shown to rearrange to give tBuNC(4)H(3)(3-ArC=C(H)(C6F5)B(C6F5)(2)) (Ar = Ph 7a, CpFe(C5H4) 7b). The related complexes RNC4H3(3-PhC=C(H)(C6F5)B(C6F5)(2)) (R = SiMe3 8, Ph 9) and MeNC4H-(2,5-Me-2)(3-PhC=C(H)(C6F5)B(C6F(5))(2)) (10) were derived directly from the corresponding reactions of the pyrrole, PhCCH, and B(C6F5)(3). In the case of the reaction of N-tert-butylpyrrole, phenylacetylene, and PhB(C6F5)2, phenyl group migration was observed, affording exclusively the species tBuNC(4)H(3)(3-PhC=C(H)(Ph)B(C6F5)(2)) (11). Reaction of 5a or 4a/4b and iBu(3)P resulted in deprotonation and formation of the salts [tBu(3)PH][RNC4H3(X-PhC=C(H)B(C6F5)(3))] (R = tBu, X = 3 12; R = Me X = 2 13a, 3 13b). Reaction of 5a-d or 6a-d with one equivalent of Et3PO mediated proton transfer to generate a series of vinyl pyrroles tBuNC(4)H(3)(3-ArC=CH2) (Ar = Ph 14a, p-C6H4Br 14b, m-C6H4Cl 14c, p-C6H4CF3 14d) and MeNC4H2(2,5-Me,)(3-ArC=CH3) (Ar = Ph 15a, p-C6H4Br 15b, m-C6H4Cl 15c, p-C6H4CF3 15d) and the byproduct Et3PO center dot B(C6F5)(3).