Multiple Pentafluorophenylation of 2,2,3,3,5,6,6-Heptafluoro-3,6-dihydro-2H-1,4-oxazine with an Organosilicon Reagent: NMR and DFT Structural Analysis of Oligo(perfluoroaryl) Compounds

Abstract

F 5 ) was used for the preparation of a series of perfluorinated, pentafluorophenyl-substituted 3,6-dihydro-2H-1,4-oxazines (2 -8), which, otherwise, would be very difficult to synthesize. Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the starting compound 1 (Scheme), but also in para position of the introduced C 6 F 5 substituent(s) leading to compounds with one to three nonafluorobiphenyl (C 12 F 9 ) substituents. While the tris(pentafluorophenyl)-substituted compound 3 could be isolated as the sole product by stoichiometric control of the reagent, the higher-substituted compounds 5 -8 could only be obtained as mixtures. The structures of the oligo(perfluoroaryl) compounds were confirmed by 19 F-and 13 C-NMR, MS, and/or X-ray crystallography. DFT simulations of the 19 F-and 13 C-NMR chemical shifts were performed at the B3LYP-GIAO/6-31++G(d,p) level for geometries optimized by the B3LYP/6-31G(d) level, a technique that proved to be very useful to accomplish full NMR assignment of these complex products.

Computational 19F NMR. 1. General features

“…Lines connect pairs of non-equivalent spins in A m X n spin systems F-C-Cl or F-C-C-Cl arrangement (quite common in chlorofluorocarbons). The reference compound (CFCl 3 ) is known to exhibit a three-line signal due to isotope shifts between isotopomers differing in 35 Cl/ 37 Cl content, so that criticisms have been leveled at its suitability as a reference signal. Computational predictions of such isotope shifts [40] are of the order of 20 ppm for 19 F in CFCl 3 ; however, experimental measurements in several chlorofluorocarbons have shown that such shifts give rise to easily detectable splittings, but amount to no more than 5-7 ppb when F and Cl are separated by 2 bonds [111].…”

“…Some early computational work (aimed at benchmarking and validation) included F 2 as test molecule, which proved to be challenging [26][27][28]. Interest in modeling 19 F shifts has steadily continued, and several papers have appeared in the last decade aimed at general structural issues, solution chemistry and physical organic chemistry, [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] solid-state issues (especially the prediction of chemical shift tensors), [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] J-couplings [65][66][67][68][69][70][71][72]…”

Formation of perfluorinated polyphenylenes by multiple pentafluorophenylation using C6F5Si(CH3)3

“…Thus, in both the previously reported results and in the cases presented here, it is considered that adventitious water molecules attacked the C 6 F 5 Si(CH 3 ) 3 in the presence of a catalytic amount of fluoride anion before the reaction of perfluoroarenes with C 6 F 5 Si(CH 3 ) 3 ; then, the hydrogenation product C 6 F 5 H reacted with another [ ( S c h e m e _ 2 ) T D $ F I G ] molecule of C 6 F 5 Si(CH 3 ) 3 resulting in the formation of p-H(C 6 F 4 ) n F (8f). The electronegative substituent stabilizes the additionelimination intermediate proposed in our previous report [18]; therefore, the intermediate easily formed before the hydrogenation of C 6 F 5 Si(CH 3 ) 3 to prevent the formation of C 6 F 5 H and p-H(C 6 F 4 ) n F.…”

“…Although these perfluorinated oligo(phenylene)s 2a-4a have been reported previously [6,14], detailed assignments of 19 F NMR peaks have not been established. We assigned the 19 F NMR peaks of linear perfluoroaryl compound 2a-4a using a 19 F-19 F homodecoupling method and employed the assignments of our previous study [18]. In similar fashion to 1a, octafluorotoluene (1b) provided linear perfluoroaryl derivatives 2b, 3b, and 4b by the terminal position attack of C 6 F 5 Si(CH 3 ) 3 (Table 1, Entries 4 and 5).…”

Reactions of Highly Branched Perfluoroolefins with (Pentafluorophenyl)trimethylsilane: Characterization of the Unique Structural Properties of Perfluorinated Super‐Congested Systems

“…A transfer reagent of a fluorinated substituent, C 6 F 5 Si(CH 3 ) 3 , which is prepared by the reaction of C 6 F 5 Br, ClSi(CH 3 ) 3 , and P[N(CH 3 ) 2 ] 3 , was known as a useful pentafluorophenylating reagent for the preparation of perfluoroolefins, perfluoroazaalkenes, or perfluorinated carbonyl compounds . We have reported that the reaction of perfluorinated 3,6‐dihydro‐2 H ‐1,4‐oxazine with C 6 F 5 Si(CH 3 ) 3 provided a series of perfluorinated perfluoroaryl‐substituted 3,6‐dihydro‐2 H ‐1,4‐oxazines . Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the oxazine ring, but also in the para position of the introduced C 6 F 5 substituent(s) leading to the compounds with one to three nonafluorobiphenyl (C 12 F 9 ) substituents.…”