Synthesis, structure, and spectral behavior of donor-acceptor substituted biphenyls

Abstract

Reaction of the activated halonitrobenzenes 2a-f with the bis-and tris(dialkylamino)benzenes la--e affords, via a direct nucleophilic substitution, the highly substituted biphenyls 3a-o; the lesser substituted biphenyls 5 and 6 were prepared by an Ullmann reaction. All these biphenyls are deeply colored; the dark red color can be assigned to an intramolecular charge transfer. A crystal structure determination was carried out for 2,4,6-tripyrrolidino-2',4',6'-trinitrobiphenyl (3a): space group C2/c, a = 16.071 (2) A, b = 14.545 (1) A, c = 20.177 (2) A, {3 = 91.361 (9)°, Z = 8 (temperature", 120 K). The dihedral angle between the two arene rings was found to be only 52.5°, despite the four bulky substituents in the o,o'-positions. With this far-from-orthogonal torsional angle about the biphenyl linkage, the strong intramolecular charge transfer from the 7r system of the donor into the 7r system of the acceptor arene becomes easily understandable. A PPP calculation with the torsional angles taken from the X-ray structure analysis satisfactorily reproduces the experimental absorption spectrum of 3a.The shift of the long-wavelength absorption between the individual biphenyls 3a-o, 5, and 6 likewise is accounted for satisfactorily by the calculation; it depends primarily on the intrinsic donor strength of the different NR2likewise mirror this gradation in N~ donor capacity; they also show that steric hindrance at the biphenyl linkage is mainly the result of interaction between the o-dialkylamino groups and the C a skeleton of the acceptor arene. This is borne out by the crystal structure analysis.In a preliminary paper 3 we have reported the facile synthesis of donor-acceptor substituted biphenyls via nucleophilic aromatic substitution of activated haloarenes by electron-rich aminobenzenes. These biphenyls are isolated as lustrous crystals which are surprisingly deep red to almost black. Because of the bulky substituents in 0-and a '-positions, one would expect a nearly orthogonal orientation, and thus negligible mesomeric interaction, of the two phenyl rings. The dark red color had to be attributed to intramolecular charge-transfer processes, though, on the basis of the spectroscopic data and of calculations. 4It seemed desirable to test the scope of the new biphenyl synthesis, beyond those examples already reported,3,4 with respect to the reactivity limits for the amino-as well as the halo benzene components. This would allow for a systematic substituent variation in both the donor and acceptor moieties of the biphenyls, a prerequisite for a definitive study of the low-energy absorption, and thence of the bonding in these compounds.We now report the preparation of a fairly wide range of donor-acceptor substituted biphenyls, together with the crystal structure analysis of one representative member, 2,4,6-tripyrrolidino-2',4',6'-trinitrobiphenyl. The IH NMR spectra are discussed in terms of ground-state solution conformation, and the nature of the long-wavelength electronic transition is established unequivocally on t...

2-[2-Hydroxy-4-(pyrrolidin-1-yl)benzoyl]benzoic acid

“…1). Bond lengths and angles within the pyrrolidine rings are normal and in good agreement with those reported previously for 2,4,6tripyrrolidino-2′,4′,6′-trinitrobiphenyl (Effenberger et al, 1983). The dihedral angles between the planes of the benzene rings in the two independent molecules are 56.8 2 (Bernstein et al, 1995).…”

“…For the synthesis and applications of the title compound, see: Lee et al (2005); Masakichi et al (1974); Luo et al (1994). For bond-length and angle data for pyrrolidines, see : Effenberger et al (1983). For hydrogen-bond motifs, see: Bernstein et al (1995).…”

1,1’,1’’-(2’,4’-Dinitro-[1,1’-biphenyl]-2,4,6-triyl)tripiperidine

“…It must be noted that Effenberger [15] reported that the reaction between 2 and 1-chloro-2, 4-dinitrobenzene in 1:1 chloroform/ethanol at reflux did not occur. In the current case, the use of the more electrophilic fluoroderivative allowed us to obtain the novel compound, bearing contemporarily an electron donor and an electron acceptor moiety, which makes it of interest in the applied field as well as a potentially useful precursor in hair-dyeing technique.…”

C-C Coupling Reactions between Benzofurazan Derivatives and 1,3-Diaminobenzenes

“…The 1,3,5-triaminobenzene derivatives—first studied by the pioneer work of Effenberger [ 1 ]—belong to neutral electron-rich aromatic substrates and are able to react at the neutral carbon atom [ 1 , 2 ]. (These kinds of nucleophiles have been reported to react with a plethora of electrophiles, such as proton [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ], halogens [ 11 , 12 ], acyl- [ 13 , 14 , 15 ], alkyl- [ 16 ], and aryl-halides [ 17 ]. The coupling between 1,3,5-triaminobenzene of types A and B and aryl diazonium salts gave stable Wheland intermediates ( W ) by the azo-coupling reaction [ 18 ] ( Scheme 1 ), conversely to what is usually reported in the textbooks.…”

“…Contrarily to the case of 1,3,5-triaminobenzenes, few examples of C-C coupling involving diaminobenzene derivatives [ 17 , 42 , 43 , 44 ] are present in the literature, likely due to their minor carbon nucleophilicity with respect to 1,3,5-triaminobenzenes.…”