5,5 -Dimethyl-2,2 -bithiophene

Figure 8.14. Chemical structures of a series of the dimethyl-substituted oligothiophenes. The structures denote dimethyl-bithiophene (dimer DMBT), dimethylterthiophene (trimer DMTT), dimethylquaterthiophene (tetramer DMQtT), di-methylquinquethiophene (pentamer DMQqT), and dimethyl-sexithiophene (hexamer DMSxT) from the top. The x and y axes represent the directions of the molecular long and short axes, respectively. Reprinted with permission from Reference 174. Copyright 1993 American Chemical Society.

The step 6 product (12 mmol) and bis(trimethylstenyl)bithiophene (12 mmol) were added to a reactor under a nitrogen atmosphere and dissolved in anhydrous dimethyl formamide (DMF) with gentle heating. The solution was then treated with tetrakis(tri-phenylphosphine) palladium(O) (about 10mol% based on the total amount of reagents) and reacted at 8°C for 6 hours. The mixture was then treated with dilute hydrochloric acid solution and extracted with CHCI3 and then concentrated by... 

Early studies showed that polymers possessing some regiospecificity exhibit improved electrical and magnetic properties when compared to random polythiophenes [234]. In this instance, P3ATs 56 were synthesized by polymerization of 3,3 -dialkyl-2,2 -bithiophene 55 as shown in Scheme 55. Polymerization either electrochemically or via Lewis acid yielded predominantly HH-coupled polymers whose absorption maxima blue shifted -90 nm for 3,3,-dimethyl-2,2 -... 

Poly(3,3,-dimethyl-2,2 -bithiophene) shows an absorption maximum at 417 nm (90MM1268). Poly(3-phenylthiophene), on the contrary, showed absorption at 425-432 nm (91MM2694). Polythienothiophene and polydithienothiophene showed absorption maxima at 2.83 and 2.67 eV, while the fluorescence maxima were at 1.95 and 1.92 eV, respectively (87SM(18)177). 

Na2C03, THF, H20, 60% (d) Pd(PPh3)4, 2-formylthiophene-5-boronic acid, Na2C03, THF, H20, 50% (e) n-BuLi, B(OBu)3 then Pd(PPh3)4, 5-iodo-5 -formyl-2,2 -bithiophene, Na2C03, THF, H20, 48% (f) 2,3-dimethyl-2,3-bis(hydroxyamino)butane sulfate, methanol then Nal04, CH2CI2, 2-15%. 

Conformational analysis was carried out on the molecules shown in Figure 42 <2002CPL(363)18>. One group consists of thiophene-phenylene-thiophene (TPT) 178, dimethyl-substituted TPT (DMTPT) 179, and dimethoxy-substituted TPT (DMOTPT) 180, and the other group is composed of dihexyl-substituted bithiophene (DHBT) 175 and dicyclohexyl-substituted bithiophene (DCBT) 181. 

Figure 8.11 Experimental and B3LYP/6-31C(d,p)-calculated Infrared spectra of 3,3 -dimethyl-2,2 -bithiophene (HH-Me2T) for the planar and distorted conformations. Reprinted from J. Serrano, J. Casado, V. Hernandez, L Favaretto, C. Distefano and j. T. Lopez Navarrete, Vibrational and theoretical DFT study of two regioregular methyl-disubstituted bithiophenes, J. Mol. Struct, 563-564, 539-540 (2001), with permission from Elsevier...

Miller and co-workers [100] described the electrochemical behavior of bithiophene and terthiophene whose terminal a-positions have been blocked with methyl or methylsulfanyl substituents to prevent polymerization. As expected, due to the presence of methyl blocking groups, anodic oxidation of dimethyl-terthiophene 26 undergoes a one reversible oxidation (Eqx = 0.99 V vs SCE). When stronger electron-donor groups such as methylsulfanyl are used, the oxidized states of both bithiophene 27 and terthiophene 28 cores are stabilized (Scheme 9.19). Consequently, their CV traces exhibit two one-electron reversible redox couples associated with the formation of stable radical cations and dications (Eox = 0.93 and Eox = 1.17 V vs SCE for 27 and ox = 0.89 and Eox = 1.02 V vs SCE for 28). As already discussed, the difference... 

Dibromo-3,3 -diinethyl-2,2 -bithiophene (2-13) [42] To a solution of 3,3 -dimethyl-2,2 -bithiophene (680 mg, 3.51 mmol) in THF (30 mL) was added A-bromosuccinimide (1.25 g, 7.01 mmol). After stirred overnight, the reaction was quenched with water. The aqueous layer was extracted with CH2CI2, the combined extracts were washed with distilled water, dried over anhydrous Na2S04. After removal of the solvents under reduced pressure, the residue was pmified via chromatography with silica (petroleum ether as eluent) to give yellow oil 12 (800 mg, yield 58 %). H NMR (CDCI3, 300 MHz, ppm) 8 6.88 (s, 2H), 2.12 (s, 6H). 

In the oxidation of dimethyl-bis-(5-trimethylsilyl-2-thienyl)silane, having two thiophene moieties, with one equivalent of m-CPBA, one thiophene ring was preferentially oxidized to afford only the mono-sulfone 52 in 36% yield. After further addition of m-CPBA, the corresponding mono-sulfone 52 and bis-sulfone 53 were obtained in 21 and 41% yields, respectively (Scheme 53) [64], In another example, the oxidation of 2,5 -bis(n-hexyl)-2,2 -bithiophene was found to be difficult the monodioxide 54 was obtained in low yield (10%), but no bis-6,6-dioxide was observed (Scheme 54) [61],... 

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