4-Alkyl-2,2’-bithiophene

In the case of poly(3-alkyl-2,2 -bithiophene)s there are no head-to-head couplings or side chain clashes even for the regiorandom polymer (Figure 6). Oxidative polymerization of 4-alkyl-2,2 -bithiophenes with FeCla results in a completely regiorandom polymer which contains head-to-head couplings (17%),(57) but no side chain clashes (Figure 6). The absorption maximum for the poly(3-octyl-2,2 -bithiophene) is red shifted relative to poly(4-octyl-2,2 -bithiophene) as expected (Table VII) due to its lack of head-to-head linkages. In the solid state spectra, there are few differences between polymers derived from the 3-alkyl and 4-alkyl isomers.(28,54,67)... 

Polythiophenes substituted regioregularly with alkyl chains were prepared by the polymerization of alkylated bithiophenes and terthiophene. Souto et al. polymerized 3,3 -dihexyl-2,2 -bithiophene (41) with iron(III)... 

A range of alkoxy groups11 5,6, 7 has also been added to the bithiophene starting material to reduce the oxidation potential even further. Attachment of the alkyl group 7 also facilitates the solubility of the polymer in nonpolar organic solvents. 

Alkoxy-substituted bithiophenes have also been successfully polymerized, using Cu(C104)2 as oxidant.50 As with related FeCl3 oxidations of alkyl-substituted bithiophenes,51 these dimeric substrates are easier to oxidize than the corresponding substituted thiophene monomers, due to their lower oxidation potentials. 

As in the cases of pyrrole and aniline polymers, both chemical and electrochemical procedures have been employed in the synthesis of polythiophene (PTH) and its derivatives. The thiophene polymers exhibit remarkable stability in air and water [119], The alkyl-substituted derivatives also exhibit a high degree of processability [120,121]. PTH has also been synthesized from bithiophane (the dimer) or terthiophene (the trimer). The resulting poly(2,2 -bithiophene) (PbTH) and polyterthiophene (PtTH) are more ordered than PTH and appear to have the same basic structure as the starting monomer [117,122],... 

The introduction of an alkoxy substituent instead of an alkyl one leads to a significant improvement of the conjugation. The maximum of the 7t—rt absorption peak in HH-TT coupled poly(3,3 -dibutoxy-2,2 bithiophene) is about 200 nm red shifted with respect to the corresponding peak in poly(3,3 -dibutyl-2,2 -bithiophene) [56,57]. 

Replacement of one PEts ligand by a phosphite leads to new series of phosphine/phosphite or bis(phosphite) complexes the differences in ability to promote HDS were accounted for in terms of donor-acceptor properties of the ligands involved in each case. Thiophene substituted with groups other than alkyls (e.g., -Cl, -NO2, -OMe, -OAc) also form thiaplatinacycles, which are notable in that they promote catalytic desulfurization. These substituted thiophenes also produced the first thiapalladacycles by reaction with the corresponding Pd-phosphine complexes, as well as Ni analogs.3,6-Dimethylthieno[3,2- ]thiophene also forms a thiaplatinacycle by activation of a C(vinyl)-S bond upon reaction with [Pt(PEt3)4] 2,2 -bithiophene and l-methyl-2-(2-thienyl)pyrrole react similarly but also promote G-H activation. 

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