Tetrazolo[1,5-a]pyridine-Containing π-Conjugated Systems: Synthesis, Properties, and Semiconducting Characteristics.

The incorporation of an electron-accepting unit into π-conjugated systems is an important approach to modulate the physical properties of such molecules. To investigate the potential of tetrazolo[1,5-a]pyridine as an electron-accepting unit, a series of diarylated tetrazolo[1,5-a]pyridine derivatives was synthesized by treating the corresponding diarylated pyridine N-oxide with diphenylphosphoryl azide. Thermogravimetric analyses of these molecules indicated that they possessed good thermal stability. The bithiophene-substituted tetrazolo[1,5-a]pyridine compound showed stable transistor characteristics under repeated bias conditions.

Murahashi coupling polymerization: nickel(II)-N-heterocyclic carbene complex-catalyzed polycondensation of organolithium species of (hetero)arenes.

Revisiting Murahashi coupling, we found that it effectively allows polymerization of lithiated (hetero)arenes by nickel(II)-catalyzed polycondensation. Deprotonative polymerization of 2-chloro-3-substituted thiophene with n-butyllithium gave head-to-tail-type poly(3-substituted thiophene). Poly(1,4-arylene)s were obtained by the reaction of the corresponding dibromides through lithium-bromine exchange. A lithiated thiophene derivative obtained via deprotonative halogen dance also underwent polymerization to afford a bromo-substituted polythiophene.

Concise synthesis of well-defined linear and branched oligothiophenes with nickel-catalyzed regiocontrolled cross-coupling of 3-substituted thiophenes by catalytically generated magnesium amide.

The synthesis of linear and branched oligothiophenes of well-defined structures is performed with regioselective deprotonation of 3-substituted thiophenes and nickel-catalyzed cross-coupling of the thus formed metalated species with a bromothiophene. The reaction of 3-hexylthiophene with EtMgCl and 2,2,6,6-tetramethylpiperidine (TMP-H, 10 mol%) induces the metalation selectively at the 5-position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2-halo-3-hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head-to-tail (HT)-type dimer. By repeating the same sequence, the linear oligothiophene up to a 4-mer is synthesized in good yield. The reaction of 3-hexylthiophene with 2,3-dibromothiophene also takes place to afford a branched oligothiophene 3-mer in quantitative yield. The obtained 3-mer is also metalated at the sterically less-hindered position in a regioselective manner furnishing a 7-mer in >99% yield after a further coupling reaction with 2,3-dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes.

Synthesis of well-defined head-to-tail-type oligothiophenes by regioselective deprotonation of 3-substituted thiophenes and nickel-catalyzed cross-coupling reaction.

Iterative growth of thiophene oligomers by single-step extensions has been realized by regioselective metalation of 3-substituted thiophenes with the Knochel-Hauser base (TMPMgCl·LiCl) and coupling with bromothiophene using a nickel catalyst. Treatment of 3-hexylthiophene with TMPMgCl·LiCl induces metalation at the 5-position selectively. Subsequent addition of 2-bromo-3-hexylthiophene and a nickel catalyst leads to the corresponding bithiophene. The obtained bithiophene is converted to the terthiophene and then to the quaterthiophene by repeating the similar protocol. A concise synthesis of MK-1 and MK-2, which are organic dye molecules bearing an oligothiophene moiety that are used in photovoltaic cells, has been achieved.

C-H functionalization polycondensation of chlorothiophenes in the presence of nickel catalyst with stoichiometric or catalytically generated magnesium amide.

Polymerization of 2-chloro-3-substituted thiophenes proceeded with a stoichiometric amount of magnesium amide, TMPMgCl·LiCl, or a combination of a Grignard reagent and a catalytic amount of secondary amine in the presence of a nickel catalyst. Although the nickel-catalyzed polymerization with NiCl(2)dppe, which exhibited high catalytic activity in the reaction of bromothiophenes, was less effective, use of a nickel catalyst bearing N-heterocyclic carbene as a ligand was found to induce polymerization with controlled molecular weight and molecular weight distribution.

Palladium-catalyzed C-H functionalization of heteroarenes with aryl bromides and chlorides.

Palladium-catalyzed C-H arylation of electron-enriched heteroarenes with aryl bromides and aryl chlorides proceeds in the presence of LiO-t-Bu as a base. The reaction allows one-pot synthesis of differently substituted 2,5-diarylthiazole with the same catalyst system by switching the solvent and the amount of base.