Pd(II)‐catalyzed base‐free oxidative homocoupling of fluorene diboronic acid ester: A new approach for the synthesis of π‐conjugated polymers

Abstract

A new route, Pd(II)‐catalyzed base‐free oxidative homocoupling, has been successfully used for the synthesis of polyfluorene. Using only diboronic esters and a stable Pd(II) catalyst in the absence of base can greatly simplify the synthetic condition of conjugated polymers.

A new procedure for the synthesis of π-conjugated polymers via ligand-free iron(iii)-catalyzed oxidative homocoupling reaction of grignard reagents

“…Removing the fractions with low molecular weight by precipitation of the obtained polymer in a mixture solvent of THF and methanol (2 : 1, v/v) gave a polymer fraction with a M n of 11 960 and a PDI of 1.34. This result is superior to that previously reported by our group via the Pd(II)-catalyzed oxidative homopolymerization of diboronic esters, 24 suggesting that Fe(III) catalyzed oxidative homocoupling can give a high molecular weight of PFO which can meet the requirements of optoelectronic devices.…”

“…23 Previously, we have reported the synthesis of polyfluorene using a Pd(II)-catalyzed base-free oxidative homocoupling reaction of diboronic esters. 24 Our interest is to find cheap and practical methods for the synthesis of p-conjugated polymers. Thus, as part of an extended investigation, in this study we report the synthesis of p-conjugated polymers using the ligand-free iron(III)-catalyzed oxidative homocoupling of Grignard reagents.…”

“Benchtop” Biaryl Coupling Using Pd/Cu Cocatalysis: Application to the Synthesis of Conjugated Polymers

“…These reports showed that a bimetallic approach to homocoupling was possible, allowing for wet benchtop coupling conditions and green solvents, such as ethanol. However, in previous reports the catalyst loading for dimerization was high (5–10% Pd). , More recently, coupling of phenyl hydrazines suggested that catalytic amounts of copper­(II) could be used instead of stoichiometric amounts . However, the yields were generally moderate with a limited substrate scope when performed in water.…”

“…However, these reactions can call for specialized equipment to maintain an inert atmosphere, high temperatures, and/or specialized catalysts . Previous literature has shown that palladium-catalyzed homocoupling of diboronates is an effective strategy for making small polyfluorenes . However, these synthetic strategies required a pure oxygen atmosphere at 80 °C under strictly dry conditions which could trigger combustion on a reactor scale.…”

“…7 Previous literature has shown that palladium-catalyzed homocoupling of diboronates is an effective strategy for making small polyfluorenes. 8 However, these synthetic strategies required a pure oxygen atmosphere at 80 °C under strictly dry conditions which could trigger combustion on a reactor scale. To enhance the accessibility of these aromatic polymers we sought to create a method that used the oxygen in air as the oxidant, was tolerant to wet solvents, and operated at room temperature.…”