Cross-coupling polycondensation via C–O or C–N bond cleavage

π-Conjugated polymers are widely used in optoelectronics for fabrication of organic photovoltaic devices, organic light-emitting diodes, organic field effect transistors, and so on. Here we describe the protocol for polycondensation of bifunctional aryl ethers or aryl ammonium salts with aromatic dimetallic compounds through cleavage of inert C–O/C–N bonds. This reaction proceeds smoothly in the presence of commercially available Ni/Pd catalyst under mild conditions, affording the corresponding π-conjugated polymers with high molecular weight. The method is applicable to monomers that are unreactive in other currently employed polymerization procedures, and opens up the possibility of transforming a range of naturally abundant chemicals into useful functional compounds/polymers.

20 mL of dry THF in an oven-dried flask was stirred and a solution of 2,7-dibromide-9,9-dihexylfluorine (0a) (1.968 g, 4 mmol) in 5 mL of dry THF was added slowly through a syringe. The solution was allowed to stir at reflux for 12 h and the obtained brown transparent solution was titrated with Te 2 Ph 2 [see: Aso, Y. et al. Simple titration method using diphenyl ditelluride as a colored indicator for the determination of organolithium and organomagnesium reagents. J. Org. Chem. 54, 5627-5629 (1989)] and kept carefully at room temperature.

Method B:
Under an argon atmosphere, a mixture of freshly cut magnesium turnings (0.972 g, 40 mmol) and 20 mL of dry THF in an oven-dried flask was stirred and 1,2-dibromoethane (7.5 mg, 0.04 mmol) was added. The mixture was heated to 50 °C over a period of 10 min, and a solution of 2,7-dibromide-9,9-dihexylfluorine (0a) (1.968 g, 4 mmol) in 5 mL of dry THF was added slowly through a syringe. The solution was allowed to stir at 50 °C for 1 h and the obtained brown transparent solution was titrated with Te 2 Ph 2 and kept carefully at 4 °C.

Method C:
In glovebox, a 50 mL Schlenk flask equipped with a Teflon-coated magnetic stirring bar was charged with freshly cut lithium (0.278 g, 40 mmol), anhydrous magnesium chloride (2.095 g, 22 mmol) and naphthalene (0.512 g, 4 mmol), and 20 mL of dry THF. Then the flask was taken out, the mixture was stirred vigorously with ultrasonic stirrer. A black precipitate started to form within a few minutes. The solution was allowed to stir at room temperature for 12 h, producing Rieke magnesium as a grey powder that settles slowly when the stirring is stopped. The Schlenk flask was moved into the glovebox and the Rieke magnesium was transferred to another Schlenk flask via cannula to separate from unreacted lithium. After about 20 minutes' standing, the supernatant was removed and 10 mL dry THF was added to the Rieke magnesium, repeated this operation until the THF is colorless, and the Rieke magnesium was ready for next usage.
Under an argon atmosphere, a mixture of Rieke magnesium (about 0.480 g, 20 mmol) and 10 mL of dry THF in an oven-dried Schlenk flask was stirred at -78 °C, and a solution of 2,7-dibromide-9,9-dihexylfluorine (0a) (1.968 g, 4 mmol) in 5 mL of dry THF was added slowly through a syringe. The solution was allowed to stir at -78 °C for 1 h and the obtained grey muddy solution was transferred into the centrifuge tubes in glovebox. The centrifuge tubes were carefully sealed and centrifuged at 3000 rpm for 30 minutes. The supernatant was removed into a Schlenk flask in glovebox and then titrated with Te 2 Ph 2 and kept carefully at 4 °C.
t BuLi (0.79 mL, 1.2 mmol, 1.52 M in n-pentane) was added dropwise and the resulted solution was stirred at the same temperature for 0.5 h. After that, solvent was removed by vacuum and the residue of 4a (0.3 mmol) was ready for next usage.
Preparation of Lithium Reagent 4c (Supplementary Fig. 1) To a solution of A (2.86 g, 10 mmol) in dichloromethane (100 mL) at 0 °C was added a solution of bromine (3.52 g, 22 mmol) and dichloromethane dropwise. After 12 hours of stirring with temperature allowed warming to room temperature, 30 mL of saturated sodium bisulfite were added and the mixture was stirred for another 30 minutes. The phases were separated and the organic phase was washed two times with 30mL of sodium bisulfite, two times with distilled water, dried over MgSO 4 and evaporated to give B (4.31 g, 97% isolated yield). Then B was dissolved in 50 mL acetone, K 2 CO 3 (5.53 g, 40 mmol) and 1-Iodododecane (8.88 g, 30 mmol) were added and the mixture was stirred at reflux for 12 hours. After the reaction, 50 mL of dichloromethane and 50 mL of water were added. The solution was washed twice with 50 mL saturated NaHCO 3 solution and once with 50 mL brine. The organic phase was dried and evaporated under reduced pressure. The yellow oil was purified by column chromatography on silica gel (Hexane/Ethyl acetate = 99/1) to give the product C (6.40 g, 82% isolated yield for two steps). The protocol for lithiation of C leading to 4c is the same as 0a to 4a.

Polycondensation between organolithium reagent 4 and dimethoxyarenes 2 (Supplementary
In a dry Schlenk flask charged with argon, organolithium reagent 4 (0.3 mmol, THF solution) was prepended according to above procedure. THF was then removed under vacuum at 0 °C. Toluene (1 mL) was then added, stirred for 1 minute and again removed under vacuum. After that, dimethoxyarenes 2 (0.3 mmol), Ni(cod) 2 (0.03 mmol), SIMes (0.03 mmol, SIMes was in-situ prepared by treating SIMes • HCl with stoichiometric amounts of EtMgBr) and toluene (1 mL) were added. This reaction mixture was stirred overnight (> 12 h) at 90 °C before quenched by 1M HCl (5 mL). The aqueous layer was extracted with CH 2 Cl 2 (3 x 5 mL), dried over MgSO 4 , filtered, and concentrated under vacuum. The residue was then dissolved in a minimum amount of CH 2 Cl 2 (ca. 1 mL) and precipitated into MeOH (100 mL). The precipitate was collected and dried under vacuum. Table. 3)

Polycondensation between Grignard reagent 1 and ammonium salts 5 (Supplementary
In a dry Schlenk flask charged with argon, Grignard reagent 1 (0.3 mmol, THF solution) was added. Then the ammonium salts 5 (0.3 mmol) and PdCl 2 (PCy 3 ) 2 (0.003 mmol) was added in to the above solution of 1. The resulted mixture was stirred overnight (> 12 h) at room temperature before quenched by water (5 mL). The mixture was extracted with CH 2 Cl 2 (3 x 5 mL), dried over MgSO 4 , filtered, and concentrated under vacuum. The resulting residue was then dissolved in a minimum amount of CH 2 Cl 2 (ca. 1 mL) and precipitated into MeOH (100 mL). The precipitate was collected and dried under vacuum.