General room-temperature Suzuki-Miyaura polymerization for organic electronics.

π-Conjugated polymers (CPs) have broad applications in high-performance optoelectronics, energy storage, sensors and biomedicine. However, developing green and efficient methods to precisely synthesize alternating CP structures on a large scale remains challenging and critical for their industrialization. Here a room-temperature, scalable and homogeneous Suzuki-Miyaura-type polymerization reaction is developed with broad generality validated for 24 CPs including donor-donor, donor-acceptor and acceptor-acceptor connectivities, yielding device-quality polymers with high molecular masses. Furthermore, the polymerization protocol significantly reduces homocoupling structural defects, yielding more structurally regular and higher-performance electronic materials and optoelectronic devices than conventional thermally activated polymerizations. Experimental and theoretical studies reveal that a borate transmetalation process plays a key role in suppressing protodeboronation, which is critical for large-scale structural regularity. Thus, these results provide a general polymerization tool for the scalable production of device-quality CPs with alternating structural regularity.

An Efficient Direct Arylation Polycondensation via C-S Bond Cleavage.

The direct arylation polycondensation (DArP) has become one of the most important methods to construct conjugated polymers (CPs). However, the homocoupling side-reactions of aryl halides and the low regioseletive reactivities of unfunctionalized aryls hinder the development of DArP. Here, an efficient Pd and Cu co-catalyzed DArP was developed via inert C-S bond cleavage of aryl thioethers, of which robustness was exemplified by over twenty conjugated polymers (CPs), including copolymers, homopolymers, and random polymers. The capture of oxidative addition intermediate together with experimental and theoretic results suggested the important role of palladium (Pd) and copper (Cu) co-catalysis with a bicyclic mechanism. The studies of NMR, molecular weights, trap densities, two-dimensional grazing-incidence wide-angle X-ray scattering (2D-GIWAXS), and the charge transport mobilities revealed that the homocoupling reactions were significantly suppressed with high regioselectivity of unfunctionalized aryls, suggesting this method is an excellent choice for synthesizing high performance CPs.

Copper-Catalyzed Radical Enantioselective Carbo-Esterification of Styrenes Enabled by a Perfluoroalkylated-PyBox Ligand.

Chiral lactones are found in many natural products. The reaction of simple alkenes with iodoacetic acid is a powerful method to build lactones, but the enantioselective version of this reaction has not been implemented to date. Herein, we report the efficient catalytic radical enantioselective carbo-esterification of styrenes enabled by a newly developed CuI -perfluoroalkylated PyBox system. Simple styrenes have been converted to useful chiral lactones, whose synthetic applications are showcased. Mechanistic studies reveal that this reaction is a rare example of an efficient ligand-decelerated system, in which the ligand decelerates the reaction, but the reaction is still efficient with reduced amounts of ligand. This uncommon catalytic system may inspire further consideration of the effect of ligands in asymmetric catalysis.

Iron-Catalyzed Alkylazidation of 1,1-Disubstituted Alkenes with Diacylperoxides and TMSN3.

An iron-catalyzed radical alkylazidation of electron-deficient alkenes is reported. Alkyl diacyl peroxides work as the alkyl source, and trimethylsilyl azide acts as the azido reservoir. This method features mild reaction conditions, wide substrate scope, and good functional group tolerance, providing a range of α-azido esters, an α-azido ketone, and an α-azido cyanide in high yields. These azides can be easily transferred into many kinds of amino acid derivatives.

Revealing the Iron-Catalyzed ß-Methyl Scission of tert-Butoxyl Radicals via the Mechanistic Studies of Carboazidation of Alkenes.

We describe here a mechanistic study of the iron-catalyzed carboazidation of alkenes involving an intriguing metal-assisted ß-methyl scission process. Although t-BuO radical has frequently been observed in experiments, the ß-methyl scission from a t-BuO radical into a methyl radical and acetone is still broadly believed to be thermodynamically spontaneous and difficult to control. An iron-catalyzed ß-methyl scission of t-BuO is investigated in this work. Compared to a free t-BuO radical, the coordination at the iron atom reduces the activation energy for the scission from 9.3 to 3.9 ~ 5.2 kcal/mol. The low activation energy makes the iron-catalyzed ß-methyl scission of t-BuO radicals almost an incomparably facile process and explains the selective formation of methyl radicals at low temperature in the presence of some iron catalysts. In addition, a radical relay process and an outer-sphere radical azidation process in the iron-catalyzed carboazidation of alkenes are suggested by density functional theory (DFT) calculations.

The Introduction of the Radical Cascade Reaction into Polymer Chemistry: A One-Step Strategy for Synchronized Polymerization and Modification.

Polymerization and modification play central roles in polymer chemistry and are generally implemented in two steps, which suffer from the time-consuming two-step strategy and present considerable challenge for complete modification. By introducing the radical cascade reaction (RCR) into polymer chemistry, a one-step strategy is demonstrated to achieve synchronized polymerization and complete modification in situ. Attributed to the cascade feature of iron-catalyzed three-component alkene carboazidation RCR exhibiting carbon-carbon bond formation and carbon-azide bond formation with extremely high efficiency and selectivity in one step, radical cascade polymerization therefore enables the in situ synchronized polymerization through continuous carbon-carbon bond formation and complete modification through carbon-azide bond formation simultaneously. This results in a series of α, ß, and γ poly(amino acid) precursors. This result not only expands the methodology library of polymerization, but also the possibility for polymer science to achieve functional polymers with tailored chemical functionality from in situ polymerization.

Copper(I)-Catalyzed Cyanoperfluoroalkylation of Alkynes.

A highly chemoselective and regioselective copper-catalyzed radical cyanoperfluoroalkylation of alkynes is described. This three-component reaction directly uses commercially available alkynes, perfluoroalkyl iodides, and trimethylsilyl cyanide as the reaction partners and delivers a variety of perfluoroalkylated cyanoalkenes in good yields. Broad substrate scope and good functional group tolerance are observed. The perfluoroalkylated cyanoalkenes that are produced can be readily transformed into useful fluoroalkylated derivatives.

Iron-catalyzed carboazidation of alkenes and alkynes.

Carboazidation of alkenes and alkynes holds the promise to construct valuable molecules directly from chemical feedstock therefore is significantly important. Although a few examples have been developed, there are still some unsolved problems and lack of universal methods for carboazidation of both alkenes and alkynes. Here we describe an iron-catalyzed rapid carboazidation of alkenes and alkynes, enabled by the oxidative radical relay precursor t-butyl perbenzoate. This strategy enjoys success with a broad scope of alkenes under mild conditions, and it can also work with aryl alkynes which are challenging substrates for carboazidation. A large number of diverse structures, including many kinds of amino acid precursors, fluoroalkylated vinyl azides, other specific organoazides, and 2H-azirines can be easily produced.

Iron(II)-Catalyzed Heck-Type Coupling of Vinylarenes with Alkyl Iodides.

An iron(II)-catalyzed radical alkyl Heck-type reaction of alkyl iodides with vinylarenes under mild conditions has been reported. t-Butyl peroxybenzoate (TBPB) behaves simultaneously as a radical relay initiator, a precursor for the generation of alkyl radical from alkyl iodides, and an oxidant to recycle iron(II)/iron(III). Unactivated primary, secondary, and tertiary alkyl iodides are compatible with the reaction conditions. The mechanistic studies suggest that a radical-polar-crossover pathway might be involved in the catalytic cycle.

Copper-Catalyzed Regioselective 1,2-Alkylesterification of Dienes to Allylic Esters.

Copper catalyzed 1,2-alkylesterification of 1,3-dienes with diacyl peroxides affords branched allylic esters in excellent regioselectivity, including products with a newly generated fully substituted carbon center. The only byproduct is CO2. The reaction proceeds by a radical mechanism as suggested by spin trap and crossover experiments.