Soluble Head-to-Tail Regioregular Polythiazoles: Preparation, Properties, and Evidence for Chain-Growth Behavior in the Synthesis via Kumada-Coupling Polycondensation

Intramolecular Palladium Catalyst Transfer on Benzoheterodiazoles as Acceptor Monomers and Discovery of Catalyst Transfer Inhibitors

Intramolecular catalyst transfer on benzoheterodiazoles was investigated in Suzuki-Miyaura coupling reactions and polymerization reactions with t Bu3 PPd precatalyst. In the coupling reactions of dibromobenzotriazole, dibromobenzoxazole, and dibromobenzothiadiazole with pinacol phenylboronate, the product ratios of monosubstituted product to disubstituted product were 0/100, 27/73, and 89/11, respectively, indicating that the Pd catalyst undergoes intramolecular catalyst transfer on dibromobenzotriazole, whereas intermolecular transfer occurs in part in the case of dibromobenzoxazole and is predominant for dibromobenzothiadiazole. The polycondensation of 1.3 equivalents of dibromobenzotriazole with 1.0 equivalent of para- and meta-phenylenediboronates afforded high-molecular-weight polymer and cyclic polymer, respectively. In the case of dibromobenzoxazole, however, para- and meta-phenylenediboronates afforded moderate-molecular-weight polymer with bromine at both ends and cyclic polymer, respectively. In the case of dibromobenzothiadiazole, they afforded low-molecular-weight polymers with bromine at both ends. Addition of benzothiadiazole derivatives interfered with catalyst transfer in the coupling reactions.

Rethinking Catalyst Trapping in Ni-Catalyzed Thieno[3,2-b]thiophene Polymerization

Catalyst-transfer polymerization (CTP) is a chain-growth method used to synthesize conjugated polymers. Although CTP works well for most donor-type monomers, the polymerization stalls with thieno[3,2-b]thiophene when using Ni catalysts. Previous reports have rationalized this result by suggesting that the catalyst is trapped in a Ni0 π-complex with the highly electron-rich arene. In this study, evidence is provided that the catalyst trap is more likely a NiII complex that arises from oxidative insertion of Ni0 into the C-S bonds of thieno[3,2-b]thiophene. This result is consistent with the known reactivity of Ni0 complexes toward S-heteroarenes and is supported herein by 31P nuclear magnetic resonance spectra acquired in situ, as well as data collected from small-molecule model reactions and density-functional theory simulations of the polymerization. We propose that this C-S insertion pathway and related off-cycle reactions may be relevant to understanding or enabling the CTP of other monomers with fused thiophenes.

Universal Suzuki-Miyaura Catalyst-Transfer Polymerization for Precision Synthesis of Strong Donor/Acceptor-Based Conjugated Polymers and Their Sequence Engineering

Catalyst-transfer polymerization has revolutionized the field of polymer synthesis due to its living character, but for a given catalyst system, the polymer scope is rather narrow. Herein we report a highly efficient Suzuki-Miyaura catalyst-transfer polymerization (SCTP) that covers a wide range of monomers from electron-rich (donor, D) to electron-deficient (acceptor, A) (hetero)arenes by rationally designing boronate monomers and using commercially available Buchwald RuPhos and SPhos Pd G3 precatalysts. Initially, we optimized the controlled polymerization of 3,4-propylenedioxythiophene (ProDOT), benzotriazole (BTz), quinoxaline (QX), and 2,3-diphenylquinoxaline (QXPh) by introducing new boronates, such as 4,4,8,8-tetramethyl-1,3,6,2-dioxazaborocane and its N-benzylated derivative, to modulate the reactivity and stability of the monomers. As a result, PProDOT, PBTz, PQX, and PQXPh were prepared with controlled molecular weight and narrow dispersity (Đ < 1.29) in excellent yield (>85%). A detailed investigation of the polymer structures using ¹H NMR and MALDI-TOF spectrometry supported the chain-growth mechanism and the high initiation efficiency of the SCTP method. In addition, the use of RuPhos-Pd showing excellent catalyst-transfer ability on both D/A monomers led to unprecedented controlled D-A statistical copolymerization, thereby modulating the HOMO energy level (from -5.11 to -4.80 eV) and band gap energy (from 1.68 to 1.91 eV) of the resulting copolymers. Moreover, to demonstrate the living nature of SCTP, various combinations of D-A and A-A block copolymers (PBTz-b-PProDOT, PQX-b-PProDOT, and PQX-b-PBTz) were successfully prepared by the sequential addition method. Finally, simple but powerful one-shot D-A block copolymerization was achieved by maximizing the rate difference between a fast-propagating pinacol boronate donor and a slow-propagating acceptor to afford well-defined poly(3-hexylthiophene)-b-poly(benzotriazole).

NiO/Poly(4-alkylthiazole) Hybrid Interface for Promoting Spatial Charge Separation in Photoelectrochemical Water Reduction

Conjugated polymers are emerging as alternatives to inorganic semiconductors for the photoelectrochemical water splitting. Herein, semi-transparent poly(4-alkylthiazole) layers with different trialkylsilyloxymethyl (R₃SiOCH₂-) side chains (PTzTNB, R = n-butyl; PTzTHX, R = n-hexyl) are applied to functionalize NiO thin films to build hybrid photocathodes. The hybrid interface allows for the effective spatial separation of the photoexcited carriers. Specifically, the PTzTHX-deposited composite photocathode increases the photocurrent density 6- and 2-fold at 0 V versus the reversible hydrogen electrode in comparison to the pristine NiO and PTzTHX photocathodes, respectively. This is also reflected in the substantial anodic shift of onset potential under simulated Air Mass 1.5 Global illumination, owing to the prolonged lifetime, augmented density, and alleviated recombination of photogenerated electrons. Additionally, coupling the inorganic and organic components also enhances the photoabsorption and amends the stability of the photocathode-driven system. This work demonstrates the feasibility of poly(4-alkylthiazole)s as an effective alternative to known inorganic semiconductor materials. We highlight the interface alignment for polymer-based photoelectrodes.

All-conjugated donor–acceptor block copolymers featuring a pentafulvenyl-polyisocyanide-acceptor

A fulvenyl-functionalized polyisocyanide (PIC2) with a high electron mobility of μ_e = 10⁻² cm² V⁻¹ s⁻¹ has been incorporated into donor–acceptor block copolymers. Their self-assembly and bulk-morphology have been studied, and potential device applications have been explored.

A Review on Recent Synthetic Strategies and Pharmacological Importance of 1,3-Thiazole Derivatives

Thiazole is the most common heterocyclic compound in heterocyclic chemistry and in drug design. Presence of several reaction sites in the thiazole moiety extends their range of applications and leads to new solutions for challenges in synthetic and medicinal chemistry. Thiazole derivatives are widely used as bioactive agents, liquid crystals, sensors, catalysts, etc. The motivating molecular architecture of 1,3-thiazoles makes them suitable moieties for drug development. In this review, our aim is to corroborate the recent data available on various synthetic strategies and biological properties of 1,3- thiazole derivatives.

Synthesis and crystallization behavior of regioregular-block-regiorandom poly(3-hexylthiophene) copolymers

Regioregular–regiorandom poly(3-hexylthiophene) copolymers, synthesized by chain-transfer polycondensation, show strong crystallinity due to their one-sided distribution of regiodefects.

Variable oxidation state sulfur-bridged bithiazole ligands tune the electronic properties of ruthenium(ii) and copper(i) complexes

The synthesis of homoleptic and heteroleptic ruthenium(ii) and copper(i) complexes containing sulfur-bridged bithiazole ligands of varying oxidation states are reported.

Electronic and structural properties of N → B-ladder boranes with high electron affinity

A series of electronically and structurally diverse N → B-ladder boranes has been prepared by hydroboration.

Bithiazole: An Intriguing Electron-Deficient Building for Plastic Electronic Applications

The heterocyclic thiazole unit has been extensively used as electron-deficient building block in π-conjugated materials over the last decade. Its incorporation into organic semiconducting materials is particularly interesting due to its structural resemblance to the more commonly used thiophene building block, thus allowing the optoelectronic properties of a material to be tuned without significantly perturbing its molecular structure. Here, we discuss the structural differences between thiazole- and thiophene-based organic semiconductors, and the effects on the physical properties of the materials. An overview of thiazole-based polymers is provided, which have emerged over the past decade for organic electronic applications and it is discussed how the incorporation of thiazole has affected the device performance of organic solar cells and organic field-effect transistors. Finally, in conclusion, an outlook is presented on how thiazole-based polymers can be incorporated into all-electron deficient polymers in order to obtain high-performance acceptor polymers for use in bulk-heterojunction solar cells and as organic field-effect transistors. Computational methods are used to discuss some newly designed acceptor building blocks that have the potential to be polymerized with a fused bithiazole moiety, hence propelling the advancement of air-stable n-type organic semiconductors.

Impact of Preferential π-Binding in Catalyst-Transfer Polycondensation of Thiazole Derivatives

Polymerizing electron-deficient arenes in a controlled, chain-growth fashion remains a significant challenge despite a decade of research on catalyst-transfer polycondensation. The prevailing hypothesis is that the chain-growth mechanism stalls at a strongly associated metal-polymer π-complex, preventing catalyst turnover. To evaluate this hypothesis, we performed mechanistic studies using thiazole derivatives and identified approaches to improve their chain-growth polymerization. These studies revealed a surprisingly high barrier for chain-walking toward the reactive C-X bond. In addition, a competitive pathway involving chain-transfer to monomer was identified. This pathway is facilitated by ancillary ligand dissociation and N-coordination to the incoming monomer. We found that this chain-transfer pathway can be attenuated by using a rigid ancillary ligand, leading to an improved polymerization. Combined, these studies provide mechanistic insight into the challenges associated with electron-deficient monomers as well as ways to improve their living, chain-growth polymerization. Our mechanistic studies also revealed an unexpected radical anion-mediated oligomerization in the absence of catalyst, as well as a surprising oxidative addition into the thiazole C-S bond in a model system.

Matchmaking in Catalyst-Transfer Polycondensation: Optimizing Catalysts based on Mechanistic Insight

Catalyst-transfer polycondensation (CTP) has emerged as a useful living, chain-growth polymerization method for synthesizing conjugated (hetero)arene-based polymers with targetable molecular weights, narrow dispersities, and controllable copolymer sequences-all properties that significantly influence their performance in devices. Over the past decade, several phosphine- and carbene-ligated Ni- and Pd-based precatalysts have been shown to be effective in CTP. One current limitation is that these traditional CTP catalysts lead to nonliving, non-chain-growth behavior when complex monomer scaffolds are utilized. Because these monomers are often found in the highest-performing materials, there is a significant need to identify alternative CTP catalysts. Recent mechanistic insight into CTP has laid the foundation for designing new catalysts to expand the CTP monomer scope. Building off this insight, we have designed and implemented model systems to identify effective catalysts by understanding their underlying mechanistic behaviors and systematically modifying catalyst structures to improve their chain-growth behavior. In this Account, we describe how each catalyst parameter-the ancillary ligand(s), reactive ligand(s), and transition metal-influences CTP. As an example, ancillary ligands often dictate the turnover-limiting step of the catalytic cycle, and perhaps more importantly, they can be used to promote the formation of the key intermediate (a metal-arene associative complex) and its subsequent reactivity. The fidelity of this intermediate is central to the mechanism for the living, chain-growth polymerization. Reactive ligands, on the other hand, can be used to improve catalyst solubility and accelerate initiation. Additional advantages of the reactive ligand include providing access points for postpolymerization modification and synthesizing polymers directly off surfaces. While the most frequently used CTP catalysts contain nickel, palladium-based catalysts exhibit a higher functional group tolerance and broader substrate scope (e.g., monomers with boron, magnesium, tin, and gold transmetalating agents). Overall, we anticipate that applying the tools and lessons detailed in this Account to other monomers should facilitate a better "matchmaking" process that will lead to new catalyst-transfer polycondensations.

Intramolecular catalyst transfer polymerisation of conjugated monomers: from lessons learned to future challenges

Eleven years after the first reports on intramolecular catalyst transfer polycondensations, this review aims to critically recap on the fundamental “lessons” that can be learned from the historic literature as well as from the fervid activity that has emerged in the last three years.