Rhodium-Catalyzed Stitching Reaction: Convergent Synthesis of Quinoidal Fused Oligosiloles

Synthesis, Characterization, and Properties of Sila-Annulated Phenanthrene Imides

A series of sila-annulated phenanthrene imides were synthesized through a three-step synthetic route, which represent a hybrid class of biphenyl-based π-conjugated molecules incorporating an imide unit and silole. A comprehensive investigation of their structural, photophysical, and electronic properties was studied by experiment and theoretical calculations. Notably, sila-annulated phenanthrene imides with significant aggregation-induced emission (AIE) properties were observed.

Rhodium-Catalyzed Stitching Reactions for the Facile Synthesis of Extended π-Conjugated Compounds

π-Conjugated compounds have been extensively investigated as potentially useful organic materials, however, accessible structures are currently still limited, mainly due to the lack of efficient synthetic methods. In this regard, a new synthetic strategy termed the ‘stitching reaction’ has been recently devised that allows facile access to novel types of bridged π-conjugated compounds in a convergent manner under rhodium catalysis. In addition, this synthetic strategy has been successfully applied to the preparation of π-conjugated polymers that cannot be synthesized via existing methods. Herein an overview that includes the physical properties of newly synthesized π-conjugated compounds is provided.

1 Introduction

2 Synthesis of Novel Fused Oligosiloles by the Stitching Reaction and Their Properties

3 Synthesis of Hydrocarbon-Based Fused π-Conjugated Compounds by the Stitching Reaction

4 Synthesis of New π-Conjugated Polymers by Stitching Polymerization

5 Conclusion

Rhodium-Catalyzed Stitching Polymerization of Alkynylsilylacetylenes

Polymers possessing a silicon-bridged π-conjugated repeating unit constitute an important class of compounds for their potential utility as optoelectronic materials. Herein we developed a rhodium-catalyzed stitching polymerization of nonconjugated and readily prepared alkynylsilylacetylenes for the synthesis of new π-conjugated polymers with ladder-type silicon-bridged repeating units. The polymerization proceeded smoothly by employing a Rh/tfb complex as the catalyst, and not only diynes but also triynes and tetraynes could be polymerized in a stitching manner to give polymers that are inaccessible by existing methods. The solubility of the polymers in different types of solvents could be controlled by introducing appropriate functional groups on the silicon atoms, and sequence-controlled functionalized polyacetylenes could be accessed by protodesilylation of the stitched polymers. Physical properties of the obtained polymers were also investigated to understand their characteristic features.

Intermolecular Three-Component Synthesis of Fluorene Derivatives by a Rhodium-Catalyzed Stitching Reaction/Remote Nucleophilic Substitution Sequence

A three-component synthesis of multisubstituted fluorene derivatives has been developed by devising a rhodium-catalyzed stitching reaction/remote nucleophilic substitution sequence. A variety of nucleophiles can be installed in the second step including both heteroatom and carbon nucleophiles. An efficient synthesis of 5H-benzo[a]fluoren-5-ones has also been realized using N-(2-alkynyl)benzoylpyrrole as the reaction partner through a new reaction pathway.

Rhodium-Catalyzed Stitching Polymerization of 1,5-Hexadiynes and Related Oligoalkynes

A new mode of polymerization, rhodium-catalyzed stitching polymerization, has been developed for the synthesis of π-conjugated polymers with bridged repeating units from nonconjugated 1,5-hexadiynes containing both terminal and internal alkyne moieties as monomers. The polymerization proceeded smoothly with a high degree of stitching efficiency under mild conditions, and 1,5,9-decatriyne and 1,5,9,13-tetradecatetrayne monomers could also be employed. The present polymerization strategy would be particularly beneficial for the synthesis of polymers consisting of a repeating unit that is difficult to prepare as a stable monomer because it does not require the use of a preformed bridged π-conjugated monomer.

Helicenes Built from Silacyclopentadienes via Ring-by-Ring Knitting of the Helical Framework

Despite the apparent diversity of the protocols developed for the synthesis of helicenes, they essentially follow the same strategy: the closure of one, or several, internal rings in a key step. Herein, we report the synthesis of a new family of the heterohelicenes consisting of fused silacyclopentadiene rings formed via a facile and novel process. The treatment of oligo(alkynilydenesilylene) precursors of type H₂ C=CH-(SiMe₂ -C≡C)_n -R (n=3-7), bearing a vinyl group on the terminal silicon atom, with 9-borabicyclononane leads first to 1,2-hydroboration of the terminal double bond which then continues with a cascade of intramolecular 1,1-carboboration reactions accompanied with the closure of a new silole ring after each step affording the target silahelicenes with, currently, up to seven condensed silole rings and with excellent yields. According XRD analysis, the seven fused silole rings of the heptacyclic compound 11 b form an almost complete turn of a helix. The presented one-pot sequence of reactions is the first example of ring-by-ring knitting of a helical framework starting from easily available linear precursors.

Synthesis of carbonyl-bridged dibenzofulvalenes and related compounds by rhodium-catalyzed stitching reaction

Various carbonyl-bridged dibenzofulvalenes were synthesized by a sequence of rhodium-catalyzed stitching reaction and post-functionalization, and other bridged dibenzofulvalenes could also be synthesized using the present stitching reaction.

Palladium-Catalyzed Double Carbonylative Cyclization of Benzoins: Synthesis and Photoluminescence of Bis-Ester-Bridged Stilbenes

A palladium-catalyzed double carbonylative cyclization of benzoins has been developed, which realizes the synthesis of bis-ester-bridged stilbenes just in two steps from aldehydes. Thus, the obtained fully fused tetracyclic π-systems have a pyrano[3,2- b]pyran-2,6-dione (PPD) core on their center, showing two reversible reductions at low potentials. In addition, their photoluminescence properties are strikingly affected by the aromatic rings fused to the PPD core; bis- thieno-fused PPDs are found to be excellent fluorophores with quantum yields up to 0.98.

Selective synthesis of unsymmetric dibenzo[a,e]pentalenes by a rhodium-catalysed stitching reaction

A rhodium-catalysed stitching reaction between 2-(silylethynyl)arylboronates and 2-(silylethynyl)aryl bromides has been developed for the synthesis of unsymmetric dibenzo[a,e]pentalenes. The introduction of appropriately sized silyl groups on the starting substrates led to a high crossover selectivity without using an excess amount of either substrate. The present stitching reaction could produce a variety of unsymmetric dibenzo[a,e]pentalene derivatives, including those with electronically different substituents on the fused benzene rings as well as heteroarene fused compounds. Desilylative halogenation was also demonstrated to synthesise the corresponding halogenated dibenzo[a,e]pentalenes, which can be used as building blocks for further chemical transformations.