An official website of the United States government
Abstract Cyclophanes are a venerable class of macrocyclic and cage compounds that often contain unusual conformations, high strain, and unusual properties. However, synthesis of complex, functional derivatives remains difficult due to low functional group tolerance, high dilution, extreme reaction conditions, and sometimes low yields using traditional stepwise synthetic methods. “Design of experiments” (DOE) is a method employed for the optimization of reaction conditions, and we showcase this approach to generate a dramatic increase in the yield of specific targets from two different self‐assembling systems. These examples demonstrate that DOE provides an additional tool in tuning self‐assembling, dynamic covalent systems.
more »
« less
Dynamic Covalent Self‐sorting in Molecular and Polymeric Architectures Enabled by Spiroborate Bond Exchange
Abstract Self‐sorting is commonly observed in complex reaction systems, which has been utilized to guide the formation of single major by‐design molecules. However, most studies have been focused on non‐covalent systems, and using self‐sorting to achieve covalently bonded architectures is still relatively less explored. Herein, we first demonstrated the dynamic nature of spiroborate linkage and systematically studied the self‐sorting behavior observed in the transformation between spiroborate‐linked well‐defined polymeric and molecular architectures, which is enabled by spiroborate bond exchange. The scrambling between a macrocycle and a 1D helical covalent polymer led to the formation of a molecular cage, whose structures are all unambiguously elucidated by single‐crystal X‐ray diffraction. The results indicate that the molecular cage is the thermodynamically favored product in this multi‐component reaction system. This work represents the first example of a 1D polymeric architecture transforming into a shape‐persistent molecular cage, driven by dynamic covalent self‐sorting. This study will further guide the design of spiroborate‐based materials and open the possibilities for the development of novel complex yet responsive dynamic covalent molecular or polymeric systems.
more »
« less
- PAR ID:
- 10419154
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 62
- Issue:
- 27
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Cyclophanes are an admirable class of macrocyclic and cage compounds that often display unusual properties due to their high strain and unusual conformations. However, the exploration of new, complex cyclophanes has been encumbered by syntheses that can be low yielding, require harsh reaction conditions, and arduous purification steps. Herein, we discuss our work using metalloid-directed self-assembly and dynamic covalent chemistry to form cryptands. These were then subjected to mild conditions to produce discrete disulfide, thioether and hydrocarbon macrocycles in high yields. ‘Design of Experiments’ was then used to selectively synthesize targeted macrocycles from complex mixtures. 1 Introduction 2 Cryptands to Cyclophanes 3 Functionalizable Macrocycles 4 ‘Design of Experiments’ Targeted Synthesis 5 Conclusions and Outlookmore » « less
-
Crystalline porous frameworks, such as covalent organic frameworks (COFs), metal–organic frameworks (MOFs), and hydrogen-bonded organic frameworks (HOFs), have demonstrated exceptional potential in diverse applications, including gas adsorption/separation, catalysis, sensing, electronic devices, etc. However, the building blocks for constructing ordered frameworks are typically limited to multisubstituted aromatic small molecules, and uncontrolled interpenetration has remained a long-standing challenge in the field. Shape-persistent macrocycles and molecular cages have garnered significant attention in supramolecular chemistry and materials science due to their unique structures and novel properties. Using such preporous shape-persistent 2D macrocycles or 3D cages as building blocks to construct extended networks is particularly appealing. This macrocycle-to-framework/cage-to-framework hierarchical assembly approach not only mitigates the issue of interpenetration but also enables the integration of diverse properties in an emergent fashion. Since our demonstration of the first organic cage framework (OCF) in 2011 and the first macrocycle-based ionic COFs (ICOFs) in 2015, substantial advancements have been made over the past decade. In this Account, we will summarize our contributions to the development of crystalline porous frameworks, consisting of shape-persistent macrocycles and molecular cages as preporous building blocks, via hierarchical dynamic covalent assembly. We will begin by reviewing representative design strategies and the synthesis of shape-persistent macrocycles and molecular cages from small molecule-based primary building blocks, emphasizing the critical role of dynamic covalent chemistry (DCvC). Next, we will discuss the further assembly of preporous macrocycle/cage-based secondary building blocks into extended frameworks, followed by an overview of their properties and applications. Finally, we will highlight the current challenges and future directions for this hierarchical assembly approach in the synthesis of crystalline porous frameworks. This Account offers valuable insights into the design and synthesis of functional porous frameworks, contributing to the advancement of this important field.more » « less
-
Abstract Thiol‐disulfide interchange has been a large field of study for both biochemists and physical organic chemists alike due to its prevalence within biological systems and fundamentally interesting dynamic nature. More recently, efforts have been made to harness the power of this reversible reaction to make self‐assembling systems of macrocyclic molecules. However, less effort has focused on the fundamental work of isolating these assemblies and studying the factors that control the assembly and sorting of these emerging cyclic systems. A more complete fundamental understanding of factors controlling such self‐assembly could also improve understanding of the complex systems biology of thiol exchange while also aiding in the design of dynamic thiol assembly to enable applications ranging from drug delivery and biosensing to new materials synthesis. We have shown previously that pnictogen‐assisted self‐assembly enables formation of discrete disulfide macrocycles and cages without competition from polymer formation for a wide variety of alkyl thiols. In this study, we report the expansion of pnictogen‐assisted self‐assembly methods to form disulfide bearing macrocycles from aryl thiol containing ligands, allowing access to previously unreported molecules. These studies complement classical physical organic and chemical biology studies on the rates and products of aryl thiol oxidation to disulfides, and we show that this self‐assembly method revises some prevailing wisdom from these key classical studies by providing new product distributions and new isolable products in cyclic disulfide formation.more » « less
-
The covalent interaction of N-heterocyclic carbenes (NHCs) with transition metal atoms gives rise to distinctive frontier molecular orbitals (FMOs). These emergent electronic states have spurred the widespread adoption of NHC ligands in chemical catalysis and functional materials. Although formation of carbene-metal complexes in self-assembled monolayers on surfaces has been explored, design and electronic structure characterization of extended low-dimensional NHC-metal lattices remains elusive. Here we demonstrate a modular approach to engineering one-dimensional (1D) metal-organic chains and two-dimensional (2D) Kagome lattices using the FMOs of NHC–Au–NHC junctions to create low-dimensional molecular networks exhibiting intrinsic metallicity. Scanning tunneling spectroscopy and first-principles density functional theory reveal the contribution of C–Au–C π-bonding states to dispersive bands that imbue 1D- and 2D-NHC lattices with exceptionally small work functions.more » « less
