Surface chemistry of N-Heterocyclic carbenes and the self-assembly, structure, and properties of polymer metal-organic cage gels

Abstract

Chapter 1. Introduction to Carbene Ligands in Surface Chemistry: From Stabilization of Discrete Elemental Allotropes to Modification of Nanoscale and Bulk Substrates In this chapter, we review the development of carbene surface chemistry from its inception through 2015, covering elemental allotrope substrates, nanomaterials, and bulk surfaces, as well as persistent and non-persistent carbenes. We synthesize from the reviewed reports a mechanistic understanding of this chemistry and outline the road ahead in this field. Chapter 2. Addressable Carbene Anchors for Gold Surfaces New strategies to access functional monolayers could augment current surface modification methods. Here we present addressable N-heterocyclic carbene (ANHC) anchors for gold surfaces and provide experimental and theoretical characterization of ANHC monolayers. Additionally, we demonstrate grafting of highly fluorinated polymers from surface-bound ANHCs. Chapter 3. Reactions of Persistent Carbenes with Hydrogen-Terminated Silicon Surfaces We report here the use of persistent aminocarbenes to functionalize via Si-H insertion reactions a range of hydrogen-terminated silicon surfaces: from model compounds, to nanoparticles, and planar Si(l 11) wafers. In particular, a cyclic(alkyl)(amino)carbene and an acyclic diaminocarbene underwent Si-H insertion, forming persistent C-Si linkages and thereby installing amine or aminal functionality in proximity to the surface. Our results pave the way for the further development of persistent carbenes as universal ligands for silicon and potentially other non-metallic substrates. Chapter 4. Cycloelimination of Imidazolidin-2-Ylidene N-Heterocyclic Carbenes: Mechanism and Insights into the Synthesis of Stable "NHC-CDI" Amidinates We report the discovery that 1,3-bis(aryl)imidazolidin-2-ylidenes, one of the most widely studied classes of N-heterocyclic carbenes (NHCs), undergo quantitative conversion to zwitterionic "NHC-CDI" amidinates upon heating to 100 °C in solution. The mechanism of this novel NHC decomposition process was studied in detail and enabled the rational synthesis of a new class of bench stable amidinates. Chapter 5. Toward Dynamic and Hierarchically Structured Polymer Gels: An Introduction to Polymer Metal-Organic Cage Gels Key challenges in polymer network/gel chemistry are overviewed. Polymer metal-organic cage gels capable of addressing some of these key challenges are introduced. Chapter 6. Highly Branched and Loop-Rich Gels Via Formation of Metal-Organic Cages Linked by Polymers We report here a new class of gels (called 'polyMOC' gels) assembled from polymeric ligands and metal-organic cages (MOCs) as junctions with M₂L₄ or M₁₂L₂₄ stoichiometries. The latter features increased branch functionality and large shear moduli, but also an abundance of elastically inactive loop defects that allow via ligand exchange the introduction of function at no cost to the gel's mechanical properties.