Designing the Macrocyclic Dimension in Main Group Chemistry

Abstract

Outside the confines and well-established domain of organic chemistry, the systematic building of large macromolecular arrangements based on non-carbon elements represents a significant and exciting challenge. Our aim in the past two decades has been to develop robust synthetic methods to construct new types of main group architectures in a methodical way, principles of design that parallel those used in the organic arena. This Concept article addresses the fundamental thermodynamic and kinetic problems involved in the design and synthesis of main group macrocycles and looks to future developments of macromolecules in this area, as well as new applications in coordination chemistry.

Guest Binding via N−H⋅⋅⋅π Bonding and Kinetic Entrapment by an Inorganic Macrocycle

“…[20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host. [20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host.…”

“…[17][18][19] Key advantages of inorganic anion receptors over organic counterparts are their inherently more polar nature and the ease by which their proton acidities can be modulated.Thehigh bond energy of PÀNs ingle bonds and their low polarity underpin the stability of adiverse range of previously reported phosphazane compounds,and provide agood foundation for the development of anew range of robust inorganic macrocycles. [20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host. Thehost properties of 1 should differ significantly from organic counterparts,e specially given the greater polarity of these P À N-bonded frameworks.Herein, we show that the highly polar nature of the binding site and the sterically congested periphery of 1 leads to unique types of host-guest binding involving NÀH···p-CX (X = CH, N, P) hydrogen bonding to organic and inorganic guests.W ea lso show that oxidation of the phosphorus periphery of 1 can be used to kinetically entrap anions within the macrocycle.T his produces chemically irreversible binding of Cl À and I À anions using acombination of hydrogen bonding and steric encasement, which results in better effective binding of these halides than in any organic or metal-organic architecture.Direct access to 1,w hich was previously prepared by ac omplicated two-step procedure involving the use of gaseous NH 3 ,i sp rovided here by an ew method wherein the cyclodiphosphazane [ClP(m-N t Bu)] 2 (A)iscombined with LiNH 2 in the presence of excess anhydrous LiI, followed by removal of the encapsulated iodide anion (Figure 2a and Section S2 in the Supporting Information).…”

“…Thehigh bond energy of PÀNs ingle bonds and their low polarity underpin the stability of adiverse range of previously reported phosphazane compounds,and provide agood foundation for the development of anew range of robust inorganic macrocycles. [20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host. Thehost properties of 1 should differ significantly from organic counterparts,e specially given the greater polarity of these P À N-bonded frameworks.…”

Guest Binding via N−H⋅⋅⋅π Bonding and Kinetic Entrapment by an Inorganic Macrocycle

“…The high bond energy of P−N single bonds and their low polarity underpin the stability of a diverse range of previously reported phosphazane compounds, and provide a good foundation for the development of a new range of robust inorganic macrocycles . Of particular interest is the pentameric host macrocycle 1 (Figure ), toroidal shape, large void volume, endo ‐cyclic N‐H functionalities, and exo ‐cyclic t Bu groups of which make it a highly unusual, sterically hindered H‐bonding host.…”

A Facile Modular Addition Approach to Size Control in the Synthesis of Oxo Bridged Phosphazane Macrocycles

“…[1][2][3][4] However, the development of their inorganic counterparts is hindered by their challenging syntheses caused by the low bond energy of element-carbon covalent bonds. [5][6][7][8][9][10] In this context, cyclodiphosphazane-based macrocycles have drawn attention due to the relatively high bond energy of their saturated P-N bonds, which is comparable with the energy of C-C bond (ca. 290 vs 348 kJ•mol -1 , respectively).…”