Adaptive Behavior of Dynamic Orthoester Cryptands

Abstract

The integration of dynamic covalent bonds into macrocycles has been at remendously successful strategy for investigating noncovalent interactions and identifying effective host-guest pairs.W hile numerous studies have focused on the dynamic responses of macrocycles and larger cages to various guests,t he corresponding constitutionally dynamic chemistry of cryptands remains unexplored. Reported here is that cryptands based on orthoester bridgeheads offer an elegant entry to experiments in which am etal ion selects its preferred host from adynamic mixture of competing subcomponents.In such dynamic mixtures,t he alkali metal ions Li + ,N a + ,K + , Rb + ,a nd Cs + exhibit pronounced preferences for the formation of cryptands of certain sizes and donor numbers,a nd the selection is rationalized by DFT calculations.Reported is also the first self-assembly of ac hiral orthoester cryptate and apreliminary study on the use of stereoisomers as subcomponents.Theunique feature of dynamic covalent bonds,their stability or dynamics depending on the reaction conditions,has led to diverse applications in chemistry and adjacent disciplines. [1] In supramolecular host-guest chemistry,t he integration of dynamic covalent bonds into macrocycles, [2] their combination with metal-ligand interactions, [3] and the structural response of macrocyclic systems to (ionic) guests have recently attracted considerable interest. [4] Them ajority of constitutionally dynamic metal-ligand cages are rigid and positively charged, ap roperty which makes them an ideal platform for the binding and recognition of anions.T he groups of Nitschke, [5] Clever, [6] and others [7] have recently reported impressive examples of adaptive cage transformations in response to different anions.B esides metal-ligand cages,t here have been numerous studies on the adaptive behavior of dynamic combinatorial macrocycles in response to guests. [1f, 8] However, in most examples reported to date,t he selection occurs between oligomeric species,f or example,d imeric and trimeric species compete for guest binding.S tudies in which adaptive behavior is based on subcomponent selection and subtle architectural differences between competing organic hosts are rare. [2c, 9] As the smallest three-dimensional hosts,d ynamic cryptands represent an attractive,y et practically unexplored [10] area of chemical (host-guest) space.W eh ave recently reported the first dynamic covalent self-assembly of amonometallic cryptate [11] ([Na + &o-Me 2 -1.1.1]), which was based on the reversible,a cid-catalyzed reaction of as imple orthoester with diethylene glycol (Scheme 1a). [12] Herein, we report the adaptive behavior of orthoester cryptands in response to cationic guests (Scheme 1b).In af irst series of experiments,w et ested whether the orthoester cyptand o-Me 2 -1.1.1 would respond to the addition of mismatched metal guests by either ad ynamic covalent shrinkage or expansion event (Scheme 2a). Thecombination of one equivalent of LiTPFPB (lithium tetrakis(pentafluorophenyl)borate), ethylene...

Self‐Assembly of a Trithioorthoformate‐Capped Cyclophane and Its Endohedral Inclusion of a Methine Group

“…Orthoesters and orthothioesters are functionalities seldom used in self‐assembling supramolecular systems despite their relevance as acylating, alkylating, and formylating agents and as protecting groups in synthetic organic chemistry. Recent work from von Delius and co‐workers features the templated synthesis of dynamic orthoester cryptates, in which kinetic stabilization is induced via metal encapsulation . Unique to this family is the addition of a single orthoformate group adjoining dissimilar ligands to generate a supramolecular heteroleptic self‐assembly.…”

Post‐Assembly Reactivity of N‐Aryl Iminoboronates: Reversible Radical Coupling and Unusual B−N Dynamic Covalent Chemistry

“…Despite varying the number of equivalents of Cp 2 Co and the reductant (Cp* 2 Co instead of Cp 2 Co) in the reaction, the crystal structures all displayed ar acemic mixture of the dimer rac 5 -2 e,c omposed of coupled five-membered NBcontaining rings (Figure 1d,Figures S87-S90). 6 ]DMSO) spectra of a) freshly redissolved rac 6 -2 a crystals,b)amixture of rac 6 -2 a and rac 5 -2 a isomers 4d ays after dissolution of rac 6 -2 a crystals, c) redissolved meso 5 -2 a crystals, and d) the 2a mixture containing rac 6 , rac 5 ,a nd meso 5 isomers.…”

“…Dynamic covalent chemistry (DCC) [1][2][3] is ap owerful tool for the self-assembly of supramolecular structures, including macrocycles, [4,5] cryptates, [6] interlockeds tructures, [7,8] and cages. [9][10][11] Disulfide, [5,12] imine, [10,13,14] boronate ester [15,16] exchange and more recently,o rthoester exchange [6,17] are well-established reversible covalentr eactions in DCC. Iminoboronates are readily assembled using DCC from the condensation of three functionalizable building-blocks:a na mine, a2 -formylphenyl boronic acid, and ad iol (Scheme 1).…”

The Dynamic Covalent Chemistry of Amidoboronates: Tuning the rac5/rac6 Ratio via the B−N and B−O Dynamic Covalent Bonds

“…Dynamic covalent chemistry [8] exploits the reversibility of bond‐breaking and formation for a variety of applications from the self‐assembly of supramolecular architectures [9] to bioconjugation, [10] and the development of self‐healing polymers, [11] malleable thermoset materials [12] and gels [10a,13] . Dynamic covalent bonds include disulfides, [9e,f,14] C−O bonds [8d] (e. g. esters, [15] acetals [16] and orthoesters [9a,b] ), Si−O bonds, [17] C=N bonds (e. g. hydrazones, [14c,18] imines [9g,i,m,19] ) and B−O bonds (e. g. boronate esters, [9h,j,k,10a,14c,20] boroxines [5b,9l,12a,21] ). Combining imine and boronate ester bonds, iminoboronates are self‐assembled from an amine, 2‐formylphenylboronic acid and a diol using dynamic covalent chemistry [8c,22] .…”