High-Yielding, Regiospecific Synthesis of cis(4,4′)-Di(carbomethoxybenzo)-30-crown-10, Its Conversion to a Pyridyl Cryptand and Strong Complexation of 2,2′- and 4,4′-Bipyridinium Derivatives

Abstract

A high yielding (93%), regiospecific synthesis of cis(4,4')-di(carbomethoxybenzo)-30-crown-10 (1c) is reported. The derived crown ether diol 1d was converted to pyridyl cryptand 12 in 44% yield by reaction with pyridine-2,6-dicarbonyl chloride. Binding of two different 4,4'-bipyridinium (paraquat) species (3) and 2,2'-bipyridinium (diquat) 4 by 12 was explored via (1)H NMR spectroscopy, NOE experiments, mass spectrometry, X-ray crystallographic analyses, and isothermal titration calorimetry. Cryptand 12 exhibits the highest association constant for diquat ever reported (Ka = 1.9 x 10(6) M(-1)) and very high association constants for paraquats (Ka > 10(5) M(-1)) in acetone at 22 degrees C. The binding constant of diquat 4 by cryptand 12 is nearly 6-times higher than any other reported host.

Improved complexation of paraquats with crown ether‐based pyridyl cryptands

“…Under similar ITC titration conditions (acetone, 23°C), the K a of 5 • 7 was 2.21 × 10 5 mol L −1 , while that of 6 • 7 was 1.12 × 10 6 mol L −1 , bringing the separation of the values for the two cryptands to just under one order of magnitude. Note that the bis( m ‐phenylene)‐32‐crown‐10‐based pyridyl cryptand 6 suffers from a low cyclization yield to form the precursor diol (cyclization yield to diester 43%), while a very high yielding, template synthesis provides the analogous precursor to cryptand 5 in very high yield (cyclization yield to diester 93%) …”

“…It is suspected that the deviation of 5 • 7 is a result of differences in data gathering. The reported K a value of 5 • 7 was derived from a 33‐point titration, while values reported here were obtained using a 60‐point titration curve; as the isotherm is fit to a mathematical construct, a more defined curve produces a better fit. As for the deviation of 6 • 7 from the literature values, this is attributed to differences in experimental methodologies; the reported value for 6 • 7 was obtained from a competitive NMR study, while the results reported here within were obtained via ITC.…”

“…Through analysis of CPK models and crystal structures, host molecules have been advanced to highly evolved crown‐based pyridyl cryptands, for example 5 and 6 . However, little improvement has been offered in way of the paraquat guest, the standard being dimethyl paraquat as the PF 6 salt ( 7 ) which displays reasonable association constants with various crown ethers[2–5] and analogous cryptands [4] …”

Functionalisation of Macroheterocycles with Preserving and Changing Their Sizes

“…[107] Cryptand (200) that forms a stable complex with the herbicide paraquat (201) was obtained by the interaction of cis (4,4')-di(carbomethoxybenzo)-30-crown-10 (202) and 2,6-piridinecarboxylic acid dichloroanhydride (203) (Scheme 42). [108] In addition to the above examples of functionalisation of macrocycles that consist in the formation of covalent bonds, there are synthetic methods for compounds with topological bonds that comprise of two or several independent parts not bound with each other by any valence bonds but nevertheless, held together. Catenanes comprised oftwo or several cycles bound as chain fragments and rotaxanes, the linear part of which is threaded through a macrocyclic ring and cannot slip out of it due to the presence of bulky end groups are referred to them.…”

Structure, Conformation, and Dynamics of P,N-Containing Cyclophanes in Solution

“…[5][6][7][8][9][10][11] Therefore, there is an explosion of interest in the design of macrocyclic hosts for specific guests. [12][13][14][15][16][17][18][19][20] From this point heterocyclophanes containing a number of P,N-heterocycles and aromatic groups are very promising. [21][22][23][24] First of all, the π-electron system of such heterocyclophanes can interact with aromatic guests.…”