The contribution of polar C–H hydrogen bonds to anion binding

Abstract

Binding abilities depend on the magnitude of C–H polarization.

The road to aryl CH⋯anion binding was paved with good intentions: fundamental studies, host design, and historical perspectives in CH hydrogen bonding

“…The unsubstituted receptor 19c showed no affinity toward a range of anions, while the slightly-more polarized receptor 19b only bound H 2 PO 4 − . 48 Receptor 19a, however, which featured the most polarized aryl CH hydrogen bond, was able to bind all four anions studied (H 2 PO 4 − , HSO 4 − , Cl − , and Br − ). In this case, the extent of polarization of this aryl CH HB, along with the favorable electrostatic interactions and possible N-methyl pyridinium CH HBs in 19a, were critical in creating a favorable host-guest interaction in solution.…”

“…The Kang group also reported on the effect of polarization of aryl CH hydrogen bonds on anion binding. 48 Their receptors utilized an amide NH HB, a central anthracene CH HB, and an aryl CH polarized by an ortho pyridinium, a para-nitro group, or a control receptor without substituents (Fig. 12b, 19a-c, respectively).…”

“…In this case, the extent of polarization of this aryl CH HB, along with the favorable electrostatic interactions and possible N-methyl pyridinium CH HBs in 19a, were critical in creating a favorable host-guest interaction in solution. 48 We previously collaborated with our colleagues in the lab of Michael Pluth at the University of Oregon to show that receptors of the type in Fig. 12c could bind the highly nucleophilic hydrosulfide anion (HS − , conjugate base of hydrogen sulfide, H 2 S).…”

N-tert-Butyl Sulfinyl Squaramide Receptors for Anion Recognition through Assisted tert-Butyl C–H Hydrogen Bonding

“…Compared to the more traditional N–H and O–H donors, the hydrogen bonding donor abilities of C–H bonds are relatively weaker . Although alkyl and aryl C–H bonds are present in the overwhelming majority (97%) of organic compounds, receptors utilizing C–H hydrogen bonds are rare. − Neutral C–H and cationic C–H donors, such as alkyl C–H donors, phenyl C–H donors, triazole-based C–H donors, and imidazolium and triazolium C–H donors, have been applied in binding anions. − Among the C–H donors, receptors containing alkyl C–H donors are very rare . Recently, Hay and Pedzisa used electronic structure calculations to determine C–H···Cl – hydrogen-bonding energies for a series of XCH 3 donor groups .…”