Multidentate Lewis acids: theoretical study of anion binding by organoboron macrocyclic hosts

Molecular orbital (AM1) calculations have been carried out on two classes of multidentate boron-containing macrocycles and their inclusion complexes with H - , F - , Cl - , and O 2- . One class of macrobicycle (I) is represented by B[(CH 2 ) n ] 3 B, where n=3-10. On the basis of calculated standard enthalpies of reaction, hydride is bound to approximately the same extent by the hosts with n=4-6, fluoride by hosts with n= 5, 6, and cliloride by hosts with n=6, 8, and oxide is bound by hosts with n≥4. While some size selectivity is apparent, the decrease in binding energy as n increases is generally not pronounced, and none of the anions show a marked preference for any particular host in this series