REVERSIBLE MOLECULAR CAPSULES COMPOSED OF 2 CAVITANDS LINKED VIA AN ASSORTMENT OF CHARGED-HYDROGEN BONDS AND COVALENT BONDS

Six new cavitand bowls are reported (6, 7, 8, 9, 11, and 12), as are t hree bis-bowl compounds (4, 13, and 14). Eight new complexes (4.guest, 7C.guest, 8C.guest, 9C.guest, 14.guest, 15.guest, 15C.guest, and 16C. guest) that reversibly encapsulate small molecules are reported. Two o r more charged-hydrogen bonds (CHBs) or covalent linkages between the bowls are required to form stable complexes. Guest exchange rates vary from milliseconds to days. Thermodynamically, these complexes display an enthalpy-entropy compensation. The relative stability of complex 3 .pyrazine versus complex 3.chloroform is 170000 in nitrobenzene-d(5) a t 298 It. Apparent stability constants in nitrobenzene-d(5) at 298 K y ield 1.1 x 10(9) M-1 for complex 3.pyrazine. The absolute stability co nstant for complex 4.pyrazine in nitrobenzene-d(5) at 333 K is 3.5 x 1 0(6) M-1.