A REINFORCED POLYAZA[N.N] PARACYCLOPHANE CONTAINING PIPERAZINE RINGS

The new [n.n]paraazacyclophane pentacyclo[32.2.2(7,10).2(25,28)]tetrat etraconta-1 (37),16(41),17,19(40),34(38),35-hexaene (L) has been prepa red. Its protonation has been studied by means of potentiometry and di rect microcalorimetry in 0.15 mol dm (3) NaClO4 at 298.1 K. A NMR anal ysis shows that protons bind alternately at both sides of L, the benzy lic nitrogens being the first sites to be protonated. From dynamic var iable-temperature NMR analysis an activation enthalpy of 61(2) kJ mol (1) has been derived for the chair-chair interconversion of the pipera zine ring. The entropy is almost negligible. Compound L forms with Cu2 + in aqueous solution complexes [Cu(H(3)L)](3+) and [Cu(2)L](4+) with stability constants log beta(CuH3L) = 33.20(6) and log beta(Cu2L) 16.6 (1) in 0.15 mol dm (3) NaClO4 at 298.1 K, respectively. The low stabil ity of the binuclear complex is attributed to the energy loss due to i nterconversion between the chair and boat conformers of the piperazine moieties. The interaction of Pd2+ with L has been monitored by NMR an alysis. The spectral features show formation of strong binuclear compl exes with the involvement of all eight nitrogens of the macrocycle.