摘要：

Two tripods (1 and 2) featuring pyrimidinyl pendant arms have been synthesized from 5-(1H-pyrazol-3-yl)-pyrimidine (5) and 1,3,5-tribromomethylbenzene derivatives. Reaction with three equivalents of [Pd(bipy)](NO"3)"2 to form a macrotricycle closed by palladium coordination unexpectedly afforded the mononuclear species [Pd(1)(bipy)]^2^+ and [Pd(2)(bipy)]^2^+. These complexes show fluxional behavior on the ^1H NMR timescale, the [Pd(bipy)]^2^+ fragment hopping between the pyrimidinyl coordinating moieties. The @DG"c^@?'s estimated by the coalescence method are temperature independent, which means that @DS"c^@?=0. This indicates that the ''merry-go-round'' process of [Pd(bipy)]^2^+ occurs intramolecularly, presumably by nucleophilic attack of the free pyrimidinyl arm to the bound Pd^2^+ center. This phenomenon permits to quantify the lability of the Pd-N coordination bond, the average @DG"c^@? ~ @DH"c^@? value being 70kJmol^-^1.

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