کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
171385 | 458455 | 2009 | 8 صفحه PDF | دانلود رایگان |
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)](NO3)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 ΔGc‡’s estimated by the coalescence method are temperature independent, which means that ΔSc‡ = 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 Pd2+ center. This phenomenon permits to quantify the lability of the Pd–N coordination bond, the average ΔGc‡ ≈ ΔHc‡ value being 70 kJ mol–1.
Journal: Comptes Rendus Chimie - Volume 12, Issue 12, December 2009, Pages 1267–1274