The [Pd(bipy)]2+ "merry-go-round": Insights into the lability of the Pd–N bond
摘要：
Two tripods ( 1 and 2) featuring pyrimidinyl pendant arms have been synthesized from 5-(1 H-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 Δ G c 's estimated by the coalescence method are temperature independent, which means that Δ S 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 Δ G c ≈ Δ H c value being 70 kJ mol –1.
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DOI：
10.1016/j.crci.2009.03.002
年份：
2009
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