Abstract
Interconversion of the syn and anti rotational isomers of cis-[Pd(2-C6BrF4)2(tht)2] (1) (tht = tetrahydrothiophene) takes place very fast in CDCl3 solution. The process has been studied by 19F NMR magnetization transfer experiments. The first-order syn-to-anti atropisomerization rate constant kab decreases with the addition of tht until it reaches an asymptotic value (1.419 ± 0.012 s-1 at 299.1 K). This behavior reveals a dual mechanism involving two competitive pathways: the rotation of the aryl group in the four-coordinate complex 1 and the rotation in a three-coordinate species formed by tht dissociation from 1. The latter is a clear-cut example of a mechanism starting with a neutral ligand dissociation in an organopalladium(II) complex. The activation parameters associated to each of these two pathways are ΔH⧧ = 83 ± 3 kJ mol-1 and ΔS⧧ = 37 ± 10 J K-1 mol-1, for the nondissociative path, and ΔH⧧= 77 ± 3 kJ mol-1 and ΔS⧧ = 28 ± 10 J K-1 mol-1 for the dissociative contribution. Similar energy is requir...
Published Version
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