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Adaptive Behavior of a Ditopic Phosphine Ligand
Author(s) -
Renard Nicolas,
Brenner Eric,
Matt Dominique,
Gourlaouen Christophe
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201900571
Subject(s) - chemistry , denticity , phosphine , steric effects , ligand (biochemistry) , stereochemistry , phosphine oxide , dissociation (chemistry) , chelation , octahedron , crystallography , medicinal chemistry , crystal structure , catalysis , receptor , inorganic chemistry , biochemistry
Synthetic, structural and computational studies have been performed to investigate ligand interchange in the fluxional chelate complex [RhCl 3 {Ph 2 P A CH 2 C( O A )OEt‐κ 2 PO A }{Ph 2 P B CH 2 C(O B )OEt‐κ P }], which contains two hybrid phosphine‐ester ligands, one acting as P,O chelator, the other as a P‐monodentate ligand. The observed ligand exchange may occur according to two pathways which both involve four elementary movements: a) oxygen dissociation with formation of a lacunary octahedral RhCl 3 P 2 intermediate; b) migration of the Cl atom trans to P A towards the position trans to P B ; c) rotations of the phosphine moieties about the Rh–P bonds, these occurring either concomitantly with the Cl displacement or in a separate step; d) coordination of an oxygen atom of the second phosphine. The two pathways thus differ by conformational changes within two distinct steps. In each pathway the rate‐limiting step is the one involving a movement of the two phosphines, which generates steric frictions between the two PPh 2 groups. The calculated theoretical energetic spans of both pathways (Δ G ≠ ≈ 17 kcal mol –1 ) is close to the energy barrier obtained from a variable temperature NMR study carried out in C 2 D 2 Cl 4 (Δ G ≠ = 15.5 kcal mol –1 ). While one of the pathways leads to an isomer with a Rh‐bound ethoxy O atom, the other results in the isomer having the metal coordinated to the adjacent C=O group. Exchange between the two O atoms of the coordinated ester group occurs readily (Δ G TS = 12.5 kcal mol –1 ).