The kinetics of trisbidentate chelate complexes revisited. A two-dimensional NMR study of the isomerization and racemization processes of the complexes [M(TTA)3] (M = AlIII, GaIII; TTA = 2-thenoyltrifluoroacetone)

Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality

“…This can be attributed to a labile behaviour of the ligands as seen for the dithiocarbamates [37] and thioureide complexes with other metals [28,38] which may be resulting in a change in isomerism for the compound. It is hypothesised that this occurs through a bond rupture‐rotation mechanism [39] . Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the Al−S bond, rotation around the C−N bond followed by the formation of either an Al−S or an Al−N bond.…”

“…It is hypothesised that this occurs through a bond rupture-rotation mechanism. [39] Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the AlÀ S bond, rotation around the CÀ N bond followed by the formation of either an AlÀ S or an AlÀ N bond. At lower temperatures, this association-disassociation is slow enough to be visible in the NMR timescale.…”

Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality

“…This can be attributed to a labile behaviour of the ligands as seen for the dithiocarbamates [37] and thioureide complexes with other metals [28,38] which may be resulting in a change in isomerism for the compound. It is hypothesised that this occurs through a bond rupture‐rotation mechanism [39] . Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the Al−S bond, rotation around the C−N bond followed by the formation of either an Al−S or an Al−N bond.…”

“…It is hypothesised that this occurs through a bond rupture-rotation mechanism. [39] Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the AlÀ S bond, rotation around the CÀ N bond followed by the formation of either an AlÀ S or an AlÀ N bond. At lower temperatures, this association-disassociation is slow enough to be visible in the NMR timescale.…”

Quantitative 2D EXSY and Dynamic19F-NMR Studies of the Dynamic Behaviour of the Bidentate Chelate Complex Ga(fox)3 (fox = 5-fluoro-8-hydroxyquinoline)

“…These facts also confirm that a bond-rupture mechanism with a pendant axial ligand did not occur, as the entropy of activation should not be the same for a mechanism with temporary rupture of a metal-ligand bond and those with twisting without any bond rupture. [4,12] The relative importance of the Bailar mechanism can also be interpreted in relation with the metal-chelating heteroatom distances in the complex. We were unable to obtain sufficiently good crystals of Ga(fox) 3 for X-ray crystallography, but in the literature we have data for closely related complexes Fe(ox) 3 and Ga(ox) 3 (where ox is for 8-hydroxyquinoline or oxine).…”

“…Several examples in the literature show that NMR spectroscopy is well adapted for kinetic measurements of such molecular rearrangements in complexes of appropriate metal cations: [1] chromium(III) complexes with the unsymmetrical bidentate (S)-tryptophan ( 1 H NMR), [7] ruthenium hydrides with triphenylphosphanes as other ligands ( 31 P NMR) [8] and several tris(unsymmetrical bidentate ligand)-metal(III) complexes of group 13 metals such as tris(trifluoroacetylacetonato)-Ga(III) complexes ( 19 F NMR), [9] tris-(substituted-tropolonato)metal(III) complexes ( 1 H NMR), [10] tris [2-(2'-hydroxyphenyl [12] tris(substituted-catecholato)metal(III) complexes ( 1 H NMR). [13] Previously, we studied a new tripodal iron chelator, OTrensox, based on 8-hydroxyquinoline.…”

Dynamic stereochemical rearrangements in chiral organometallic complexes

“…For example, in [Ga(tta) 3 ] (tta = 2-thenoyltrifluoroacetone) the rate of racemisation increases 10-fold on changing the solvent from (CDCl 2 ) 2 to d 6 -DMSO. 78 Of the three possible intermediates that can be envisaged in the bond rupture mechanism, namely (i) a trigonal bipyramidal intermediate with a pendant equatorial ligand, (ii) a trigonal bipyramidal intermediate with a pendant axial ligand and (iii) a square pyramidal intermediate, only the latter two (depicted in Scheme 14) lead to racemisation.…”

Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality

“…This can be attributed to a labile behaviour of the ligands as seen for the dithiocarbamates [37] and thioureide complexes with other metals [28,38] which may be resulting in a change in isomerism for the compound. It is hypothesised that this occurs through a bond rupture‐rotation mechanism [39] . Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the Al−S bond, rotation around the C−N bond followed by the formation of either an Al−S or an Al−N bond.…”

“…It is hypothesised that this occurs through a bond rupture-rotation mechanism. [39] Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the AlÀ S bond, rotation around the CÀ N bond followed by the formation of either an AlÀ S or an AlÀ N bond. At lower temperatures, this association-disassociation is slow enough to be visible in the NMR timescale.…”

Quantitative 2D EXSY and Dynamic19F-NMR Studies of the Dynamic Behaviour of the Bidentate Chelate Complex Ga(fox)3 (fox = 5-fluoro-8-hydroxyquinoline)

“…These facts also confirm that a bond-rupture mechanism with a pendant axial ligand did not occur, as the entropy of activation should not be the same for a mechanism with temporary rupture of a metal-ligand bond and those with twisting without any bond rupture. [4,12] The relative importance of the Bailar mechanism can also be interpreted in relation with the metal-chelating heteroatom distances in the complex. We were unable to obtain sufficiently good crystals of Ga(fox) 3 for X-ray crystallography, but in the literature we have data for closely related complexes Fe(ox) 3 and Ga(ox) 3 (where ox is for 8-hydroxyquinoline or oxine).…”

“…Several examples in the literature show that NMR spectroscopy is well adapted for kinetic measurements of such molecular rearrangements in complexes of appropriate metal cations: [1] chromium(III) complexes with the unsymmetrical bidentate (S)-tryptophan ( 1 H NMR), [7] ruthenium hydrides with triphenylphosphanes as other ligands ( 31 P NMR) [8] and several tris(unsymmetrical bidentate ligand)-metal(III) complexes of group 13 metals such as tris(trifluoroacetylacetonato)-Ga(III) complexes ( 19 F NMR), [9] tris-(substituted-tropolonato)metal(III) complexes ( 1 H NMR), [10] tris [2-(2'-hydroxyphenyl [12] tris(substituted-catecholato)metal(III) complexes ( 1 H NMR). [13] Previously, we studied a new tripodal iron chelator, OTrensox, based on 8-hydroxyquinoline.…”

Dynamic stereochemical rearrangements in chiral organometallic complexes

“…For example, in [Ga(tta) 3 ] (tta = 2-thenoyltrifluoroacetone) the rate of racemisation increases 10-fold on changing the solvent from (CDCl 2 ) 2 to d 6 -DMSO. 78 Of the three possible intermediates that can be envisaged in the bond rupture mechanism, namely (i) a trigonal bipyramidal intermediate with a pendant equatorial ligand, (ii) a trigonal bipyramidal intermediate with a pendant axial ligand and (iii) a square pyramidal intermediate, only the latter two (depicted in Scheme 14) lead to racemisation.…”

Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality

“…This can be attributed to a labile behaviour of the ligands as seen for the dithiocarbamates [37] and thioureide complexes with other metals [28,38] which may be resulting in a change in isomerism for the compound. It is hypothesised that this occurs through a bond rupture‐rotation mechanism [39] . Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the Al−S bond, rotation around the C−N bond followed by the formation of either an Al−S or an Al−N bond.…”

“…It is hypothesised that this occurs through a bond rupture-rotation mechanism. [39] Possibly due to the poor bonding between the hard Al acid and the weak S base, there is momentary rupture of the AlÀ S bond, rotation around the CÀ N bond followed by the formation of either an AlÀ S or an AlÀ N bond. At lower temperatures, this association-disassociation is slow enough to be visible in the NMR timescale.…”

Quantitative 2D EXSY and Dynamic19F-NMR Studies of the Dynamic Behaviour of the Bidentate Chelate Complex Ga(fox)3 (fox = 5-fluoro-8-hydroxyquinoline)

“…These facts also confirm that a bond-rupture mechanism with a pendant axial ligand did not occur, as the entropy of activation should not be the same for a mechanism with temporary rupture of a metal-ligand bond and those with twisting without any bond rupture. [4,12] The relative importance of the Bailar mechanism can also be interpreted in relation with the metal-chelating heteroatom distances in the complex. We were unable to obtain sufficiently good crystals of Ga(fox) 3 for X-ray crystallography, but in the literature we have data for closely related complexes Fe(ox) 3 and Ga(ox) 3 (where ox is for 8-hydroxyquinoline or oxine).…”

“…Several examples in the literature show that NMR spectroscopy is well adapted for kinetic measurements of such molecular rearrangements in complexes of appropriate metal cations: [1] chromium(III) complexes with the unsymmetrical bidentate (S)-tryptophan ( 1 H NMR), [7] ruthenium hydrides with triphenylphosphanes as other ligands ( 31 P NMR) [8] and several tris(unsymmetrical bidentate ligand)-metal(III) complexes of group 13 metals such as tris(trifluoroacetylacetonato)-Ga(III) complexes ( 19 F NMR), [9] tris-(substituted-tropolonato)metal(III) complexes ( 1 H NMR), [10] tris [2-(2'-hydroxyphenyl [12] tris(substituted-catecholato)metal(III) complexes ( 1 H NMR). [13] Previously, we studied a new tripodal iron chelator, OTrensox, based on 8-hydroxyquinoline.…”

Dynamic stereochemical rearrangements in chiral organometallic complexes

“…For example, in [Ga(tta) 3 ] (tta = 2-thenoyltrifluoroacetone) the rate of racemisation increases 10-fold on changing the solvent from (CDCl 2 ) 2 to d 6 -DMSO. 78 Of the three possible intermediates that can be envisaged in the bond rupture mechanism, namely (i) a trigonal bipyramidal intermediate with a pendant equatorial ligand, (ii) a trigonal bipyramidal intermediate with a pendant axial ligand and (iii) a square pyramidal intermediate, only the latter two (depicted in Scheme 14) lead to racemisation.…”