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Solid state isostructural behavior and quantified limiting substitution kinetics in Schiff-base bidentate ligand
Alice Brink1, Hendrik G Visser, Andreas Roodt
1Department of Chemistry, University of the Free State , P.O. Box 339, Bloemfontein 9300, South Africa.
Inorganic Chemistry
|November 14, 2014
Summary
This study explores N,O-donor salicylidene complexes, revealing how bidentate ligands activate methanol substitution. Sterically hindered ligands demonstrate novel kinetic behavior, confirming a dissociative interchange mechanism for ligand exchange reactions.
Area of Science:
- Organometallic Chemistry
- Coordination Chemistry
- Chemical Kinetics
Background:
- Salicylidene complexes with N,O-donor atoms and a fac-[M(O,N-Bid)(CO)3(L)] structure were investigated.
- These complexes crystallize in a monoclinic isostructural space group, particularly when methanol (MeOH) is the coordinated ligand (L).
- The study focuses on the reactivity and stability of these metal complexes.
Purpose of the Study:
- To evaluate the reactivity and stability of N,O-donor salicylidene complexes.
- To investigate the mechanism of methanol substitution by pyridine-type ligands.
- To understand the role of sterically demanding and electron-rich bidentate ligands in modulating reaction kinetics.
Main Methods:
- Rapid stopped-flow techniques were employed to study the kinetics of methanol substitution.
- A series of pyridine-type ligands were used as entering ligands.
- Equilibrium and rate constants were determined for the substitution reactions.
Main Results:
- N,O-salicylidene bidentate ligands significantly activate methanol substitution, as evidenced by variations in second-order rate constants.
- The introduction of a cyclohexyl salicylidene moiety led to novel limiting kinetic behavior for all entering ligands.
- Dissociative interchange mechanism was confirmed for methanol substitution, with specific rate (k3) and equilibrium (K2) constants provided for fac-[Re(Sal-Cy)(CO)3(MeOH)] with various pyridine ligands.
Conclusions:
- N,O-salicylidene ligands play a crucial role in activating ligand substitution reactions in metal carbonyl complexes.
- Steric and electronic properties of the bidentate ligand can be systematically tuned to control and probe reaction mechanisms.
- The study provides clear evidence for a dissociative interchange mechanism in these systems, offering insights into ligand exchange dynamics.
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