title: Reversible methanol addition to copper Schiff base complexes: a kinetic, structural and spectroscopic study of reactions at azomethine C[double bond, length as m-dash]N bonds.
abstract: The reversible methanolysis of an azomethine C[double bond, length as m-dash]N in a series of copper(ii) Schiff base complexes has been investigated through combined spectroscopic, structural, and kinetic studies. Pentadentate copper(ii) complexes [L1-Cu(X)]Y (L1= 1,2-bis[(1-methyl-2-imidazolyl)methyleneamino]ethane; X = Y = ClO4-(1); X = Y = TfO-(2); X = Y = BF4-(3); X = H2O, Y = (ClO4-)2(4) spontaneously add methanol in a ligand centered reaction to yield stable, isolable hemiaminal ether product complexes 5-8. In methanol free solution, 5-8 spontaneously release alcohol to regenerate 1-4. The methanol addition reaction is first-order in methanol and first-order in complex with second-order rate constants varying from 1.1 × 10-4to 187 × 10-4M-1s-1dependent on the donor ability of the axial ligand. Rate constants for methanol elimination vary from 0.67 to 3.7 × 10-4s-1with dependence on the counterion and water content of the solvent. Equilibrium constants for methanolysis range from 1.5 to 51 M-1. Structural comparisons of the Schiff base complexes 1-4 and the hemiaminal ether complexes 5-8 suggest methanol addition is favored by the release of ligand strain associated with three planar five-membered chelates in 1-4.
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Wuyu
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Nina
authors.initials: N
authors.lastname: Saraei
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Hanlin
authors.initials: H
authors.lastname: Nie
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: John R
authors.initials: JR
authors.lastname: Vaughn
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Alexis S
authors.initials: AS
authors.lastname: Jones
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Mashuta
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Buchanan
authors.affiliation: Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY, 40292 USA. grapperhaus@louisville.edu.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Grapperhaus