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Issue 40, 2016
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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

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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 × 10−4 to 187 × 10−4 M−1 s−1 dependent on the donor ability of the axial ligand. Rate constants for methanol elimination vary from 0.67 to 3.7 × 10−4 s−1 with 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.

Graphical abstract: 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

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Article information


Submitted
16 May 2016
Accepted
21 Jun 2016
First published
21 Jun 2016

Dalton Trans., 2016,45, 15791-15799
Article type
Paper

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

W. Zhang, N. Saraei, H. Nie, J. R. Vaughn, A. S. Jones, M. S. Mashuta, R. M. Buchanan and C. A. Grapperhaus, Dalton Trans., 2016, 45, 15791
DOI: 10.1039/C6DT01955B

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