Syntheses, structures and electrochemistry of copper(II) salicylaldehyde/tris(3-phenylpyrazolyl)borate complexes as models for the radical copper oxidases

Halcrow, M.A. and Chia, L. M. L. and Liu, X. and McInnes, E. J. L. and Yellowlees, L. J. and Mabbs, F. E. and Scowen, I. J. and McPartlin, M. and Davies, J. E. (1999) Syntheses, structures and electrochemistry of copper(II) salicylaldehyde/tris(3-phenylpyrazolyl)borate complexes as models for the radical copper oxidases. Journal of the Chemical Society - Dalton Transactions (11). pp. 1753-1762. ISSN 0300-9246, 1477-9226

Full content URL: http://dx.doi.org/10.1039/A900741E

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Item Type:Article
Item Status:Live Archive

Abstract

2-Hydroxy-5-methyl-3-methylsulfanylbenzaldehyde(HL2) and 2-hydroxy-5-methyl-3-methylselanylbenzaldehyde (HL3) have been synthesized from 2-hydroxy-5-methylbenzaldehyde (HL1), as have Schiff bases HL4R and HL5R (R = Me or Ph) derived from RNH2 and HL1 or HL2 respectively. The complexes Cu(L)(TpPh) (L1- = L1-, 1; L2-, 2; L3-, 3; L4Me-, 4; or L4Ph-, 5) have been prepared. Single crystal structure determinations of 1, 2, 4 and 5 show copper(II) centres with square pyramidal CuN3O2 (1, 2) or CuN4O (4, 5) co-ordination spheres; for 4 and 5 the basal plane of the complex is twisted by 20-25° because of the steric properties of the Schiff base Me or Ph substituent. The UV/vis and EPR spectra of 1-5 in CH2Cl2 show the presence of tetragonal copper(II) centres. Cyclic voltammograms of 1-5 and the uncomplexed phenols in CH2Cl2-0.5 M Bu4nNPF6 exhibit an irreversible or (for 2) reversible 1-electron oxidation to a phenoxyl radical. The oxidation potentials of HL2 and HL3, and of 2 and 3, are barely distinguishable. However, the irreversibility of this process for 3 compared to that of 2 suggests that a selenoether substituent kinetically stabilises the phenoxyl unpaired spin less efficiently than a thioether one; this is borne out by EHMO calculations on L1�-L3�. Spectroelectrochemical characterisation of 2+, whose UV/vis/NIR spectrum is very similar to that of galactose oxidase, confirms its formulation as the antiferromagnetically coupled species CuII(L2�)(TpPh)+.

Keywords:Chemistry
Subjects:F Physical Sciences > F100 Chemistry
Divisions:College of Science > School of Chemistry
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ID Code:13066
Deposited On:19 Mar 2014 17:53

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