Issue 45, 2011

Interactions of an asymmetric amine with a non-C2 symmetric Cu–salen complex: An EPR/ENDOR and HYSCORE investigation

Abstract

Single enantiomers of R-/S-methylbenzylamine (MBA) were found to selectively form adducts with the chiral non-C2 symmetric Cu–salen complex N-(3,5-di-tert-butylsalicylidene)-N′-(salicylidene)-cyclohexane-1,2-diamine copper(II), hereafter labelled [Cu(3)]. The g/A spin Hamiltonian parameters of this Cu(II) complex showed a decrease in symmetry from axial to rhombic upon formation of the [Cu(3)] + MBA adducts. The selectivity in enantiomeric discrimination was found to be only 59 ± 5% in favour of the heterochiral R,R′-[Cu(3)] + S-MBA and S,S′-[Cu(3)] + R-MBA adducts. This was directly evidenced by W-band EPR spectroscopy. The observed low selectivity for enantiomer discrimination is primarily attributed to the loss of the bulky tert-butyl groups from the 3,5 positions of [Cu(3)] compared to the parent N,N′-bis(3,5-di-tert-butylsalicylidene)-cyclohexane-1,2-diamine copper(II) ligand (labelled [Cu(1)]). The structure of the [Cu(3)] complex in the presence and absence of coordinating amine was further investigated by analysis of the ligand hyperfine interactions, as revealed through Q-band CW-ENDOR, X-band Davies ENDOR and HYSCORE. 1H couplings from the –NH2group of the amine, observed by ENDOR and HYSCORE, provided direct evidence of amine coordination.

Graphical abstract: Interactions of an asymmetric amine with a non-C2 symmetric Cu–salen complex: An EPR/ENDOR and HYSCORE investigation

Supplementary files

Article information

Article type
Paper
Submitted
05 Aug 2011
Accepted
23 Sep 2011
First published
13 Oct 2011

Phys. Chem. Chem. Phys., 2011,13, 20427-20434

Interactions of an asymmetric amine with a non-C2 symmetric Cu–salen complex: An EPR/ENDOR and HYSCORE investigation

I. Caretti, E. Carter, I. A. Fallis, D. M. Murphy and S. Van Doorslaer, Phys. Chem. Chem. Phys., 2011, 13, 20427 DOI: 10.1039/C1CP22522G

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