title: 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-C(2) 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. (1)H couplings from the -NH(2) group of the amine, observed by ENDOR and HYSCORE, provided direct evidence of amine coordination.
authors: University of Antwerp, Department of Physics, SIBAC laboratory, Universiteitsplein 1, B-2610 Wilrijk, Belgium. caretti@icmm.csic.es
authors: Ignacio
authors: I
authors: Caretti
authors: Emma
authors: E
authors: Carter
authors: Ian A
authors: IA
authors: Fallis
authors: Damien M
authors: DM
authors: Murphy
authors: Sabine
authors: S
authors: Van Doorslaer
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D003514:Cyclohexylamines / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005029:Ethylenediamines / Q000737:chemistry*; D007536:Isomerism; D010627:Phenethylamines / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D003514:Cyclohexylamines; D005029:Ethylenediamines; D010627:Phenethylamines; D003300:Copper; C011452:disalicylaldehyde ethylenediamine; C030435:1,2-cyclohexanediamine; C033198:1-phenethylamine