Interactions of an asymmetric amine with a non-C2 symmetric Cu-salen complex: an EPR/ENDOR and HYSCORE investigation.
Interactions of an asymmetric amine with a non-C2 symmetric Cu-salen complex: an EPR/ENDOR and HYSCORE investigation.
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DOI：
10.1039/c1cp22522g
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发表时间：
2011-11
期刊：
影响因子：
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通讯作者：
I. Caretti;Emma Carter;I. Fallis;D. Murphy;S. Van Doorslaer
中科院分区：
文献类型：
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作者：
I. Caretti;Emma Carter;I. Fallis;D. Murphy;S. Van Doorslaer
R-/S-甲基苄胺的单一对映体选择性地与手性非C(2)对称的铜-Salen络合物N-(3，5-di-tert-butylsalicylidene)-N‘-(salicylidene)-cyclohexane-1，2-diamine铜(II)形成加合物，此后标记为[Cu(3)]。该铜(II)络合物的g/A自旋哈密顿参数表明，随着[Cu(3)]+MBA加合物的形成，对称性从轴向菱形逐渐减小。对杂手性R，R‘-[Cu(3)]+S-MBA和S，S’-[Cu(3)]+R-MBA加合物的选择性仅为59±5%。W波段EPR谱直接证明了这一点。观察到的低对映体识别选择性主要是由于与母体N，N‘-bis(3，5-di-tert-butylsalicylidene)-cyclohexane-1，2-diamine铜(II)配体(标记为[Cu(1)])相比，[Cu(3)]的3，5位失去了大量的叔丁基。通过Q带CW-Endor、X带Davies Endor和HYSCORE分析，进一步研究了配位胺存在和不存在时[Cu(3)]配合物的结构。(1)Endor和HYSCORE观察到的胺的-NH(2)基团的H偶联提供了胺配位的直接证据。
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.