Unveiling controlled breaking of the mirror symmetry of Eu(fod)3 with α-/β-pinene and BINAP by circularly polarised luminescence (CPL), CPL excitation, and 19F-/31P{1H}-NMR spectra and Mulliken charges
Unveiling controlled breaking of the mirror symmetry of Eu(fod)3 with α-/β-pinene and BINAP by circularly polarised luminescence (CPL), CPL excitation, and 19F-/31P{1H}-NMR spectra and Mulliken charges
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DOI：
10.1039/c8qi00509e
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发表时间：
2018-11-01
影响因子：
7
通讯作者：
Fujiki, Michiya
中科院分区：
文献类型：
--
作者：
Jalilah, Abd Jalil;Asanoma, Fumio;Fujiki, Michiya
研究了非光学活性Eu（fod）（3）（fod = 6，6，7，7，8，8，8-七氟-2，2-二甲基-3，5-辛二酮）在四种手性烃（1 S）-/（1 R）-α-蒎烯、（1 S）-/（1 R）-β-蒎烯、（1 S）-/（1 R）-反式-蒎烷和（S）-/（R）-柠檬烯）中的Pfeiffer效应。在这些溶剂中，由于Eu（III），α-蒎烯和β-蒎烯在593 nm处的电偶极（艾德）-禁止/磁偶极（MD）-允许的D-5（0）-> F-7（1）跃迁和613 nm处的ED-允许/MD-禁止的D-5（0）-> F-7（2）跃迁处在CPL-沉默的Eu（fod）3中诱导清晰的圆偏振发光（CPL）信号。CPL激发（CPLE）光谱监测D-5（0）-> F-7（1）和D-5（0）-> F-7（2）跃迁，证实这些CPL谱带是由α-蒎烯的手性诱导的。Eu（fod）（3）在不带电荷的手性芳香族添加剂（包括（S）-/（R）-2，2 '-bis）存在下（二苯基膦基）-1，1 '-联萘（BINAP）、（S）-/（R）-[1，1'-联萘] 2，2 '-二基双[1，1-二苯基-1，1'-氧化膦]（BINAPO）和（S）-/（R）-α-苯乙胺（PEA），也显示出镜像CPL光谱与不同程度的不对称因子在其CPL信号。F-19-NMR谱显示CPL信号有两个不同的来源，这可以归类为在外层的Pfeiffer微扰系统和在内层Eu（III）的强配位相互作用。前者以α-蒎烯、BINAP和稀释的PEA为例，而后者则以BINAPO和纯PEA为例。通过比较Eu（fod）3与BINAP的P-31{H-1}-NMR谱，证实了Eu（fod）3与BINAPO之间存在较强的配位作用。通过MP2（6- 311 G）计算得到的Eu（fod）（3）和手性化合物的Mulliken电荷，我们推测剩余的电荷中和可以作为Eu（III）配合物中几个配体和CPL诱导的手性化合物之间的一种看不见的吸引力。
We investigated whether the 'Pfeiffer effect' of optically inactive Eu(fod)(3) (fod = 6,6,7,7,8,8,8-heptafluoro-2,2- dimethyl-3,5-octanedionate) is detectable when it is dissolved in four chiral hydrocarbons, namely, (1S)-/(1R)-alpha-pinene, (1S)-/(1R)-beta-pinene, (1S)-/(1R)-trans-pinane and (S)-/(R)-limonene. Among these solvents, alpha-pinene and beta-pinene induced clear circularly polarised luminescence (CPL) signals in CPL-silent Eu(fod) 3 at the electric dipole (ED)-forbidden/magnetic dipole (MD)-allowed D-5(0)-> F-7(1) transition at 593 nm and the ED-allowed/MD-forbidden D-5(0)-> F-7(2) transition at 613 nm due to Eu(III). The CPL excitation (CPLE) spectra monitoring the D-5(0)-> F-7(1) and D-5(0)-> F-7(2) transitions confirmed that these CPL bands are induced by the chirality of alpha-pinene. Eu(fod)(3) in the presence of non-charged chiral aromatic additives, including (S)-/(R)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP), (S)-/(R)-[1,1'-binaphthalene]2,2'-diylbis[1,1-diphenyl-1,1'-phosphine-oxide] (BINAPO) and (S)-/(R)-alpha-phenylethylamine (PEA), also showed mirror-image CPL spectra with different extents of dissymmetry factors in their CPL signals. The F-19-NMR spectra revealed that the CPL signals had two different origins, which can be categorized as the Pfeiffer-perturbed system at an outer-sphere and a strong coordinative interaction at an inner-sphere Eu(III). The former was exemplified by alpha-pinene, BINAP and dilute PEA, whereas the latter was observed with BINAPO and neat PEA. The strong coordinative interaction of Eu(fod) 3 with BINAPO was verified by comparing its P-31{H-1}-NMR spectrum with that in the presence of BINAP. The Mulliken charges of Eu(fod)(3) and the chiral compounds obtained with MP2(6-311G) calculations led us to hypothesize that the surplus charge neutralization can act as an invisible attractive force between several ligands in the Eu(III) complexes and CPL-inducible chiral compounds.