Supramolecular Architectures with π-Acidic 3,6-Bis(2-pyridyl)-1,2,4,5-tetrazine Cavities: Role of Anion-π Interactions in the Remarkable Stability of Fe(II) Metallacycles in Solution
Supramolecular Architectures with π-Acidic 3,6-Bis(2-pyridyl)-1,2,4,5-tetrazine Cavities: Role of Anion-π Interactions in the Remarkable Stability of Fe(II) Metallacycles in Solution
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DOI：
10.1021/ja3082473
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发表时间：
2013-02-27
影响因子：
15
通讯作者：
Dunbar, Kim R.
中科院分区：
文献类型：
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作者：
Chifotides, Helen T.;Giles, Ian D.;Dunbar, Kim R.
本文报道的综合研究提供了令人信服的证据，证明阴离子-pi相互作用是高产率地与bptz[3，6-双(2-吡啶)-1，2，4，5-四嗪]形成自组装Fe(II)模板金属环的主要驱动力。X-射线结晶学、(1)H-核磁共振、溶液和固态MAS F-19核磁共振谱、循环伏安和质谱学研究表明，阴离子[X](-)=[BF4](-)，[ClO4](-)和阴离子[Y](-)=[SbF6](-)，[AsF6](-)，[PF6](-)模板分子方块[Fe-4(Bptz)(4)(CH3CN)(8)][X](8)和五边形[Fe-5(Bptz)(5)(CH3CN)(10)][Y](10)。2SbF(6)的[{Fe-4(Bptz)(4)(CH3CN)(8)}[BF4][BF4](7)和[{Fe-5(Bptz)(5)(CH3CN)(10)}][SbF6](8)的X射线结构表明，[BF4](-)和[SbF6](-)阴离子占据了pi-酸性空穴，与比F中心点C van der Waals半径之和(Sigma R-VDW(VDW)F中心点C=3.17埃)短0.4埃的四嗪环建立紧密的定向F中心点C(四嗪)接触。F中心点C(四嗪)接触的数目和强度最大；F中心点C(四嗪)距离和阴离子相对于与四津环相对的多边形的位置与密度泛函理论计算的C(2)N4R(2)中心点中心点[X](-)中心点C(2)N4R(2)(R=F，CN；[X](-)=[BF4](-)，[PF(6)](-))一致。在史无前例的固态(19)F-MAS核磁共振研究中，模板阴离子在固态中参与阴离子-pi相互作用，表现出与外围阴离子相比，Delta Delta(F-19)约3.5-4.0ppm的下场化学位移。核磁共振、循环伏安和质谱学研究也证实了Fe(II)金属环在溶液中保持不变。此外，在(1)H-核磁共振波谱的监测下，Fe(II)金属环之间的相互转化研究强调了金属五环[Fe-5(Bptz)(5)(CH3CN)(10)][PF6](10)的显著稳定性
The comprehensive investigation reported herein provides compelling evidence that anion-pi interactions are the main driving force in the formation of self-assembled Fe(II)-templated metallacycles with bptz [3,6-bis(2-pyidyl)-1,2,4,5-tetrazine] in high yields. It was demonstrated by X-ray crystallography, (1)H NMR, solution and solid-state MAS F-19 NMR spectroscopies, CV and MS studies that the anions [X](-) = [BF4](-), [ClO4](-) and the anions [Y](-) = [SbF6](-), [AsF6](-), [PF6](-) template molecular squares [Fe-4(bptz)(4)(CH3CN)(8)][X](8) and pentagons [Fe-5(bptz)(5)(CH3CN)(10)][Y](10), respectively. The X-ray structures of [{Fe-4(bptz)(4)(CH3CN)(8)} [BF4][BF4](7) and [{Fe-5(bptz)(5)(CH3CN)(10)}subset of 2SbF(6)][SbF6](8) revealed that the [BF4](-) and [SbF6](-) anions occupy the pi-acidic cavities, establishing close directional F center dot center dot center dot C(tetrazine) contacts with the tetrazine rings that are by similar to 0.4 angstrom shorter than the sum of the F center dot center dot center dot C van der Waals radii (Sigma R-vdw(vdW) F center dot center dot center dot C = 3.17 angstrom). The number and strength of F center dot center dot center dot C(tetrazine) contacts are maximized; the F center dot center dot center dot C(tetrazine) distances and anion positioning versus the polygon opposing tetrazine rings are in agreement with DFT calculations for C(2)N4R(2)center dot center dot center dot[X](-)center dot center dot center dot C(2)N4R(2) (R = F, CN; [X](-) = [BF4](-), [PF(6)](-)). In unprecedented solid-state (19)F MAS NMR studies, the templating anions, engaged in anion-pi interactions in the solid state, exhibit downfield chemical shifts Delta delta(F-19) approximate to 3.5-4.0 ppm versus peripheral anions. NMR, CV, and MS studies also establish that the Fe(II) metallacycles remain intact in solution. Additionally, interconversion studies between the Fe(II) metallacycles in solution, monitored by (1)H NMR spectroscopy, underscore the remarkable stability of the metallapentacycles [Fe-5(bptz)(5)(CH3CN)(10)][PF6](10)