Overcrowded 1,8-diazafluorenylidene-chalcoxanthenes. Introducing nitrogens at the fjord regions of bistricyclic aromatic enes
作者:Amalia Levy、Shmuel Cohen、Israel Agranat
DOI:10.1039/b303041e
日期:——
The effects of introducing nitrogen atoms in the fjord regions and chalcogen bridges on the conformations of overcrowded bistricyclic aromatic enes (1, X ≠ Y) (BAEs) were studied. 9-(9′H-1′,8′-Diazafluoren-9′-ylidene)-9H-thioxanthene (12), 9-(9H-1′, 8′-diazafluoren-9′-ylidene)-9H-selenoxanthene (13), 9-(9′H-1′,8′-diazafluoren-9′-ylidene)-9H-telluroxanthene (14), 9-(9′H-1′,8′-fluoren-9-ylidene)-9H-xanthene (15) and 9-(9′H-1′,8′-fluoren-9′-ylidene)-9H-fluorene (16) were synthesized by two-fold extrusion coupling reactions of 1,8-diaza-9H-fluoren-9-one (19)/chalcoxanthenthiones (24–27)
(or /9H-fluorene-9-thione (30)). The 1′,8′-diazafluoren-9-ylidene-chalcoxanthenes (11) were compared with the respective fluoren-9-ylidene-chalcoxanthenes (10). The structures of 12–16 were established by 1H, 13C, 77Se, and 125Te NMR spectroscopies. The crystal and molecular structures of 12–14 were determined by X-ray analysis. The yellow molecules of 12–14 adopted mono-folded conformations with folding dihedrals in the chalocoxanthylidene moieties of 62.7°
(12), 62.4°
(13) and 59.9°
(14). The folding dihedrals in the respective 1′,8′-diazafluorenylidene moieties were very small, ca. 2°, compared with 10.2/8.0° in (9′H-fluoren-9′-ylidene)-9H-selenoxanthene (7). A 5° pure twist of C9C9′ in 14 is noted. The degrees of overcrowding in the fjord regions of 12–14
(intramolecular non-bonding distances) were relatively small. The degrees of pyramidalization of C9 and C9′ were 17.0/3.0°
(12), 17.4/2.4°
(13) and 2.2/2.2°
(14). These high values in 12 and 13 stem from the resistance of the 1,8-diazafluorenylidene moiety to fold and from the limits in the degrees of folding of the thioxanthylidene and selenoxanthylidene moieties (due to shorter S10–C4a/S10–C10a and Se10–C4a/Se10–C10a bonds, as compared with the respective Te–C bonds in 14). The molecules of 15 and 16 adopt twisted conformations, a conclusion drawn from the 1H NMR chemical shifts of the fjord regions protons (H1 and H8) at 8.70 (15) and 9.00 ppm (16) and from their colors and UV/VIS spectra: 15 is purple (λmax
= 521 nm) and 16 is orange–red. A comparison of the NMR spectra of 11 and 10
(Δδ
=
δ(11)
–
δ(10)) showed substantial downfield shifts of 0.56–0.62 ppm of the fjord regions protons of twisted 15 and 16: Δδ
(C9) were negative (upfield): −4.0 (12), −3.7 (13), −3.4 (14), −7.1 (15), −5.0 ppm (16), while Δδ
(C9′) were positive (downfield)
=
+6.8 (12), +6.5 (13), +5.8 (14), +11.7 (15), +7.7 ppm (16). In 15, Δδ
(C9)
–
Δδ
(C9′)
=
+18.8 ppm, attributed to a push–pull character and significant contributions of zwitterionic structures in the twisted conformation. The 77Se and 125Te NMR signals of 13 and 14 were shifted upfield relative to the respective fluorenylidene-chalcoxanthene derivatives: Δδ77Se = 17.2 ppm and Δδ125Te = 22.0 ppm. The presence of the nitrogen atoms (N1′ and N8′) in 13 and 14 causes shielding of the selenium and tellurium nuclei.
在峡湾区域引入氮原子以及硫族桥对过度拥挤的双环芳香烯(1,X ≠ Y)(BAEs)构象的影响进行了研究。通过两步挤出耦合反应合成了9-(9′H-1′,8′-二氮荧光素-9′-亚烯基)-9H-硫茚(12)、9-(9H-1′,8′-二氮荧光素-9′-亚烯基)-9H-硒茚(13)、9-(9′H-1′,8′-二氮荧光素-9′-亚烯基)-9H-碲茚(14)、9-(9′H-1′,8′-荧光素-9-亚烯基)-9H-茚(15)和9-(9′H-1′,8′-荧光素-9′-亚烯基)-9H-荧光烯(16),反应物为1,8-二氮-9H-荧光素-9-酮(19)/二硫茚(24–27)或/9H-荧光烯-9-硫(30)。将1′,8′-二氮荧光素-9-亚烯基-二硫茚(11)与相应的荧光素-9-亚烯基-二硫茚(10)进行了比较。通过1H、13C、77Se和125Te NMR光谱确定了12–16的结构。12–14的晶体和分子结构通过X射线分析确定。黄色分子12–14呈现单重折叠构象,在二硫茚基团中的折叠二面角分别为62.7°(12)、62.4°(13)和59.9°(14)。相应的1′,8′-二氮荧光素基团的折叠二面角相对较小,约为2°,而在(9′H-荧光素-9′-亚烯基)-9H-硒茚(7)中为10.2/8.0°。在14中注意到C9C9′有5°的纯扭曲。12–14的峡湾区域拥挤程度(分子内非键合距离)相对较小。C9和C9′的金字塔化程度分别为17.0/3.0°(12)、17.4/2.4°(13)和2.2/2.2°(14)。12和13中的较高数值源于1,8-二氮荧光素基团折叠的抵抗性以及二硫茚基团和硒茚基团的折叠程度的限制(由于S10–C4a/S10–C10a和Se10–C4a/Se10–C10a键较短,与14中的相应Te–C键相比)。15和16的分子呈现扭曲构象,这一结论根据峡湾区域质子的1H NMR化学位移(H1和H8)为8.70(15)和9.00 ppm(16)以及它们的颜色和UV/VIS光谱得出:15呈紫色(λmax = 521 nm),16为橙红色。对11和10的NMR光谱进行比较(Δδ = δ(11) - δ(10))显示,扭曲的15和16的峡湾区域质子明显向下移位0.56–0.62 ppm:Δδ (C9) 为负(向上移):−4.0 (12)、−3.7(13)、−3.4(14)、−7.1(15)、−5.0 ppm(16),而Δδ (C9′) 为正(向下移)= +6.8(12)、+6.5(13)、+5.8(14)、+11.7(15)、+7.7 ppm(16)。在15中,Δδ (C9) - Δδ (C9′) = +18.8 ppm,归因于推拉特征和扭曲构象中两性离子结构的显著贡献。13和14的77Se和125Te NMR信号相对于各自的荧光素-二硫茚衍生物向上移位:Δδ77Se = 17.2 ppm 和Δδ125Te = 22.0 ppm。13和14中氮原子(N1′和N8′)的存在导致对硒和碲核的屏蔽效应。