Carbolong Chemistry: Planar CCCCX-Type (X = N, O, S) Pentadentate Chelates by Formal [3+1] Cycloadditions of Metalla-Azirines with Terminal Alkynes

Open AccessCCS ChemistryCOMMUNICATION1 Feb 2021Carbolong Chemistry: Planar CCCCX-Type (X = N, O, S) Pentadentate Chelates by Formal [3+1] Cycloadditions of Metalla-Azirines with Terminal Alkynes Ming Luo, Yuhui Hua, Kaiyue Zhuo, Lipeng Long, Xinlei Lin, Zhihong Deng, Zhenyang Hong Zhang, Dafa Chen and Haiping Xia Luo College Chemistry Chemical Engineering, Xiamen University, Fujian Province Google Scholar More articles this author , Hua Zhuo Long Lin Deng Department Chemistry, The Kong University Science Technology, Clear Water Bay, Kowloon, Zhang Southern Shenzhen, Guangdong *Corresponding author: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000223 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Three-membered unsaturated rings have been widely utilized in organic synthesis due their inherent highly strained structures. Although much research has applied ring-expansion reactions such ring systems, pathways other than [3+2] cycloadditions rarely observed alkynes, date, no isolated three-membered alkynes reported. Here we demonstrate an unprecedented cycloaddition which a fused metalla-azirine is used as template generate series planar CCCCX-type pentadentate carbolong complexes 3–6. A substituted was tested for further exploration the scope mechanism reactions. Complexes 3– 6 represent rare examples that assemble four ?-conjugated one bridgehead atom. These novel are thermally stable air absorb ultraviolet, visible, near-infrared light, thus potentially applicable photoelectric devices pharmaceuticals. Download figure PowerPoint Introduction Ring-expansion compounds small fundamental transformations synthesis.1–6 Among various rings, common can serve three-atom synthons variety addition taking advantage high reactivity, derived from strain.4,6 With exception certain synthetic equivalents or analogues,7–12 however, previously reported these were seen transformations, typically following pathway. For example, cyclopropenes be form five-membered (Figure 1a, left).13–15 Analogous also low-valent metal-mediated oxidative cyclometalation yield metallacyclopentadienes via metalla-cyclopropenes right).16,17 As another paradigm azacyclic 2H-azirines successfully undergone diverse different bond cleavage modes, providing expedient approaches N-heterocyclic skeletons 1b, left).18–21 In sharp contrast, there appear reports on analogous azametallacycles—that is, metalla-azirines—with alkynes. fact, reactivities metalla-azirines explored.22,23 Figure 1 | (a) Cycloaddition (b) terminal Polydentate among most studied because fascinating structures functions. expanding bidentate, tridentate, tetradentate ligands attracted tremendous interest,24–28 high-coordination complexes, proven very difficult achieve.29–31 coordinating atoms those polydentate primarily drawn range donor heteroatoms including P, S. To carbons sole principal sites ligand rare,32–34 probably owing inaccessible atypical geometries. Recently, developed unique metal polycyclic frameworks featuring long carbon chain (?7 C) coordinated atom at least three metal?carbon bonds.35 Herein, report first alkynes; therefore, aza-metallacyclobutene skeleton generated congested metallacyclic leading formation remarkable all five lie equatorial plane. Results Discussion Osmapentalyne 136 employed precursor desired metalla-azirine. Treatment sodium azide (NaN3) dichloromethane (DCM) room temperature led complex 2, green solid 65% 2). Crystals 2 suitable X-ray crystallographic analysis obtained saturated solution DCM temperature. Reactions osmapentalyne (c) Solid-state 3a? (the counterion Cl?) crystallography 50% probability ellipsoids. Solvent molecules, counterion, phenyl groups PPh3 omitted clarity. Selected experimental distances (Å) angles (deg) 2: Os(1)?C(1) 2.092(8), Os(1)?C(4) 2.078(8), Os(1)?C(7) 2.011(8), Os(1)?N(1) 2.424(7), C(1)?C(2) 1.460(12), C(2)?C(3) 1.371(12), C(3)?C(4) 1.420(12), C(4)?C(5) 1.355(12), C(5)?C(6) 1.416(13), C(6)?C(7) 1.407(12), C(1)?N(1) 1.207(11); Os(1)–C(1)–C(2) 119.2(6), C(1)–Os(1)–N(1) 29.9(3), C(1)–N(1)–Os(1) 59.7(5), N(1)–C(1)–Os(1) 90.5(6). 3a: 2.063(4), 2.078(5), 2.088(4), Os(1)?C(8) 2.102(4), Os(1)?O(1) 2.129(3), 1.455(6), 1.378(6), 1.425(6), 1.374(7), 1.424(6), 1.385(6), 1.324(6), C(8)?N(1) 1.404(6), C(8)?C(9) 1.333(6), C(9)?C(10) 1.458(6), C(10)?O(1) 1.309(6); Os(1)?C(1)?N(1) 110.1(3), C(1)?N(1)?C(8) 89.9(3), N(1)?C(8)?Os(1) 104.7(3), C(8)?Os(1)?C(1) 55.16(17). data 2b) show moiety bicyclic framework, osmium adopting pentagonal bipyramidal coordination geometry. Os?N distance 2.424(7) Å within 1.636?2.544 Å37 single distances. Os?C comparable osmapentalenes,38 osmapentalene C?C lengths invariably intermediate between double bonds. coplanar two reflected mean deviation 0.005 least-squares Probably stabilization aromatic persist several months when exposed even heated 80 °C 3 h. carboazidation azides, example trimethylsilyl azide, extensively explored afford 1-azidoalkenes, subsequently converted 2H-azirines.39,40 Such not yet achieved carbyne triple-bond systems. Very recently, constrained transition-metal units into tricyclic system realized late azides.33 Here, ( 2) metallapentalyne 1) [2+1] reaction azide. hand, proceeded investigate its reactivity shown 2a, containing carboxyl ester presence AgBF4 furnished unexpected tetracyclic 3) good yields. unsymmetrical molecular structure 3a elucidated single-crystal analysis. It turns out added alkynyl four-membered osmacycle 2c). retain almost same geometry quite similar: 2.063(4) Å, 2.078(5) 2.088(4) Å. newly formed Os?C8 [2.102(4) Å] slightly longer unit, but falls Os–C bonds (1.894–2.162 Å),37 could attributed strain induced ring. Close inspection C?C/C?N/C?O framework suggests length equalization rings. metallacycles nearly coplanar, indicated 0.0630 plane through Os1, O1, N1, C1–C10. corresponding lengths, together planarity metallacycles, indicate extensive ?-electron delocalization over 13 3a. facts suggest 3a-A dominant resonance possible 3). Four shed light unusual number under conditions. situ NMR experiments unreactive toward internal (such dimethyl acetylenedicarboxylate acetylenedicarboxylic acid), alkyl-substituted cyclopropylacetylene 1-pentyne), ethynyltrimethylsilane 3-bromopropyne). phenylacetylene derivatives 4-nitrophenylacetylene) mixtures without target products. Furthermore, methyl 3-deuteriopropiolate instead propiolate performed, deuterated product 3b? (see Supporting Information S13 details). We inferred might favored O-heterocycle, important contribution tethered structure. Accordingly, investigated whether heteroatom-containing substituents reactive. similar took place 2-ethynylthiophene, 2-ethynylpyridine, 2-ethynylaniline. 4, 5, 6, respectively) yields identified elemental noteworthy 4 represents CCCCS complex. On basis observations, propose using 5 4). alkyne silver salt may initially ?-alkyne A). Subsequent isomerization mononuclear ?2-complex metal-vinylidene ?1-complex B),41 kinetically favorable barrier 8.8 kcal/mol. Nucleophilic nitrogen ?-carbon would lead aza-metallacyclobutene. At point, allows pyridyl coordinate center, affording metallacycle contributor final 5). Our density functional theory (DFT) calculations support mechanisms reveal formal process B indeed exergonic. Gibbs free-energy profile DFT-calculated 298 K. computed free energies CCCCX exhibit thermal stability both state. survive temperature, 130 more originates only frameworks, chelating effects steric protection groups). large ?-systems possess some properties, therefore examined ultraviolet–visible (UV–Vis) absorption spectra chelates (at concentration × 10?4 M). metal-bridgehead remarkably broad UV visible up 850 nm region). instance, maximum (?max 703 nm) redshifted better conjugation. Time-dependent DFT B3LYP/6-31G(d) level describe 6. assigned HOMO?LUMO electronic transitions Table S1 UV–vis 3–6 measured CH2Cl2 Conclusion summary, Substituents crucial success reactions, since they enable systems stabilize resulting This method operationally straightforward provides distinct advance production Collectively, our findings offer valuable supplement construction chelates. Studies delivery structurally sophisticated subject ongoing work. available. 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