8 research outputs found

    Photochemically Switching Diamidocarbene Spin States Leads to Reversible Büchner Ring Expansions

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    The discovery of thermal and photochemical control by Woodward and Hoffmann revolutionized how we understand chemical reactivity. Similarly, we now describe the first example of a carbene that exhibits differing thermal and photochemical reactivity. When a singlet ground-state <i>N,N</i>′-diamidocarbene <b>1</b> was photolyzed at 380 nm, excitation to a triplet state was observed. The triplet-state electronic structure was characteristic of the expected biradical σ<sup>1</sup>p<sub>π</sub><sup>1</sup> spin configuration according to a combination of spectroscopic and computational methods. Surprisingly, the triplet state of <b>1</b> was found to engage a series of arenes in thermally reversible Büchner ring expansion reactions, marking the first examples where both cyclopropanation and ring expansion of arenes were rendered reversible. Not only are these photochemical reactions different from the known thermal chemistry of <b>1</b>, but the reversibility enabled us to perform the first examples of photochemically induced arene exchange/expansion reactions at a single carbon center

    Organosulfonates aid argentophilic forces in the crystal engineering of [2+2] photodimerisations: reactivity involving 3-pyridyl groups

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    <div><p>Photoreactive Ag(I) organosulfonate complexes involving (<i>E</i>)-methyl-3-(pyridin-3-yl)prop-2-enoate (3-PAMe) are reported. Argentophilic interactions stack 3-PAMe to undergo a head-to-head intermolecular [2+2] photodimerisation to generate (<i>rctt</i>)-dimethyl-3,4-bis(pyridine-3-yl)cyclobutane-1,2-dicarboxylate (3,3′-MeBPCD) in the solid state regioselectively and in quantitative yield. The organosulfonate participates in C–H…O interactions with the coordinated 3-pyridyl groups to effectively aid in crystal engineering of the reactivity.</p></div

    Edge-to-Edge C–H···N Hydrogen Bonds in Two-Component Co-crystals Aide a [2 + 2] Photodimerization

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    C–H···N hydrogen bonds support an intermolecular [2 + 2] photodimerization in the solid state. The photocycloaddition occurs in a co-crystal of composition (<b>tbrb</b>)·(<b>4,4′-bpe</b>) (where <b>tbrb</b> = 1,2,4,5-tetrabromobenzene; <b>4,4′-bpe</b> = <i>trans</i>-1,2-bis­(4-pyridyl)­ethylene) that consists of one-dimensional (1D) chains that self-assemble to form corrugated sheets. Stacking of <b>4,4′-bpe</b> between sheets conforms to the topochemical postulate of Schmidt. The alkene reacts to form <i>rctt</i>-tetrakis­(4-pyridyl)­cyclobutane (<b>4,4′-tpcb</b>) stereoselectively and in quantitative yield. C–H···N hydrogen bonds also support the assembly of the components in (<b>tbrb</b>)·(<b>4,4′-azo</b>) (where: <b>4,4′-azo</b> = 4,4′-azopyridine) into planar sheets. Density-functional theory calculations reveal identical face-to-face stacks of <b>tbrb</b> to aide in the stabilization of the structures of the co-crystals

    A solid-state [2 + 2] photodimerization involving coordination of Ag(I) ions to 2-pyridyl groups

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    <p>Photoreactive Ag(I) complexes of <i>p</i>-toluenesulfonate ions with the unsymmetrical alkene <i>trans</i>-1-(4-acetoxyphenyl)-2-(2-pyridyl)ethylene <b>1</b> is reported. The crystal [Ag(<i>p</i>-tol)(<b>1</b>)<sub>2</sub>]•(H<sub>2</sub>O) (<i>p</i>-tol = <i>p</i>-toluenesulfonate) undergoes a [2 + 2] photocycloaddition reaction in quantitative yield to afford the head-to-tail (ht) photoproduct <i>rctt</i>-1,3-bis(2-pyridyl)-2,4-bis(4-acetoxyphenyl)cyclobutane <b>2</b> regioselectively. The aromatic rings of the olefin participate in face-to-face π–π interactions and adopt an anti-conformation to position the carbon–carbon double bonds (C = C) in a suitable orientation to undergo photoreaction between neighboring complexes.</p

    Regiocontrol of the [2 + 2] Photodimerization in the Solid State Using Isosteric Resorcinols: Head-to-Tail Cyclobutane Formation via Unexpected Embraced Assemblies

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    Regiocontrolled head-to-head and head-to-tail [2 + 2] photodimerizations of (<i>E</i>)-methyl-3-(pyridin-3-yl)­prop-2-enoate are achieved in the solid state using 4,6-di-X-res (where X = Cl, Br, I; res = resorcinol) as small-molecule templates. The components in each co-crystal form discrete, three-component supramolecular assemblies sustained by two O–H···N hydrogen bonds. Whereas the head-to-head photoproduct (<i>rctt</i>)-dimethyl-3,4-bis­(pyridin-3-yl)­cyclobutane-1,2-dicarboxylate forms using 4,6-di-X-res (X = Cl or Br), the head-to-tail regioisomer (<i>rctt</i>)-dimethyl-2,4-bis­(pyridin-3-yl)­cyclobutane-1,3-dicarboxylate forms using 4,6-di-I-res. The head-to-tail product is generated via unexpected embraced dimeric assemblies. The stereochemistry of the head-to-tail product is confirmed using single-crystal X-ray diffraction

    Synthesis, Spectroscopic Properties, and Photoconductivity of Black Absorbers Consisting of Pt(Bipyridine)(Dithiolate) Charge Transfer Complexes in the Presence and Absence of Nitrofluorenone Acceptors

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    The diimine–dithiolato ambipolar complexes Pt­(dbbpy)­(tdt) and Pt­(dmecb)­(bdt) (dbbpy = 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine; tdt<sup>2–</sup> = 3,4-toluenedithiolate; dmecb = 4,4′-dimethoxyester-2,2′-bipyridine; bdt<sup>2–</sup> = benzene-1,2-dithiolate) are prepared herein. Pt­(dmecb)­(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm<sup>2</sup> from a 20 nm thin film) <i>across the entire visible region of the solar spectrum</i> in a Schottky diode device structure. Pt­(dbbpy)­(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor–acceptor stacking patterns. The crystalline solids are “black absorbers” that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor–acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. <sup>1</sup>H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further substantiated by ν<sub>C–O</sub> and ν<sub>N–O</sub> IR bands and solid-state tight-binding computational analysis
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