Communication Chemistry—A European Journal doi.org/10.1002/chem.202002872 & Organophosphorus Chemistry Phosphorus-Containing Dibenzonaphthanthrenes:Electronic Fine TuningofPolycyclic Aromatic Hydrocarbonsthrough Organophosphorus Chemistry Johannes D. R. Ascherl,[a, c] Christian Neiß,[b] Alexander Vogel,[a, c] JürgenGraf,[a] Frank Rominger,[a] ThomasOeser,[a] FrankHampel,[d] AndreasGçrling,[b] and MilanKivala*[a, c] Abstract: Aconcise synthetic route towards anew family by means of synthetic organic chemistry.Controllingthe size of phosphorus-containingpolycyclic aromatic hydrocar- and shape of the p-conjugated systemallows to adjust the bons startingfrom the versatileacridophosphine has been energylevels of frontier molecular orbitals (FMOs) and conse- established. The structuraland optoelectronicproperties quently to modulate the UV/Vis absorption and emission char- of these compounds were efficiently modulated through acteristics.[2] Aparticularly potent strategy to tune the proper- derivatizationofthe phosphorus center. X-ray crystallo- ties of PAHs involves the incorporation of differentheteroa- graphicanalysis,UV/Vis spectroscopic, and electrochemi- toms into the sp2 carbon framework.[3–5] cal studies supported by DFT calculations identified the In this context, the highly tunable electronic nature of triva- considerable potentialofthesescaffolds for the develop- lent phosphorus renders phosphorus-containing PAHs promis- ment of organophosphorus functional materialswith tail- ing candidatesfor novel functional materials.[6,7] Hence, the ox- ored propertiesupon further functionalization. idationoftrivalent phosphorus with its Lewis basic lone pair affordselectron-withdrawing pentavalent phosphoryl species. In these systems p back donation from the filled porbital at the oxygen into the antibonding s*orbital at the phosphorus, Polycyclic aromatic hydrocarbons(PAHs) are of great interest called negative hyperconjugation, results in ahighly polarized for the developmentoffunctional materials for diverse applica- phosphorus–oxygen bond. This effect concomitantlyincreases tions such as organic solar cells, field-effect transistors, and the relative electronegativity of the phosphorus center,turning light emitting diodes.[1] However,the crucial step towards it into an electron acceptor.[6b,8] In this regard, acridophos- these applicationsisthe ability to tailor the properties of PAHs phineswith their bridging carbonylmoiety represent an ap- pealing compound family for molecular engineering.[9,10] Hence, the reactive carbonyl group providesfor the introduc- [a] Dr.J.D.R.Ascherl, A. Vogel, Dr.J.Graf, Dr.F.Rominger, Dr.T.Oeser, Prof. Dr.M.Kivala tion of functional groups in the periphery throughcarbonyl Institute of Organic Chemistry chemistry,while the derivatization of the phosphorus center Ruprecht-Karls-UniversitätHeidelberg enablesfine tuning of the resulting compounds in terms of Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) their optoelectronic properties.[11] Despite their indisputable E-mail:[email protected] synthetic versatility,acridophosphines remained largely dor- [b] Dr.C.Neiß, Prof. Dr.A.Gçrling Department of Chemistry and Pharmacy mant until we recently recognized their potentialtorealize a Chair of Theoretical Chemistry seriesofdicyanomethylene-bridged scaffolds with tunable Friedrich-Alexander-UniversitätErlangen-Nürnberg electron acceptor properties.[11] The ability of the bridging car- Egerlandstrasse 3, 91058 Erlangen (Germany) bonyltoundergo aKnoevenagel condensation with malononi- [c] Dr.J.D.R.Ascherl, A. Vogel, Prof. Dr.M.Kivala trile stimulated us to explore its reactivity towards p expansion Centre for Advanced Materials Ruprecht-Karls-UniversitätHeidelberg in order to achieveanew type of phosphorus-containing Im Neuenheimer Feld 225, 69120 Heidelberg (Germany) PAHs. [d] Dr.F.Hampel Herein, we report the first, to the bestofour knowledge, Department of Chemistry and Pharmacy Barton–Kellogg olefination of acridophosphine, which was fol- Chair of Organic Chemistry lowedbyMalloryphotocyclization to achieve unprecedented University of Erlangen-Nürnberg Nikolaus-Fiebiger-Str. 10, 91058 Erlangen (Germany) phosphorus-containing PAHs of general formula A (Figure 1). Supporting information and the ORCID identification number(s) for Subsequentderivatization of the phosphoruscenterprovided the author(s) of this article can be found under: for fine-tuning of the FMO energy levels and the photophysical https://doi.org/10.1002/chem.202002872. properties of the newly synthesizedphosphorus-containing 2020 The Authors. Published by Wiley-VCH GmbH. This is an open access PAHs. In fact, the newly synthesizedPAHsrepresent organo- article under the terms of Creative Commons Attribution NonCommercial- phosphorus analogues of the hithertoelusive dibenzonaph- NoDerivs License, which permits use and distribution in any medium, pro- [12] vided the originalwork is properly cited, the use is non-commercial and no thanthrene (8H-benzo[gh]naphtho[1,2,3,4-pqr]tetraphene). modifications or adaptations are made. Boron-containing counterparts B of this interesting PAHwere Chem. Eur.J.2020, 26,13157 –13162 13157 2020 The Authors. Published by Wiley-VCH GmbH Communication Chemistry—A European Journal doi.org/10.1002/chem.202002872 dene-bridged 3 as awhite crystalline solid in an overall yield of 90%. In accordance with the recently reported successful oxidative photocyclizations of p-expanded phosphole sulfides by Hissler and co-workers,[15] Mallory reaction involving 3 af- forded amixture of the monocyclizedcompound 4 (52% yield) andthe fully cyclized counterpart 5 (29 %yield), both as pale-yellow solids. Increasing the reaction time did not im- prove the yield of 5.Both compounds are air stable and can be readily purified by column chromatography on SiO2.It should be emphasized that the attempted syntheses of 5 (and Figure 1. The relationofthe heteroatom-containing PAHs to their hitherto elusive all-carbon congeners. 4)byLewis acid-mediated oxidative cyclodehydrogenation (Scholl reaction) from 3 as well as from the corresponding phosphine oxide and the trivalent phosphine failed,[16] most recently realized as exceptionally stable redox-active lumino- likely due to incompatibility of the reactive phosphorus center phores by Wagner and co-workers.[13] with the required reactionconditions. Parent compound 1 was synthesized by carbanion-mediated To explore the impact of phosphorus functionalization on cyclization of acarbamoyl-substituted triphenylphosphine the properties of the dibenzonaphthanthrene scaffold, the thi- oxide precursor according to Snieckus and co-workers (for syn- ophosphoryl unit in 5 was reduced with P(nBu)3 to afford triva- thetic details, see the Supporting Information).[9,11] Reaction of lent phosphine 6 in 88 %yield as awhite solid. Phosphine 6 is compound 1 with Lawesson’sreagent afforded thioketone 2 fairly stable in the solid state but oxidizes readily in solution as adark blue crystalline solid (Scheme 1). Thioketone 2 was under ambient conditions in air towards phosphine oxide 7. subjected to aBarton–Kellogg olefination[14] reaction with di- On apreparative scale, phosphine oxide 7 was accessible in phenyldiazomethane(S2)followed by reduction of the result- 89%yield from oxidation of 6 with H2O2.Methylation of 5 and ing intermediate thiirane with coppertoafforddiphenylvinyli- 6 with methyl triflate furnished the phosphonium salts 8 and Scheme1.Synthesis of phosphorus-containing PAHs 3–10.PO: propylene oxide. Chem. Eur.J.2020, 26,13157 –13162 www.chemeurj.org 13158 2020 The Authors. Published by Wiley-VCH GmbH Communication Chemistry—A European Journal doi.org/10.1002/chem.202002872 9,respectively.Inaddition, phosphine 10 was synthesized ported previously for the dicyanovinylidene-bridged system 1 [11] upon reduction of precursor 3 (72%yield) as amodel com- with DG¼6 = 14.3 kcalmolÀ . pound in order to evaluate the impact of cyclization on the Single crystals of compounds 3–5 and 7 suitable for X-ray structural and optoelectronic properties (Scheme 1). The crystallographic analysiswere obtained by slow evaporation of 31 PNMR resonances of compounds 3–5 and 7–9 (25.7, 22.8, the compound solutionsinCH2Cl2/n-hexane mixture [18] 21.1, 7.3, 29.2 and 0.0 ppm, respectively)inCD2Cl2 at room (Figure 3). The noncyclized phosphine sulfide 3 exhibits a temperature appear low-field shiftedincomparison to the tri- characteristic distorted butterfly-shaped conformation caused valent phosphines 6 and 10 (6: 37.0 ppm, 10: 17.7 and by the spatial demands of the phosphorus centerincombina- À À 25.2 ppm);this is in accordance with their increased elec- tion with the repulsion of the diphenylvinylidene moiety and À tron-deficient nature. Whereas only sharp signals are observed the adjacent hydrogens at the phosphaanthracenyl fragment. in the room temperature 1HNMR spectrum of the twofold cy- Each cyclization step enforces amore planar polycyclic scaf- clized phosphine 6,the model compound 10 shows broad- fold. The fully cyclizedphosphine sulfide 5 and phosphine ened signals under the same conditions, thus indicating the oxide 7 comprise a[4]helicene-like subunit embedded within occurrence of aconformationalprocess. the organophosphorus p system.The helical pitch as ex- This process is most likely analogous to the wing-flip motion pressed by the distance “ortho–ortho” carbons differs only of the butterfly-shaped phosphaanthracenyl fragment, as al- slightly between compounds 5 (2.96 )and 7 (2.95 ), and