Rhodaelectrocatalysis for Annulative C−H Activation: Polycyclic Aromatic Hydrocarbons through Versatile Double Electrocatalysis

Abstract

Rapid access to structurally diversified polycyclic aromatic hydrocarbons (PAHs) in ac ontrolled manner is of key significance in materials sciences.H erein, we describe as trategy featuring two distinct electrocatalytic CÀHt ransformations for the synthesis of novel nonplanar PAHs.T he combination of rhodaelectrooxidative C À Ha ctivation/ [2+ +2+ +2] alkyne annulation of easily accessible boronic acids with electrocatalytic cyclodehydrogenation provided modular access to diversely substituted PAHs with electricity as as ustainable oxidant. The unique molecular topology as well as the photophysical and electronic properties of the thus obtained PAHs were fully analyzed. The unique power of this metallaelectrocatalysis method was demonstrated by the chemoselective assembly of synthetically useful iodo-substituted PAHs.Polycyclic aromatic hydrocarbons (PAHs) have found widespread applications in optoelectronics,bioimaging,and catalysis. [1] Thep hysicochemical properties of PA Hs are determined by their shape, p-extension, and edge topology,which strongly depend on their mode of fabrication. Thus,t he bottom-up synthesis of PA Hs with atomic precision has attracted considerable attention in molecular engineering and materials sciences.S yntheses of PA Hs have thus far largely relied on multistep methods involving Diels-Alder cycloadditions,c yclotrimerizations,o rc ross-couplings. [2] Recently, catalytic C À Hactivation has emerged as atransformative tool for the rapid construction of extended p-systems,w ith major contributions by the groups of Itami [3] and You, [4] among others. [5] However,t he sustainable nature of this approach is largely compromised by the need for prefunctionalized substrates and/or metal oxidants,s uch as silver(I) salts, which generate stoichiometric amounts of undesired chemical waste.In recent years,t he use of electricity as ar edox agent to power chemical reactions [6] has undergone ar enaissance. [7,8] Significant recent impetus was gained by the merger of electrocatalysis with organometallic C À Ha ctivation, thus avoiding the use of toxic and expensive metal oxidants. [9,10] While electrochemical polymerization has been exploited for the synthesis of conducting materials, [11] the bottom-up assembly of atomically precise PA Hm otifs by electrooxidative catalysis has thus far unfortunately proven elusive.I n sharp contrast, we have now devised an ovel strategy for merging two distinct electrocatalytic transformations for the chemoselective assembly of decorated PA Hs.T he development of an unprecedented rhodaelectrocatalyzed [12] C À H activation for the annulative [13] [2+ +2+ +2] cycloaddition of userfriendly boronic acids set the stage for an electro-catalyzed dehydrogenation in ar esource-economical manner (Figure 1). Salient features of our method include 1) rapid, modular access to PA Hs through double electrocatalysis, 2) electricity as as ustainable oxidant, 3) the formation of six new C À Cb onds in ap rogrammable fashion, and 4) outstanding levels of chemoselectivity thr...

Scalable Rhodium(III)‐Catalyzed Aryl C−H Phosphorylation Enabled by Anodic Oxidation Induced Reductive Elimination

“…[10] Recently,m any elegant examples of electrochemically driven transition metal catalyzed C À Hf unctionalizations have been reported, [11,12] including aPd-catalyzed C À H phosphorylation reaction [11l] and af ew Rh III -catalyzed CÀC cross-coupling reactions. [12] Herein, we describe an unprecedented Rh III -catalyzed electrochemical phosphorylation of aryl CÀHb onds that can be used to efficiently synthesize triarylphosphine oxides from diarylphosphine oxides.E xperimental results suggest that the mechanism of the C À Pb ond formation in our method involves oxidation-induced reductive elimination rather than the Rh III /Rh I catalytic cycle that has previously been proposed for similar transformations with chemical oxidants. [5] We began our studies by first optimizing electrochemical conditions for the phosphorylation of N-(2-pyridyl)aniline (1) with diphenylphosphine oxide (2), ar eaction which has not been reported previously.T he electrosynthesis was performed in an undivided cell (a three-necked round-bottomed flask) equipped with ar eticulated vitreous carbon (RVC) anode and aplatinum plate cathode.The optimal results were obtained at reflux (65 8 8C) and ac onstant current of 3mA, with areaction mixture consisting of Cp*Rh(OAc) 2 (5 mol %) as the catalyst, KPF 6 (1 equiv) as the supporting salt, and MeOH as the solvent (Table 1).…”

Electrochemical Access to Aza‐Polycyclic Aromatic Hydrocarbons: Rhoda‐Electrocatalyzed Domino Alkyne Annulations

“…With our ongoing interest in material syntheses by metalla-electrocatalysis, we have now developed a one-step electrochemical assembly of aza-PAHs via rhoda-electrocatalyzed cascade C À H annulations ( Figure 1). [12] Salient features of this electrocatalytic transformation include: a) electricity as a green oxidant, b) excellent functional group tolerance, c) three CÀH bonds activated and six new bonds formed, and d) user-friendly scale-up.…”

Elektrochemischer Zugang zu aza‐polycyclischen aromatischen Kohlenwasserstoffen: Rhoda‐elektrokatalytische Domino‐Alkin‐Anellierungen

“…Aufbauend auf unserem Interesse an der Synthese neuer Materialien durch Metallaelektrokatalyse, haben wir nun eine einstufige elektrochemische Herstellung von Aza-PAKs über Rhoda-elektrokatalytische Kaskaden-C-H-Anellierungen entwickelt (Abbildung 1). [12] Die hervorstechenden Aspekte dieser elektrokatalytischen Synthese sind: a) Strom als grünes Oxidationsmittel, b) exzellente Toleranz für funktionelle Gruppen, c) konsekutive Aktivierung von drei C-H-Bindungen und Bildung von sechs neuen Bindungen und d) benutzerfreundliche Skalierung des Reaktionsansatzes.…”